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2011 Seminars Archive

Date Details
November 17, 2011

My STM Quest at CNMS: Phonons, Molecules and Oxides,” MInghu Pan, Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, hosted by Jeff Guest

Abstract: Scanning tunneling microscopy (STM) has been well developed for decades and has proven to be a very useful technique to detect surface structure, nanostructures, surface defects, and related electronic properties. Here, I introduce two homemade STMs from the Center for Nanophase Materials Sciences. By choosing three examples, I will demonstrate the research we are performing now.

Inelastic electron tunneling spectroscopy (IETS) by STM becomes a powerful tool to detect vibronic excitation (phonons) on surface/molecular system. We will show the role surface state electrons play in vibronic excitations on Au surface. In second example, a small molecule, phenylacetylene, forms a hexamer - a six-member superamolecule - via attractive, cooperative, multicentral weak CH/pi bondings between ethyne groups. STM and theoretical calculations help us to investigate such molecular system. The third example is ruthenate. Sr3(Ru1-xMnx)2O7 is a strong correlated electron materials involving coupling of lattice, charge, orbital, and spin. The role of Mn dopants is especially surprising and interesting for understanding phase transitions in these materials. Here, we observe the √2 superstructure of surfaces, which reflects the octahedral rotation of the actual bulk unit cell for Sr3(Ru1-xMnx)2O7. By visualizing Mn dopants in different doping levels and different phases, we are able to elucidate the nature of doping-induced changes in the physical properties of doped ruthenate.

November 15, 2011

Joint CNM-ES Seminar

"Ultrasmall Nanocrystals: Colloidal Synthesis, Magnetic and Optical Properties, Growth Mechanism, and Electrophoretic Deposition," Weidong He, Vanderbilt University, hosted by Richard Brotzman and Xiao-Min Lin

Abstract: As the size of a nanocrystal becomes small enough, size-dependent properties, increased astoichiometry, and defects can give rise to interesting property transitions, including a transition between diamagnetism and ferromagnetism. This talk focuses on colloidal synthesis, and size-dependent optical and magnetic properties of several nanocrystals, such as EuX (X=O, S, Se, Te), Eu2O2S, and tellurium nanoparticles and nanorods. Significant Néel temperature enhancement and diamagnetic-magnetism transition were observed on EuTe and Eu2O2S nanocrystals, respectively.

To better control the synthesis and improve the properties of these materials, the reaction kinetics and growth mechanism of the nanocrystals were evaluated by using our newly derived model for the van der Waals interaction between a nanorod and an attaching nanoparticle. Towards the application of these nanocrystals, the synthesized nanocrystals were deposited into uniform nanofilms by using an automatic electrophoretic deposition technique. A highly efficient nonchemistry method was also invented for the synthesis of gold nanocrystals, including gold nanocages and gold nanoprisms. These nanostructures may find applications in various optical fields, such as second-harmonic generation and surface-enhanced Raman spectroscopy.

November 10, 2011

"Spatially Resolved Ionic Diffusion and Electrochemical Reactions in Solids – A Biased View of Lithium-Ion Batteries," Nina Balke, Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, hosted by Paul Fenter and Andreas Roelofs

Abstract: The functionality of energy storage and generation systems such as lithium-ion batteries or fuel cells is not only based on but also limited by the flow of ions through the device. To understand device limitations and to draw a roadmap to optimize device properties, the ionic flow has to be studied on relevant length scales of grain sizes, structural defects, and local inhomogeneities (i.e., over tens of nanometers). Knowledge of the interplay among the ionic flow, material properties, and microstructure can be used to optimize the device properties. For example, to maximize energy density, increase charging/discharging rates, and improve cycling life for lithium-ion batteries for applications in electric vehicles and aerospace. Until recently, existing solid-state electrochemical methods were limited to a spatial resolution of ~10 mm or greater, well above the characteristic size of grains and subgranular defects. Our development of electrochemical strain microscopy (ESM) has reduced this resolution limit to length scales down to 100 - 10 nm, which allows studies of the local lithium-ion flow in electrode materials and across interfaces. ESM is a scanning probe microscopy (SPM) based characterization method that utilizes the intrinsic link between lithium-ion concentration and molar volume of electrode materials.

In this talk, we aim to provide an overview of current local SPM-based techniques applicable for the characterization of energy storage and energy conversion materials and discuss potential advantages and drawbacks of SPM-based approaches. We will explore in detail how ESM can be used to characterize lithium-ion transport in important battery materials The results can be used to conclude on the role of microstructure and interfaces on lithium-ion transport. Theoretical calculations are shown to support the experimental data and to give insight into the signal-generating mechanism.

October 27, 2011

"Hard X-ray microscopy activities at SPring-8 public beamlines," Yoshio Suzuki, Japan Synchrotron Radiation Research Institute, hosted by Gary Wiederrecht

Abstract: Before the SPring-8 synchrotron radiation facility was commissioned in 1997, the X-ray microimaging activities in Japan were at a very primitive stage. A few groups were struggling to develop microfocusing and imaging techniques using Photon Factory beamlines. Establishing imaging techniques and organizing user groups were some of the most important issues. The tentative goals were as follows:

  1. Routine experiments in the energy region of 5-37 keV with spatial resolution of 1-0.1 micron,
  2. Application of microprobe in various fields of X-ray science (e.g., scanning microscopy, micro-XAFS, fluorescent X-ray trace-element analysis, micro-diffraction)
  3. Three-dimensional imaging by computer tomography .

Now, microbeam applications are routinely capable of spatial resolution of about 100 nm. It is possible to carry out full-field imaging microscopy with a spatial resolution of better than 100 nm, and 200-nm resolution measurements are routinely performed in imaging tomographic microscopy. The best record of nanofocusing is now better than 30 nm for 8-keV X-rays using an electron-beam lithography zone plate fabricated at NTT Advanced Technology. Submicron resolution is also attained in the higher energy region up to 100 keV. Some phase-sensitive imaging techniques have also been developed and applied to user experiments. Experiments are now carried out at four public beamlines in SPring-8: 20B2, 20XU, 37XU, and 47XU. User groups cover a wide variety of disciplines, from medical applications to elementary particle physics.

In my talk, development of optics and results of microfocusing, full-field imaging microscopy, and microtomography will be shown, and some applications will be presented.

June 6, 2011

"Nanofabrication Laboratory at Chalmers University of Technology," Peter Modh, Chalmers University of Technology, hosted by Leonidas E. Ocola

Abstract: Our presentation is on the centralized cleanroom facility and Nanofabrication Laboratory at Chalmers University of Technology, with an overview of the organization, the cleanroom usage, and some equipment high lights. In addition, we will describe the Swedish cleanroom network Myfab, now recognized as a national research infrastructure where Chalmers is one of the three nodes.

May 23, 2011

"Single-Digit Nanofabrication using Directed Assembly," Deirdre Olynick, Lawrence Berkeley National Laboratory, hosted by Leonidas E. Ocola

Abstract: One of our themes at the Molecular Foundry is “Single-Digit Nanofabrication (SDN),” which describes our efforts to pattern materials with resolution, precision, and control at the sub-10-nm scale. To reach this scale, the nanofabrication facility has a focus on nanofabrication science in areas of resist development, electron-beam-induced deposition, atomic layer deposition, directed assembly, and plasma etching. In this talk, I will highlight general Molecular Foundry work and applications for SDN, and then focus on patterning with directed self-assembly and plasma etching.

As an alternative to directed assembly of block copolymers using substrate prepatterning, we guide the order of BCPs by using thermal imprint. Cylindrical PDMS phases in PS-b-PDMS thin films were imprinted and annealed to generate linear arrays of sub-10-nm half-pitch features on the substrates. I will discuss the critical roles of BCP-mold chemistry, polymer mobility, and polymer flow in the imprint guided alignment process.

With the ability to generate SDN with self-assembly techniques, the next critical challenge is how to reliably transfer these patterns. Plasma etching has been a workhorse in nanofabrication but at SDN we must ask, “What are the limits?” I will discuss nanoscale etching work from 30 to 3 nm to address this question for SDN nanopatterning

May 13, 2011

"Applications of Ultrasound to the Synthesis of Nanostructured Materials," Kenneth S. Suslick, University of Illinois at Urbana-Champaign, hosted by Elena Shevchenko

Abstract: Recent advances in nanostructured materials have been led by the development of new synthetic methods that provide control over size, morphology, and nano/microstructure. The use of high-intensity ultrasound offers a facile, versatile synthetic tool for nanostructured materials that are often unavailable by conventional methods.

The primary physical phenomena associated with ultrasound that are relevant to materials synthesis are cavitation and nebulization. Acoustic cavitation (the formation, growth, and implosive collapse of bubbles in a liquid) creates extreme conditions inside the collapsing bubble and serves as the origin of most sonochemical phenomena in liquids or liquid-solid slurries. Nebulization (the creation of mist from ultrasound passing through a liquid and impinging on a liquid-gas interface) is the basis for ultrasonic spray pyrolysis (USP) with subsequent reactions occurring in the heated droplets of the mist. In both cases, we have examples of phase-separated nano-reactors: for sonochemistry, it is a hot gas inside bubbles isolated from one another in a liquid, while for USP it is hot droplets isolated from one another in a gas.

Cavitation-induced sonochemistry provides a unique interaction between energy and matter, with hot spots inside the bubbles of ~5000 K, pressures of ~1000 bar, heating and cooling rates of >1010 K s-1. These extraordinary conditions permit access to a range of chemical reaction space normally not accessible, which allows for the synthesis of a wide variety of unusual nanostructured materials.

Complementary to cavitational chemistry, the microdroplet reactors created by USP facilitate the formation of a wide range of nanocomposites. In this lecture, we summarize the fundamental principles of both synthetic methods and recent development in the applications of ultrasound in nanostructured materials synthesis.

April 26, 2011

"Assembly, Chirality, and Polymorphism of Large Molecules on Metal Surfaces," Erin V. Iski, hosted by Nathan Guisinger

Abstract: The high-resolution capabilities of low-temperature UHV STM were exploited to examine the packing of a pharmaceutical compound, Carbamazepine (CBZ), on Au(111) and Cu(111) single crystals, which resulted in the formation of complex chiral molecular architectures that were previously unreported. The identity of the metal surface altered the way in which the molecules packed both in density and in chirality, indicating that different metallic surfaces could be used as templates to control the molecular packing density or polymorphism of pharmaceutical compounds. Furthermore, we were able to examine how the packing of CBZ changed as a result of an increase in surface coverage and how second layer growth began to replicate a predicted, but previously not observed, structure for the bulk crystal. The study of chiral surface chemistry was extended to include the spontaneous transmission of chirality through multiple length scales for a simple, robust polyaromatic hydrocarbon, Napht ho[2,3-a]Pyrene (NP), on a Cu(111) surface. Additionally, the interaction of that technologically important molecule with a Au(111) surface was examined in an effort to understand the changes in the organic-metal interface as a function of various annealing treatments.

April 22, 2011

"Nematic Liquid Crystal Interfaces for Biological and Chemical Detection," by Bharat R. Acharya, Platypus Technologies, LLC, hosted by Amanda Petford-Long

Abstract: Nematic liquid crystals (NLCs), the electrically responsive fluid behind most of flat-panel displays, consist of anisotropic molecules that possess long-range orientational correlation but lack positional order. In recent years, there have been significant advances in unconventional applications of NLCs in photonics, sensors, and diagnostics.

In this talk, the application of NLCs for detection of biological entities and vapor-phase chemicals is presented. Interfaces functionalized with select biological and entities promote alignment of NLCs in predetermined orientations (perpendicular or parallel to that interface) that are primarily dictated by local interactions at the interface. When these interfaces are exposed to target analytes, the interactions at the interfaces are perturbed, and the NLC films undergo orientational transitions from perpendicular to parallel alignment, or vice versa. The orientational transition can easily be detected by viewing the film of NLCs between crossed polarizers. By engineering surfaces with different interfacial properties, sensors based on this principle have been demonstrated to selectively detect a wide variety of chemical and biological analytes that have relevance in industrial hygiene, environmental monitoring, homeland security, diagnostics, and biomedical applications.

April 18, 2011

"How nanotechnology can solve the End of the Silicon Roadmap problem," by Juan Alejandro Herbsommer, Texas Instruments, hosted by Amanda Petford-Long

Abstract: Moore’s Law is the empirical observation that component density and performance of integrated circuits doubles every year, which was then revised to doubling every two years. Guided by smart optimization, timely introduction of new processing techniques, device structures, and materials, Moore’s Law has continued unabated for 40 years. Driven by tremendous advances in lithography, the 65-nm logic technology node featuring ~30-nm transistors is currently in high-volume production. With such small feature sizes in high-volume production and under development, silicon CMOS technologies are now leading the field of nanotechnology for semiconductor applications.

However, this standard technology path of scaling down the size of the devices will not be able to be sustained in the near future. It is wrongly said that “the ultimate limit of the current silicon technology is the molecular dimension.” The “End of the Silicon Roadmap” is around the corner and will not be due to reaching the ultimate quantum dimension but to the parasitic at nanometer level dominating the physics of the devices.

In fact, transistor scaling limits arise from practical limits related to leakage current at small gate lengths. The problem at small gate lengths is that the drain voltage reduces the barrier height at the source, thereby causing a low source-to-channel barrier height even with the gate voltage off, which leads to undesirable large off-state leakage. This undesirable effect affects traditional MOSFET transistors, which constitute 99% of all the transistors manufactured today. The enormous leakage issue grows with every standard scaling-down generation of technology creating a thermal dissipation problem so big that we refer to it as the “thermal wall.”

I will show the results we obtained in the development of the most efficient power MOSFET of the market. The NexFet technology developed by my team at Ciclon Semiconductors reduces the leakage in a very innovative way to make the power loss of the device negligible.

I will also show how the End of the Silicon Roadmap could be addressed by using nanotechnology in a nonstandard way. I will describe the projects I am leading (in collaboration with the universities) to develop nanotechnologies linked to spintronics, new III-V nano-engineered devices and nano-composites to improve the materials used in the microelectronics industry.

April 7, 2010

"Imaging and manipulation of nanoscale materials with coaxial and triaxial AFM probes," by Keith Brown, Harvard University, hosted by Daniel Lopez

Abstract: The atomic force microscope (AFM) has had an enormous impact on the study of nanoscale materials as it allows the measurement of piconewton forces on nanometer length scales. In this talk, I will discuss our recent research developing custom AFM probes that enable new ways to image and manipulate nanoscale materials. We deposit shielding electrodes on conducting AFM probes and etch their tips to create nanoscale coaxial apertures. We begin by showing that the capacitive structure of these cantilevers couples the mechanical deformation of the cantilever to the electrostatic energy stored in the probe. This effect is used to create self-driving probes that can image topographical features without mechanical excitation. The electrical field created by a coaxial probe can be modeled as the field from an electric dipole, which makes coaxial probes useful for high-spatial resolution imaging of electrical properties. We show nearly an order of magnitude improvement in the step resol ution of Kelvin probe force microscopy. We further demonstrate that coaxial probes can image materials with dielectrophoresis (DEP), which allows coaxial probes to effectively image with a smaller tip radius. Coaxial probes create strong DEP forces which we combine with the nanometer precision of the AFM to create a nanoscale pick and place tool. Finally, we construct triaxial probes with three coaxial electrodes that can create more complex electric fields. In particular, triaxial probes can create an electric field zero displaced from the tip which we use to trap nanoscale beads with negative dielectrophoresis. The Triaxial AFM Contact-free Tweezers have applications in novel force sensing and nanoscale pick and place.

April 1, 2010

"Nanocrystal Syntheses and Applications for Composite Magnet and Fuel Cell Catalysis," Yi Liu, Brown University, hosted by Xio-Min Lin

Abstract: I will present my graduate research studies on solution-phase chemistry syntheses of nanocrystals and their applications. I will first outline the controlled synthesis of Fe3BO5 nanorods to demonstrate how to use these nanorods to fabricate exchange-coupled Nd2Fe14B-Fe nanocomposite magnets via high-temperature reductive annealing. I will then focus on the syntheses of platinum alloy (PdPt and PtSn) nanocrystals as fuel cell catalysts for methanol oxidation reaction (MOR).

In the MOR condition, pure platinum catalysts suffer from CO poisoning and quickly lose their initial activity . By incorporating an appropriatesecond metal with platinum, the catalyst should lessen the CO poisoning problems and show higher MOR activity and stability. We synthesized PdPt alloy nanocrystals with Pd/Pt composition tunable from 5/1 to 1/2 and studied the composition-dependent MOR. We found thatPdPt catalyst at Pd/Pt = 2/1 showedMOR activity that was superior to any of the single-component palladium and platinum catalysts. When palladium was replaced with tin, the Pt3Sn nanocrystals showed even higher MOR activity. Our work proves that MOR catalysis can be optimized via a controlled nanoscale alloying process.

March 24, 2010

"Nanostructured Silicate-Based Materials: From Environmental Remediation to Energy Storage Applications," Eduardo Ruiz-Hitzky, Materials Science Institute of Madrid

Abstract: Nanostructured solids derived from synthetic and natural silicates can be considered eco-friendly materials for advanced applications in diverse fields ranging from energy storage to environmental remediation. Recent examples from our laboratory include:

  • Graphene-like based nanocomposites, or hybrid buckypapers comprised of carbon nanotubes with clay minerals or produced from precursors of natural origin (e.g., table sugar). These materials have unique characteristics such as simultaneous electrical conductivity and elevated specific surface areas. Examples of potential applications include electrodes for rechargeable lithium batteries, supercapacitors, electrochemical sensor devices, and electromagnetic shielding panels.
  • Bio-nanocomposites, prepared by the assembly of biopolymers and other entities of biological origin with inorganic solids. These materials are biodegradable, biocompatible and exhibit other properties such as fire retardancy or with cellular structures imparting ultralightweight characteristics. Applications lie in highly efficient thermal and acoustic insulating eco-materials, active phases of sensors, and materials for biomedical uses.
  • Clay-heterostructures based on the assembly of metal-oxide nanoparticles with silicates. Anatase and magnetite nanoparticles/clay systems, for example, are useful for environmental applications such as (a) improving photocatalytic behavior and (b) creating superparamagnetic materials for easy and safe recovery of pollutants and radionuclides in oil spill and nuclear accident remediation.

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February 15, 2011

"Nanoplasmonics: A foundation for new optical materials," Jonathan Fan, Harvard University, hosted by Gary Wiederrecht

Abstract: The self-assembly of colloids is an alternative to top-down processing that enables the fabrication of nanostructures. I will show that self-assembled clusters of metal-dielectric spheres are the basis for nanophotonic structures. By tailoring the number and position of spheres in close-packed clusters, plasmon modes exhibiting strong magnetic and Fano-like resonances emerge. The use of identical spheres simplifies cluster assembly and facilitates the fabrication of highly symmetric structures. Dielectric spacers are used to tailor the interparticle spacing in these clusters. These types of chemically synthesized nanoparticle clusters can be generalized to other two- and three-dimensional structures and can serve as building blocks for new metamaterials.

February 7, 2011

"Ultrafast Nanoscale Diffraction with Convergent Beam Electron Microscopy," Aycan Yurtsever, California Institute of Technology, hosted by Elena Shevchenko

Abstract: Diffraction with femtosecond electron pulses is a fast-emerging and promising technique for investigating ultrafast dynamics at the atomic scale. One common approach in the field is to use collimated electron beams with micrometer diameters. Although the spatial information obtained from such diffraction data is at the subatomic scale, any nanosized dynamical heterogeneity, such as propagating elastic waves, has been difficult to observe. This seminar will present recent experiments in which nanoscale diffraction with picosecond temporal resolution by using focused electron pulses inside an electron microscope has been achieved. In particular, I will discuss the intensity dynamics at the Bragg reflections and the induced ultrafast heating. In addition, I will talk about ultrafast Kikuchi nanodiffraction and its implication for propagating elastic waves.

February 1, 2011

"Characterization of Nanostructures and Defects in Functional Materials using Advanced Electron Microscopy," Jiaqing He, Northwestern University, hosted by Elena Shevchenko

Abstract: Understanding the structure-property relationship of thermoelectric materials and strongly correlated electron system,s including giant colossal magnetoresistive (GMR) manganite materials and superconductive materials, is a major challenge in condensed matter physics, material sciences, and nanosciences.

We present studies of PbTe-based thermoelectric materials by scanning transmission electron microscopy (STEM). We find and characterize nanoscale precipitates, dislocations, strains, and phase boundaries that have vital effects on phonon and electron scattering and the figure of merit (ZT) of materials. We also present an unusual observation of increase and then decrease in electrical conductivity as a function of temperature in a “dual-nanostructured” bulk PbTe thermoelectric system. By combining in situ TEM and theoretical calculations, we find a plausible new mechanism — interdiffusion between the lead and antimony when they are present together.

We also report on measurements of the spin configuration across ferromagnetic domains in La0.325Pr0.3Ca0.375MnO3 films obtained by means of low-temperature Lorentz electron microscopy with in situ magnetizing capabilities. We also describe the MR as a function of applied magnetic field at constant temperature and show how local spin inhomogeneities contribute directly to macroscopic GMR properties in a strongly correlated electron system.

Finally, we detail our results in exploring mutilayered La1-xSrxCuO4 superconductor films on LaSrAlO4 substrates by STEM and EELS.

January 31, 2011

"Transmission Electron Microscopy of Nanomaterials," Yuzi Liu, Materials Science Division, Argonne National Laboratory, hosted by Elena Shevchenko

Transmission electron microscopy (TEM) is an advanced analytical tool used to investigate the critical role of microstructure on the unique properties exhibited by nanomaterials. Several examples will be presented of the application of advanced TEM techniques to the study of nanomaterials.

ZnO thin films exhibit a number of important properties (e.g., semiconductor, piezoelectric and bio-compatibility). To improve the quality of ZnO film electron diffraction, dark field imaging and high-resolution TEM were employed to study 30-deg rotation domains and inversion domains that are detrimental to ZnO properties. The distribution of dopants in the diluted magnetic film of ZnO:Co is critical in understanding the origin of the anomalous Hall effect in these materials. The distribution of cobalt was measured with TEM by a combination of atomic channeling enhanced microanalysis and electron energy loss spectroscopy.

A magnetic tunnel junction (MTJ) is another example of a thin-film nanostructure whose properties depend critically upon its microstructure at the nanoscale. The tunnel barrier of the MTJ (e.g., ~2 nm of MgO) is particularly important to its transport properties. Energy-filtered TEM and in situ off-axis electron holography were used to investigate the effects of annealing and electrical bias on the tunnel barrier shape. Electron tomography was also used to measure quantitatively the roughness of the top and bottom barrier interfaces before and after annealing. Annealing was observed to affect both the barrier interfacial roughness and transport properties of the MTJ. Electrical bias was also found to affect the symmetry of the barrier potential and the effective barrier width as a result of charge accumulation at the MgO-CoFe interface.

In situ microscopy experiments provide unique insights into how materials behave on the nanoscale. It is desirable, however, to investigate these materials in their native environment, which is typically incompatible with the high-vacuum requirements of TEM. Therefore, an environmental liquid cell is required to conduct these in situ TEM experiments in a realistic environment. Building up a liquid cell experiment platform and using it to understand the assembly of nanoparticles within biological materials in different liquid media and nanomaterials dispersion in different solvents is a very interesting future research direction.

   

 

2010 Seminars Archive

Date Title
December 17, 2010

"Microsystems for Control of Light-Matter Interaction at the Nanoscale," Il Woong Jung, hosted by Daniel Lopez

Abstract: It has been shown that electromagnetic fields incident upon metal particles can be confined over dimensions on the order of or smaller than the wavelength of light. This strong light-matter interaction leads to an enhanced optical near-field at metallic interfaces or in small metallic nanostructures. These highly enhanced fields can be used to probe materials with subwavelength resolution (near-field scanning optical microscopy) and allow single-molecule surface-enhanced Raman spectroscopy detection. The ability to control these interactions (i.e., tune the plasmonic resonance) is highly desirable for developing ultrasensitive Raman and fluorescence detectors, highly efficient optical antennas, tunable single-emitters, nano-patterning, and novel nanophotonic devices.

In contrast to the strong light-matter interaction observed for metallic structures, photonic crystals are periodic dielectric structures that support many weak interactions to combine coherently to a strong interaction. By controlling the structure and geometrical dimensions, photonic crystal slabs can support guided resonances that couple to external radiation in ways that profoundly change its optical properties. By using nanofabrication tools such as focused ion beam, these nanophotonic elements can be integrated with micromechanical devices for added functionality to control the electromagnetic radiation.

In this talk, I will give an introduction to photonic crystal integrated microsystems and then present current research efforts focused on using micromechanical devices to actively control the optical properties of plasmonic nanostructures. In addition, just as microsystems have advanced the capability to manipulate light at the visible to infrared wavelengths, they can vary the focus, scan, modulate, and dynamically adjust the beam profile for X-rays, thereby enhancing the capability to probe materials at the nanoscale.

December 15, 2010

"Nanotechnology Enabled Research: from Superconductivity to Nanocomposites," Dmitriy Dikin, Northwestern University, hosted by Daniel Lopez

I will talk about the importance of nanotechnology from different aspects of my past, present, and wishful research. Superconductivity, nanomechanics, graphene-based materials, and many other interesting research areas always require precise control of the sample fabrication, inspection, and in some cases nanomanipulation for measurements, an adequate understanding and correct interpretation of new results. Quite often in my practice a microscope was not only the tool for taking images (which is very important in itself), but a research method and a laboratory space. I am going to describe (i) nanomechanical and other experiments performed inside of the scanning electron microscope, (ii) some perspectives and technologies based on the graphene sheets, (iii) some examples of new nanotools for research and development.

December 7, 2010

"Heusler compounds: Multifunctional materials for spintronics," Claudia Felser, Institute of Inorganic Chemistry, Johannes Gutenberg University Mainz, hosted by Amanda Petford-Long

Abstract: In 1905, Fritz Heusler discovered that the compound Cu2MnAl is ferromagnetic, even though none of its elemental constituents are themselves magnetic. This remarkable material and its cousins, a vast collection of more than 800 compounds, are now known as Heusler materials. Surprisingly, the properties of many of the Heuslers can be forecast simply by counting the number of their valence electrons. For example, Co2-Heusler compounds with more than 24 valence electrons are half-metallic ferromagnetics: electrons of one spin orientation are semiconducting. whereas electrons with the opposite spin orientation are metallic. Such compounds display nearly fully spin-polarized conduction electrons. making them very useful for spintronic applications. Mn2-Heusler compounds have attracted interest because their excellent performance for spin torque transfer applications.

Another subclass of more than 250 Heusler compounds are semiconductors. Their band gaps can readily be tuned from zero to ~4 eV by changing their chemical composition. These materials have thus attracted attention as potential candidates for both solar cell and thermoelectric applications. Indeed, excellent thermoelectric properties have recently been demonstrated. Finally, we discuss a third class of Heuslers that have been predicted, on the basis of their calculated electronic band structures, to be topological insulators, a new state of matter in which spin-polarized edge and surface states are topologically protected from impurity scattering.

December 6, 2010

"Scanning tunneling microscopy investigation of the heteroepitaxial interfacial electronic properties," Ya-Ping Chiu, National Sun Yat-Sen University, hosted by Te-Yu Chien

Abstract: Motivated by the importance of critical nanoscale interfacial science, the objective of our studies is the interfacial characteristics of heteroepitaxial structures and the fundamental mechanisms that pertain in these systems.

Cross-sectional scanning tunneling microscopy (XSTM) is employed to observe directly the epitaxial interfacial structures and the local electronic properties with atomic-level insight. Measurements of the local density of states (DOS) characteristics with local atomic precision enable us to directly demonstrate the natural evolution of the electronic properties across the heteroepitaxial interfacial properties. In this talk, topics to be discussed include the high-*'s/III-V's system (Gd2O3/GaAs) and multiferroic materials (BiFeO3). The significant heteroepitaxial interfacial electronic properties of the systems will be discussed.

December 3, 2010

"High-Spatial-Resolution Chemical Imaging: Biomedical Applications for Pathology and in vivo Imaging,"Carol Hirschmugl, University of Wisconsin, Milwaukee, hosted by Leonidas Ocola

Abstract: Chemical imaging concurrently provides morphological and chemical information about a sample by combining microscopy and spectroscopy. An emerging technology for this is synchrotron based wide-field Fourier Transform infrared (FTIR) imaging, which uses a chemically sensitive infrared microscope illuminated with a stable, broadband source and equipped with multiple, parallel detection channels. This instrument will greatly expand the ability to examine biological structures, and to track their chemical changes. The probe is nondestructive, making it feasible to study living cells, and one obtains chemical images with diffraction-limited resolution in minutes. In comparison, more commonly used visible light microscopy reveals the morphology of a sample through colour and contrast from labels such as fluorescent proteins or other sample preparation techniques that are frequently chemically specific. Importantly, infrared imaging provides new opportunities, since it delivers both morphological and chemical information without the need for stains or labels. The design of this facility and initial applications of biomedical interest will be presented.

High-resolution synchrotron imaging has the potential to be very useful for biomedical research. Whilst the major cell types within human tissue; epithelial and stromal cells, may be resolved using conventional FTIR imaging, there are a number of very important cell types that cannot be easily identified including basal cell, endothelial cells and immune cells. The identification of cell types within tissue using IR imaging is critical for understanding cell and tissue systems and is the key approach to diagnosis of diseases within tissue. The work demonstrated here shows a significant improvement in spatial resolution, potentially allowing for the identification of very small cell types in prostate and breast tissues.

Another example of the research enabled by this system includes subcellular spatially resolved spectra of molecular changes in brain tissue induced by Alzheimer disease (AD). The hallmark characteristics of AD include formation of extraneuronal plaques (aggregated ß-amyloid protein) and intraneuronal neurofibrillary tangles (NFT, fibrillar hyperphosphorylated tau protein). Numerous models for their biogenesis have been proposed but the etiology and pathogenesis are still not well understood. Our work is based on two mouse lines that express two familial AD mutations, K670N/M671L and V717F mutant form of human APP695, and a different, triply mutant mouse.

November 22, 2010

"A New Portable Nucleic Acid Impedance Detection Platform based on Electrokinetic Nanosensors," Chia Chang, University of Notre Dame, hosted by Leonidas Ocola

Abstract: We report a new label- and PCR-free portable DNA/RNA detection platform based on nanomembrane sensors embedded in continuous flow microfluidic biochips. The nanomembranes are synthesized or fabricated on the sides of the microflow channel to allow a large flow throughput, and are functionalized with oligo probes. Fabricated microelectrodes sustain a dc or ac electric field across the membrane to create an ion depleted zone on the probe-covered membrane surface: to remove inhibitors and contaminants but also to effect a dielectrophoretic trapping action to rapidly transport the target molecules from the flowing solution to the probe. The same electrodes are used to measure both impedance and conductance signals of the hybridized molecules on the membrane surface, with the conductance signals amplified by charge inversion effects and the impedance Warburg signals by the ion depletion dynamics. The shear force due to the high throughput flow minimizes nonspecific binding and yields highly selective hybridization. Preliminary data with dengue virus, Carcinus maneas, green crab and Daphinia magna-water flea show picoM detection limit, large dynamic range, single-mismatch (SNP) discrimination in a 26 docking sequence of a kb target and 1-minute assay time without pretreatment and with a single turnkey operation. RNA detection with this rapid portable platform is particularly attractive, as most organisms produce many (ten thousand) more copies of mRNA than DNA but the RNAs degrade within 30 minutes without preservation. Plasmonic sensors are being integrated into this platform to allow multitarget detection.

November 19, 2010

Research and Developments on Spintronics at AIST,” Shinji Yuasa, National Institute of Advanced Industrial Science and Technology, hosted by Tiffany Santos

Abstract: AIST is one of the biggest national research institutes in Japan. The Spintronics Research Center at AIST was established in 2010 to promote research and development in spintronics. We are working on various topics ranging from basic studies of semiconductor spintronics to device applications such as magnetoresistive random access memory (MRAM). In this seminar, I will talk about our research activities based on magnetic tunnel junctions such as spin-transfer-torque MRAM, spin-torque microwave oscillator, and novel physical random number generator.

October 20, 2010 Hybrid porous materials for responsive nanomachine and catalyst,” Rui Liu, University of California, Riverside, hosted by Elena Rozhkova

Abstract: A series of hybrid porous materials have been synthesized by combining the unique features of mesoporous materials and functional molecules. Several responsive nanomachines have been developed by using mesoporous materials as reservoir and functional polymers or nanoparticles as valves to perform the controlled responsive functionalities. Sulfonated mesoporous carbons have been synthesized and show stable and highly efficient catalytic performance in biodiesel production.

October 20, 2010

"What in the World is M2D2?", John Mitchell, Materials Science Division, Argonne National Laboratory, hosted by Amanda Petford-Long

Abstract: Materials and molecular fesign and fiscovery (M2D2) is one of Argonne's major initiatives that will cross-cut divisions, disciplines, and programs in the coming years. But who and what exactly is M2D2? What are we trying to accomplish, what scientific and technological directions do we plan to follow, how are we organized, where are we headed? And most importantly, how does the CNM fit in? I will present the M2D2 vision as it stands today, tell you how we have seeded an initial program, and briefly highlight our path forward. I hope this will be a very interactive discussion and I welcome your questions, comments and thoughts on how to help define the CNM's role in M2D2.

October 18, 2010 Engineering Single Nanostructures as Plasmonic Antennas for Giant Raman Enhancements,” Matthew Rycenga, Washington University, hosted by Elena Rozhkova

Abstract: Antennas, like radio antennas, can collect radio waves and convert them into an electric current. Similarly, metal nanostructures can serve as antennas to convert light into surface plasmons, which are electromagnetic waves coupled to the collective oscillations of free electrons in a metal nanostructure. By tailoring the size, shape, and environment of a metal nanostructure, light can be manipulated in remarkable ways far below the diffraction limit. For example, light can be concentrated into tiny volumes with specially designed nanostructures, creating giant electromagnetic field (E-field) enhancements. These types of nanostructures are ideal for surface-enhanced Raman scattering (SERS), whereby the enhanced E-fields of a nanostructure can increase the Raman scattering of molecules in their vicinity by factors up to 1012. This talk will discuss the methods we have developed to study and characterize the SERS of single nanostructures, one at a time. This allows for an accurate comparison between a nanoparticle’s structure to its SERS. Such close scrutiny can reveal variables connected to SERS that have largely gone unnoticed. In particular, we have developed a new strategy for creating giant Raman enhancements by using the substrate supporting a nanoparticle. This allows for a single silver nanocube to approach single molecule detection with SERS. This simple technique will be discussed in context to our previous work using individual silver nanostructures for SERS.

October 8, 2010

Material properties of self-assembled actin bundles," Alec Robertson, Massachusetts Institute of Technology, hosted by Amanda Petford-Long

Abstract: Actin is an ubiquitous structural protein fundamental to such biological processes as cell motility and muscle contraction. Our model system is the acrosome of the Limulus sperm, which extends a 60-m-long actin bundle during fertilization. It is an example of a biological spring where the force of elongation derives from twist energy stored within the bundle during spermatogenesis. In addition to actin, the acrosome comprises only one other protein: scruin, an actin-binding protein specific to Limulus that decorates and cross-links actin filaments into a crystalline bundle. This talk will present the self-assembly of acrosome structure using these two proteins and their characterization by optical means, in order to elucidate the role of cross-linking in actin bundle formation and mechanics.

A multiscale approach is adopted wherein the bending rigidity of actin bundles and their constituent filaments are probed individually, then interrelated by simple mechanical models. Material properties of filaments and bundles are measured using a combination of optical tweezers, electron and fluorescence microscopy. Actin-scruin bundles assembled off acrosome fragments are found to display an ordered structure and a bending rigidity orders of magnitude higher than their individual filaments, while actin-only bundles formed by osmotic pressure exhibit similar properties, suggesting an intrinsic regime of crosslinked actin bundle formation. A second regime also emerges, spanning several orders of magnitude in bending rigidity and mediated by scruin conformation and bundle crystallinity. These highlight a cell’s ability to tailor the rigidity of its cytoskeleton to meet specific mechanical requirements, either by varying stiffness over orders of magnitude through conformation changes to a single actin-binding-protein, or through the use of different cross-linking mechanisms to achieve comparable rigidities.

September 14, 2010

Spin Currents: New Opportunities at the Nanoscales,” IAxel Hoffman, Argonne National Laboratory, Materials Science Division, hosted by Amanda Petford-Long

Abstract: The recent development of spintronics aims at utilizing the spin degree of freedom for electronic applications. To date, in most investigated spintronics systems and devices, spin currents are mainly considered as spin-polarized charge currents, and as a result, the spin and charge currents are in parallel and directly coupled. However, using nonlocal geometries allows us to separate spin and charge currents, which in turn enables the investigation of pure spin currents This approach opens up new opportunities to study spin-dependent physics and gives rise to novel approaches for generating and controlling angular momentum flow.

In this talk, I will review our work on pure spin currents generated in various different ways. First, I will discuss electrical injection coupled with nonlocal spin-dependent potentiometric detection, from which we can directly determine spin-diffusion lengths and spin relaxation times. In particular, by investigating the temperature dependence of spin and charge relaxation times, we can identify different spin relaxation mechanisms. In mesoscopic silver wires, we observed that the spin flip probability for surface scattering is significantly larger than for the bulk.

Second, I will discuss the practical usefulness of using spin Hall effects due to spin-dependent electron scattering, which has been suggested as a pathway to pure spin currents without the need to employ ferromagnetic materials. However, in our measurements, we can exclude any large spin Hall effects in gold, which nevertheless has relatively strong spin-orbit coupling. In fact, we found an upper limit for the spin Hall angle of 0.022 at 4.5 K and 0.027 at 300 K.

Lastly, I will discuss spin pumping, which allows the generation of pure spin currents by exciting ferromagnetic resonance in an adjacent ferromagnet. This later approach is attractive, since it allows the macroscopic generation of pure spin currents without the need of directly applied charge currents. These measurements allow us to uniquely quantify spin Hall effects in a wide variety of materials, such as platinum, palladiu, gold, and molybdenum.

August 26, 2010

Perspectives on Resistance Change Random Access Memory (ReRAM) Technologies,” In Kyeong Yoo, Samsung Electronics, hosted by Amanda Petford-Long

Abstract: Oxide materials have attracted much attention for their memory switching properties and electron mobility, which are higher than those for amorphous silicon. Some applications such as ReRAM for nonvolatile memory and oxide TFT for display were proposed, and excellent progress has been demonstrated. However, it is not clear yet whether or not new services will require oxide devices integrated into IT devices, because of uncertainty in technology trends and directions. For example, ferroelectric random access memory (FRAM) was one of the promising candidates for nonvolatile RAM in 1996; however, NAND Flash is replacing hard disk drives (HDDs) with a form of solid-state disks (SSDs), and dynamic random access memory (DRAM) is still a core device in the computer system. This is because new product concepts are developed by utilizing existing feasible technologies, components, and devices. It is thought that new technology alone cannot meet the product trends, so that there are gaps between service patterns and technology evolution. It is suggested that the gap stems from the differences in the way of reasoning in service concept and technology prediction. Evolution pattern in products and technologies are analyzed in order to understand the reasoning differences. Approaches on how to connect product concept with technology forecast will be proposed with an example. Finally, the mechanisms and issues in ReRAM will be reviewed in the viewpoint of possible new products.

August 4, 2010

Radiation-Enhanced Transverse and Lateral Diffusion in Nanoscale Structures,” Bhupendra N. Dev, Indian Association for the Cultivation of Science, hosted by Jin Wang and Xiao-Min Lin

Abstract: Ion irradiation of a material usually gives rise to enhanced diffusion. To use it or to avoid unwanted diffusion, the diffusion enhancement process needs to be understood. We follow ion-beam-induced migration of iron impurity atoms in a Pt/C multilayer, where each layer is about 2 nm thick, by the X-ray standing wave (XSW) technique. We find that iron atoms migrate from C- to Pt-layers, forming FePt ferromagnetic nanoparticles. As a consequence, an ion-beam-induced nonmagnetic-to-ferromagnetic transformation is revealed by magnetooptical Kerr effect measurements.

For nanoelectronic applications, p-type doped nanoscale structures can be fabricated by implanting gallium ions from a focused ion beam source into an n-type silicon substrate. However, how closely these structures can be fabricated would be governed by the lateral diffusion coefficient of the implanted atoms. Determination of lateral diffusion coefficient is difficult. We demonstrate a method for the determination of lateral diffusion coefficient based on photoemission electron microscopy and discuss the extent of diffusion in the light of nanoscale fabrication.

July 19, 2010

Domain-wall dynamics in ferromagnetic nanowires with spiral order and minimization of Ohmic losses,” Oleg Tretiakov, Texas A&M University, hosted by Amanda Petford-Long

Abstract: I will talk about current-induced magnetization dynamics in thin ferromagnetic wires. It is known that there are two regimes of the domain wall motion in the wire, depending on applied current. Below the critical value of current, the magnetization in the domain wall does not rotate, whereas above the critical current domain wall both moves and rotates. We determine the domain wall dynamics as a function of applied current and calculate the drift velocity of the domain wall along the wire. First, I will show that the critical current is suppressed in the presence of Dzyaloshinskii-Moriya interaction (DMI). This suppression is exponential at large DMI. Second, I will propose a novel way to move domain walls with a resonant time-dependent current.

This method dramatically decreases the Ohmic losses in the wire and allows to drive the domain wall with higher speed without burning the wire. For any domain wall velocity, we find the time dependence of the current needed to minimize the Ohmic losses. Furthermore, I will identify the wire parameters for which the losses reduction from its dc value is the most dramatic. I will show that our approach gives a dramatic power reduction even in the least favorable cases of the systems with very weak or very strong nonadiabatic spin transfer torque (conventionally described by the parameter beta), thus opening new doors for using materials with much wider range of beta for spintronic devices.

June 14, 2010

STM Manipulation of Charge, Spin, and Conformation of Atoms and Molecules,” Saw-Wai Hla, Ohio University, hosted by Axel Hoffmann

Abstract: Scanning tunneling microscope (STM) manipulation of single atoms and molecules on surfaces allows construction of artificial structures on an atom-by-atom basis and demonstration of single-molecule devices one molecule at a time. STM is not only an instrument used to "see" individual atoms by means of imaging, but also a tool used to "touch" and "take" atoms and molecules or to "hear" their vibration by manipulations. Therefore, STM can be considered as the "eyes, hands, and ears" of the scientists connecting our macroscopic world to the exciting world of atoms and molecules.

In our research projects, we combine a variety of STM manipulation schemes with tunneling spectroscopy techniques to investigate properties of atoms and molecules on surfaces. This talk will include our recent achievements: In spintronic research, we will show imaging and manipulation of spin directions in individual atoms. In superconductivity, we will present the smallest molecular superconductor ever studied to date. Here, the finding of superconductivity in just four pairs of (BETS)2-GaCl4 molecules not only provides the possibility of investigating this phenomenon locally, but also opens the potential for applications in nanoelectronics. In molecular devices, single-molecule switches and molecular rotors operated by injecting tunneling electrons from an STM tip will be presented. These innovative experiments are tailored to address several critical issues covering both basic science and demonstration of novel atomic and molecular devices.

June 10, 2010

Polarization Dynamics and Ionic Currents on the Nanoscale: New Applications of Piezoresponse Force Microscopy and Spectroscopy,” Sergei V. Kalinin,Oak Ridge National Laboratory, hosted by Axel Hoffmann

Abstract: Coupling between the electric fields and strains is ubiquitous on the nanoscale, ranging from piezoelectricity and electrostriction in ferroelectrics to complex phenomena mediated by the ionic currents in energy storage and conversion materials and correlated oxides. In this presentation, I will summarize recent advances in piezoresponse force microscopy applied for studies of bias-induced phase transitions in ferroelectrics and multiferroics, and demonstrate potential for mapping polarization switching on a single-defect level. Phase-field modeling allows the corresponding mesoscopic mechanisms to be deciphered and further suggests strategies for (symmetry forbidden) manipulation of in-plane polarization component. Controlled creation of ferroelectric closure domains is demonstrated.

In the second part of the talk, I will demonstrate how scanning probe microscopy can be use to probe electrochemical behavior of nanoscale volumes based on the strong strain-bias coupling inherent for lithium-ion and oxygen conductive materials. The imaging capability, as well as time and voltage spectroscopies analogous to traditional current-based electrochemical characterization methods are developed. The reversible intercalation of lithium and mapping electrochemical activity in LiCoO2 is demonstrated, illustrating higher lithium diffusivity at non-basal planes and grain boundaries. In silicon anode device structure, the direct mapping of lithium diffusion at extended defects and evolution of lihtium activity with charge state is explored. The electrical field-dependence of lihtium mobility is studied to determine the critical bias required for the onset of electrochemical transformation, potentially allowing reaction and diffusion processes in the battery system to be separated at each location. The scanning probe microscopy measurements are compared with classical characterization methods such as cyclic voltammetry and electrochemical impedance spectroscopy. The prospects for using scanning probe microscopy for battery and fuel cell characterization are discussed.

June 3, 2010

Biological and electrochemical approaches towards tunable synthesis and assembly of nanostructures,” Joun Lee, University of California, RIverside, hosted by Elena Rozhkova

Abstract: Noble metal and semiconducting nanostructures have received much attention for their exciting optical, catalytic, and electrical properties, which can be tuned further by changing size, shape, and composition. A number of conventional synthesis and assembly methods have been studied by taking chemical and physical approaches. However, environmental concerns and the pursuit of highly selective self-assembly have motivated scientists to explore alternative methods for the synthesis and assembly of nanostructures, in particular using biological entities. In this talk, tunable synthesis and assembly techniques using amino acids and DNA will be presented with a combination of electrochemical methods. The research outlined in this talk will describe recent advances on (1) environmentally benign processes to synthesize gold nanostructures in controlled shape and size by use of amino acids, (2) spatially controlled assembly of nanowires via DNA hybridization, and (3) growth of tellurium and palladium on the surfaces of silicon using galvanic displacement.

May 28, 2010

Measurements and Coupling of Electrical and Electromechanical Characteristics of Piezoelectric Thin Films for piezo-MEMS Applications,” Andreas Roelofs, aixACCT Systems Inc., hosted by Amanda Petford-Long

Abstract: Micro-electromechanical systems (MEMS) based on piezoelectric thin films are leading candidates for a broad range of new applications (e.g., energy harvester for autonomous devices and self-controlled sensors for space applications, piezoelectric printer heads and tilted mirror arrays). The characterization of the piezoelectric film properties is essential for device design as well as device simulation and critical for process qualification. Especially process qualification requires characterization of the piezoelectric films after steps such as etching and annealing as the piezoelectric properties can be altered by thermal cycles and exposure to different chemical environments. Therefore, comprehensive electrical and electromechanical characterization of the integrated piezoelectric material is necessary.

Different measurement methods for the investigation of the piezoelectric thin film properties are discussed. The first method presented focuses on dedicated test samples adapted to a four-point bending set-up in which a new characterization method is presented that combines the measurement of the effective longitudinal (d33,f) and the transverse piezoelectric coefficient (e31,f). This new set-up allows fast and accurate measurements of both coefficients on the same sample under well-defined homogeneous mechanical strain. Stress and corresponding strain distributions in the film were verified by finite element simulations.

To ramp up to production, the testing cannot be carried out solely on dedicated test samples; the only feasible method is wafer level testing. This is necessary to capture distributions across the wafer and variations in the manufacturing process. However, in wafer level testing only d33,f can be accessed directly but not e31,f, which is the relevant coefficient for piezo-MEMS functionality.

This issue will be addressed in the second part of the paper where we present a method to determine the correlation between e31,fand d33,f, resolving the wafer level testing challenge.

May 27, 2010

"Quantum Optical Applications in Spectroscopy: Investigation of Entangled Two-Photon Absorption in Organic Dendritic Systems," Özgün Süzer, University of Michigan - Ann Arbor, hosted by Jeffrey Guest

Abstract: Entangled states of light have received great interest in recent years for the purposes of spectroscopy as well as for applications such as quantum information manipulation, quantum communication, and investigations of the foundations of quantum mechanics. It has been theoretically shown that the interaction of entangled light with matter will exhibit interesting non-classical effects, which have been demonstrated in experiments carried out in our laboratory. This presentation will discuss the application of entangled states of light toward spectroscopy wherein entangled pairs of photons are utilized to excite two-photon transitions in various organic molecules under extremely low excitation flux levels. The entangled-pair flux utilized to excite two-photon transitions in our experiments constitutes approximately 10 orders of magnitude fewer photons than any classical counterpart requires. Further, collection of fluorescent light from an organic dendrimer subsequent to two-photon excitation by entangled pairs of photons is presented. A novel, high geometric efficiency, spherically-enclosed optical collection system for collection of the resulting fluorescence photons is introduced, which is utilized to circumvent any drawbacks related to the low flux conditions under which experiments are carried out and the weak quantum yield of the organic materials. These novel results have widespread impact in applications ranging from spectroscopy to chemical and biological sensing, imaging, and microscopy.

May 26, 2010

"Quantum Optical Applications in Spectroscopy: Investigation of Entangled Two-Photon Absorption in Organic Dendritic Systems," Özgün Süzer, University of Michigan - Ann Arbor, hosted by Jeffrey Guest

Abstract: Entangled states of light have received great interest in recent years for the purposes of spectroscopy as well as for applications such as quantum information manipulation, quantum communication, and investigations of the foundations of quantum mechanics. It has been theoretically shown that the interaction of entangled light with matter will exhibit interesting nonclassical effects, which have been demonstrated in experiments carried out in our laboratory. This presentation will discuss the application of entangled states of light toward spectroscopy wherein entangled pairs of photons are utilized to excite two-photon transitions in various organic molecules under extremely low excitation flux levels. The entangled-pair flux used to excite two-photon transitions in our experiments constitutes approximately 10 orders of magnitude fewer photons than any classical counterpart requires. Further, collection of fluorescent light from an organic dendrimer subsequent to two-photon excitation by entangled pairs of photons is presented. A novel, high-geometric-efficiency, spherically enclosed optical collection system for collection of the resulting fluorescence photons is introduced, which is used to circumvent any drawbacks related to the low flux conditions under which experiments are carried out and the weak quantum yield of the organic materials. These novel results have widespread impact in applications ranging from spectroscopy to chemical and biological sensing, imaging, and microscopy.

May 26, 2010

"Oxygen Reduction Reaction on Core-Shell Metal Alloy Catalysts: Density functional Theory Studies," Pussana Hirunsit, Texas A&M University, hosted by Jeffrey Greeley

Abstract: Platinum-based alloys are used to catalyze the molecular oxygen decomposition and its subsequent reduction to water on fuel cell electrodes. In particular, core-shell structures with a monolayer of platinum on the surface have been proposed and are being intensively tested to determine activity and durability in acid medium. In this presentation, I will report results of surface segregation and other factors that influence oxygen reduction reaction (ORR) activity and surface stability against dissolution. Density functional theory (DFT) analysis of calculated surface Pourbaix diagrams and reaction mechanisms provides useful predictions on onset water oxidation potential, surface atomic distribution, most stable coverage of oxygenated species, and activity. I will first discuss structures proposed by Adzic and collaborators, consisting of a surface platinum-skin monolayer over an IrCo or Ir3Co core, with or without a palladium interlayer between the platinum surface and the Ir-Co core. I will emphasize the role of the palladium interlayer in the core-shell structures that have experimentally shown higher ORR activity relative to Pt(111) surfaces. Second, I will analyze a new core-anchor-shell material that, based on DFT calculations, is predicted to have improved stability and maintain relatively high ORR activity. Here I will focus on the stability and activity enhancement of Pt/Fe-C/core, Pt/Co-C/core and Pt/Ni-C/core demonstrated with core materials of Ir, Pd3Co, Ir3Co, IrCo and IrNi.

May 24, 2010

"Ubiquinone analogs and their reactivity with the bc1 complex and a cytochrome b mutant," Diana Cedeno, University of Arizona, hosted by Elena Rozhkova

Abstract: Cytochrome bc1 (Complex III) is an important enzyme that takes part in the respiratory electron transport chain in vertebrates, yeast, and many bacteria. The complex exists as a dimmer and each monomer contains three catalytic subunits: cytochrome c1, cytochrome b and the Rieske iron-sulfur protein or ISP. Within the inner mitochondrial membranes of eukaryotes, Complex III catalyzes the transfer of two electrons from ubiquinol (UQH2) to cytochrome c, a water-soluble protein. At a separate site of the same complex, two electrons are sequentially transferred from a ubiquinone molecule (UQ) to form UQH2. These redox processes and the associated proton transfers ultimately establish a proton gradient across the membrane that is used to drive ATP synthesis. This process is known as the Q-cycle mechanism. Under very specific conditions, avoidance of the Q-cycle mechanism leads to bypass reactions including the formation of superoxide and reactive oxygen species. The structure of UQ consists of a p-quinone head group and a hydrophobic isoprene unit (tail) that can vary in length depending on the species in which it is found. The present work highlights modifications to the substituent groups attached to the quinone head and to the length of the isoprene unit. Since the midpoint potentials of these molecules are pH dependent, cyclic voltammetry and spectroelectrochemistry studies in buffered aqueous solutions have been carried out on these molecules (analogs of UQ). Modifications of the substituent groups attached to the quinone head gave the molecules a different ability to either donate or receive electrons, while modifications to the length of the tail either increased or decreased the solubility of these molecules inside the phospholipid membrane. We examined the normal activity and the production of superoxide in wild-type and a cytochrome b mutant (T61V) of bacterial Rhodobacter sphaeroides in the presence of these analogs. We confirmed that, to prevent damaging side reactions, normal operation of the Q-cycle requires a fairly narrow window of reduction potentials with respect to the ubiquinol substrate.

May 13, 2010

"Stability in a Turbulent (Fermi) Sea: The Ever More Remarkable High-Temperature Superconductors ," Eric Hudson, Massachusetts Institute of Technology, hosted by Axel Hoffman

Abstract: For over two decades high-temperature superconductivity has captured the attention of scientists the world round. However, rather than finding a simple explanation for the properties of these materials, as was done for their low-temperature cousins half a century ago, intensive research has instead led to an increasingly complex picture of materials characterized by an intricate phase diagram, full of competing or coexisting states, yet still dominated by a superconducting state that persists, at least in some materials, almost halfway to room temperature.

In this talk I will describe nanoscale investigations of the electronic structure of high-temperature superconductors using scanning tunneling microscopy. We have recently found that a still-not-understood high-temperature phase in these materials, the pseudogap, is characterized by strong charge inhomogeneity. Surprisingly, although this disorder persists into the superconducting state, it does not seem to perturb coexisting homogeneous superconductivity. The resolution of this apparent contradiction gives new insight into the onset of superconductivity and its relationship with the pseudogap phase.

May 4, 2010

"Uncovering the Atomic-Scale Physics of Graphene," Gregory M. Rutter, National Institute of Standards and Technology, hosted by Nathan Guisinger

Abstract: Graphene, a two-dimensional honeycomb lattice of sp2-bonded carbon atoms, has received considerable attention in the scientific community due to its unique electronic and mechanical characteristics. Distinct symmetries of the graphene wave functions lead to unique properties, such as reduced back scattering and a half-integer quantum Hall effect. These quantum properties combined with its atomic thickness make graphene enticing for post-CMOS electronic applications. However, before graphene can be used as a new paradigm for nanoelectronics, a complete understanding of its electronic properties at the atomic scale is vital.

In this presentation, I will illustrate how scanning tunneling spectroscopy (STS) can be effectively used to investigate the atomic scale properties of graphene. First, I show how point defects can be used as local probes of the electronic structure via images of the energy-dependent standing-wave patterns that appear in maps of the differential conductance. Simple Fourier transform analysis can extract scattering wave vectors, leading to a local measurement of the energy-momentum dispersion, E(k). Then, I will discuss how STS can be used to uncover the unique magnetic quantization of graphene, the hallmark of the half-integer quantum Hall effect. In addition, I will show how such observations can be used to judge the quality of the graphene. Finally, recent STS data of exfoliated graphene on SiO2 in high magnetic field will be discussed. I will show clear evidence of single-electron charging and spatial mapping of localized states in the quantum Hal l regime.

May 3, 2010

"Advanced Confocal Microscopy," Wibool Piyawattanametha, National Electronics and Computer Technology Center (Thailand), hosted by Daniel Lopez

Abstract: Biomedical research needs new advances in imaging. Existing modalities of in vivo imaging, such as magnetic resonance imaging (MRI) or ultrasound, lack the spatiotemporal resolution required to image the fundamental building block of living tissue, namely ,the cells. By contrast, existing high-resolution techniques for imaging cells and their subcellular features are technologies that are best suited for in vitro experiments in tissue slices. Yet, the ability to make direct connections between human pathological symptoms and behavior and the underlying cells and molecules responsible for such behavior requires in vivo techniques that can image cellular constituents.

My research aim is to develop novel high-resolution (submicron to 5-micron) optical endoscopes to satisfy unmet needs in the clinical environment. These differ from medical endoscopes, which are generally larger and designed to image macroscopic abnormalities. Most importantly, this novel optical endoscopic imaging might suggest new approaches to disease diagnoses and treatment. This talk will be focused on the development of a novel confocal imaging modality integrated with microelectromechanical systems (MEMS) technology and their imaging applications.

Confocal microscopy is an attractive tool for three-dimensional imaging because of its optical sectioning property. Conventional single-axis confocal microscopes have a trade-off among resolution, field of view, and objective lens size, since a high numerical aperture lens is needed for sufficient resolution, and a long focal length is needed for a large field of view and working distance. A dual-axis confocal (DAC) microscope architecture has been proposed that uses two overlapping low numerical aperture beams and effectively decouples these trade-offs.

The DAC architecture offers several advantages over the traditional single-axis confocal architecture, such as simplicity in miniaturization from deploying low numerical aperture lenses and aberration-free beam scanning from post-objective scanning configuration. Another important advantage is the ability to achieve a much superior optical sectioning. The microscopes are miniaturized into form factors (5- and 10-mm diameter). The imaging demonstrations of the probes will be on both ex vivo and in vivo samples from mice and human for cancer oncology and genetic research.

April 29 2010

"Nanostructuring Thin Films for Optical Applications," Rosalia Serna, Instituto de Optica (Spain), hosted by Amanda Petford-Long

Abstract: The development of thin films with functionalized optical response is relevant in technological areas such as photonics and photovoltaics. Optical doping by incorporating rare-earth ions and/or nanoparticles is a particularly useful method to produce active materials with novel and improved optical response, including light emission, optical gain, and enhanced nonlinear optical properties. This talk will show how nanostructured optically doped dielectric thin films are prepared by pulsed laser deposition with a control within the nanometer scale on the dopant location, and how such a nanometric control is a powerful tool to provide a new insight in the understanding of ion-ion and nanoparticle-ion energy transfer processes. Special consideration will be given to recent results on the enhancement of Er3+ infrared emission by codoping with silicon nanoparticles. The erbium-silicon nanoparticle codoped films benefit from the broad absorption band (ultraviolet-visible) of the silicon nanoparticles and their ability to transfer the absorbed energy to a nearby Er3+ ion. However, for an efficient performance this system requires the formation of silicon nanoparticles with an appropriate size and density, and an erbium spatial distribution that maximizes the number of ions separated from a silicon nanoparticle at a distance below the interaction length (≤ 1 nm). The design of nanostructured doped films allows successfully meeting these demands and photoluminescence measurements show that this method allows to obtain the larger fraction of erbium ions efficiently excited through silicon nanoparticles ever reported.

April 26, 2010

"Ultrafast Spectroscopy Study of Hot Carrier Dynamics and Coherent Controlled Photocurrent Generation in Epitaxial Graphene," Dong Sun, University of Michigan–Ann Arbor, hosted by Jeff Guest

Abstract: We have performed ultrafast pump-probe experiment in a wide range of wavelength on epitaxial graphene to study the ultrafast relaxation of hot Dirac fermionic quasiparticles. Our infrared DT spectra are well described by interband transitions with no electron-hole interaction. Our experiment time resolves the optical phonon and acoustic phonon scattering process. We also observed thermal coupling of hot carriers between graphene layers in epitaxial graphene and thermal coupling to the SiC substrate, both coupling are strong in the first few picosecond at high carrier temperature and significant slows down when electrons cools down. This indicates a high energy optical phonon related thermal coupling at initial cooling stage. Another work we can do with ultrafast spectroscopy is spectrally resolving the precise doping profile of heavily doped layers. We determined the screening length to be 1 layer in carbon face grown epitaxial graphene using ultrafast 800 nm pump, mid-infrared probe spectroscopy.

On the other hand, we have generated coherently controlled electrical currents in epitaxial graphene using both 3.2 μm/1.6 μm and 4.8μm/2.4 μm, 280fs pulses. These ballistic currents depend on relative phases between pulses. By pre-injection background hot carriers in the system and cool down to low temperature with a novel near field THz detection technique, we have studied effect of hot carriers in the coherent controlled photocurrent generation.

April 21, 2010

"Nanostructured Organic Semiconductor Solar Cells," Charles T. Black, Brookhaven National Laboratory, hosted by Amanda Petford-Long

Abstract: Solar cells based on organic semiconductors inspire a long-term vision of electrical power generation from low-cost materials. A reason for optimism is that these materials can convert incident photons to electrons with high quantum efficiencies. Devices based on organic semiconductors operate with maximum overall power conversion efficiencies of ~5-7%, half of their potential and a quarter of the thermodynamic efficiency limit for a single-junction solar cell.High-performing organic bulk heterojunction active layers form via a self-assembly process of phase separation of blended donor and acceptor materials. Optimizing the device performance is a delicate balance of trapping the blended material in a nonequilibrium configuration.

I will discuss examples of our experimental efforts to improve organic bulk heterojunction solar cell performance by modifying the internal device architecture. In one case, we have incorporated nanostructured electrodes into the bulk heterojunction active layer to improve photovoltaic performance by shortening the travel distance for dissociated free charge carriers. Nonplanar electrodes permit a 20% increase in the blend layer thickness for optimal device performance, enhancing photocurrent output and associated photovoltaic power conversion efficiency by as much as ~10%. We are also pursuing a self-assembly-based approach to confining both organic semiconductors and semiconductor blends within nanometer-scale volumes for better control of material phase separation and understanding the effects of geometry on material structure, electronic properties, and photovoltaic performance. Changes in polymer chain alignment within the confined volumes lead to electronic mobility enhancements of more than two orders of magnitude, with associated improvements in solar cell efficiency.

April 13, 2010

"Basic characterization of Nanoparticles by X-ray absorption based-techniques: effect of environment on their fundamental properties," Felix G. Requejo, National University of La Plata, Argentina, hosted by Elena Shevchenko

Abstract: Basic properties of nanoparticles depend on (i) morphology and size , (II) crystal structure, and (iii) composition. Nanoparticles are usually too small to have bulk-like properties and, because of surface effects, they avoid interaction with the substrate, support, capping (from the synthesis process), or solvent media where they are immersed. A comprehensive characterization (with local-order sensibility, chemical selectivity, suitable to be performed in situ conditions) is mandatory to understand the correlation between "structure" and "property," and consequentially controlled and intelligent design in nanomaterials with specific aims.

In this work, we discuss the analysis of the distortion of homogenously dispersed and shaped colloidal platinum nanoparticles of about 2-nm diameter by their interaction with SBA-15 mesoporous silica and the effect of PVP capping on the thermodynamics of platinum nanoparticles, and the effect on synthesis route of the final atomic distribution in PtCo nanoparticles. Our independent characterization tools include those based on synchrotron radiation sources such as small-angle X-ray scattering (SAXS) and X-ray Absorption fine structure (XAFS).

April 7, 2010

"Ultrafast Dynamics of Photoexcited Bismuth Films," Yu-Miin Sheu, University of Michigan, hosted by Jeffrey Guest

Abstract: The carrier and lattice relaxation processes following photoexcitation in solids occur over time scales ranging from femtoseconds to nanoseconds. The eventual conversion of the light to lattice heating involves carrier-carrier, carrier-phonon, and phonon-phonon interactions. More fundamental understandings of these processes may lead to advances in thermoelectrics, photovoltaics, and other technologically important materials. Even for bismuth, a well-studied thermoelectric material, detailed information on these processes is still unavailable. I will present ultrafast optical andXx-ray studies of photoexcited carrier diffusion and recombination, acoustic phonon generation and propagation, and lattice heating and diffsion in thin bismuth films. The combination of laser and x-ray experiments confims that carriers relax by rapidly heating the lattice before diffusing and ultimately recombining, leaving an inhomogeneous temperature profile near the surface. We observe a temperature di scontinuity across Bismuth/sapphire interface and derive Kapitza conductance by depth- and time-resolved X-ray diffraction. Comparing counter-propagating and conventional pump-probe measurements at low excitation, we find that the carrier density is not determined by the electron-hole plasma temperature after a few picoseconds.

April 6, 2010

"Fabrication and characterization of plasmonic thin films and fluorescence spectroscopy based on an integrated optofluidic chip," Aiqing Chen,University of California, Santa Cruz, hosted by Jeffrey Guest

Abstract:: I will present my doctoral research on the fabrication and optical characterization of nanostructured ordered and disordered plasmonic thin films, specifically (a) polarization-sensitive optical response from circular and elliptical cross-section gold nanopillar arrays, ordered nanostructures prepared by electron beam lithography and (b) design and fabrication of large, broadband asymmetric mirrors through disordered silver nanoparticle coatings based on Tollen's reaction. Such nanoparticle coatings are extended to decorate the surface of silica microspheres (nanoshells) and self-assembly photonic crystals. Potential application such as increasing light trappings for thin-film solar cells with disordered silver nanoparticle coatings will be addressed.

I will also introduce my current research on fluorescence resonance energy transfer (FRET) and fluorescence correlation spectroscopy (FCS) based on an integrated optofluidic chip. FRET and FCS are two useful techniques to study the dynamics of biomolecules. Here we demonstrate a novel way of measuring FRET from oligonucleotides using an integrated optofluidic chip containing a planar liquid-core waveguide that can guide liquid and light simultaneously. By photobleaching the acceptors and manipulating the fluidic flow, we also demonstrate controllable FRET events: an increase in donor signal, a decrease in acceptor signal and the recovery of FRET due to the influx of new FRET pairs. I will also introduce the first implementation of two-color fluorescence cross correlation spectroscopy in liquid-core waveguide and apply the technique to discriminate between singly and doubly labeled fluorescent nanobeads.

March 10, 2010

"Molecular Architectures based on Heteroborane Clusters: Electronic Structure and Applications in Nanosciences," Josep M. Oliva, Institute of Chemical-Physics (Spain), hosted by Stephen Gray

Abstract: In the last ten years, we have been interested in determining interesting properties derived from borane and heteroborane clusters, isolated and connected among them in different dimensions. Since their first syntheses in the 1960s, heteroborane clusters may become interesting tools for applications in recently developed nanosciences, such as ion/spin transport within molecular networks.

March 5, 2010

"Tuning between the Ferromagnetic and Antiferromagnetic Phases of La(1-x)Sr(x)MnO3 by Digital Synthesis,” Tiffany Santos, Distinguished Postdoctoral Fellow, Center for Nanoscale Materials, Argonne National Laboratory, hosted by Matthias Bode

Abstract: The perovskite manganite La(1-x)Sr(x)MnO3 has a rich magnetic and electronic phase diagram, exhibiting ferromagnetism for La-rich compositions and antiferromagnetism for those that are Sr-rich. Our interest lies in the region near the x=0.5 doping level containing the F-AF phase transition, particularly the role of disorder and strain in nucleating the F or AF state. Using ozone-assisted molecular beam epitaxy, we have synthesized fully-epitaxial superlattices of LaMnO3 and SrMnO3, designed to be equivalent in composition to random alloys of La(1-x)Sr(x)MnO3 in the vicinity of x=0.5. In our digital synthesis method, whereby we interleave single unit-cell layers of undoped LaMnO3 and SrMnO3 layers, we are able to tune between the ferromagnetic and antiferromagnetic metallic states by inserting an extra LaMnO3 or SrMnO3 layer, respectively. We have achieved atomic layer precision in the synthesis of these superlattices, as confirmed by our structural characterization.

Using neutron diffraction we have verified the A-type antiferromagnetic spin structure and measured a Néel temperature of 300 K, which is an enormous enhancement of 160 K over the value for bulk (unstrained crystal) La(0.5)Sr(0.5)MnO3. A large enhancement was also found for x=0.55. However, this material is on the verge of ferromagnetism. We find that inserting an additional single unit cell layer of LaMnO3 into the superlattice, and thereby delta-doping a layer of electrons, causes a significant increase of the net magnetic moment while still retaining the A-type spin structure. Our polarized neutron reflectometry experiments revealed a highly modulated moment commensurate with the structural periodicity of the superlattices, with higher moment in the region of the extra LaMnO3 layer. Thus, introducing a single La dopant layer results in a localized enhancement of ferromagnetic double exchange along the c-axis and a canted moment in an otherwise antiferromagnetic structure. The polarized neutron reflectometry measurements determined the length scale over which these delta-doped charges extend normal to the interfaces.

March 4, 2010

"Electrical and magnetic properties of epitaxial (SrMnO3)n/(LaMnO3)2 superlattices," Carolina Adamo, Cornell University, hosted by Matthias Bode

Abstract:: A variety of interesting and unexpected electronic and magnetic phenomena have been observed at the interfaces between different oxides and the role of the charge transfer across those interfaces has been actively studied in the recent years. In this context, (SrMnO3)n/(LaMnO3)2n superlattices, consisting of n planes of SrMnO3 alternated by 2n planes of LaMnO3, show a remarkable interfacial modification of the bulk properties of the two constituent materials: Although SrMnO3 and LaMnO3 are insulators, (SrMnO3)n/(LaMnO3)2n superlattices can become metallic. Dynamical mean field theory calculations have suggested that the metallic behavior nucleates from an electronic reconstruction at the interface and that the charge transfer effects extend deeply in the layers away from the interfaces, thus leading to original electronic and magnetic properties of the superalttices as a whole. In particular, (SrMnO3)n/(LaMnO3)2n superlattices are particularly interesting for having the same La/Sr stoichiometry ratio (i.e., Mn3+/Mn4+) as La2/3Sr1/3MnO3 (LSMO), the optimally doped Sr-based manganite.

However, in bulk LSMO La/Sr A-sites are randomly populated resulting in a disordered Coulomb trapping potential, whereas in SMOn/LMO2n superlattices an ordered sequence of SrMnO3 and LaMnO3 planes occurs. As a consequence the Mn3+/Mn4+ mixed valence arises only on the interfacial MnO2 planes, which are thus ferromagnetic (FM) and metallic (M) as opposite to the individual constituent blocks, where the MnO2 planes are antiferromagnetic (AF) and insulating (I). In fact LaMnO3 is a Mott insulator and SrMnO3 can be considered as a high spin "band" insulator. As a result, along the MnO2 plane sequence one should expect a region of transition from pure FM to pure AF ordering, possibly characterized by a spin canting regime.

The resistivity temperature dependence has been investigated by varying n from 1 to 8,. It can be observed that the (SrMnO3)n/(LaMnO3)2n superlattices with n ? 2 behave like the FM conductor LSMO. As n increases, themagnetic properties become dominated by the LaMnO3 layers, but the electronic transport properties continue to be controlled by the interfaces.

March 3, 2010

"Engineered Magneto-electric Heterostructures," Jaydip Das, Virginia Tech, hosted by Matthias Bode

Abstract: Engineered magneto-electric (ME) monolithic heterostructures are an extremely attractive option for high-performance, low -ost, and energy-efficient logic devices, sensors, communications, and RF applications. Such layered and composite structures can offer two kinds of cross-tuning: 1) electric field control of the magnetic response and 2) magnetic field control of the electric response. I will show evidence of both mechanisms for controlling thin-film ME heterostructures. Electric field control of the magnetic response in monolithic structures allows one to achieve a tuning of the ferromagnetic resonance frequency at 10- to 25-V applied voltages in the 10- to 60-GHz frequency range. All-oriented multilayered structures with low-loss yttrium iron garnet or barium hexaferrite and barium strontium titanate show frequency shifts of 2 MHz/V and 3.5 MHz/V at 10 and 60 GHz, respectively. These structures indicate a factor-of-10 improvement over the previous works on non-m onolithic structures and demonstrate substantial hybrid mode ME coupling between the magnetic and electric layers.

Further, our recent results for an ordered cobalt ferrite-bismuth iron oxide nano-array structure demonstrate a local control in the magnetic responses with electric fields. The tuning of electric response with magnetic fields allows one to use ME structures as magnetic field sensors. I will briefly present our approaches to develop highly sensitive ME laminate sensors at Virginia Tech. These optimized structures show magnetic field sensitivity as low as 0.3 nT and better object sensing capacity than some of the presently available sensors. Moreover, this work will present initial attempts to make semi-monolithic ME heterostructures that shows a control in the electric response with magnetic fields.

February 11, 2010

"Diruthenium Alkynyl Compounds and Their Role in Molecular Electronics," Tong Ren, Purdue University, hosted by Al Sattelberger and Derrick C. Mancini

Abstract:Our long-term goal is to achieve both molecular wires and devices based on Ru2-alkynyl species, for which facile charge transfer across the conjugated backbone of Ru2-alkynyl species is the key. Charge transfer properties have been carefully examined in Ru2- alkynyl compounds of extended carbon bridges and the voltammetric and spectroelectrochemical measurements revealed the facile electron transfer across both the carbon-rich bridges and the Ru2 fragment. Scanning tunneling microscopy study of Au-bound Ru2(ap)4((C≡CC6H4)2S)- indicated that the intrinsic conductance was significantly improved over the pure organic species of comparable lengths. The current-voltage characteristics of related compounds trans-(S(C6H4C≡C)k)Ru2(ap)4((C≡CC6H4)kS)- was also investigated using electromigration break junction technique, and highly reproducible conductance switching were uncovered at low potential bias.

February 5, 2010

"Nanostructured Semiconducting, Ferroelectric, and Multiferroic Crystals: Synthesis, Characterization and Energy Application," Jun Wang, Iowa State University, hosted by Elena Shevchenko

Abstract: Dye-sensitized solar cells (DSSCs), a photo-electrochemical technology, are one of the most promising of several alternative cost-effective concepts for solar-to-electric energy conversion that have been offered to challenge conventional silicon solar cells over the past decade. Compared with sintered TiO2 nanoparticle films, highly ordered TiO2 nanotube arrays possess excellent electron percolation pathway for vectorial charge transfer. Functional and multifunctional nanocrystals have attracted tremendous interest in various fields, such as energy conversion, bio-imaging, and drug delivery. Much attention has thus been given to the controlled synthesis of nanocrystals and their surface functionalization. In this presentation, our efforts on the synthesis and energy applications of various functional nanostructured materials will be presented. First I will introduce the electrochemical synthesis of nanoporous metal oxide thin films (i.e., porous alumina membrane and TiO2 nanotube arrays) and application of highly ordered TiO2 nanotube arrays for dye-sensitized solar cells where markedly improved photovoltaic performance is induced by rational surface engineering on TiO2 nanotubes. After that, I will show our recent progress on functional and multifunctional nanocrystals, including CdSe quantum dots, Cu2ZnSnS4 (CZTS) nanoparticles, TiO2 nanoparticles, magnetic nanoparticles, BaTiO3, and BiFeO3. These nanocrystals possess potential applications in solar cells, light emitting diodes, biosensors, thin-film capacitors, transducers, actuators, and magnetically recorded ferroelectric memory.

January 27, 2010

"Phosphorylated Peptide Enrichment Based on Nanoporous Metal Oxides," Dong-Keun Lee, Michigan State University, hosted by Elena Shevchenko

Abstract: Reversible protein phosphorylation is a key regulatory process in controlling many cellular events, such as cell cycle, cell growth, cell differentiation, and metabolism. To achieve detailed insights into the regulation of these reversible phosphorylation processes, it is often necessary to characterize the phosphorylation sites of specific proteins. However, the identification of phosphopeptides including phosphorylation sites by analytical technique, such as mass spectrometric methods, remains challenging. Therefore, specific isolation and enrichment of phosphorylated peptides are needed prior to the analytical process. So far the most common enrichment method is immobilized metal affinity chromatography (IMAC). However, because of the less selective interaction between phosphorylated proteins and the separation media, this technique still has limitations.

In the present work, mesoporous metal oxide films were designed and synthesized for the enrichment and separation of peptides down to pico- or femto-mole level. These functionalized media have rigid framework structures, regular mesoscopic pores (2.0 – 50 nm), and high surface areas (500 – 1200 m2g-1), which are a great advantage for protein separation. To increase the selectivity toward phosphopeptides, the mesoporous phases have been organically modified with diazo groups for coupling to the phosporylated proteins. In addition, other high-surface-area metal oxides films (functionalized silica, titania, and alumina) were synthesized, which also improves the selectivity and sensitivity toward phosphate enrichments in small volume fractions. Esterified and nonesterified tryptic digests of ovalbumin and β-casein were used to demonstrate phosphopeptide enrichment. The properties of the porous media and the methods used to achieve surface functionalization and phosphorylated peptides enrichment will be discussed.

January 20, 2010

"A Discussion of the Utility of Dealloyed Nanoporous Metals for Electrocatalysis," Jonah Erlebacher, Johns Hopkins University, hosted by Jeffrey Greeley

Abstract: Dealloying refers to the electrochemical dissolution of a majority component from a uniform multicomponent alloy. In certain controlled cases, the remaining components diffuse along the metal/electrolyte interface to restructure each grain of the polycrystalline alloy to possess high surface area and open porosity. Depending on the system of interest, one may find extremely small pores and extremely high surface areas, rivaling nanoparticles but with the added advantage of good electrical contact to all surfaces (e.g., ~2-nm ligaments and pores with ~50 m^2/g in dealloyed Ni/Pt). Dealloyed metals are also quite beautiful porous materials where the underlying crystallography is strikingly apparent, such as in dealloyed Ag/Au alloys. In this talk, I will discuss our current understanding of the physics and chemistry controlling the competition between dissolution and surface diffusion that leads to porosity evolution, as well as electrochemical methods to control pore and ligament size and the relative core/shell compositions of the dealloyed materials.

Dealloyed nanoporous materials naturally find utility in electrochemical catalysis, and we will also discuss their activity toward electrochemical oxygen reduction in aqueous solution. Oxygen reduction is famous for its inefficiency in hydrogen/oxygen fuel cells and the dealloyed Ni/Pt system is quite interesting for this application. Large roughness factors, well over 100, are easily fabricated, and we have measured half-waves for oxygen reduction in rotating disk electrode experiments over 0.98 V vs. RHE, a less-than 250 mV over potential. The origin of this effect is related to the high surface area, but not in a simple way, and we will argue that the effective "active area" of the porous metal is itself dependent on the overpotential. Finally, we will discuss composite nanoporous metals that further improve oxygen reduction activity.

 

2009 Seminars Archive

Date TItle

December 17, 2009

"Nanoplates by design and novel acoustic plasmons," Bogdan Diaconescu, University of New Hampshire, hosted by Jeffrey Guest

Abstract: Bottom-up synthesis methods open a path toward the growth of advanced and designable functional nanomaterials. I will show how rational self-assembly can be achieved on the basis of specific hierarchies of interactions between the molecular components. One compelling method for initiating the growth of nanostructured materials is to employ the natural tendency of layered thin films of dissimilar materials to form ordered arrays of misfit dislocation networks. On such systems, the self-assembly is driven by strain relaxation in the metal film. Another avenue is to use the intermolecular interactions to form ordered molecular arrays, where designed molecules yield predictable structures. This talk will focus on a few test systems highlighting such self-assembly processes and unraveling the underlying driving interactions. I will compare the different self-assembly mechanisms of molecules on strained metallic films of Ag on Ru(0001) and Au(111). Both growth processes are generally applicable to many functionalized C60 molecules, thus opening avenues towards functional and designable self-assembled structures based on a lock-and-key type approach.

The recent discovery of a fundamentally new sound-like plasmon on a bare metal surface of beryllium may introduce a new research direction in the area of plasmonics. While conventional surface plasmons are optical modes and have finite excitation energy of a few electron-volts, the novel acoustic surface plasmon (ASP) mode can be excited with very low energies of a few milli-elelctron-volts. This allows, in principle, for coupling with infrared and visible light for optical signal processing and advanced microscopies as well as low-energy chemistry on metallic surfaces. I will present results showing the acoustic character of the new plasmon as measured on the compact surfaces of beryllium, copper, and gold. Furthermore, I will show that the novel ASP is a general phenomenon on metal surfaces that support a partially occupied surface state within a wide bulk energy gap. The ASP is caused by the nonlocal screening of the surface electrons due to bulk electrons.

December 15, 2009

"Exploring Photomechanical Molecular Switching at Surfaces," Jongweon Cho, University of California - Berkeley, hosted by Nathan Guisinger

Abstract: The possible reduction of mechanical devices to molecular length scales provides many exciting possibilities for enhanced speed, device density, and new functionality. Optical actuation of nanomechanical systems through the conversion of light to mechanical motion is particularly desirable because it promises reversible, ultrafast remote operation. Past studies in this area have mainly focused on solution-based molecular machine ensembles, but surface-bound photomechanical molecules are expected to be important for future applications in this area. We have used cryogenic ultrahigh-vacuum scanning tunneling microscopy to study the surface-based photomechanical switching properties of a photomechanical molecular candidate called azobenzene. I will discuss our observations of the switching properties of individual azobenzene derivatives on gold, including wavelength-dependent photoswitching cross sections, new surface-based photoswitching dynamical pathways, and the effects of molecular environment on molecular photoswitching behavior.

December 10, 2009

"Molecular Technologies for Sustainable Energy, Nanoelectronics and Gene Delivery Applications: Contributions from Modeling Towards Rational Design,"Sean C. Smith, University of Queensland

Abstract: We summarize several recent modeling studies within the Centre for Computational Molecular Science at The University of Queensland, which shed light "from the bottom up" on key structural, dynamical, and mechanistic questions that are central to attempts at rational design strategies in the application areas of the title. Specifically, the following topics are considered: (i) control of TiO2 nanoparticle morphology and visible light response for enhanced photocatalytic properties, (ii) exploration of electronic properties of novel nanotube and nanoribbon systems for nanoelectronic and spintronic devices and (iii) modeling of gene-nanoparticle complexation to facilitate a rational design approach to optimizing gene delivery efficiencies in mammalian cells.

December 3, 2009

"Radiative Coupling and Decay Properties of Quantum Confined Semiconductors,"Julian Sweet, University of Arizona, hosted by Matthew Pelton

Abstract: The first portion of my talk will explore excitonic polaritons in quasi-crystals. In contrast to traditional periodically spaced multiple quantum wells. Fibonacci-spaced multiple quantum wells represent an exciting example of a quasi-crystal; a structure that while lacking complete periodicity, still exhibits self-similarity and long range order. These active one-dimensional quasi-crystals can be grown by using a quantum well stack where the spacing between each quantum well is defined by the Fibonacci recursion relation.

As with its traditional periodic counterpart, a high reflectivity stop band arises when the Bragg condition is fulfilled. However, unique to the Fibonacci structure are both broad and fine structure dips within its stopband. The spectrally broad heavy-hole susceptibility curve and its proximity to the light hole make the nonlinear properties of this active Fibonacci quasi-crystal an excellent candidate for optical switching and slow light applications.

In the second part of my talk, I will discuss the radiative decay properties of self-assembled indium arsenide (InAs) quantum dots grown by molecular beam epitaxy. The measurement of radiative lifetime is used to determine dipole moment. In addition, evidence is presented of radiative lifetime reduction for quasi-resonant and strictly resonant time-resolved measurements. This lessening is attributed to carrier correlations that exist during resonant excitation but are not present during above-band pumping. Time-resolved PL spectra will be presented with respect to excitation power, energy,and polarization as well as sample temperature in order to determine dephasing times.

The final aspect will cover recent progress in the fabrication of GaAs photonic crystal slab nanocavities for use in cavity QED experiments. Factors such as cavity axis orientation and employing a potassium hydroxide etch to remove debris resulted in a substantial improvement in cavity quality factor.

November 20, 2009

"A Salt and Batteries: Applications of Nonresonant Inelastic X-Ray Scattering to Model and Applied Systems," Ken Nagle, University of Washington, hosted by Jorg Maser

Abstract: The rational design of improved electrodes for lithium ion batteries faces many barriers, not the least of which is a correct, fundamental understanding of the changes in electronic structure that accompany insertion and removal of lithium. For this reason, the DOE report "Basic Research Needs for Electrical Energy Storage" singled out nonresonant inelastic X-ray scattering (NIXS) as a promising technique for in situ studies of these basic electrochemical processes. NIXS at ~1-eV energy resolution provides a bulk-sensitive alternative to X-ray absorption spectroscopy for studies of low-energy (<1.5-keV) electronic transitions. Furthermore, at sufficiently high momentum transfer, NIXS is sensitive to dipole-forbidden transitions, providing additional information about electronic structure. After illustrating these issues with a study of Na 1s core excitons in NaCl and NaF, I will discuss the application of NIXS to ex situ and in situ studies of lithiation of transition met!

November 19, 2009

"Study of Novel Materials for Nanoelectronics: A Scanning Probe Microscope Study of Graphene and Graphite Oxide," Deepak K. Pandey, Purdue University, hosted by Nathan Guisinger

Abstract: Approaching the miniaturization limit of silicon based microelectronics has presented ample research and development opportunities to grow and characterize materials for next-generation electronic devices. Scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), and atomic force microscopy (AFM) offer unique capabilities for investigating the structural and electronic properties of these materials. Novel materials such as hybrid organomolecular silicon, graphene, and graphite oxide were examined during this study.

STM and STS studies were performed on two organic molecules, 4-trifuoromethylbenzenediazonium tetrafluoroborate and 4-methylbenzenediazonium tetrafluoroborate, covalently bonded to hydrogen passivated Si(111) substrate. It was established that STS can provide reproducible current-voltage response, I(V), on organic films of these molecules covalently bonded to Si(111) substrate. With the help of STS we were able to demonstrate that conductance is strongly dependent on the terminal molecular end-group of the molecule attached to the substrate.

STM studies were performed on epitaxial graphene films grown on the carbon face of 4H-SiC (0001) substrate by thermal annealing. The hexagonal arrangement of carbon atoms on few-layer graphene (FLG) were identified, conforming the good quality of graphene prepared.

STM and AFM studies were also performed on graphene films grown by chemical vapor deposition (CVD) on a thin metal film of nickel/copper and transferred on to silicon dioxide (SiO2) substrate. Large area STM/AFM scans (5 × 5 μm) demonstrated the presence of ridges and wrinkles arising from thermal mismatch of the carbon and the metal underneath. High-resolution STM images demonstrated the hexagonal lattice of carbon atoms, confirming the growth of FLG.

STM/STS and AFM studies were performed on atomically thin graphite oxide flakes deposited on highly oriented pyrolytic graphite (HOPG) substrate. AFM topography and phase images indicated the presence of graphite oxide flakes of mean area 5 μm 2 on HOPG. AFM images also showed varied topography including wrinkles, folds, and cracks in graphite oxide flakes, possibly arising during deposition process. Low-resolution STM images supported the topography obtained by the AFM study. High-resolution STM images revealed a surface decorated with a rectangular lattice of oxygen atoms with lattice constants 0.273±0.008 nm and 0.406±0.013 nm. STS measurement indicated the presence of a finite band gap of 0.25 eV when graphite oxide is deposited on HOPG.

November 5, 2009

"Understanding Porphyrin Supermolecules for Energy Conversion In Dye-sensitized Solar Cells," Chunxing She, Northwestern University, hosted by Matthew Pelton

Abstract: The Ru-dye based champion dye-sensitized solar cell (~11% efficiency) faces the challenge of gaining more photovoltage without enhancing recombination and sacrificing photocurrent. One strategy to this challenge is using supramolecular chemistry — dyes with high extinction coefficient to shorten transport distance and thus reduce recombination, and replacing redox shuttle. We are developing porphyrin supermolecules and understanding charge separation and energy transfer in those supermolecules for eventually replacing conventional Ru-based dyes. I will show what we have learned about photophysical and photochemical properties of such supramolecular systems. Relevance of those understanding to applications in DSSCs will be discussed. Examples of applications will also be given.

November 5, 2009

"Plasmonic Nanostructures for Unifying Surface Enhanced Raman Scattering and Infrared Absorption Spectroscopy," Janardan Kundu, Rice University, hosted by Elena Shevchenko

Abstract: Plasmon resonances control the electromagnetic near-field and far-field properties of various metallic nanostructures (e.g., nanoparticles, nanoshells, metallic thin films). The enhanced electromagnetic near-field, strongly localized on the metal surface, has been successfully exploited for a variety of surface enhanced spectroscopies. Visible and near-infrared surface enhanced Raman spectroscopy (SERS) is an example of such a technique that has attracted substantial attention due to its huge enhancement factors (~108-109) and wide range of applications. However, surface-enhanced infrared absorption (SEIRA) spectroscopy, complementary to SERS, has not received nearly the same attention because engineering the necessary strong near-fields in the mid-IR is challenging.

This talk outlines the successful efforts for developing rationally designed gold nanoshell-based substrates for SEIRA and for combining SERS and SEIRA to unify the field of surface enhanced vibrational spectroscopy for comprehensive biochemical sensing applications. Specifically, I will talk about the utilization of interparticle junction hot spots for SEIRA. Applications of SEIRA in conjunction with SERS are demonstrated for a variety of biologically relevant processes such as drug intercalation in lipid membranes, lipid transfer/exchange, and adsorption of nucleic acid bases. Finally, the random aggregate geometry for SEIRA is elegantly extended into two-dimensional periodic array of nanoshells that truly unifies SERS and SEIRA on a common single substrate by simultaneously enhancing both Raman and infrared signals in two diverse frequency regimes with high spectral sensitivity. I will conclude the talk with a brief mention of e-beam lithography-fabricated nanostructure assembly for LSP R sensing application.

November 3, 2009

Recent Advances in Electron-Beam Patterning with and without Resists,” J. Todd Hastings, University of Kentucky, hosted by Alexandra Imre

Abstract: Focused electron-beam induced deposition (EBID) and etching (EBIE) allow the direct (resistless) deposition or removal of materials at the nanoscale. These techniques are important for nanoscale rapid prototyping and mask/template repair. Traditionally, EBID and EBIE have been implemented by using gaseous reactants; for example, metalorganic precursors are often used for deposition processes. Such gaseous precursors introduce high impurity levels (up to 80%), limit materials that can be processed, are expensive and/or toxic, and yield low processing rates and efficiency.

Recently, the Hastings group has developed a new approach to EBID and EBIE that relies on bulk liquid reactants. Dr. Hastings will present results showing that deposition from true liquids can dramatically improve material purity (>85at.% Pt using chloroplatinic acid solutions) and deposition rate, while retaining high resolution (sub-30-nm features on a 60-nm pitch).

Electron-beam lithography (EBL) using resists remains the primary process for direct-write nanofabrication and mask/template patterning. EBL can attain sub-10-nm resolution; however, the nanometer-level pattern placement accuracy and critical dimension control required for next-generation electronic and photon devices remain elusive. In addition, the high cost and inadequate throughput of EBL limits its application in many other areas of interest.

Dr. Hastings will discuss the recent efforts of his group and its collaborators to improve accuracy in EBL through feedback control for electron beam position, beam shape, and pattern dose. In addition, he will present the first steps toward integration of these techniques with a highly parallelizable electron-beam micro-column developed by Novelx Inc. This combination holds the potential to reduce cost and increase throughput in order to greatly expand the range of EBL applications.

October 29, 2009

"Inventions and Patents at Argonne – Who, What, How and Why?," Mark D. Hillard, Chief Patent Counsel, Argonne National Laboratory, hosted by Derrick Mancini

Abstract: An invention is a novel and nonobvious idea or discovery that can only be protected by the timely filing of a patent application. Argonne's inventions are a valuable asset that are essential to the Laboratory's technology transfer mission and, if patentable, can return significant research funds to the Laboratory. To protect the Laboratory's intellectual property, DOE requires the Laboratory to report Argonne's inventions in a timely manner. The presentation will review the Laboratory's process for reporting and patenting Argonne's inventions and the benefits to inventors, the Laboratory and DOE of the patenting process.

October 28, 2009

"Synthesis and Characterization of Colloidal Semiconductor Nanocrystals: CuInSe2, CuInS2, and CdTe/CdSe/CdTe," Bonil Koo, University of Texas at Austin, hosted by Elena Shevchenko

Abstract: Colloidal semiconductor nanocrystals are interesting candidates as new light-absorbing materials since they can be synthesized in large quantities and easily dispersed in common organic solvents, two key characteristics that facilitate the production of nanocrystal inks. This presentation will focus on the synthesis and characterization of I-III-VI2 semiconductor nanocrystals (e.g., CuInSe2 and CuInS2) and also CdTe/CdSe/CdTe heterojunction nanorods. I will also expand on experimental subtleties that I have found to affect nanocrystal morphology, monodispersity, and crystalline phase.

October 23, 2009

"Excited State Distortions Caused by Photo-Induced Electron Transfer," Rachel Stephenson, University of California-Los Angeles, hosted by Matt Pelton

Abstract: Charge-transfer compounds exhibit a change in normal coordinates (bond lengths and angles) due to electron rearrangement after absorption of a photon. The magnitude of these excited-state distortions are obtained from electronic and resonance Raman spectra modeled within the time-dependent theory of spectroscopy. These methods are applied to two distinct types of systems.

  1. The first system is a supramolecular [2]rotaxane that displays an intermolecular charge transfer from the thread component to the ring component. The active modes are identified and the absolute change in the normal coordinates in Ångstrom units are calculated.
  2. In the second system, diammino(o-benzoquinonediimine)dichlororuthenium(II), a metal- to-diimine intramolecular charge transfer causes a change in the Ru-N bond distance. Detailed information about the wavepacket dynamics can be obtained from the presence of overtone bands of the Ru-N stretching fundamental observed in the resonance Raman spectrum. These overtones provide an internal clock that will be used to determine the absolute change in normal coordinates.
October 22, 2009

"Soft Lithography: Materials and Applications to Surface Plasmonic Resonance Sensing and Surface-Enhanced Raman Scattering," Tu Truong, University of Illinois at Urbana-Champaign, hosted by Yugang SUn

Interest in unconventional techniques for nanofabrication has grown exponentially in recent years because of demanding requirements in mico/nanoscale structures for photonics, microfluidics, biotechnology, and flexible electronics. Soft lithographic methods use elastomeric stamps, molds, and conformable photomasks as patterning elements to provide capabilities that are unavailable with conventional techniques: patterning at molecular-scale resolution (~1 nm); ability to form three-dimensional structures directly, in a single step; experimental simplicity and applicability to large areas. In this presentation, we explore the use of a commercially available perfluoropolyethylene (a-PFPE) in a variety of soft lithographic techniques for high-fidelity, high-resolution patterning. As an application example, we describe classes of quasi-three-dimensional plasmonic crystals for biosensing and well as surface-enhanced Raman scattering, with connection to theoretical results obtained in collaboration with S. Gray and others at Argonne.

October 21, 2009

"Diamond-based Nanomaterial Platforms for High Efficiency Cancer Treatment," Dean Ho, Northwestern University, hosted by Anirudha V. Sumant

Abstract: Nanodiamond surface properties mediate clinically relevant improvements to drug delivery that can be realized through enhanced cancer treatment efficiency. Additional characteristics that enable their application as versatile drug delivery vehicles include their functionalization with a broad array of therapeutics that includes small molecules, proteins, antibodies, and RNA/DNA for applications in cancer treatment, cardiovascular medicine, wound healing, and beyond. In addition, nanodiamonds possess uniform dimensions (~4nm in diameter per particle) and material stability that are coupled with observed biocompatibility in vitro and in vivo. Furthermore, nanodiamonds can be batch-purified and functionalized for scalable and high-yield processing. Among other functional groups, nanodiamonds also possess an abundance of surface-bound carboxyl groups, which are conducive towards facile, application-dependent molecular linking/conjugation onto the diamond surface. Furthermore, nanodiamonds can be functionalized with additional chemical species to enable direct drug conjugation. Our previous studies have confirmed robust drug binding to nanodiamonds through transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR) coupled with in vitro tracking of cellular internalization and quantitative demonstration of bio-amenable cell response through quantitative real time polymerase chain reaction (RT-PCR) assays of inflammatory and apoptosis-regulating gene expression programs. Furthermore nanodiamond-mediated drug release against HT-29 and Raw 264.7 cell lines has also been observed. Toward the broadening of nanodiamonds applicability in clinically significant treatment scenarios, recent work pertaining to simultaneous high-efficacy/high-biocompatibility gene delivery, nanodiamond-based microfilm device formation for localized chemotherapy, pH-dependent therapeutic protein release, and preclinical trials will be discussed.

October 20, 2009

"Atomistic Simulations for Understanding the Effect of the Local Environment on the Properties at the Nanoscale," Handan Yildirim, University of Central Florida, hosted by Jeffrey Greeley

Abstract: In the first part of the talk, using the examples of homo- and hetero-epitaxial systems, I will show how an understanding of the microscopic processes that control the diffusion of metal adatoms and then clusters on metal surface can lead to prediction of growth modes and morphological evolution of surfaces, interfaces, and thin films. For example, the excess energy for a single atom to overcome a step (Ehrlich-Schowebel barrier) presents significant differences from one system to another, which may be related to the observed dissimilarities in growth modes. Single-atom diffusion barriers, both on strained terraces and near (strained) step edges, show that their strain dependence is universal and may be used to manipulate growth modes. In addition, I will talk about the pre-exponential factors for single-atom and cluster diffusion for both homo and hetero systems and discuss the origin of the quasi-constant prefactors. The contribution of the substrate dynamics to the calculatio n of the prefactors will also be discussed.

In the second part of the talk, I will use the example of a set of 34-atom bimetallic nanoparticles AgnCu34-n to show how the degree of alloying affects the vibrational dynamics, the thermodynamic,s and the electronic structure of each nanoparticle in this family.

September 30, 2009

 

"An ab initio Perspective of the Nickel Catalyzed Hydrocarbon Dissociation," Bin Liu, Colorado School of Mines, hosted by Jeffrey Greeley

Abstract: Theoretical methods represented by density functional theory (DFT) among others have made a tremendous leap in dealing with clusters, oxides, surfaces defects, and interfaces that are involved in heterogeneous catalysis. Thanks to the advancement of computation power, the modeling can be performed in a practical manner such that knowledge obtained this way can be used directly to explain experimental observations. Nickel has been a very important catalyst for reactions such as steam reforming and Fischer-Tropsch. This talk will present DFT calculations performed on various forms of nickel to study their catalytic properties, using the dissociation reactions of hydrogen and methane as examples. The goal is to understand how the reactivity of nickel clusters and nickel single-crystal surfaces can be related to respective sizes and geometries. For example, the icosahedral Ni13 clusters are found to show higher reactivity for methane dissociation by lowering the C-H bond breaking energy barrier compared to the Ni(111) surface. DFT calculations were also used to obtain thermochemical properties, and kinetic parameters of surface reactions. The knowledge gained from DFT calculations will not only help us explain the experimental phenomena, but also guide us design more effective catalyst surfaces to meet specific requirements in industrial applications.

September 24, 2009

"Metallic film growth on quasi-crystals," Joseph A. Smerdon, University of Liverpool, hosted by Matthias Bode

Abstract: Quasi-crystals, alloys of two or more metals, exhibit structures that, before their discovery, were considered impossible in condensed matter, relying as they do on a kind of order not based on periodicity. They also exhibit some unusual physical and electronic properties, such as high hardness, low frictional coefficients (comparable to Teflon), and a negative thermal coefficient of resistance. They are also bulk-terminated, meaning that their surfaces do not reconstruct and as such are as well-ordered and aperiodic as the bulk of the material. This opens up the study of quasi-crystals to standard surface microscopy, diffraction, and photoemission techniques. Also, it allows for the growth of epitaxial films that adopt the ordering of the quasi-crystal substrate, as the study and elucidation of structural, physical, and electronic properties should be easier for an elemental film as opposed to the chemically complex quasi-crystalline substrate.

This talk will explore some of the recent work done in the Surface Science Research Centre in the University of Liverpool. Many systems in which an elemental overlayer will adopt the structure of the underlying quasi-crystals have been identified, and I will explore two particular systems in depth: Cu/AlPdMn and Bi/AlPdMn. Copper deposited on the fivefold surface of icosahedral Al-Pd-Mn forms a multilayered film, of which the structure is an intriguing mix of aspects of crystalline copper and the AlPdMn substrate. The film has been extensively studied with STM, LEED, and MEIS in Liverpool and through a collaboration between Liverpool, PSU, and Lappeenranta University, Finland, also with LEED-IV. These studies have demonstrated the possibility of applying Monte Carlo techniques to the study of aperiodic systems.

Bismuth deposited on the fivefold surface of icosahedral Al-Pd-Mn forms an initial quasi-crystalline wetting layer followed by islands of various types. Unprecedented STM resolution of bismuth nanoclusters and comparison with DFT results has allowed the unambiguous determination of the nucleation network for this film and has followed the nucleation and growth of the film to the monolayer. Similarly well-resolved data of the surfaces of bismuth islands atop the wetting layer shows evidence of a phase change of the crystalline islands that can be controlled by manipulating the growth rate of the film.

The benefit of this work for the quasi-crystal community has been in the initial observation that it is surprisingly common for elemental overlayers to adopt the quasi-crystalline symmetry, the identification of the nucleation process for quasi-crystalline monolayers, and the demonstration that conventional computational techniques can contribute to the elucidation of aperiodic structures.

September 18, 2009

"MEMS Thrusters and Inertial Sensors for Space Applications," Herbert R. Shea, Ecole Polytechnique Federale de Lausanne, hosted by Daniel Lopez

Abstract: Microelectromechanical systems (MEMS) offer great promise for increasing the functionality of spacecrafts while decreasing their mass, thus enabling new satellite architectures and allowing nanosatellites to match the performance of conventional spacecraft. Our lab at the EPFL in Switzerland develops micromachined thrusters and inertial sensors for spacecraft propulsion and navigation, as well as polymer-based microactuators and components for chip-scale atomic clocks for use on Earth and in space.

An overview of our lab's activities will be given, with an emphasis on three topics: 1) arrays of microfabricated colloid thrusters emitting ions at 35 km/s; 2). MEMS inertial sensor directly measuring the gravity gradient in orbit, used as an Earth sensor requiring no optical access; 3) micro-actuators based on silicone membranes with compliant electrodes that generate vertical displacements greater than 50% of the device radius, with applications in tunable optics and cell manipulation.

September 11, 2009

"Synthesis, characterization and functionalization of advanced hybrid carbon nanomaterials," G.R. S. Iyer, Nanotechnology and Integrated Bio-Engineering Research Center (UK), hosted by Anirudha Sumant

Abstract: Over the last two decades, nanocarbon materials have attracted great interest due to their ability to bond in different configurations (sp3, sp2), leading to various new carbon nanostructures (CNSs) with unique properties. Material preparation, characterization, and device fabrication are intertwined in the development of nanoscience and nanotechnology. The development of new CNSs is the trend in miniaturization of devices for various path-breaking applications such as sensing, energy storage, and permeable membranes.

In the first instance, I’ll describe how diamond nanoflake/nanorod spherules (DNFSs), a novel hybrid carbon nanostructure, composed of nanoflakes or nanorods with a diamond core and graphitic envelope, was synthesized using the MPCVD system. The microstructure composition was investigated by HRTEM and the electronic structure by spatially resolved microscopic XPEEM coupled with NEXAFS. These nanorods/flakes are electron-emitting spherules, exhibiting a low-threshold, high-current-density (10 mA/cm2 at 2.9 V/m) field emission. Low-energy nitrogen ion bombardment was another exciting area of research to tailor the surface selectivity, and understand the surface chemistry of the carbon-host system to tune the materials for new applications.

In another instance, I shall describe the use of novel, nontoxic single-step method by nitrogen-ECR plasma, an unconventional technique from the acclaimed chemical methods for the purification (i.e., the removal of metal catalyst) of nanotubes and how that can be used for the purification, functionalization and tip opening of the nanotubes. Further studies carried out on understanding the nitrogen bonding configuration with carbon nanotubes using NEXAFS techniques will also be discussed .

August 31, 2009

"Compositional tuning of ultra-thin oxides grown on metal and alloy substrates via externally applied electric fields: A molecular dynamics simulation study," Subramanian Sankaranarayanan, Harvard University, hosted by Stephen Gray

Abstract: Synthesis of ultrathin metal oxides with controlled functional properties is desirable for a plethora of technological applications but is elusive because of growth kinetics. These applications include but are not limited to tunneling barriers in electronic devices, templates for model catalysts, and passivation layers to protect against corrosion. Three important factors can affect the functional properties: oxide density, oxide stoichiometry, and oxide composition in case of alloys.

Using representative examples of aluminum, zirconium, and Ni-Al oxidation, we demonstrate the ability to modify the density, stoichiometry (metal/oxygen), and alloy composition of ultrathin oxides grown on metal surfaces at room temperature by using externally applied electric fields such as those typically generated in photon-assisted synthesis. Molecular dynamic simulations employing dynamic charge transfer between metal atoms are used to model the oxidation process in the presence of external electric fields. Precise understanding of the microscopic processes involved in electric-field-assisted oxidation of metal substrates is provided by atomistic models employing dynamic charge transfer between atoms. We show that electric-field-assisted synthesis can be used to overcome the activation energy barrier for ionic migration. leading to significantly enhanced oxidation kinetics, which enables us to control the oxide composition at atomic length scales.

Our simulations indicate that the rate of oxygen incorporation into the near-surface regions of the passive oxides can be dramatically enhanced with atomic oxygen and/or electric field compared with natural oxidation. Increasing the electric field (~ 107 V/cm) drives the surface chemisorbed oxygen to the vacancy sites in the oxide interior, leading to dramatic density and stoichiometry improvements in ultrathin oxide film grown on pure metals.

For Ni-Al alloy oxidation, our atomistic simulations suggest that photo n-assisted synthesis overcomes the activation energy barrier for chemisorption through the creation of activated atomic oxygen and ionic migration due to an electric field produced across an oxide film, leading to significantly enhanced oxidation kinetics, which enables us to control the complex oxide composition at atomic length scales. Our simulations thus demonstrate a pathway to athermally controlled oxygen concentration in near-surface regions that is of great importance to contemporary problems in the use of ultrathin oxides, ranging from catalysis to energy technologies.

August 27, 2009

"Determining Interactions and Interfaces Between Self-Assembled Peptide Amphiphile Nanofibers and Biological Molecules, " Chung-Yan Koh, Northwestern Univeirsity, hosted by Elena Rozhkova

Abstract:: Self-assembled peptide amphiphile (PA) nanofibers are versatile building blocks for the creation of biomimetic cell scaffolds and delivery systems. One obstacle with using this platform is accurately determining optimal interfacial interactions with biological molecules and also determining the interaction between the PA and biologically significant molecules. Using model systems with immobilized enzymes mimicking membrane-bound cellular receptors to probe the biological accessibility of these nanofibers, we found that the recognition and rate of degradation trends with the placement of the recognition site in the primary structure of the PA. Interestingly, incorporation of aromatic moieties decreased accessibility to undetectable levels, allowing for a wide range of tailored biological accessibility from a single molecular platform. In order to study the interface between PA nanofibers and biomacromolecules, I examined complexes formed from PA with protein and PA with double-stranded plasmid DNA. Through hydrogen-deuterium exchange analysis, I mapped the interaction surface between a PA nanofiber and a developmentally important protein, Activin A. We found that changes in the binding interface, even with equivalent binding strengths, significantly impacted in vitro cellular response. Through biophysical and biochemical assays, we found that PA-DNA complexes are significantly more efficient transfection agents for cellular aggregates compared to commercially available agents such as Lipofectamine.

August 10, 2009

"Steps on Vicinal Surfaces: Density-Functional Theory Calculations and Transcending Minimal Statistical-mechanical Models, " Rajesh Sathiyanarayanan, University of Maryland, hosted by Jeff Greeley

Abstract: Steps on vicinal surfaces can be used as templates for fabrication of metallic nanowires and for microstructure growth. They can also enhance the catalytic activity of a surface, especially when they have many kinks. This makes the modeling of stepped surfaces technologically important. Using a combination of density-functional theory calculations and Monte Carlo simulations, we have computed various parameters, such as stiffness, step formation energy, and step-step interaction strength, that are normally used to model morphological evolution on stepped surfaces. We show that in certain cases, a minimal model is not sufficient to get accurate results. This talk discusses such scenarios and ways to handle them.

August 3, 2009

"Atomistic Studies of Oxidation Catalysis and Surface Poisoning on RuO2(110) Surface," Dr. Hangyao Wang, University of Notre Dame, hosted by Jeffrey Greeley

Abstract: Base-metal oxides have long been of interest as catalysts for oxidation of small molecules such as CO and NO. As an example, ruthenium metal becomes active for catalytic oxidation only after partial surface oxidation. The (110) surface of RuO2 is a convenient model for the oxidized metal surface because it is active for CO oxidation and well characterized. In this study, we employ plane-wave, supercell DFT calculations to examine the mechanisms of oxygen activation, CO/NO oxidation as well as surface poisoning on RuO2(110) surface.

We first consider O2 adsorption and dissociation and show that the molecular O2 species observed in TPD experiments and identified as a precursor to O2 dissociation is in fact a spectator present only at high coverages of surface O. We then study the CO and NO oxidation mechanisms on the RuO2(110) surface and compare the fundamental differences that lead to complete different catalytic reactivity of this surface on CO and NO oxidations.

Practical applications of oxidation catalysts are limited by surface poisoning, so it is important to understand and ultimately to learn to bypass surface poisoning. We investigate catalytic CO oxidation and its competition with surface poisoning by employing first-principles thermodynamics as well as micro-kinetic modeling method. We identify both carbonate and bicarbonate surface poisons and show that the coverage of the latter is highly sensitive to water concentration and likely accounts for the surface poisoning observed experimentally.

July 16, 2009

"Charge Transfer in DNA and Its Application for Mismatch Detection," Tetsuro Majima, Osaka University, hsoted by Tijana Rajh

Abstract:: Charge transfer (CT) in DNA offers a unique approach for detectng a single-base mismatch in a DNA molecule. While a single-base mismatch would significantly affect the CT in DNA, the kinetic basis for the drastic decrease in CT efficiency through DNA containing mismatches remains unclear. Recently, we determined the rate constants of CT through fully matched DNA, and we can now estimate the CT rate constant for a certain fully matched sequence. We assumed that further understanding of the kinetics in mismatched sequences can lead to detection of the DNA single-base mismatch based on kinetics. In this study, we investigated the detailed kinetics of CT through DNA containing mismatches and tried to detect a mismatch sequence based on the kinetics of the CT in DNA containing a mismatch.

July 7, 2009

Polymer-Assisted Deposition, ”Anthony K. Burrell, Los Alamos National Laboratory, hosted by Al Sattelberger

Abstract: Polymer-assisted deposition (PAD) is a chemical solution route to high-quality thin films of metal oxides, nitrides, and carbides. This technique employs metal ions coordinated to polymers as the film precursor. The use of polymer bound metals has several advantages. The polymer controls the viscosity and binds metal ions, resulting in a homogeneous distribution of metal precursors in the solution and the formation of uniform metal oxide, nitride, and carbide films. The nature of the metal oxide, nitride, and carbide deposition is dominated by bottom-up growth, leading to ready formation of crack-free epitaxial metal oxides, nitrides, and carbides and the ability to coat nanofeatured substrates in a conformal fashion. Incorporation of nanomaterials in the thin films yields composite materials with interesting properties.

June 22, 2009

"Materials and Processes Development for Advanced Micro/Nanotechnologies," Jyoti K. Malhotra, Brewer Science, Inc., hosted by Derrick C. Mancini

Abstract: The fabrication of surfaces and films with controlled features has been a very active area of research for Brewer Science. Brewer Science's R&D division has many years of experience in developing polymeric thin-film technologies and advanced materials and processes for micro- and nanofabrication.

The following technologies are an extension of Brewer Science's knowledge and expertise in polymeric coatings and will be highlighted in the presentation:

  • Smart surface imaging for nanodevices: Beyond its immediate applications to advanced lithography, SSI also holds promise as a means to selectively deposit nanomaterials into defined arrays for device and non-device fabrication purposes, including the creation of three-dimensional nanostructures.
  • Functionalizing carbon nanotubes for biosensing applications: Microelectronics-grade carbon nanotube (CNT) aqueous solution has been prepared by using Brewer Science's purification protocols. CNT and polymer composite materials are being developed by blending and dissolving polymers into CNT solutions. The proposed work can be used to bind biomolecules on the surfaces of CNTs. This process promises exciting applications, such as constructing intelligent drug vector systems, designing biosensors for the assay of biomolecules, and elucidating protein structures.
  • Alkaline and acid deep silicon wet etching for micro-electro-mechanical systems (MEMS) fabrication: Traditionally, silicon nitride and metal hardmasks have been used in the development of wet- and dry-etched silicon via formation. Brewer Science has developed new polymeric etch protective coatings that provide attractive alternatives for deep silicon wet etching in alkaline etchants. Development of coatings that protect from acidic etchants is under way. These advancements will enable low-cost through-silicon via etching and wafer protection during sensitive wafer handling steps. Applications can be found in the production of future devices, such as sophisticated pressure sensors in MEMS.

June 19, 2009

"Nano and biotechnologies for development of an array of electrochemical biosensors," Mihaela Ilie, Institute of Photonics and Nanotechnology, National Research Council, Rome, and University 'Politehnica' Bucharest, Romania , hosted by Ralu Divan

Abstract: Biosensors, as functional analogs of chemoreceptors, are based on the direct spatial coupling of immobilized biologically active compounds, acting as a chemical recognition system, with a signal transducer and an electronic amplifier. If the physicochemical changes caused by either the complex formation or the chemical conversion of the analyte (e.g., owing to enzymes) are of an electrical nature (charge or enzyme activity), they can be detected by means of potentiometric or amperometric electrodes. A continuous flow micro-cell array that works on this principle has been developed by the IFN/CNR-ENEA/Biosensing Lab team, with potential applications in environmental and clinical analysis.

The cell contains miniaturized electrochemical electrodes in a fluidic chamber and their connections to the control and processing unit. The sensitivity of the chrono-amperometric measurement performed with the cell is increased by (a) integrating the reference electrode on the same chip with the counter and working electrodes, (b) designing a specific pattern of gold electrodes, and (c) serially distributing them along the pipeline reservoir. Borosilicate glass is used as substrate for the electrodes, allowing, via its transparency, an accurate and easy pad-to-pad alignment of the up-side-down chip versus a PCB soldered on a standard DIL 40 socket. This alignment is necessary to accomplish the elastomer-based solderless electric contact between chip and PCB. The solderless contact significantly improves both reliability and signal processing accuracy. The reservoir and its cover are micromachined of silicone rubber or photosensitive glass to easily assemble the fluidic chamber without damage. Both the thickness and the elasticity of the photosensitive glass render the device less brittle. A plug-in-plug-flow device with improved characteristics has been obtained with a modular structure that allows further extension of the number of electrodes and array integration. Details of the fabrication, data acquisition, and functional testing are given. The results are compared with those obtained from a nanoelectrode assembled on screen-printed substrates.

June 15, 2009

"Efficient Prediction and Optimization of thermoelectric and Photovoltaic Properties," Maria Kai Yee Chan, Massachusetts Institute of Technology, hosted by Jeff Greeley

Abstract: The accurate prediction and optimization of physical properties in the vast spaces of nanoscale structures and chemical compounds is made increasingly possible through the use of atomistic and ab initio computation. In this talk I will describe two specific examples, the prediction and optimization of lattice thermal conductivity in SiGe nanostructures and the prediction of bulk semiconductor band gaps, which are of importance for thermoelectric and photovoltaic applications respectively. In the former, the use of classical molecular dynamics to predict lattice thermal conductivity in the Kubo-Green formalism allows for the selection of optimal nanostructures.

Additional optimization with respect to alloy configuration is carried out by cluster expansion. In the latter, I propose a method for efficient ab initio estimation of bulk semiconductor band gaps.

June 9, 2009

"Junctions and Interfaces in Bottom-Up Nanoscale Semiconductor Devices," Yu-Chih Tseng, University of California at Berkeley, hosted by Seth Darling

Interface and junction between materials critically determine the behavior of bulk semiconductor devices. Similar studies have not been carried out in a direct and systematic way for nanoscale devices based on bottom-up materials, such as carbon nanotubes and semiconductor nanowires, because of the smallness of the junctions in question. Capacitance-voltage measurement is commonly used to characterize bulk semiconductor devices and interfaces. An instrument capable of measuring capacitances as small as a few attofarads (10-18 F) at low temperatures was developed and used extensively in this work. This method is applied to characterize the metal-carbon nanotube Schottky contact, and various kinds of junctions in nanowires. This study should shed light on the electrical properties of nanoscale semiconductor interfaces, and be valuable in providing direct feedback to novel fabrication techniques.

June 3, 2009

"Spatial Light Modulators and Photonic Integrated Microsystems," Il Woong Jung, Stanford University, hosted by Daniel Lopez

Abstract: The ability of spatial light modulators (SLMs) to modulate the amplitude and/or phase of light make it a compelling technology for a variety of applications in displays, adaptive optics, and communications. An important functional advantage of MEMS implementation is that the small size and mass of the elements allow high switching speeds. This also leads to a compact design resulting in systems that are much more economical to fabricate with the millions of elements required of some applications. The size, complexity, and required precision of the devices introduced in this talk show the unique capability of MEMS technology but also its many technical challenges.

In this talk, I will first present my PhD dissertation research on the design and fabrication of SLMs for applications in adaptive optics and optical maskless lithography and more recent work with Agilent Labs on the development of tunable filters with vertical mirrors micro-assembled on movable MEMS platforms for applications in communications and spectroscopy.

It has been shown theoretically and experimentally that broadband mirrors with high reflectivity can be made from freestanding two-dimensional photonic crystal (PC) slabs and from PCs placed on a thin dielectric film on a silicon substrate. By controlling the structure and geometrical dimensions, PC slabs can support guided resonances that couple to external radiation in ways that profoundly change its optical properties. This can be utilized to design compact optical devices such as mirrors, filters, lasers, and sensors. The main advantage of 2-dimensional PC slabs is that they can be designed to achieve comparable performance of one-dimensional PCs, or Bragg-stacks, but in a more compact form.

As another part of this talk, I will present the many applications of two-dimensional PC slab integrated optical microsystems and applications such as my work on PC mirror MEMS scanners for high-power beam steering and PC fiber tip sensors for remote sensing in harsh environments.

May 28, 2009

"First-principles nanoelectronics: Oxide thin-film devices by design," Massimiliano Stengel, Ecole Polytechnique Federale de Lausanne, hosted by Stephen K. Gray

Abstract: With the continued demand for portability and speed in consumer electronics, there is an increasing motivation to consider alternative paradigms to conventional silicon-based semiconductor designs. Heterostructures based on ferroelectric and/or magnetic complex oxide thin films are a very promising route to the realization of ultracompact and ultrafast electronic devices, due to the high tunability and multiple functionality of these materials. Such properties, however, are often dramatically modified at the nanoscale, and the physics of this size reduction is often poorly understood. First-principles electronic structure methods are a very powerful tool in addressing these key questions with high predictive power. However, proper treatment of an applied external bias potential in density-functional theory, which is mandatory for the simulation of realistic devices, has been a very challenging task until very recently. In the first part of this talk, I will show how our recent methodological advances in finite-field techniques have overcome this obstacle, thus providing full control over the electrical boundary conditions in periodic insulators and capacitors. In the second part of this talk, I will present some recent applications of these methods to a number of important technological problems, including the dielectric "dead layer" in paraelectric and ferroelectric thin-film capacitors, carrier-mediated magnetoelectricity at the interface between an insulator and a ferromagnetic metal, and the nonlinear piezoelectric response of PbTiO3 in high electric fields.

May 14, 2009

"Epitaxial Growth of Oxides on Semiconductors using MBE," Venu Vaithyanathan, Seagate Technologies, hosted by Stephen K. Streiffer

Abstract: Integration of functional oxides on semiconductors (such as Si, GaN) in an epitaxial form is useful for a variety of device applications. Integrating epitaxial oxides on semiconductors is lot more challenging compared to homoepitaxial or heteroepitaxial growth of oxides on single crystal oxide substrates, even using MBE. An overview of the challenges involved and the processes developed using MBE (Penn State University) to overcome these issues will be presented with some examples.

April 23, 2009

"Fabrication and Experiments on Electron Fabry-Perot Interferometer," Fernando Camino, Center for Functional Nanoscale Materials, Brookhaven National Laboratory, hosted by Leonidas Ocola

Abstract: We report fabrication and experiments on GaAs/AlGaAs heterostructure-based quantum interferometers in the integer quantum Hall regime. These devices consist of a lithographically defined two-dimensional electron island connected to the bulk electron region via two wide constrictions. When tunneling between counterpropagating edge channels occurs at the constrictions, electrons perform closed orbits around the electron island, causing an interferometric Aharonov-Bohm signal in the conductance. We observe conductance oscillations on quantum Hall plateaus at fillings f =1, 2, and 4. For a given filling, we observe f oscillations per flux period h/e. However, for all fillings, we observe one oscillation per charge period of e, corresponding to the addition of one electron to the area of the interference path.

April 17, 2009

"Organic Semiconductor Based Resistive Switching Memory," Yue Shao, hosted by Derrick C. Mancini

Abstract: Organic memory devices are receiving considerable attention as possible alternatives for conventional semiconductor memories because of their simple device structures, ease of processing, low cost, and compatibility with flexible substrates. In this talk, organic semiconductor-based memory devices with a metal/insulator/metal sandwich structure are demonstrated. It was found that resistive switching in these organic memory devices occurred in localized areas of the device. To investigate the localized conductive pathways,a focused ion beam was used to prepare a cross section of the device. It was found that the distance between the two electrodes was not uniform in the device. The closest distance was about 5 nm, while the average distance in the uniform area was about 50 nm. Transmission electron microscope-energy dispersive X-ray analysis of the cross section of the device confirmed that metal ions were injected into the polymer film by a locally enhanced electric field near the irregularities of the electrodes.

April 14, 2009

"Extending Electron Beam Lithography: Variable Pressure, Soft Lithography, Direct Writing," Benjamin D. Myers, Northwestern University, hosted by Derrick C. Mancini

Abstract: The development of tools and processes for fabrication of nanometer-scale structures is critical for the implementation of practical nanoscale devices and the study of the unique phenomena at this length scale. Electron- beam lithography (eBL) using focused electron-beam irradiation of organic thin-film resists is among the most promising and widely applied techniques, owing largely to its capability for high-resolution patterning. We extend the use of this technique for nonstandard substrates and material systems and address some of the inherent limitations of conventional eBL.

Electron-beam exposure carried out under high-vacuum conditions for nonconductive substrates often leads to charging effects that can result in significant pattern distortion and displacement. We have developed a variable pressure eBL (VP-eBL) process that allows in situ charge dissipation for direct patterning on insulating substrates with no conductive coating or additional process steps. This is accomplished through the introduction of a low gas pressure (~1 Torr H2O, Ar, N2) to the chamber, which generates positive gas ions to balance the surface charge. In addition to the utility of this method for fabrication of structures on technologically significant substrates, such as GaN, Si3N4, glass and polymers, the VP-eBL method serves as a useful platform to study the scattering of the primary electron beam by the chamber gas. We have also developed a technique that utilizes eBL for soft lithographic patterning of a range of materials from functional ceramics (ferroelectric, ferromagnetic, optoelectronic) to conducting polymers. In this process, we create trenches in a PMMA resist layer, which are subsequently filled by spin coating liquid or sol-gel precursors and then lift-off processed in acetone to remove the PMMA and material outside the trenches. In addition to resist-based processes, we have used eBL for the direct modification of supraspherical nanoparticle films to form nanoporous metal structures with controlled size and shap. The dual-beam focused ion beam/scanning electron microscope offers unique capabilities for nanofabrication and materials characterization and recent work on this instrument will be presented.

April 3, 2009

"Design and Fabrication of Surface Plasmon Polariton Supporting Structures on Silver Thin Films," Alexandra Imre, Argonne National Laboratory, hosted by Derrick C. Mancini

Abstract: In this talk, a set of recent experiments on the launching, focusing, and propagation of surface plasmon polaritons (SPPs) on nanostructured silver surfaces will be introduced. The constructive interference of SPPs launched by slits through silver films allows us to focus the SPP near-field intensity into a spot of subwavelength size. We show that the high SPP intensity in the focal spot can be launched and propagated on silver strip guides with a 250 by 75 nm cross section, the SPP wavelength is 509 nm in the experiment. Furthermore, a plasmonic device that generates and steers tightly focused plasmon beams between neighboring subwavelength Ag strip waveguides is demonstrated. The local electromagnetic-field enhancement in the focal spot is studied experimentally by near-field scanning optical microscopy, and it is applied for surface enhanced Raman spectroscopy (SERS). By exploiting the polarization dependence of the focusing effect, a Raman signal enhancement of a factor of ~6 is observed from Rhodamine 6G molecules.

The basic properties of SPP-based planar devices, and further developments towards viable SERS sensors will be discussed.

March 30, 2009

"Assembly, Spectroscopy and Applications of Semiconductor Nanocrystals," Andrey L. Rogach, Ludwig-Maximilians-Universität München, hosted by Elena Shevchenko and Tijana Rajh

Abstract: High-quality semiconductor nanocrystals with controllable surface properties and strong, size-dependent emission can be synthesized nowadays by methods of colloidal chemistry. They are attractive objects for use as building blocks in different functional nanostructures, in particular in combination with polymers. Advanced optical spectroscopy provides important insights into fundamental photophysical properties of semiconductor nanostructures. Different application aspects of functional composites based on semiconductor nanocrystals ranging from energy and charge transfer structures to biological markers will be discussed.

March 27, 2009

"Polymer-Based Nanomedicine: Multivalent Targeting and Rolling-Based Cell Capturing," Seungpyo Hong, University of Illinois, Chicago, hosted by Derrick C. Mancini

Abstract: Cancer remains one of the world's most devastating diseases, with more than 10 million new cases every year. With the ongoing efforts in cancer research, mortality from cancer has decreased in the past two years owing to better understanding of tumor biology and improved diagnostic devices and treatments. This presentation will discuss the current technology to improve cancer treatment approaches. The enhancement could be achieved via targeted drug delivery and targeted capturing of specific cells.

For the development of nanocarriers for targeted drug delivery, we performed a fundamental study on the biological interactions of synthetic polymers, which revealed that polycationic polymers of linear and dendritic architecture induce membrane permeabilization (nanoscale hole formation) in living cells. Polyamidonamine dendrimers were further studied to be used as a targeted delivery vector. The targeted dendritic nanodevices provide the multivalent interaction with a receptor protein target as observed in unprecedented quantitative and systematic evidence. These data support the hypothesis that multivalency, rather than an enhanced rate of endocytosis, is the key factor resulting in the improved biological targeting by these drug delivery platforms, thus providing a design guide for future receptor targeting agents. A strategy to capture/separate specific target cells based on cell rolling will be also discussed, focusing on the development of controlled covalent immobilization methods of proteins and its translation into device technology. This approach is essential for mimicking relevant complexities of the in vivo rolling response and for future development of devices for isolating specific cell types such as circulating tumor cells with metastasis potential.

March 20, 2009

"Materials-by-Design: The Membrane Analysis and Simulation System (MASS) and Possible Application to Nanomaterials Design," Ron S. Faibish, Nuclear Engineering Division, Argonne National Laboratory, hosted by Derrick C. Mancini and Michael Sternberg

Abstract: A multidisciplinary team at Argonne is conducting advanced research in membrane science and applications for the advancement of energy-efficient separation processes and better materials design paths for new and improved membranes. The Membrane Analysis and Simulation System (MASS) would offer a revolutionary modeling tool to a priori determine the combination of materials that would yield a suitable membrane for any given separation applications (both for gas and liquid phase separations). The simulation and modeling tool employs advanced modeling tool, such as molecular dynamics, computational fluid dynamics, and Lattice Boltzmann methods. The multiscale, multi-physics tool will also introduce an economic module that would evaluate and optimize the economics of the large-scale engineering system as part of the overall membrane system design. It is envisioned that the tool could support the design of, among other membranes types, membranes for advanced high-temperature separations (e.g., for reducing greenhouse gas emissions), membranes to replace energy-intensive distillation processes, and high temperature membranes for desalination of seawater in energy-water cogeneration applications. The tool is expected to save millions of U.S. dollars in development costs of membrane systems and optimize the design process. Other uses of a modified version of the tool for general materials-by-design applications are also foreseen.

March 19, 2009

"Scattering of Surface Plasmon Polaritions by Metallic Nanostructures," Lina Cao, Columbia University, hosted by Stephen Gray and Norbert Scherer

Abstract: We present a comprehensive study of linear and nonlinear effects observed in the scattering process of surface plasmon polaritions (SPPs) from localized surface deformations at a metal/dielectric interface. The electromagnetic field at the fundamental frequency is first determined by solving the corresponding set of reduced Rayleigh equations. The complete solution of these equations then allows us to investigate both the complex structure of the scattered electromagnetic field as well as the subtle mechanisms by which incident SPPs are scattered into radiative modes (light) and outgoing SPP waves. Furthermore, the electromagnetic field at the fundamental frequency is used to determine the nonlinear surface polarization at the second harmonic and subsequently both the electromagnetic field distribution as well as the amount of light generated at the second harmonic. We will discuss our results, including the size dependence of the scattering into both surface and radiated waves for several defect shapes. Our talk will also discuss the computational issues and the physical phenomena of the scattering process. Finally, we will comment on potential applications for our findings in surface spectroscopy, surface chemistry, or new surface-defect imaging techniques.

March 9, 2009

Bioinspired Molecular Machines for Manipulation of Molecules," Kazushi Kinbara, Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, hosted by Elena Rozhkova

Abstract: Molecular machinery is a hot issue in nanotechnology. We have been taking two approaches for construction of elaborate molecular machines: (1) a bottom-up approach based on synthetic organic chemistry and (2) a semi-biological approach based on chemical modification of biological molecular machines. The topics include light-driven molecular scissors that undergo scissoring motion upon irradiation of ultraviolet or visible light, supramolecular machines that can transfer motions through intermolecular interactions, molecular glues that can control protein assemblies, and nanocontainers consisting of biological molecular machines called chaperonin proteins, where catch and release of the guest molecules can be controlled by stimuli such as ATP and light.

March 9, 2009

"Multifunctional Self-Assembled Transition-Metal Oxide Nanotubes: A View from the Bottom," Lia Krusin-Elbaum, IBM T.J. Watson Research Center, hosted Stephen K. Streiffer and George Crabtree

Abstract: Self-organization offers to nanotechnology a powerful alternative to standard nanofabrication approaches. Using self-assembly we have synthesized nanotubes of transition-metal oxides, such as VOx or RuOx, using monoamines as structure-directing templates. In this talk I will focus on the mixed-valent oxides of vanadium that belong to the class of strongly correlated systems which can host unusual spin states and exhibit a wide variety of charge transport and optical behaviors. I will discuss the quantum spin-liquid formed in the `as-assembled' nanotubes with a spin-gap Ds ~ 665 K, that succumbs to ferromagnetism upon electron or hole doping, and how this magnetic particle-hole complementarity can arise from the low-dimensionality of the nanotube structure with crystal field splittings that enforce a Mott gap. Strong electron interactions in VOxl2 can lead to a 1st order metal-insulator transition with an abrupt change in conductivity that can be as much as 11 orders of magnitude; at this transition there is also a sharp change in optical transmission in the infrared spectrum. Thus, numerous applications such as electrical, optical, and spin ─ temperature- or voltage-controlled ─ switches can be envisioned.

March 4, 2009

Understanding Oligo (Ethylene Glycol) Monolayers," Julia Ruemmele, Boston University, hosted by Seth Darling

Abstract: A concern for the design of biosensors for protein interactions is fouling of, or nonspecific binding to, the sensor surface that corrupts the signal due the binding event of interest. Two-component mixed oligo(ethylene glycol) (OEG) self -ssembled monolayers (SAMs) have become a standard surface coating used to minimize fouling of gold sensor surfaces. The source of fouling resistance is still uncertain and it has been shown that the resistance integrity can be affected by the method of SAM fabrication. Toward understanding what gives rise to this behavior, the mole fraction, phase segregation, stability, and pKa of OEG SAMs were investigated under a variety of fabrication conditions and correlated with the fouling resistance of the SAMs with respect to standard proteins. The results imply that a difference in the structure of OEG molecules in the SAMs may regulate fouling resistance.

March 3, 2009

"CuAlNi Shape Memory Alloy and Some Thin Film Studies," Hanshen Zhang, University of California, Berkeley, hosted by Jorg Maser

Abstract: Mr. Hanshen Zhang is a final-year PhD candidate. His research mainly includes shape-memory alloy (SMA) and thin-film synthesis. Shape-memory alloy exhibits special atomic microstructures that can experience reversible phase transformations. Mr. Zhang’s work is focused on CuAlNi SMA, which despite its significant application potential, has been less investigated than other SMAs. He will show the complex mechanical behaviors of this material, which open the potential for in situ experimental studies, such as synchrotron and TEM. His discovery about the underlying complex phase transformation mechanisms and further hypothesis of SMA martensite variant formation show promising scientific endeavors. Mr. Zhang will also briefly talk about his experience with thin-film synthesis, such as filtered cathodic vacuum arc, radio-frequency sputtering, and ion-beam implantation. These topics will show his broad understanding of materials sciences and invite discussions of possible collaborative research.

March 2, 2009

"STM studies of high-temperature superconductors: clues to the pairing mechanism," Vidya Madhavan, Boston College, hosted by Matthias Bode

Abstract: The question of the pairing mechanism in the high-temperature cuprates is an important issue. Scanning tunneling spectroscopy (STS) is the one of the best techniques to obtain information on bosonic modes (phonons, spin excitations, etc.) that couple to electrons. We present STS data on the electron-doped superconductor Pr0.88LaCe0.12CuO4-δ (PLCCO). Below the superconducting transition temperature Tc in addition to the superconducting gap, STM spectra show features at approximately 3 and 10 meV (gap-referenced) that can be associated with bosonic modes. A comparison of these energy scales with neutron scattering data on the same material indicates that both features may be associated with spin resonance modes.

While prior STM data on hole-doped BSCCO revealed coupling to a phonon mode, our data is the first indication that spin excitations have a substantial effect on the electronic density of states. The implications of this will be discussed. We will also briefly discuss recent atomic resolution images and spectroscopy on the parent compound of a pnictide superconductor, SrFe2As2. We will compare our data with LEED on identical samples and discuss the implications.

February 18, 2009

"Tailoring the Glow of Nanostructured Metals: From Thermophotovoltaics to Thermal Beaming," David J. Norris, University of Minnesota, hosted by Gary Wiederrecht

Abstract: When materials are heated that are structured on an optical length scale, their thermal emission can be modified. This has been explored as a possible route to eliminate unwanted heat from thermal emission sources, such as the filament in a conventional light bulb. In addition, this effect may lead to efficient thermophotovoltaic devices, which convert heat (from the sun or another source) into electricity. Here, we will discuss two recent results on the thermal emission of periodically structured metals. First, we will examine tailoring the thermal emission spectrum. In particular, we will show that in thermophotovoltaic applications, properly designed molybdenum structures at 650°C should generate over ten times more electrical power than solid emit­ters while having an optical-to-electrical conversion efficiency above 32%. At such relatively low tempera­tures, these emitters have potential not only in solar energy but also in harnessing geothermal and industrial waste heat. Second, we will discuss tailoring the thermal emission direction. In particular, we examine simple metallic films with surfaces that are patterned with a series of circular concentric grooves (a bull's eye pattern). Due to thermal excitation of surface plasmons, a single beam of light can be emitted from these films in the normal direction that is amazingly narrow, both in terms of its spectrum and its angular divergence. Thus, metallic films can generate laser-like beams of light by a simple thermal process.

February 16, 2009

"Fabrication of Si Single-Electron Transistor with Oxide Tunnel Barriers for a High-Operating- Temperature Device," Vishwanath Joshi, University of Notre Dame, hosted by Derrick Mancini

February 12, 2009

"Synthesis, Characterization, and Applications of Novel Monodisperse Nanoparticles"
Sheng Peng, Brown University
hosted by Gary Wiederrecht and Yugang Sun

Abstract: Monodisperse nanoparticles in the size range below 20 nm are of intense current interest for a variety of applications, not only for the general miniaturization of devices, but also for their novel physical and chemical properties. Recent advances in organic-phase chemical synthesis have led to various monodisperse nanoparticles with controlled size, shape, composition, and crystallinity. In this talk, I will present my recent work on the development of monodisperse nanoparticles of magnetic iron, cobalt, FeCo, and SmCo5, as well as metallic gold and AuAg nanoparticles for various applications in high-density magnetic energy storage, catalysis, and biomedicine.

January 23, 2009

“Towards Non-Centrosymmetric Arrangement of an Electro-Optically Active De Novo Designed Protein”
H. Christopher Fry, University of Pennsylvania
hosted by Tijana Rajh

Abstract: The de novo design of helical bundles capable of binding natural heme complexes is well established. Extending this knowledge to include abiological metalloporphyrin-based chromophores will enhance the utility as well as test the reliability of computationally derived proteins. Success has been found in the design and characterization of a series of a-helical bundles that incorporate the synthetic metalloporphyrins, FeDPP and ZnDPP (DPP = diphenylporphyrin). The incorporation of an abiological, nonlinear optic chromophore ((porphinato)zinc-ethyne-(terpyridyl)ruthenium complex, RuPZn) into a computationally designed, asymmetric single chain helix bundle (SC_RPZ) exploits the natural helical chirality potentially enhancing and macroscopically organizing the complex of interest. Furthermore, generation of self-assembled monolayers on silicon surfaces present a significant advancement towards controlling the spatial orientation of the active chromophore necessary for devising a functional nonlinear optic material.

January 20, 2009

“Part 1: Bioengineering of Protein Nanotubes and Protein-Nanomaterial Composites"
Part 2: DNA Scaffolding Precision Assembly of Nano-Objects and DNA Devices”

Tilak Kumara Mudalig, Center for Functional Nanomaterials, Brookhaven National Laboratory
hosted by Tijana Rajh

Abstract Part 1: An E. coli flagellin protein, termed FliTrx, was investigated for use as a novel form of self-assembling protein nanotube. This protein was genetically engineered to surface display constrained peptide loops with a series of different thiol, cationic, anionic, and imidazole functional groups. Various metal ions were bound to peptide loops and reduced in a controlled manner to generate nanoparticle arrays and nanotubes. Quantum dots (CdTe, ZnS) of 3 ±0.3-nm diameters were bound to histidine peptide loops to generate ordered arrays of quantum dots on the flagella.The optical properties of these assembled quantum dots were studied. The flagella with cysteine loops aggregated through disulfide bond formation to form bundles that could be dissociated into single flagella nanotubes by a reducing agent such as TCEP. The nanotube bundles exhibited an interesting behavior in optical traps generated with 1064 nm laser light. They were repelled by the laser beam instead of being trapped, resulting in their escape. Significant results of these studies will be presented.

Abstract Part 2: We studied a system for analyzing the assembly pathway of DNA nanostructures, which enables the identification, explanation, and avoidance of obstacles to proper structure formation. Potential problems include strand end-pinning and misfolding caused by the structural bias of nominally flexible junctions. We have used this system to guide the construction of parallel motifs that had previously, for unknown reasons, resisted assembly. Further, I will discuss the use of DNA scaffolding for the precision assembly of nano-objcets via multiple anchors and the use of DNA-based mechanical devices to reconfigure nanoparticle assemblies.

January 16, 2009

Nanoparticle Functionalization and its Application for Cancer Imaging and Treatment,”
Yan Zhao, University of Chicago, Ben May Institute for Cancer Research
hosted by Tijana Rajh

Abstract:Surface chemistry and ligand structure are both important for successfully functionalizing nanoparticles. By using the ligand which comprised hydrophobic and hydrophilic part, we prepared highly stabilized gold nanorods, which are ready to conjugate with various organic and bioorganic molecules. One significant property of this ligand is that it made the nanoparticle hydrophilic and lipiphilic at the same time, and dissolve in water as well as in many organic solvent. Dithiocarbamate formation was applied as a simple method for conjugating amines onto metal surfaces, and form strongly adsorbed species which are stable under various types of environmental stress. This method should expand the range of synthetic or biomolecular structures for applications involving surface or nanoparticle functionalization.

As a promising alternative to current organic dyes, quantum dots (QDs) are widely studied as targeted imaging agent, while the desorption of conjugated ligands and nonspecific binding are frequently encountered issues which will lead to reduced contrast or unsuccessful labeling. In this work, estradiol (E2) ligand conjugated QDs were prepared and successfully applied to staining MCF-7 K1 cell with over expressed estrogen (ER) receptor by blocking nonspecific binding sites using E2 ligand-free QDs. By substituting E2 with fluorescein, we studied the numbers of conjugated ligand per QDs and free ligand in the QDs solution, both of which are important in controlling the staining intensity and best results were achieved by balancing the two factors.

January 15, 2009

"Surface Templates for Assembly of Polystyrene Nanoparticles and Oligonucleotides," Dorjderem Nyamjav, Loyola University, hosted by Tijana Rajh

Abstract Template-based approaches to fabricate surface structures have been investigated extensively in the last decade. Among them, scanning probe microscope (SPM)-based nanolithography offers an ability to generate templates with unprecedented precision in a preprogrammed manner. Novel approaches to pattern oligonucleotides and nanoparticles onto silicon substrates via SPM-based nanolithography and microcontact printing technique will be discussed. The patterned oligonucleotides maintained their biological activity. The strategy does not require premodified substrates and offers a cheap and robust way to immobilize oligonucleotides or nanoparticles on electronically important semiconductor surfaces. The method can be utilized in the construction of novel structures and biosensors.

2008 Seminars Archive

Date Title
December 18, 2008

"Interactions of Single Molecules with Gold Surfaces: Kondo Effect and Molecular Rotors," Li Gao, University of California ­ Los Angeles, hosted by Nathan Guisinger and Jeffrey Guest

Abstract: Detecting and manipulating the properties of single molecules are of great importance for the development of single molecular devices. Scanning tunneling microscope (STM) has been used to study the electronic and mechanical properties of single molecules on the metal surfaces. Kondo resonances are a very precise measure of spin-polarized transport through magnetic impurities. We detected Kondo resonances for single iron phthalocyanine molecules on Au(111) surface. The Kondo resonances were found to be greatly dependent on the molecular adsorption site, which provides a method for manipulating molecular Kondo effect. Precisely controlling the motion of single molecules is crucial for fabricating smart molecular machinery. Molecular rotors with a fixed off-center rotation axis have been observed for single tetra-tert-butyl zinc phthalocyanine molecules on Au(111). Experiments and first-principles calculations reveal that the rotation axis is formed by a chemical bonding between a nitrogen atom in the molecule and a gold adatom on the surface. These single-molecule rotors self-assemble into large scale ordered arrays on cryogenic gold surfaces.

December 18, 2008

 

"Chemical Routes to the Nanocrystalline Thermoelectric Materials: AgPbmSbTem+2 and Pb1-xSnxTe Nanocrystals," Indika Arachchige, Northwestern University, hosted by Matthew Pelton

Abstract: Significant progress in the synthesis of narrow-gap quantum dots, such as PbTe nanocrystals, has triggered recognition of their potential in photovoltaic, thermovoltaic, and thermoelectric (TE) applications. Some recent advances in enhancing the TE figure of merit (ZT) are associated with these materials, due to the strong quantum-confinement effect as well as large phonon scattering. This presentation will highlight the recent efforts in the synthesis of thermoelectrically relevant nanocrystalline lead chalcogenide materials that have been the major focus of my research over the last two years.

Nanocrystals of the Quaternary Thermoelectric Materials AgPbmSbTem+2: Materials with compositions AgPbmSbTem+2 or LAST ( Lead-Antimony-Silver-Telluride) have been shown to have promising TE properties with large ZT values ranging from 1.2 to 1.7 at 700K. Although by many measures, bulk LAST materials behave as solid solutions, high-resolution TEM micrographs indicate phase segregation with the presence of coherent, endotaxially embedded nanodots that are rich in Ag and Sb. The nanocrystals are believed to affect the TE properties at least in part by causing enhanced phonon scattering leading to low thermal conductivity.

However, the nature of the Ag/Sb-rich nanodots found in bulk LAST materials and their full impact on TE performance is not well understood. It would therefore be interesting to develop a synthetic methodology to prepare nanocrystals of LAST materials to investigate the link to enhance TE performance. We have recently developed a new general methodology for the synthesis of nanocrystalline LAST materials with control over size, shape and atomic composition. Herein we describe the influence of synthetic parameters on the primary particle size, morphology, optoelectronic properties as well as the TE performance.

Anomalous Band Gap Evolution from Band Inversion in Pb1-xSnxTe Nanocrystals: Ternary Pb1-xSnxTe alloys are narrow gap semiconductors with absorption band energies that are nonlinearly proportional to the Sn concentration (x). At 300 K, the energy gap of PbTe is 0.29 eV and pure SnTe is a p-type semiconductor with energy gap of 0.18 eV, but with conduction and valence bands are inverted from those of PbTe. Hence, the energy gap of Pb1-xSnxTe materials initially decreases with increasing Sn concentration (x) and vanishes for an intermediate alloy composition. With further increase in Sn fraction (x), the energy gap starts to increase up to the SnTe value.

However, it is very difficult to precisely determine the band edge structure of the intermediate compositions near and beyond the band inversion region, since only high carrier concentration samples can be obtained due to deviation from stoichiometry. On the other hand, nanocrystals of Pb1-xSnxTe would not have high carrier concentrations and can serve as ideal samples to determine the band edge structure near and beyond the inversion region.

Recently we have developed a general methodology for the synthesis of nanocrystalline Pb1-xSnxTe materials which exhibit anomalous trend in optoelectronic properties. Herein we describe the effect of synthetic parameters on the primary particle size, morphology, atomic composition, and optoelectronic properties.

December 17, 2008

"Synthesis and Self-Assembly of One-Dimensional Nanostructures," Bishnu P. Khanal, Rice University, hosted by Matthew Pelton

Abstract: Gold nanorods exhibit strong optical scattering and absorption in the visible and near-infrared regions due to the localized surface-plasmon resonance. The longitudinal plasmon of gold nanorods is dependent on their aspect ratio. However, the nanorods synthesized by classical seed-mediated method have a very limited range of achievable aspect ratios (3-5). Numerous attempts to increase the aspect ratio to values >5 have met little success so far. This presentation will describe methods to tune the plasmon peak in a reversible fashion and obtain nanorods with any aspect ratio ranging from 1 to 300. One-dimensional growth and shortening of nanorods in aqueous solution in the presence of Au (I) and Au (III) ions, respectively, will be discussed. In addition, the self-assembly of one-dimensional nanostructures in the form of ring like superstructures and colloidal crystals will be discussed.

December 16, 2008

"Second-Order Nonlinear Optic Materials and Bridging Nanoscale Devices with Functional Molecular Wires," Yiliang Wang, Northwestern University, hosted by Matthew Pelton

Abstract: There are two different topics in the area of material chemistry in this talk. The first part is the research on second-order NLO materials, including EO chromophore synthesis, EO thin film fabrication, and the design of a transparent conductive oxide-based EO modulator. The second part is the study of the electrical properties of molecular wires. Functional molecular wires were used to to covalently connect nanoscale electrodes, which were cut single-walled carbon nanotubes. Reliable and reproducible results were obtained, and oligoaniline wires were fully studied for the pH-sensitive conductance.

December 15, 2008

 

"Patterning of Nanoparticles Using DNA Directed Self-Assembly," Jaswinder Kumar Sharma, Arizona State University, hosted by Matthew Pelton

Abstract: Recently research in the field of noble metal nanoparticles has received a great interest due to their unique optical properties. Uniqueness of these optical properties arises from the enhanced electromagnetic fields near the particle surface, which in turn are result of resonant oscillation of their conduction electrons caused by their interaction with the incident light. This collective oscillation of conduction electrons is called localized surface plasmon, which can be exploited to create a variety of photonic devices like plasmon waveguides and plasmonic rulers. But all these devices can only be created by organizing nanoparticles with constant interparticle spacings at nanoscale. DNA nanotechnology has emerged as an excellent approach to organize metallic nanoparticles at nanometer scale with predetermined position and interparticle distances. In today’s presentation, I will talk about the use of DNA scaffolds for patterning gold nanoparticles and Quantum Dots. I will also talk about some strategies developed to strengthen the bond between DNA oligonucleotides and gold nanoparticles, and their use in increasing the yield of nanoparticles patterned by DNA scaffolds.

November 17, 2008

 

"Micromagnetic investigations of current and field-induced vortex core reversal," Sebastian Gliga, Forschungszentrum Jülich, hosted by Matthias Bode

Abstract: Micromagnetic simulations are routinely employed for the modeling of magnetic structures in mesoscopic ferromagnets. In recent years, the simulations have achieved a very high degree of reliability and accuracy, yielding in most cases perfect agreement with experiments, thereby demonstrating their predictive power. Micromagnetic simulations are now therefore being applied to investigate phenomena on time and length scales beyond the present limits of experimental resolution, where new dynamic processes are expected to be found.

One such recently discovered process is the ultrafast reversal of vortex cores in magnetic thin-film elements, which may find application in non-volatile storage media. Magnetic vortices are naturally-forming fundamental magnetization structures possessing a nanometric core around which the magnetization direction circulates in the film plane. In the core, the magnetization aligns perpendicular to the plane, pointing 'up' or 'down'. Recent experiments have shown that the core magnetization can be switched by means of weak in-plane pulses, but the details of the switching mechanism could not be resolved. Our three-dimensional micromagnetic finite-element simulations elucidate the dynamics of this complex mechanism and describe the fastest field-induced switching process ever reported.

I will present recent results on the reversal of the vortex core induced by external fields and, more technologically relevant, by electric currents. I will show that in both cases, the switching mechanism is identical.

Moreover, two distinct routes exist through which a vortex core can be switched: a slow route, in which the reversal is achieved within nanoseconds and an ultrafast route unfolding on the picosecond time scale. In both cases, the switching occurs as soon as the internal energy exceeds well-defined threshold values, providing insight into the origin of this process.

Micromagnetic simulations have allowed furthering the understanding of arguably the most complicated micromagnetic switching mechanism known to date. They also make clear predictions for possible experimental studies.

November 11, 2008

"Growth, Characterization and Application of Nanocrystalline Diamond Films," James E. Butler, Naval Research Laboratory, hosted by Anirudha Sumant

Abstract: The nucleation and growth of nanocrystalline diamond films by chemical vapor deposition will be presented. Nanodiamond films grown by chemical vapor deposition exhibit a number of remarkable properties desirable for MEMS and NEMS. These include high Young's Modulus, thermal diffusivity, dielectric breakdown strength, mass density, secondary electron yields, fracture toughness, optical transparency, corrosion resistance, biological stability, and more. The nucleation, growth, and doping of these films on diverse substrate materials, including silicon, poly silicon, SiO2, and various metals, will be described along with various methods of processing into structures and devices.

November 3, 2008

"MEMS Micromirror Arrays for Spatial and Temporal Light Shaping and Its Application in Optical Communication and Infrared Image Detection," Roland Ryf, Alcatel-Lucent Bell Laboratories, hosted by Daniel Lopoez

Abstract MEMS micromirror arrays exhibit some unique properties, such as high optical throughput, pixel size as small as 3 um, and fast response in the order of 10 us. I will describe two types of MEMS array fabricated at Bell Labs. The first type has mirrors that have an electrostatic actuated piston motion for the individual pixel-mirrors and is in essence a spatially programmable phase modulator. The second type of array offers the additional ability to tilt the individual mirror around two axis and thus can act as a programmable Fresnel optical element. I will describe how these two arrays can be used for applications such as adaptive optics, optical tweezers, or optical lattices. Further, with the help of a diffractive element, the arrays can be used for time domain filtering, which is useful for pulse shaping and dispersion compensation. I will present the result for a programmable dispersion compensator with no impairment on the passbands. Finally I will report on a MEMS-based infrared detector array (8- to 14-um wavelength range) based on an optical readout scheme at visible wavelength.

October 23, 2008

"Accelerating development of membranes using materials modeling: metal organic frameworks and metal alloys," David Sholl, Georgia Institute of Technology, hosted by Jeffrey Greeley

Abstract: Membranes have potential to play an important role in many energy-related chemical separations, but experimental development of new membrane materials is challenging and time-consuming. Materials modeling can play an important role in this area by screening potential membrane materials in advance of experimental studies. I will describe work in my group on several classes of materials following this theme, including metal organic frameworks as potential nanoporous membranes for light gas separations and metal alloys as dense films for hydrogen purification.

October 23, 2008

"Revisiting optical manipulation with surface plasmons," Romain Quidant, ICFO ­ The Institute of Photonic Sciences, Barcelona, Spain, hosted by Gary Weiderricht

Abstract :Force fields originating from evanescent waves open new opportunities to integrate optical manipulation in a coplanar geometry and extend optical trapping to the subwavelength scale. Within this scope, it was recently suggested that surface plasmon (SP) fields bound to metal-dielectric interfaces be used. In addition to offering enhanced magnitude over conventional evanescent fields, SP fields are also expected to achieve further spatial confinement toward the nanoscale. We review recent advances achieved in the use of SP fields engineered at a patterned metal surface for on-a-chip optical manipulation of small objects in solution.

We first discuss trapping of microsized colloids with gold micropads illuminated under total internal reflection. It is shown how enhanced and confined SP fields at the pad surface can be engineered to provide stable wells able to trap colloids at predefined locations of the surface with laser intensity much weaker than is required for conventional three-dimensional optical tweezers. This method also enables parallel trapping with a single unfocused beam.

We then discuss the specificities of SP traps over conventional three-dimensional tweezers. In particular, we show how the dependency of the gradient and scattering force components on the illumination parameters enables tuning their trapping ability and achieving a trapping selectivity to the specimen polarizability.

Finally, we explore new trapping platforms, directly inspired from the latest advances in plasmon nano-optics to extend our method to the manipulation of subwavelength objects that otherwise could not be trapped with conventional tweezers.

October 23, 2008

"Magnetism on the Atomic Scale," Andreas J. Heinrich, IBM - Almaden Research Center, hosted by Matthias Bode

Abstract: Understanding and controlling the magnetic properties of nanoscale systems is crucial for the implementation of future data storage and computation paradigms. Here we show how the magnetic properties of individual atoms can be probed with a low-temperature, high-field scanning tunneling microscope when the atom is placed on a thin insulator. We find clear evidence of magnetic anisotropy in the spin excitation spectra of individual magnetic atoms embedded in a nonmagnetic surface. In extended one-dimensional spin chains, which we build one atom at a time, we find strong spin coupling into collective quantum spins, even for the longest chains of length 3.5 nm. The spectroscopic results can be understood with the model of spin excitations in a system with antiferromagnetic coupling, controlled on the atomic scale.

High-spin atoms can show an interesting form of the Kondo effect when the magnetic anisotropy places a degenerate, low-spin Kramers doublet in the ground state.

October 15, 2008

"Engineering Nanomaterial Platforms: Toward Highly Sensitive and Specific Biomedical Detection," Jong-in Hahm, Pennsylvania State University, hosted by Seth Darling

Abstract: This talk presents an overview of our ongoing nanomaterials research, aiming to provide more rapid, sensitive, and accurate detection of genetic and protein markers. Current research efforts pertaining to nanotubes, nanowires, and polymers will be briefly highlighted.

Following the introduction of various nanomaterials research in our group, this talk will focus on the remarkably enhanced optical detection of DNA and proteins which is enabled by the use of nanoscale zinc oxide platforms. Fluorescence detection is currently one of the most widely used methods in the areas of basic biological research, biotechnology, cellular imaging, medical testing, and drug discovery. Using model protein and nucleic acid systems, we demonstrate that engineered nanoscale zinc oxide nanostructures can significantly enhance the detection capability of biomolecular fluorescence. Without any chemical or biological amplification processes, nanoscale zinc oxide platforms enabled increased fluorescence detection of these biomolecules when compared to other conventional substrates. This ultrasensitive detection was due to the presence of ZnO nanomaterials which contributed greatly to the increased signal to noise ratio of biomolecular fluorescence.

We also demonstrate the easy integration potential of zinc oxide nanostructures into periodically patterned platforms which, in turn, will promote the assembly and fabrication of these materials into multiplexed, high-throughput, optical sensor arrays. These zinc oxide platforms will be extremely beneficial in accomplishing highly sensitive and specific detection of biological samples involving nucleic acids, proteins and cells, particularly under detection environments involving large scale population screening and early biomarker detection.

October 9, 2008

"Organizing atoms, clusters, and proteins on surfaces," Richard Palmer, University of Birmingham, hosted by Stefan Vajda

Abstract: We will address two complementary methods to organize many-atom systems on the sub-10-nm scale: room temperature STM manipulation of individual polyatomic molecules and deposition of size-selected atomic clusters. The common theme will be precision and uncertainty in the organization of atoms.

Bond-selective molecular manipulation is one of the frontiers of atomic manipulation with the STM. Traditionally such experiments are conducted in the stable, low-temperature regime; room-temperature manipulation is much more challenging. Here we demonstrate room-temperature, bond-selective manipulation ("molecular dissection") in a polyatomic molecule, chlorobenzene (C6H5Cl), anchored to the Si(111)-7x7 surface by chemisorption. Electron (or hole) injection from the STM tip into the p* LUMO (p HOMO) orbitals of the benzene ring leads to controlled molecular desorption - a one-electron process. We focus on C-Cl bond dissociation in the chemisorbed chlorobenzene molecule. Detailed STM images identify the azimuthal orientation of the individual chlorobenzene molecules and allow us to correlate the final location of the liberated chlorine "daughter" atoms with their parents. We identify Cl atoms up to 50Å from the parents. We find that dissociation is a two-electron process and propose a vibrationally mediated electron attachment mechanism.

The controlled deposition of size-selected clusters, assembled in the gas phase, is an alternative route to the fabrication of surface features of size 1-10 nm - also the size scale of biological molecules such as proteins.

Scaling relations that describe the implantation and pinning of the clusters enable the preparation of stable, three-dimensional surface features, which can act as protein binding sites. Specifically, we report the pinning of size-selected AuN clusters (N = 1­100) to the (hydrophobic) graphite surface to create films of arbitrary, submonolayer density. Gold presents an attractive binding site for sulphur and thus for cysteine residues in protein molecules. AFM measurements in buffer solution show that GroEL chaperonin molecules (15-nm rings), which contain free cysteines, bind to the clusters and are immobilized]. Peroxidase and oncostatin molecules behave similarly. By contrast, green fluorescent protein does not bind, consistent with detailed analysis of the protein surface; the cysteine residues lie in the interior of the folded protein. The results provide "ground rules" for residue-specific protein immobilization by clusters and have led to the development of a novel biochip for protein screening by a spin-off company.

October 2, 2008

"Label-free Mapping of Near-field Transport Properties Using Surface Plasmon Resonance Reflectance Imaging," Iltai Kim, University of Tennessee, hosted by David Tiede and Gary Wiederrecht

Abstract: A label-free visualization technique based on surface plasmon resonance (SPR) reflectance sensing is presented for real-time and full-field mapping of microscale concentration and temperature profiles. The key idea is that SPR reflectance sensitivity varies with the refractive index of the near-wall region of the test mixture fluid. The Fresnel equation, based on Kretschmann’s theory, correlates the SPR reflectance with the refractive index of the test medium, and the refractive index correlates with the mixture concentration or temperature. The basic operation principle is that when noble metal is illuminated by p-polarized light or electron at a specific angle above critical, an evanescent wave is generated to excite a surface plasmon wave in the interface between the thin noble metal film and the test medium. The surface plasmon wave is highly sensitive to variation of the refractive index of the test medium with an accuracy of 10-8 in RIU to provide a powerful tool for chemical/bio sensing. The existing SPR-related techniques, however, are effectively pointwise and mostly lack a systematic, quantitative approach.

In this study, SPR is applied and demonstrated to detect near-field microfluidic properties, such as concentrations and temperatures, in a label-free, real-time, and full-field manner using a laboratory-developed SPR reflectance imaging system. Three example applications are presented: (1) micromixing concentration field development of ethanol penetrating into water contained in a microchannel, (2) full-field detection of the near-wall salinity profiles for convective/diffusion of a saline droplet into water, and (3) SPR imaging thermometry of the cooling of a hot-water droplet in air and cold water medium as well as a parametric study of optical properties. Also presented are discussions on measurement sensitivity, uncertainties, and a parametric study of optical properties such as refractive indices of prisms and thin metal films, and detection limitations of the implemented SPR imaging sensor. Furthermore, SPR reflectance imaging can be effectively applied in biochemical sensing, such as interactions between cell and substrate, because of its high sensitivity in the near surface less than 1 μm, and SPR can be coupled with nanoparticles to present various applications, such as in nanophotonics and nanomedicine.

September 26, 2008

"Nano-Nanocomposites: An Emerging Class of Materials," Pushan Ayyub, Tata Institute of Fundamental Research Mumbai, India, hosted by Derrick C. Mancini

Abstract: The possibility of obtaining some degree of control over different physico-chemical properties by means of varying the size and shape of the crystallographic grains constituting bulk matter is now well known. In this talk, we will review our recent results on nano-nanocomposites (NNC), defined as a random, bi-phasic nanodispersion, in which the characteristic size of both phases present is in nanometers. This is a subset of the larger family of nanocomposites, which commonly consist of one phase nanodispersed in an extended matrix phase. NNCs afford the possibility of tuning physico-chemical properties via a large number of parameters, such as the nature of the components, the composition, and the size and morphology of both phases. In certain especially interesting situations, the properties of the NNC are not simple linear superpositions of the properties of the individual nanocrystalline species. I will discuss three such special cases:

  1. NNCs of II-VI semiconductors with different band gaps that show enhanced photoluminescence, photoconductivity, and nonlinear optical properties;
  2. NNCs of a superconductor and a normal metal, whose properties are predominantly controlled by the superconducting proximity effect; and
  3. Metal-metal NNCs that are actually nanoscale phase-separated alloys of "immiscible" metals.
September 11, 2008

"Multiple Excitons in PbSe Nanocrystals: From Generation using Single Photons to Auger Recombination," Richard D. Schaller, Los Alamos National Laboratory, hosted by Stephen K. Streiffer

Abstract: PbSe nanocrystals are efficient infrared (IR) emitters with potential applications ranging from telecommunications to optical tagging. These nanocrystals can be synthesized with narrow size dispersion and high photoluminescence quantum yields (up to ~80% at room temperature), providing size-controlled tunability of the energy gap from near- to mid-IR wavelengths. By means of novel transient absorption experiments, we were able to observe in 2004 that single photons of sufficient energy can produce multiple electron-hole pairs in PbSe nanocrystals with a low energetic onset in comparison to the bulk. This result has been verified by other research groups, and is of significant interest to the photovoltaics community because of the potential for this physical effect to increase power conversion efficiencies of single junction devices above the apparent Shockley-Queisser thermodynamic limit. We find experimentally that the generation of multiple excitons takes place exceptionally fast, which has invited novel mechanisms to be posited. Time permitting, I will present research into the mechanism of Auger recombination in nanocrystals via the unique approach of using hydrostatic pressure to tune nanocrystal energy gap via the material deformation potential. In these studies, we find that Auger recombination is energetically barrierless in distinction from bulk materials. This finding has several important ramifications for nanocrystal material applications.

September 8, 2008

"Self-Assembly for Nanostructured Photovoltaic Devices," Charles T. Black, Center for Functional Nanomaterials, Brookhaven National Laboratory, hosted by Stephen K. Streiffer

Abstract The Center for Functional Nanomaterials at Brookhaven National Laboratory is a science-based user facility devoted to nanotechnology research addressing challenges in energy security. The five internal research groups (Electronic Nanomaterials, Catalysis/Surface Science, Biology/Soft Materials, Electron Microscopy, and Theory/Computation) accompany a broad portfolio of scientific capabilities and an active external user program. Our research program in electronic materials incorporates nanostructured materials with precisely defined and tunable internal dimensions as experimental platforms for understanding and improving the three critical steps of photovoltaic energy conversion: solar light absorption by the active photovoltaic material; dissociation of photogenerated electron-hole pairs into free charge carriers; and charge collection.

Nanometer-scale material self-assembly has applications in both today¹s and future technology. I will present thoughts and preliminary experimental results showing the promise of self-assembling materials for improving photovoltaic device performance, while at the same time framing the discussion around our prior successful implementation of self-assembly processes in high-performance semiconductor devices.

August 22, 2008

"Heusler Compounds: Materials for Spinelectronic Devices," Andy Thomas, Bielefeld University, hosted by Tiffany Santos

Abstract: Spinelectronic devices try to utilize the electric charge as well as the electron spin to enable new devices such as magnetic sensors, memory, and logic. These devices could be based on magnetic tunnel junctions (MTJs). The signal change -- which is crucial for most applications -- of the MTJs depends on the spin polarization of the ferromagnetic electrodes. There are a few material classes that have a predicted spin polarization of 100%, one of which is the Heusler alloys. Here, we present our investigations of Heusler alloys integrated in magnetic tunnel junctions and compare them with band structure calculations.

July 14, 2008

"Exploring the complex magnetic phase space at surfaces," Stefan Heinze, University of Hamburg, hosted by Matthias Bode

July 11, 2008

"Synchrotron Microbeam X-Ray Radiation Damage in Crystalline Semiconductor Layers," Ismail C. Noyan, Columbia University, hosted by Jorg Maser

Abstract: Radiation-induced structural damage is observed in silicon-on-insulator and SiGe samples illuminated with monochromatic (11.2 keV) X-ray microbeams approximately 250 nm in diameter. The X-ray diffraction peaks from the irradiated layers degrade irreversibly with time, indicating permanent structural damage to the crystal lattice. The size of the damaged regions is almost an order of magnitude larger than the beam size, and the magnitude of damage drops as one moves away from the center of the illuminated volume. We discuss the threshold dosage required for damage initiation and possible mechanisms for the observed damage.

July 10, 2008

"Tunneling and spin transfer torques in Fe/MgO/Fe," Christian Heiliger, Center for Nanoscale Science and Technology, National Institute of Standards and Technology/ Maryland NanoCenter, University of Maryland, hosted by Nathan Guisinger

Abstract: Very high tunneling magnetoresistance (TMR) ratios in crystalline Fe/MgO/Fe tunnel junctions result from coherent transport. The MgO barrier material selects high symmetry states that are only present in the majority spin channel of Fe leading to a high spin polarization and to a high TMR. In this talk, I show that this half metallicity of Fe with respect to the high symmetry states leads to a strong localization of the spin transfer torque (STT) to the interface. As a result, the STT in realistic tunnel junctions is independent of the free layer thickness for more than three monolayers of Fe. For ideal samples, however, quantum size effects are visible. I also discuss the bias dependence of the STT and compare our results to recent measurements.

July 8, 2008

"Polyvalent DNA-Functionalized Gold Nanoparticles: Investigating DNA Loading and Aggregate Stability," Sarah Hurst, Northwestern University, hosted by Tijana Rajh

Abstract: Polyvalent DNA-functionalized gold (DNA-Au) nanoparticles (13-30 nm in diameter) have become widely used as nanoscale building blocks in assembly strategies, antisense agents in nanotherapeutics, and probes in biodiagnostic systems. Recently, we have developed protocols to finely tune the density of DNA on the surface of gold nanoparticles ranging from 15 to 250 nm in diameter. These protocols have afforded us the opportunity to investigate the relationship between nanoparticle size and the cooperative melting transition associated with aggregates of DNA-Au nanoparticles. Specifically, we have determined the minimum number of base pairings necessary to stabilize DNA-Au nanoparticle aggregates as a function of salt concentration for particles between 15 and 150 nm in size. Significantly, we have found that under certain conditions a single possible base pair interaction per DNA connection is capable of evoking hybridization of 150-nm DNA-Au nanoparticles. In addition, we have investigated the curvature-induced contributions of non-Watson-Crick base pairings to nanoparticle aggregate stability. Knowledge of the relative contributions of these parameters to the stability of DNA-Au nanoparticle aggregates will be important in the aforementioned applications where DNA-Au nanoparticles, especially those greater than 50 nm, are used.

June 30, 2008

Miniature Flow Cytometry Systems Employing Microfluidics, Dielectrophoresis, and Microacoustics for Medical Diagnosis and Biothreat Detection,” Surendra Kumar Ravula, Sandia National Laboratories, hosted by Derrick Mancini

Abstract: Flow cytometry is an indispensable tool in clinical diagnostics for screening of cancer, AIDS, infectious disease outbreaks, microbiology,and others. The cost and size of existing cytometers precludes their entry into field clinics, water monitoring, agriculture/veterinary diagnostics, and rapidly deployable biothreat detection. Much of the cost and footprint of conventional cytometers is dictated by the high speed achieved by cells or beads in a hydrodynamically focused stream. This constraint is removed by using dielectrophoretic and acoustic focusing in a parallel microfluidic architecture. In this presentation, I will describe our progress towards a microfabricated flow cytometer that uses bulk planar piezoelectric transducers in microfluidic channels. In addition to experimental data, initial modeling data to predict the performance of our systems are discussed.

June 26, 2008

"Single-Molecule Absorption Detected by Scanning Tunneling Microscopy," Erin Carmichael, University of Illinois at Urbana-Champaign, hosted by Nathan Guisinger

Abstract: Scanning tunneling microscopy (STM) consistently provides the highest spatial resolution among the scanning probe methods, allowing surfaces to be investigated on the atomic level. With the addition of optical excitation, STM promises to become a powerful technique for single molecule spectroscopy, enabling one to examine the response of single molecules on a surface. Atomic scale laser-assisted STM has thus far remained an elusive goal, with few recent experiments reaching subnanometer resolution. This is due to the many difficulties faced as a result of light perturbing the tunneling junction. We combine a novel rear-illumination geometry with frequency-modulated laser excitation to probe the optical absorption of single-walled carbon nanotubes on silicon surfaces. Modulations in the local electronic density of states can be detected with near-atomic resolution, and measurements of the molecular absorption coefficients can provide information about the chirality of a nanotube.

June 24, 2008

"Extreme Ultraviolet Interferometric and Holographic Lithography at the University of Wisconsin-Madison," Artak Isoyan, Center for Nano Technology, University of Wisconsin-Madison, hosted by Derrick Mancini

Abstract: Initial results from a 4X reduction interferometric lithography technique using extreme ultraviolet radiation from a new undulator on the Aladdin storage ring at the Synchrotron Radiation Center of the University of Wisconsin-Madison will be reported. Extended traditional interferometric lithography by using second diffraction orders instead of first orders will be discussed. This change considerably simplifies mask fabrication by reducing the requirements for mask resolution. Interferometric fringes reduced by 4X (from 70-nm half-period grating to 17.5 nm) have been recorded in a 50-nm-thick hydrogen silsesquioxane photoresist using 13.4 nm wavelength EUV radiation.

June 12, 2008

"Synthesis and applications of conducting polymer nanostructures," Jiaxing Huang, Northwestern University, hosted by Dave Gosztola and Yugang Sun

Abstract: There are exciting opportunities at the interface between the fields of nanostructured materials and conducting polymers. In this talk, conducting polymer polyaniline nanofibers will be used as an example to illustrate how nanoscale morphology impacts the material¹s processing and applications. A chemical method was developed to synthesize the nanofibers in high purity and large quantity without the need for templates. With this nanofiber morphology, the dispersibility and processibility of polyaniline are now much improved. The nanofibers show dramatically enhanced performance over conventional polyaniline applications such as in chemical sensors. They can also serve as a template to grow inorganic/polyaniline nanocomposites that lead to exciting properties for nonvolatile memory devices and catalysis. Additionally, a flash welding technique for the nanofibers has been developed that can be used to make asymmetric polymer membranes, form patterned nanofiber films, and create polymer-based nanocomposites based on an enhanced photothermal effect observed in these highly conjugated polymeric nanofibers. Polyaniline nanofibers are also a great model material for use in chemical / materials science education

May 29, 2008

"Lead Sulfide Nanocrystals Embedded in Organic Films for Nonlinear Optical Devices," Luke Hanley, University of Illinois at Chicago, hosted by Seth Darling

Abstract: Lead sulfide nanocrystal/oligomer composite films are examined here for nonlinear optical materials, but are also of interest for applications in photodetectors, light-emitting diodes, and photovoltaics. PbS-oligomer nanocomposite films are deposited with a modified commercial cluster beam deposition source and also prepared by traditional colloidal methods, then transferred to polymer films. These PbS nanocomposite films are examined by X-ray photoelectron spectroscopy, transmission electron microscopy, and nonlinear optical absorption measurements. It is well established that the linear optical properties of such composites can be tuned by varying the nanocrystal size and concentration within the organic matrix. Controlling the PbS nanocrystal surface properties at the nanocrystal-oligomer or polymer interface strongly affects their nonlinear optical absorption at 532 nm. This effect will be discussed in terms of differences in excited state absorption controlled by this interface. The relative merits of gaseous deposition and colloidal synthesis will also be discussed for the preparation of nanocomposite films.

May 2, 2008

"Nanomechanical switching at 1 ns and 1 V using an in-plane switch," David Czaplewski, Sandia National Laboratories, hosted by Derrick C. Mancini

Abstract: Nanomechanical switches have been proposed to replace CMOS switches to operate at temperatures greater than 200°C and with almost no static power dissipation. Ideally, the NEMS switches would be integrated with standard CMOS to realize power savings in computing applications. Ideally, to realize this goal, the switches would switch at similar voltages and with similar times to their CMOS counterparts. For integration purposes, the NEMS switch fabrication would have to be CMOS compatible.

This presentation will summarize the progress of the work on a program to create a nanomechanical switch that switches in 1 ns using 1-V drive actuation. A summary of the modeling effort will show the critical parameters of the design for fast, stable switching while avoiding mechanical failures of the switch. Then the fabrication performed to realize these devices will be shown. Finally, electrical testing results will be presented on the switches that have been fabricated and released.

May 1, 2008

"Synthesis and Tailoring the Surface Chemistry of Nanostructured Carbon Materials for Applications in Micro/Nano Systems," Anirudha V. Sumant, Argonne National Laboratory, hosted by Derrick C. Mancini

Abstract: The current progress in fabricating microelectromechanical and nanoelectromechanical systems (MEMS/NEMS) involving rotating, sliding, or impacting surfaces in contact based on silicon has achieved limited success primarily due to the poor mechanical, chemical, and tribological properties of silicon. At the nanoscale, due to increased surface-to-volume ratio, surface properties, such as adhesion/stiction dictates the performance of a device, and therefore development of new materials with superior mechanical, chemical, and tribological properties than those of silicon are necessary. Nanostructured carbon materials such as ultrananocrystalline diamond (UNCD) and tetrahedral amorphous carbon (ta-C) have demonstrated exceptional physical, chemical, and tribological properties at the macro- and microscale, and therefore are considered promising materials for MEMS and NEMS applications. However, little is known about their surface chemistry, morphology, and bonding configuration at the tribological interface and how it will affect tribological performance at the nanoscale. I will discuss methodologies to tune surface chemistry, morphology, and bonding configuration of UNCD surface via changes in the UNCD nucleation and growth process. Using these methodologies, we achieve extremely low adhesion energies (down to van der Waal's limit) and friction forces at the nanoscale.

Additionally, recent preliminary measurements of nanomechanical properties of UNCD carried out using in situTEM nano-indentation will also be presented. In case of ta-C, I will discuss how film-annealing processes alter both the bonding in the film and the nanotribological response.

In the next part of my talk, I will discuss current progress in synthesizing large area UNCD films (up to 8-in diameter) at low temperatures (400°C) at CNM and demonstration of its CMOS compatibility with a goal to develop monolithically integrated UNCD based MEMS/NEMS devices driven by CMOS. I will present work under progress in this direction on the fabrication of RF-MEMS switches based on UNCD by taking advantages of its unique dielectric properties as well as on the fabrication of UNCD based resonators by integrating with piezoelectric materials. At the end of my talk, I will present brief highlights of research that is being carried out under collaborative CNM user's proposal that I have developed with various outside collaborators.

April 22, 2008

"How Macromolecules Pass Through a Nanopore or Ultrafiltration of Macromolecules through Nanopores," Chi (Qi) Wu, The Chinese University of Hong Kong, hosted by Yugang Sun and Gary Wiederrecht

Abstract: Using a special double-layer membrane to avoid interaction among flow fields generated by different pores, we have, for the first time, observed the predicted discontinuous first-order transition in ultrafiltration of flexible linear polymer chains. That is, the chain could pass through a pore much smaller than its unperturbed radius only when the flow rate is higher than a certain value. When only one chain and one pore are considered, in theory, such a threshold is surprisingly independent of both the chain length and the pore size. Our results reveal that for a membrane with many pores and at a microscopic flow rate (q) lower than the threshold, the inevitable blocking of some pores by longer nonstretched coiled chains increases q in those nonblocked pores because the macroscopic flow rate (Q) is a constant.

Our results reveal that the force needed to stretch a polymer coil in an athermal solvent is only ~10 fN. Further, using this method, we are able to measure how "soft" a polymer chain is and how strong the interchain interaction is when they are collapsed and entangled with each other.

April 17, 2008

"MEMS-Based Spatial Light Modulators: Recent Developments and Future Directions," Daniel Lopez, Alcatel-Lucent, hosted by Eric Isaacs

Abstract: Micro electro mechanical dystems (MEMS) technology enables mass production of microscopic mechanical systems through batch fabrication techniques similar to the ones used in the electronics integrated circuit (IC) industry. Similar to ICs containing millions of individual transistors, mechanical systems with millions of independent moving parts (degrees of freedom) can now be fabricated on a single small silicon chip. While a variety of applications will benefit from this technology, nowhere is the potential as clear and compelling as in optical systems, at the intersection of electronic, mechanical and optical domains.

The unique advantages of MEMS are high-speed and excellent optical quality, wavelength and polarization independence, and low optical loss. Dense integration of millions of individually controlled micro-mirrors onto a single silicon chip leads to creation of a reconfigurable fast digital diffractive optical element that allows an unprecedented degree of control and manipulation of the optical field. This new kind of spatial light modulator (SLM) reveals potential to bring revolutionary new capabilities for projection, information processing, and telecommunications.

In this talk I will describe the fundamentals of this technology and our recent work in the development and fabrication of a MEMS-based phase-only SLM originally envisioned as a substitute for expensive optical photomasks. I will also describe the new and distinctive capabilities that these SLMs offer for miniature projection systems, optical nano-manipulation, holographic data storage, and free space communications.

April 14, 2008

"Device Implications of Spin Transfer Torques," Jordan Katine, Hitachi San Jose Research Center, hosted by Axel Hoffman

Abstract: This presentation looks at spin transfer torques from the perspective of three technological applications: hard disk drives, MRAM, and current-tunable high-frequency oscillators. In hard disk drives, spin transfer torques are a source of noise, and I will discuss the implications spin transfer noise will have on future sensor designs. For MRAM, I evaluate the feasibility of spin transfer driven switching. Finally, I consider the possibility of GHz communication applications enabled by nanoscale spin transfer oscillators, including Hitachi's recent results in MgO-based devices.

March 19, 2008

"Shape Changes induced by Chemical Transformation of Nanocrystals," Can K. Erdonmez, Massachusetts Institute of Technology, hosted by Yugang Sun and Gary Wiederrecht

Abstract: Colloidal nanoparticles (NPs) of a great number of materials can now be produced with well-controlled size, shape and surface properties. However, it is still often difficult to extend an existing synthetic recipe. For example, a particular size range and shape might be easy to produce for one composition, but not another, similar one. Analogous to cases in organic chemistry, inorganic NPs can participate in chemical reactions as preformed precursors and form product particles with modified size, composition, and properties. Recent research shows that this approach not only allows the realization of new compositions, but can also yield morphologies derived from, but also distinct from, the shapes of the starting materials.

I will present several examples of morphological evolution of NPs as a consequence of chemical transformation. The major focus is on the transformation of solid particles into hollow nanoshells due to directional diffusive mass transport (the Kirkendall effect) accompanying chemical transformation. This process is predicted to be easily achieved for a large number of materials and experimental results support the general nature of the effect. In one case, the transformation of cobalt NPs into Co3S4 nanoshells, existing bulk studies are complete enough and the nanoshell synthesis mature enough for making inferences about the shell formation process.

I will also highlight two more examples of simultaneous composition and shape modification and discuss their likely mechanisms: transformation of solid silver particles into octahedral cages upon galvanic exchange and formation of periodically ordered Ag2S inclusions in CdS nanorods upon partial exchange of Cd2+ with dissolved Ag+. The former process illustrates one possible end result of etching and redeposition occurring simultaneously in a nanoscale system; the latter involves a complex and still not fully understood interplay between elastic stress, nucleation and diffusion-limited segregation kinetics in a one-dimensional system.

February 21, 2008

"Quantum dots based energy transfer to photodynamic therapy agents," Smita Dayal, Case Western Reserve University, hosted by Matthew Pelton

February 12, 2008

"Nanoscale Imaging with the Coherent Diffraction Microscope," Changyong Song, University of California, Los Angeles, hosted by Jorg Maser and Ian McNulty

Abstract: The coherent diffraction microscope (CDM) is a versatile imaging probe with applications spanning a wide range of nano- and biosystems at nanometer resolution. The simple experimental schemes of the CDM have led to immediate adaptations over broad spectra of coherent light sources including hard X-ray, soft X-ray, and tabletop EUV lasers. Extensive research over the past several years has advanced the technique significantly – three-dimensional tomography, resonant imaging and tabletop diffraction microscopy – to address certain scientific questions as a practical microscope. The ultimate interest for the technique is to resolve structures within single macromolecule complexes at near atomic resolution, which will be feasible with the emergent X-ray free electron lasers (XFELs). The coherent diffraction microscope combined with the XFELs will shed a new light on nano- and biotechnology.

January 29, 2008

"Spectroscopic Studies of Novel Nanomagnetic Materials," Saritha Nellutla, National High Magnetic Field Laboratory, hosted by Tijana Rajh

Abstract: Nanomagnets are fascinating materials not only from a basic research point of view but also because of their relevance in memory storage, quantum computation, spintronics, and sensors. They can be thought of as "bridges" between the isolated single-ion spin systems and bulk magnetic materials.

The talk will focus on magnetic and electron paramagnetic resonance (EPR) studies of polynuclear transition metal ion clusters, Cu3, Cu20, and Mn6, while addressing such potential applications as catalysts and nanomagnets.

The two extreme diluted spin systems compared with correlated magnetic lattices will also be highlighted. Potassium niobate doped with Cr5+ ions, a dilute spin S = 1/2 system, has been characterized by using pulsed EPR and electron nuclear double resonance techniques and will be introduced as a new transition metal-ion-based electron spin qubit. As illustrative examples of correlated magnetic lattices, thermomagnetic data of spin S = 1/2 and S = 1 antiferromagnetic peroxychromates will be presented and nature and origin of the three-dimensional magnetic ordering in these compounds will be discussed.

January 15, 2008

"Nanocrystal based 'artificial solids': a modular approach to materials design," Dmitri Talapin, The University of Chicago, hosted by Tijana Rajh

Abstract: The development of applications ranging from displays and photovoltaic cells to thermoelectric, light-emitting devices and sensors could be accelerated by introducing lower cost alternatives to conventional silicon technology.

Chemically synthesized semiconductor nanocrystals are considered promising candidates that allow inexpensive solution-based device fabrication with precise engineering of electronic structure due to quantum size and shape effects. Self-assembly of chemically synthesized nanocrystals can yield complex long-range ordered and quasicrystalline structures that can be used as model systems for studying transport in low-dimensional materials. At the same time, employing nanocrystals in these and other electronic and optoelectronic applications require deep understanding of charge transport and collective phenomena in nanocrystal solids.

We propose the techniques for engineering nanocrystal surfaces to improve exchange coupling in self-assembled nanocrystal solids. The conductivity of nanocrystal solids can be switched between n- and p-type transports by surface transfer doping. Thus, hydrazine-capped PbSe nanocrystal solids show n-type conductivity ~1.4 S cm -1 with electron mobility of 2.5 cm2V-1s-1, successfully competing with organic electronic materials. Doping of PbSe and PbTe nanocrystal solids can also occur through the exchange coupling with other semiconductor (Ag 2Te) or metal (Au) nanocrystals intentionally introduced in the nanocrystal solids. By using various approaches to nanoparticle surface engineering, we demonstrated n- and p-channel field-effect transistors based on PbS, PbSe, PbTe, CdSe, and SnTe nanocrystals.

We develop a general approach to solution-processed semiconductor nanocomposite materials based on incorporation of nanocrystals into a matrix of another crystalline inorganic semiconductor. This approach opens up broad avenues for designing novel functional materials. We demonstrate memory devices using CdSe/ZnS core-shell nanocrystals as floating gates, solar cells employing CdS nanorods integrated into CuIn(1-x)Ga(x)Se 2 matrix and Sb2Te3-Bi2Te3 nanocomposites promising for thermoelectric applications.

January 9, 2008

"Development of novel photocatalytically active materials on the base of porous silica and titania," Galyna Krylova, Université de Rennes, hosted by Tijana Rajh and Elena Shevchenko

Abstract: Photocatalysis is a promising, energy-saving approach for purification of the environment from toxic pollutants. The most current studies are based on TiO2 photocatalyst as a rather inexpensive and chemically stable material. Surface modification of TiO2 photocatalyst allows efficient use of sunlight, leads to an increase in the active surface, and improves charge separation. We discovered that the addition of 3-aminopropyltrimethoxysilane (APTES) to the precursors of the mixed TiO2/ZnO sol-gel nanostructure films drastically affects the size of crystallites and their crystal lattices, leading to much smaller (6-10 times) domains of Zn2TiO4 spinel and TiO2 anatase, instead of relatively large ZnTiO3 and TiO2 rutile crystallites. As compared with widely used titania films prepared from P25 Degussa sol, our APTES-modified mixed-oxide nanostructures demonstrate two times higher photocatalytical efficiency in such model reactions as decomposition of methylene blue (model pollutant of waste water) and stearic acid (model reagent to study antifouling properties). The excellent hydrophobic properties of TiO2/ZnO sol-gel films allows their use as self-cleaning, antifogging glass and mirror coatings.

Highly adsorptive porous silica is another excellent platform for designing hybrid photocatalysts. Modification of porous silica with photoactive organic molecules promotes the reduction of metals cations noble and allows the formation of nanoparticles of noble metals. Surface modification of mesoporous powders of films of silica with benzophenone shifts the barrier of photosensitized reduction of Ag+, AuCl4–, Pd2+, Сu2+, Cr2O72–, and Hg2+ ions from far (253.7 nm) to near (365 nm) ultraviolet region. The mechanism of photosensitized reduction in these systems was proposed. Variation in the reaction conditions allows both synthesis of stable colloidal solutions of noble metals with controllable sizes and shapes and silica-noble metal nanostructures composites. As compared witih the chemical synthesis of such structures, our photo-induced approach has a number of advantages associated with low energy consumption and the possibility of removing side reaction products by absorption at silica surface.

January 4, 2008

"Enhancing the open-circuit voltage of dye-sensitized solar cells by coadsorbents and alternative redox couples," Zhipan Zhang, Swiss Federal Institute of Technology, hosted by Gary Wiederrecht

Abstract: The interface between a nanocrystalline semiconducting metal oxide film and a redox electrolyte was optimized in order to enhance the photovoltage and performance of dye-sensitized solar cells. It features the application of ω-guanidino acids as the coadsorbent with ruthenium amphiphilic sensitizers.

Meanwhile, fast one-electron-transfer couples were employed as alternative redox mediators to the normal iodide/iodine system to reduce the potential mismatch between the Nernst potential of the dye cation and that of the redox mediator. Although a much faster recombination was observed as compared with I- / I3- redox, the device with 2,2,6,6 -Tetramethylpiperidine-1-oxyl (TEMPO/TEMPO+) showed an overall solar to electric power conversion efficiency of 5.4 % under AM 1.5 illumination at 100 mW/cm2.

2007 Seminars Archive

Date Title

December 14, 2007

"Tailoring the Plasmonic Properties of Silver and Gold Nanostructures through Shape-Controlled Synthesis," Younan Xia, Washington University, hosted by Matt Pelton and Yugang Sun

Abstract: By controlling the presence of twin defects in silver nanocrystallite seeds, we can selectively grow them into pentagonal nanowires, nanocubes with controllable corner truncation, right bipyramids, or triangular plates. The key to removal of twinned particles is oxidative etching. Without oxygen in the reaction, fivefold twinned decahedrons preferentially form because of their lower surface energy, and these seeds grow anisotropically into pentagonal nanowires. With the addition of chloride and oxygen, twinned particles are etched away, leaving only single crystal seeds that grow to form nanocubes. If bromide is added in place of chloride, an intermediate level of etching results in formation of seeds with a single twin that grow to form right bipyramids. The symmetry of plasmon resonance within each of these nanostructures is distinct, and thus each has a unique spectral signature that may find application in multiple-analyte surface plasmon resonance sensors. We can further tune the spectral properties of silver nanostructures through a galvanic replacement reaction that converts them into hollow gold nanostructures. Gold nanocages obtained from silver nanocubes have extremely high extinction coefficients in the near-infrared (800-1000 nm, transparent window for soft tissues). For this reason, we functionalized gold nanocages with tumor antibodies to enable contrast-enhanced imaging of cancer tissue and photothermal destruction of tumor cells.

December 12, 2007

 

“A tightly regulated, information-dependent molecular motor based upon T7 RNA polymerase,” William T. McAllister, University of Medicine and Dentistry of New Jersey, hosted by Elena Rozhkova

Abstract: Controlled movement of materials or molecules within the nanometer range is essential in many applications of nanotechnology. Here we report the capture, movement, and release of cargo molecules along DNA by a modified form of T7 RNA polymerase (RNAP) in a manner that is controlled by the sequence of the DNA. Using single-molecule methods, we visualize the assembly and manipulation of nanodevices and the ability to harness rotary and linear forces of the RNAP motor.

December 7, 2007

"Fundamental Insights and Improvements in Solar Cells from Theoretical Calculations," Jeffrey Grossman, Berkeley Nanosciences and Nanoengineering Institute, hosted by Larry Curtiss

Abstract: Classical and quantum mechanical calculations are employed to understand important microscopic mechanisms in photovoltaic materials and interfaces.

Our goal is to predict key properties that govern the conversion efficiency in these materials, including structural and electronic effects, interfacial charge separation, electron and hole traps, excited state phenomena, and band level alignment. An overview of our work will be presented, with focus given to two different types of solar cells, based on polymer blends and amorphous silicon, that illustrate how these computational approaches can improve our understanding and lead to more efficient devices.

December 5, 2007

"Interface Effect on the Activity of Metal/Oxide and Catalyst Searching for Multistep Reactions using DFT Simulation," Tao Song, University of California San Diego, hosted by Jeffrey Greeley

Abstract: NO dissociation at the interfaces of metal/Al2O3 (metal = gold, silver, and copper) and on the corresponding pure metal surfaces is studied to obtain the physical origin of the metal/oxide interface effect using density functional theory calculations. It is found that: (i) the barriers are significantly reduced at the interfaces of metal/Al2O3, (ii) there is a linear relationship between the reaction barrier at the interface and the total chemisorption energy, and (iii) the significant decrease in reaction barrier at the interface is mainly due to an increase in oxygen chemisorption energy at the interface. The anomaly of Ag/Al2O3 and the general implications of the results on metal/oxide system are discussed.

To find good catalysts for yield efficient processes is a major task in physical science. Up to now, new catalysts have been searched by utilising try-and-error methods experimentally, despite a huge effort spent to discover an approach using which a good catalyst for a particular reaction can be identified. A fundamental discovery in heterogeneous catalysis regarding the catalyst search and its understanding is the volcano curve, and it is traditionally explained by the Sabatier¹s principle. However, the principle remains largely empirical. Here we investigate all the relevant elementary steps for a key catalytic reaction, ammonia synthesis, from hydrogen and nitrogen on the entire 4d transition metal series. Our first principles volcano curves, which are obtained without any key assumptions agree with experiment. A simple equation containing only a few thermodynamic properties, using which the volcano curves can be reproduced, is derived.

This method may lead to better catalyst search strategies.

December 3, 2007

“Electronic Transport through Single-Molecule-Based and -Controlled Devices using Metal-Molecule-Metal Structures,” Ajit K. Mahapatro, Purdue University, hosted by Seth Darling

Abstract: In this work, we studied electronic transport through various organic/DNA molecules in a metal-molecule-metal (MMM) device structure using newly developed techniques for fabrication of molecular devices at micro- and nanometer dimensions and demonstrated potential nanoelectronics and sensor applications.

An enabling technology has been developed for realizing atomically flat gold surfaces by e-beam evaporation of gold over oxidized silicon (SiO2) substrates using an organic adhesion. High-resolution scanning tunneling microscope (STM) topography reveals atomically flat surface and gold atomic arrangements in face -centered-cubic (111) and hexagonal closed packed (111) domains. These gold layers have been further used in fabricating single- or few-molecule contained nanogap molecular junctions (NMJs) and molecular monolayer based large area (≈ 100 µm2) molecular devices (LAMDs).

Electronic transport properties of various π-bonded and diruhenium contained redox-active organic molecules were studied using STM and NMJ techniques. The energy states for the molecular orbitals were estimated from the observed conductance peaks. Devices with evidence of molecular states close to the contact Fermi level would allow resonant tunneling. Devices employing redox-active molecules, which allow resonant tunneling, along with observation of the molecules in specific charge states, could provide suitable structures for memory or chemical-sensing applications. Sequence specific electronic conduction through short (15 base pairs) double-stranded DNA molecules in NMJ structure infers an exponential decrease in single DNA conductance values with the length of A:T pairs replacing G:C pairs at the center of a G:C rich strand, consistent with a barrier at the A:T sites. Junction conductance of LAMDs containing n-alkanedithiol SAMs scales linearly with the device area and decreases exponentially with increasing number of carbons in the chain.

This study demonstrates realization of molecular electronics at micro/nano-meter scale device dimension. Self-organization and electronic properties of various organic/bio molecules could be characterized and tested using currently developed test beds (atomically flat gold layer, NMJ and LAMD) for specific utilization in nanoelectronic circuitry and biosensor applications.

November 30, 2007

"Atomic Structure and Domain Specific Chemical Reactivity on Ferroelectric Oxide Surfaces," Dongbo Li, University of Pennsylvania, hosted by Matthias Bode

Abstract: Although ferroelectric oxides have been extensively studied over the last five decades, surface structures and properties have received relatively little attention as a consequence of a variety of experimental challenges. The fundamental aspects of reactions on ferroelectric surfaces are critical to a range of device applications. This talk will present our recent studies on the atomic structure of a model ferroelectric surface, BaTiO3 (001), and polarization-dependent surface reactivities on BaTiO3 and lead zirconate titanate (PZT). For a surface structure study on BaTiO3 (001), we have used STM, nc-AFM, LEED, and AES to show that this surface adopts a family of reconstructions depending on thermochemical history. Most of these structures have not been observed previously.

Using a combination of density functional theory and ab initio thermodynamics, we compute the surface phase diagrams with oxygen potential as a dependent variable, since this is a critical variable in the experiment. The stabilities of reconstructions with Ba-adatoms, O-vacancies and Ti-O clusters are compared for different thermochemical conditions. Comparisons of the results from the calculations with the STM and nc-AFM results are used to construct atomic models for the reconstructed surfaces.

For domain-specific chemical reactivity studies, we have used an in situ method to control domain orientation and quantify the effect of polarization on CO2 molecular adsorption on BaTiO3 and PZT surfaces. Using a conductive AFM tip, we pole the ferroelectric substrates such that submicron-sized out-of-plane domains terminate the surfaces. Surface potentials of these positive and negative domains are then measured by a frequency modulation scanning surface potential microscopy. The influence of domain polarization on molecular adsorption is examined by comparing surface potential variation as a function of CO2 exposure. Positive and negative domains have exhibited quantitatively different variations in surface potential. The differences are discussed in terms of possible adsorption mechanisms. The effect of defects is examined by comparing results on BaTiO3 single crystals before and after UHV annealing to produce oxygen vacancies.

October 19, 2007

"Enhancing and Tailoring the Optical Responses of Metallic Nanostructures," Stephen Gray, Argonne National Laboratory, hosted by Peter Zapol

Abstract: Optical interactions with metallic nanostructures are of interest in part because it may be possible to excite and manipulate surface plasmons in them. Surface plasmons are electronic excitations confined near metallic surfaces that may be useful in a variety of applications, including chemical and biological sensing, and optoelectronics. Since plasmons can be intense and localized, correctly describing their behavior in complex systems requires numerically rigorous modeling techniques. I discuss recent results of electrodynamics modeling aimed at learning how to enhance or tailor the optical responses of metallic nanostructures. Two recent studies are highlighted. In one study, it is shown how the propagation lengths of surface plasmon polaritons (SPPs) on thin metal films can be significantly increased by coupling SPPs into waveguiding structures. In the other study, it is shown how to design arrays of subwavelength holes in thin metal films such that their transmission spectra are especially sensitive to substrates with specific refractive index values. A special resonance involving both a Wood's anomaly diffraction effect and an SPP is responsible for this enhanced sensing capability. Finally, I indicate future research directions.

October 19, 2007

“Simple Models for Molecular Transport Junctions,” Michael Galperin, Los Alamos National Laboratory, hosted by Eric Isaacs

Abstract: We review our recent research on role of interactions in molecular transport junctions. We consider simple models within a nonequilibrium Green function approach in the steady-state regime. An important feature of molecular junctions is the role played by nuclear motions in the conduction process.

We start by reviewing approaches used to describe limits of weak and strong electron-phonon interactions. We treat the weak interaction case in a self-consistent Born approximation. The scheme is used to describe features observed in the inelastic electron tunneling spectroscopy. We treat the strong electron-phonon coupling within nonequilibrium equation-of-motion (EOM) method coupled with linked cluster expansion. The approach is useful in describing resonant inelastic tunneling.

Electron-electron interaction is responsible for effects such as Coulomb blockade in molecular junction transport. We consider electron-electron and electron-phonon interactions within Hubbard-Holstein Hamiltonian. considerations similar to the equilibrium EOM approach by Meir et al. are used on the Keldysh contour to account for the nonequilibrium nature of the junction, and dressing by appropriate Franck-Condon factors is used to account for vibrational features. Results of the equilibrium EOM scheme by Meir et al. are reproduced in the appropriate limit. Strong electron-vibration interaction may lead to formation of polaron on the bridge. We propose a polarization model as a possible mechanism for the negative differential resistance and hysteresis observed in molecular junctions. The consideration is based on the static limit of the Born approximation. We discuss theimportance of taking into account the open character of the system. Electron-vibration interaction is the cause of junction heating. We obtain a unified description of heating in current-carrying molecular junctions as well as electron and phonon contributions to the thermal flux, including their mutual influence. Ways to calculate these contributions, their relative importance and ambiguities in their definitions are discussed. A general expression for the phonon thermal flux is derived and used in a new “measuring technique,” to define and quantify ‘local temperature’ in nonequilibrium systems. Finally, in our ongoing project, we use a two-level (HOMO-LUMO) model to study Raman scattering of current-carrying molecular junctions.

October 12, 2007

“Controlling Magnetic Anisotropy and Probing Magnetic Structure in Magnetic Nanoparticles and Ferromagnetic/Antiferromagnetic Bilayers,” Minn-Tsong Lin, National Taiwan University, hosted by Matthias Bode

Abstract: Controlling magnetic orientation and imaging magnetic structure are two crucial issues in both fundamental science and application for magnetic nanomaterials. In particular, tuning perpendicular magnetic anisotropy by a more concise and efficient process draws much attention because of the possible application of a perpendicular medium with high-storage density. In this work, an enhanced perpendicular magnetic anisotropy of ferromagnetic thin films is demonstrated by introducing an antiferromagnetic (AF) underlayer. A new kind of spin-reorientation transition is observed with varying thickness of the AF layer. This finding is shown to be related to the strength of the AF coupling of the AF layer.

Controlling the magnetic anisotropy can be also important in magnetic domain imaging with in-plane sensitivity by spin-polarized scanning tunneling microscopy (SP-STM). A simple method using a ring-shaped magnetically coated wire as the tip of SP-STM is shown to be able to show spin contrast easily in the in-plane direction of the film. A well-defined magnetization orientation of magnetic tip is achieved with controlled anisotropy caused by geometrical asymmetry.

Finally, magnetic coupling and magnetic structure in magnetic self-aligned iron particles grown on a single-crystalline oxide layer Al2O3/NiAl(100) will be also discussed. By using scanning electron microscopy with polarization analysis (SEMPA), the magnetic domain is imaged, revealing a vortex structure, which may be attributable to a dipole-dipole interaction. Furthermore, capping the magnetic particles with a nonmagnetic metallic layer (copper) can enhance the magnetic coupling, and in turn the Curie temperature of the system. This finding can also be confirmed in the enhanced spin contrast observed by SEMPA for magnetic particles with capping layer. The magnetic coupling under magnetic particles is shown to be able to propagate through the copper layer.

October 10, 2007

"Bottom-Up Fabrication as a Route towards Unique and Multifunctional Nanostructured Materials: From Biomimetics to Ultrastrong Nanocomposites," Paul Podsiadlo, University of Michigan, hosted by Tijana Rajh and Elena Shevchenko

Abstract: Layer-by-layer (LBL) assembly technique, based on sequential adsorption of oppositely charged compounds, is one of the most popular and well-established methods for the preparation of multifunctional nanostructured thin films. Since its inception nearly two decades ago, a wide variety of species, ranging from polymers and biomolecules, to nanoparticles and viruses, have been successfully used as assembly components. This remarkable versatility has led to a number of novel designs and applications, including: superhydrophobic surfaces, chemical sensors and semi-permeable membranes, drug and biomolecules delivery systems, optically active and responsive films, cell and protein adhesion resistant coatings, fuel cells and photovoltaic materials, biomimetic and bio-responsive coatings, semiconductors, catalysts, and magnetic devices.

Recently, our group has also shown preparation of architecturally and mechanically unique LBL nanocomposites incorporating carbon nanotubes and clay nanosheets. Assembly of negatively charged clay platelets of Na+-montmorillonite (MTM) with a polycation, Na+poly(diallyldimethylammonium chloride) (PDDA), resulted in a nanocomposite with very high loading of uniformly distributed MTM nanosheets (~70 wt.% of clay) organized into a well-defined layered architecture. Further, the structure, deformation mechanism, and mechanical properties (ultimate tensile strength, σUTS ~100 MPa and Young’s modulus, E ~11 GPa) of the material were found to be similar to those of two exceptional natural composites: seashell nacre and lamellar bones.

In this talk I will present my results from the exploration of mechanical properties of the LBL assembled nanocomposites from MTM nanosheets and another natural nanomaterial: cellulose nanocrystals, with an ultimate goal of developing high strength, high stiffness, and tough nanocomposites. I will show that understanding of the nanoscale mechanics and the interfacial interactions is a key to preparation of high-performance nanocomposites. To this end we have been able to generate a transparent clay nanocomposite with record-high strength and stiffness: σUTS ~400 MPa and E’ ~110 GPa, which on the per-weight basis can be compared to steel and its alloys. I will further discuss my ongoing work with different designs of the LBL nanocomposites and their applications.

October 3, 2007

"Chemical- and Bio-Inspired Route to Functional Nanostructures: Synthesis, Preparations, and Some Applications," Yongdong Jin, University of California, Los Angeles, hosted by Yugang Sun and Gary Wiederrecht

Abstract: Functional metallic (or organic) nanoparticles , nanostructures, hybrids, and composites are being exploited for a variety of applications, including sensing, catalysis, and electronics. This presentation focuses on the wet chemical- and bio-inspired route to functional nanostructures, and some interesting applications will be discussed. Examples include

  1. A wet-chemical and colloidal approach for preparing surface plasmon resonance active gold substrates;
  2. One-pot synthesis of shell-type Ag-Au bimetallic nanoparticles (and their fractal monolayer films) with nano-spikes, based on colloid seed-engaged replacement reaction and colloid-mediated deposition reactions;
  3. An electrochemical strategy to nanoparticle-based catalyst design using the underpotential deposition redox replacement technique,
  4. Vesicle or protein cage-templated synthesis of functional core and shell nanostructures;
  5. Proton pumping protein, Bacteriorhodopsin-based metal-protein-metal planar junctions using biomimetic monolayer preparation; and
  6. Plasmonic gold nanoparticles based monolayer junctions and enhancement in current transport through nanometer-scale insulating layers.

September 14, 2007

"Studying a single Kondo atom in a precisely known anisotropic environment," Sander Otte, Leiden University, hosted by Matthias Bode

Abstract: Using a 3He STM, we employ a new technique called spin excitation spectroscopy to study the magnetic properties of single d-metal atoms( manganese, iron, and cobalt) on a thin insulating copper nitride layer. This surface provides a well-defined anisotropic environment that partly breaks the degeneracy of the spin states even in the absence of an external magnetic field. For cobalt, this results in an effective S = 1Ž2 system that exhibits Kondo behavior. We show that the splitting of the Kondo peak, though in itself a multibody effect, is dictated by the quantum mechanics of the single spin. By performing atom manipulation we can let a Kondo spin interact with other spins and tune their coupling strength, opening the way to building Kondo chains and lattice.

August 8, 2007

“Carbon Nanostructures – New Opportunities in Material Science,” Dirk Guldi, Friedrich-Alexander-Universität Erlangen-Nürnberg, hosted by Tijana Rajh

July 11, 2007

“Near 100% Spin Filtering in Europium Oxide,” Tiffany S. Santos, Massachusetts Institute of Technology, hosted by Anand Bhattacharya

Abstract: Essential to the emergence of spin-based electronics is a source of highly polarized electron spins. Conventional ferromagnets have at best a spin polarization P~50%. Europium monoxide (EuO) is a novel material capable of generating a highly spin-polarized current when used as a tunnel barrier. EuO is both a Heisenberg ferromagnet (Tc=69 K) and a semiconductor. Exchange splitting of the conduction band creates different tunnel barrier heights for spin-up and spin-down electrons, thus filtering the spins during tunneling. High-quality EuO films at the monolayer level are necessary for efficient spin-filtering. Because nonferromagnetic, insulating Eu2O3 forms more readily, growth of an ultrathin, high-quality film is quite challenging. For this reason, EuO on such a small thickness scale had never been studied previously.

Films of EuO were grown by reactive thermal evaporation, and various thin film characterization techniques were employed to determine the structural, optical, and magnetic properties, even on the thickness scale needed for tunneling (<3 nm). A reduction in Curie temperature for ultrathin EuO was experimentally demonstrated, in agreement with theoretical calculation. Controlling the smoothness and chemical nature of the interfaces between EuO and metallic electrodes was found to be of critical importance, as proven by careful interfacial chemical and magnetic analysis at the monolayer level, using X-ray absorption spectroscopy, magnetic circular dichroism, diffuse X-ray resonance scattering, and polarized neutron reflectivity techniques, through collaborative efforts.

EuO was successfully prepared as the barrier in Al/EuO/Y tunnel junctions. By fitting the current-voltage characteristics of these junctions to tunneling theory, exchange splitting in an ultrathin layer of EuO was quantitatively determined for the first time, indicating near-complete spin filtering, P=100%. In an alternative approach, P was directly measured using the superconducting aluminum electrode as a spin detector. Spin filtering in EuO barriers was also observed in magnetic tunnel junctions (MTJs), using a ferromagnetic electrode as the spin detector. In Cu/EuO/Gd MTJs, a tunnel magnetoresistance (TMR) of 280% was measured by changing the relative alignment of magnetization of EuO and gadolinium, which is the largest TMR measured by using a spin-filter barrier. Co/Al2O3/EuO/Y junctions, in which the Al2O3 barrier magnetically decoupled cobalt and EuO, also showed substantial TMR. Its matching band gap (1.1 eV) and compatibility with silicon open up the novel possibility of using EuO to inject highly polarized spins into silicon-based semiconductors.

June 29, 2007

“Intermittent fluorescence from CdSe core and core-shell nanorods,” Catherine Crouch, Swarthmore College, hosted by Matthew Pelton

Abstract: One intriguing feature of the fluorescence observed from a wide variety of single fluorophores is intermittency, colloquially called “blinking.” Under steady excitation, single fluorophores do not emit light steadily, but switch between bright and dark states, remaining bright (“on”) or dark (“off”) for milliseconds to minutes at a time. The mechanism of this intermittency is still poorly understood in semiconductor nanocrystals. In particular, the durations of “off” periods observed from NCs follow a power-law distribution rather than the exponential distribution that would be expected from transitions between a single “on” state and a single “off” state. This talk will present our measurements of fluorescence intermittency measured from single CdSe nanorods of seven different sizes with aspect ratio ranging from 3 to 11 and compare our findings with measurements on spherical CdSe core and CdSe/ZnS core/shell nanocrystals, to explore the effect of sample geometry on intermittency. Our findings are consistent with the increasingly one-dimensional nature of excitonic states in nanorods as the aspect ratio increases.

June 27, 2007

"Shaping the Future of Desalination and Water Treatment: the Union of Nanotechnology and Membranes," Eric M.V. Hoek, University of California, Los Angeles, hosted by Ron Faibish

Abstract: The basic reverse osmosis (RO) membrane technology that has revolutionized desalination is now more than 30 years old. Optimal separation performance, energy efficiency, and fouling resistance of conventional polymer membranes are nearly fully realized, but RO processes remain relatively nonselective, energy-intensive, and fouling-prone. These constraints remain in the face of rising worldwide demand for clean water and the sustainability imperatives to control energy use. However, the "age of nanotechnology" has brought forth entirely new classes of functional materials that can be explored for use in desalination as well as other water treatment applications.

I will review the history of RO membrane development and relevant aspects of nanotechnology and discuss examples of how the future of desalination may be shaped from the union of nanotechnology and membranes. Specifically, I will present preliminary results from our efforts to create of a new class of RO membranes through use of nanotechnology. Low-energy and fouling-resistant membranes already have been created and tested in the laboratory at UCLA. Eventually, nanotechnology may produce membranes with advanced functionality like on-demand tuning of rejection and catalytic reactivity as well as sensing, antifouling, and regenerative interfaces.

June 21, 2007

"Field-Resolved Femtosecond Vibrational Spectroscopies of Solutions and Nonequilibrium Studies of Anisotropy in Protein Unfolding,” Rene Nome, The James Franck Institute, The University of Chicago, hosted by Norbert Scherer

Abstract: In Part I, solute and solvent femtosecond dynamics in the visible and infrared spectral regions are studied with full-electric field-resolved techniques. Resonant linear propagation of ultrashort mid-infrared pulses through optically dense samples of HDO in liquid D2O is studied experimentally and computationally. This combined approach was used to test the accuracy of various correlation functions in describing the fast vibrational dynamics of water. Using visible laser pulses, we have performed electric field-resolved transient grating measurements of a pyridinium iodide charge transfer complex. These experiments showed how the pump-probe delay may be used to directly control the magnitudes of resonant and nonresonant third-order polarizations. In Part II, we present a comprehensive study that integrates experimental and theoretical nonequilibrium techniques to map energy landscapes along well-defined pull-axis specific coordinates to obtain thermodynamic, kinetic, and structural information about protein unfolding. Single-molecule force extension experiments along two different axes of photoactive yellow protein (PYP) combined with nonequilibrium statistical mechanical analysis and atomistic simulation reveal energetic and mechanistic anisotropy in protein unfolding.

June 15, 2007

“High-Frequency EPR and ENDOR Spectroscopy on Semiconductor Nanocrystals,” Jan Schmidt, Leiden University, hosted by Tijana Rajh

Abstract: There is great interest in semiconductor nanocrystals because the electronic and optical properties of these structures are strongly affected by quantum confinement owing to the reduced dimensions of these systems. We have recently shown that ZnO nanocrystals can be doped with shallow donors by the introduction of interstitial lithium and sodium atoms. This finding opens up the possibility of studying the effect of quantum confinement on the electronic structure of these donors. I will show that high-frequency EPR and ENDOR spectroscopy at 95 GHz and 275 GHz is the method of choice to identify the atomic structure of these donors and to probe for the first time the effect of confinement on their electronic wave function.

June 14, 2007

“Magnetic reversal, magnetodynamics and imaging of magnetic nanostructures,” Justin M. Shaw, National Institute of Standards and Technology, hosted by Kristen Buchanan

Abstract: Magnetic nanostructures are currently receiving much attention due to their potential use in “beyond CMOS” technology, sensors, and media storage. In the current hard drive technology, information is stored in magnetic domains written to a continuous magnetic thin film. In order to increase storage densities beyond 1 Tbit/in2, the size of these domains must be reduced below 12 nm. In thin-film media, lower exchange-coupled systems must be used to prevent neighboring bits or domains from interacting. However, these lower exchange-coupled materials also have lower thermal stability, and at a critical grain size, they become superparamagnetic at room temperature and can no longer store information. A proposed solution to this problem is patterned bit media, whereby information is stored in nanopatterned single-domain structures or islands that are laterally isolated. Because the structures are physically isolated, highly exchange-coupled materials can be used that have significantly more thermal stability. However, when these magnetic layers undergo nanopatterning, a switching field distribution (SFD) results whereby each nanostructure magnetically reverses at a different value of applied magnetic field. The fundamental source of the SFD and understanding the reversal mechanisms in these nanostructures have been and continue to be a large effort. We use several magnetic imaging techniques, such as magnetic force microscopy, Lorentz microscopy, and electron holography, to probe the “nanomagnetic” structure as well as high-resolution transimission electron microscopy. The combination of magnetic imaging with materials characterization allowed us to isolate the source of switching field distributions in Co/Pd nanodots. Although still under investigation, this source is found to reside in the intrinsic material properties of the Co/Pd and is not due to lithographic variations or other extrinsic sources as previously thought. In addition, temperature-dependent studies indicate that the reversal mechanism is not that of coherent rotation as predicted.

The increased dimensional confinement of magnetic nanostructures also has a profound effect on the high-frequency (ferromagnetic resonance) behavior of the structures. Direct measurement of such properties will require new methods and techniques as many traditional techniques do not have the signal-to-noise and/or spatial resolution needed. We have recently developed a new frequency resolved magneto-optic Kerr effect system to study ferromagnetic resonance in our magnetic nanostructures. We have demonstrated excellent signal-to-noise in nanodot arrays in 3-nm-thick magnetic layers down to 50 nm in diameter. With this technique we can directly measure the ferromagnetic resonance frequency, damping, dynamic inhomogeneity, edge effects, and (more indirectly) interdot interactions.

In this talk, I will present our recent results on magnetic reversal, ferromagnetic resonance and magnetic (and non-magnetic) imaging of both in-plane and perpendicularly magnetized nanopatterned structures. Emphasis will be on understanding sub-100-nm features which are required in patterned bit media and spin-momentum transfer devices. I will also discuss the new techniques we developed to study the magnetic properties of such structures.

June 13, 2007

“Spin-torque induced dynamics and switching behavior in spin-valve devices,” Michael Schneider, National Institute of Standards and Technology, hosted by Kristen Buchanan

Abstract: The state of a magnetic device is commonly manipulated using an applied magnetic field. However, in 1996 it was predicted that a magnetic device could also be manipulated with a spin-polarized dc current. In particular, a spin-polarized current propagating into a ferromagnetic layer will exert a torque on that layer. This effect is often referred to as spin torque. It has been shown that the spin torque effect is an efficient way to change the orientation of the free layer in a spin valve nanopillar when using a high current density perpendicular to the film plane. This effect has recently been demonstrated as a viable alternative to the cross-point writing scheme of conventional magnetic random access memory (MRAM). Spin torque switching of MRAM has the advantage that as the device size is reduced, the current needed to switch the free layer orientation is decreased.

We investigated the influence of thermal effects on the critical switching current in spin torque nano-pillars. We compared zero temperature critical current values extrapolated from room temperature pulsed current switching measurements to those of quasi static current sweeps at 5 K. In addition, we compared both of these experimental results to zero temperature Slonczewski theory. There is substantial variation in the hysteretic region from device to device at room temperature for devices of the same nominal size and resistance. While this is not expected, it has been attributed to thermal effects having a strong influence on the response of the freelayer to applied field as well as the coercivity. We find that by reducing the temperature, and thus any thermal fluctuations, the device to device variations are drastically reduced. Furthermore, the values extrapolated from the low temperature measurements were robust with respect to device size and in quantitative agreement with theoretical predictions from Slonczewski theory.

In addition to complete switching of the orientation of the free layer in a spin valve device, the spin torque can be used to counteract the damping torque and thus set up sustained microwave oscillations of the magnetic moment in the free layer. There are two distinct regions of microwave oscillations that can be accessed with this method. The first, and best characterized, is consistent with uniform magnetization precession similar to ferromagnetic resonance oscillations. These oscillations can occur at frequency from several GHz to more than 40 GHz. In addition to uniform mode oscillations, we also observe lower frequency oscillations with small in-plane applied fields. Unlike previous measurements, the frequency of oscillation is far below the uniform-mode ferromagnetic resonance frequency and is only a weak function of applied field. These oscillations can be hysteretic with applied dc bias current; once they are “turned on” they remain active at currents below the initial current necessary to instigate the oscillations. These observations are consistent with dynamics of a vortex-like state in the vicinity of the contact, one nucleated by the Oersted fields generated by the dc current and with dynamics driven by the spin transfer torque.

June 12, 2007

“Using Ab Initio Methods to Help Design Materials and Applications at the Atomic Scale: Importance of Resolving Energetic Differences Associated with Minor Changes in Geometry or Configuration,” Rees B. Rankin, University of Pittsburgh, hosted by Larry Curtiss and Jeffrey Greeley

Abstract : As the need for novel complex materials rises appreciably every year, the ability to eventually develop fully predictive multiscale models often relies firstly and most importantly on the development of a comprehensive understanding of atomic-scale processes and their associated energies. This presentation will highlight the application of ab initio DFT methods in two distinct research problems: the first involving design of multicontaminant sorbent material for remediation of IGCC syngas streams, the second involving control of chiral adlayer assembly in amino acids with reconstruction of copper surfaces. In both cases, it will be shown that the use of high-level calculations at this scale allows for the resolution of extant questions that were previously generated from experimental observations regarding the energetics of nonequivalent structures. In both cases, the critical fundamental result will be that even seemingly minor changes in geometry and/or configuration of the materials in question can lead to interesting effects and exploitable differences in energy for potential applications.

May 30, 2007

“Quantum mechanics, classical mechanics and molecular dynamics on bio- and nanosystems,” Kurt Mikkelsen, University of Copenhagen, hosted by Larry Curtiss

May 22, 2007

“Study of Nanostructures and Surface Plasmons by Ultrafast THz-TDS,” Jiaguang Han, Oklahoma State University, hosted by Norbert Scherer

Abstract: I will intrroduce some of my present work in the study of nanostructures and surface plasmons by ultrafast terahertz lasers, such as terahertz dielectric properties and low-frequency phonon resonances of ZnO nanostructures; phonon confinement in ZnS nanoparticles; transition from photonic effect to surface plasmon resonance based on pump-probe measurement on subwavelength hole array; and surface plasmon sensors.

May 17, 2007

“Light-Induced Charge Separation across Bio-Inorganic Interface,” Nada Dimitrijevic, Chemistry Division, hosted by Tijana Rajh

Abstract: Rational design of hybrid biomolecule – nanoparticulate semiconductor conjugates enables coupling of functionality of biomolecules with the capability of semiconductors for solar energy capture, which can have potential application in energy conversion, sensing, and catalysis. The particular challenge is to obtain efficient charge separation analogous to the natural photosynthesis process. The synthesis of axially anisotropic TiO2 nano-objects, such as tubes, rods, and bricks, as well as spherical and faceted nanoparticles has been developed in our laboratory. Depending on their size and shape, these nanostructures exhibit different domains of crystallinity, surface areas, and aspect ratios. Moreover, in order to accommodate for high curvature in the nanoscale regime, the surfaces of TiO2 nano-objects reconstruct, resulting in changes in the coordination of surface titanium atoms from octahedral (D2d) to square pyramidal structures (C4v). The formation of these coordinatively unsaturated titanium atoms thus depends strongly on the size and shape of nanocrystallites, and they affect trapping and reactivity of photogenerated charges. We have exploited these coordinatively unsaturated titanium atoms to couple electron-donating (dopamine) and electron-accepting (pyrroloquinoline quinone) conductive linkers that allowing wiring of biomolecules and proteins, resulting in enhanced charge separation, which increases the yield of ensuing chemical transformations.

May 17, 2007

"Nanostructure Matters," Olle Heinonen, Seagate Technology, hosted by Larry Curtiss

Abstract: Bulk systems generally have well-defined physical properties, examples of which are conductivity, charge density, or magnetization density. These are macroscopic properties obtained by averaging over many microscopic volumes or configurations. When the characteristic dimensions of a system, such as system size or layer thickness, become equal to or smaller than characteristic length scales, such as mean free path, magnetic exchange length, or phase-breaking length, the physical properties may become distinctly different from those of a bulk system. In particular, the observable properties depend very critically on the material micro- or nanostructure.

In this talk, I will give some examples of the interplay between dimension, nanostructure, and physical properties for a variety of systems, as well as of the tools that can be used to study them theoretically. These latter include unusual flavors of density functional theory, semiclassical transport theory coupled with first-principle electronic structure calculation, and finite-temperature micromagnetics. The first example is given by quantum Hall dots. By changing the shape of the potential confining the electrons in these dots, the spin-charge texture of the edge can be modified. This is important because the behavior of these dots is controlled by the ground-state electronic structure of their edges. A second example is given by giant magnetoresistive spin-valve sensors. One can design quantum-mechanical properties that directly affect the magnetoconductance of these devices by carefully controlling the layer structures and interfaces. Another example is given by magnetic tunnel junctions. In these structures, there is a very delicate interplay between the nanostructure near the ultrathin insulating tunneling barrier and the conductance and thermal magnetic noise. The final example is given by bilayer Permalloy/IrMn disks. By setting the exchange bias of the IrMn in a vortex configuration, one can tune the dynamics of both the gyrotropic motion as well as the spin-wave eigenmodes by controlling the exchange bias strength.

April 19, 2007

“Magnetic Nanostructures Probed on the Atomic Scale,” Cyrus F. Hirjibehedin, IBM Almaden Research Center, Matthias Bode

Abstract: Magnetic nanostructures are increasing data storage capacities and are promising candidates for implementations of novel spin-based computation techniques. The relative simplicity and reduced dimensionality of nanoscale magnetic structures also make them attractive model systems for studying fundamental interactions between quantum spins. We used a scanning tunneling microscope to probe the interactions between spins in individual atomic-scale magnetic structures. Linear chains of 1 to 10 Mn atoms were assembled one atom at a time on a thin decoupling layer of copper nitride on bare copper. The spin excitation spectra of these structures were measured with inelastic electron tunneling spectroscopy. We observed excitations of the coupled atomic spins that can change both the total spin and its orientation. Comparison with a model spin interaction Hamiltonian yielded the collective spin configuration and the strength of the exchange coupling between the atomic spins. Anisotropy effects were directly manifested in the excitation spectra as finite energy excitations in the absence of a magnetic field. The effects of anisotropy were found to be relatively weak for Mn atoms but were substantially larger in atoms with strong spin-orbit coupling, such as iron.

 

April 13, 2007

“Multiscale Coarse-Grained Modeling of Condensed-Phase and Nanoscale Systems,” Sergey Izvekov, University of Utah, hosted by Peter Zapol

Abstract: The multiscale coarse-graining (MS-CG) method for condensed phase and nanoscale systems is presented. The MS-CG approach systematically maps atomistic interactions into effective pairwise interactions between coarse-grained structural units. The MS-CG method is based on a rigorous force-matching procedure to determine the generalized forces associated with the coarse-grained degrees of freedom. The resulting simulation of the coarse-grained representation of the system is much faster than its all-atom counterpart and while accurately reproducing structural and thermodynamic properties. The MS-CG method has been successfully applied to many complex condensed phase systems, including water, ionic liquids, carbonaceous nanoparticles, lipid bilayers, peptides, and various solvent-free models. The MS-CG method has also been recently used to study hydrophobic hydration and the hydrophobic effect. Future applications include studies of the mesoscopic structures formed by systems of biomolecules and nanoparticles.

April 12, 2007

“The Characterization, Processing, and Application of Hybrid Organic/Inorganic Nanomaterials,” Nathan Guisinger, Center for Nanoscale Science and Technology, NIST, hosted by Matthias Bode

Abstract: The study of organically functionalized semiconductor surfaces has become an active pursuit, both for its fundamental significance and technical relevance. This talk covers three topics relevant to the application of hybrid organic/inorganic nanomaterials: silicon-based molecular electronics, molecular charge transfer visualized at the atomic scale, and epitaxial graphene grown on SiC.

April 12, 2007

"Synthesis of Nanoparticles and Their Self-Assembly into Periodic Arrays," Elena Shevchenko, Lawrence Berkeley National Laboratory, hosted by Tijana Rajh

Abstract: Nanoparticles of different size and functionality (e.g., noble metals, semiconductors, oxides, magnetic alloys) can be synthesized by using a solution phase approach. Nanoparticle building blocks can self-assemble into ordered binary superlattices (also known as opals or colloidal crystals) that retain the size tunable properties of their constituents. Control over particle size and their monodispersity are key issues in the self-assembly process. Depending on nanoparticle type, different approaches to control their sizes, shapes, and monodispersity can be applied.

A variety of multicomponent superlattices from monodisperse nanoparticles nanocrystals can be obtained by mixing and matching these nanoscale building blocks to yield multifunctional nanocomposites. Superlattices with AB - AB13 stoichiometry with cubic, hexagonal, tetragonal, and orthorhombic symmetries have been identified. Assemblies with the same stoichiometry can be produced in several polymorphous forms by tailoring the particle size and deposition conditions. Electrical charges on sterically stabilized nanoparticles, in addition to such parameters as particle size ratio and their concentrations, can provide the formation of much broader pallet of binary nanoparticle superlattices as compared with the limited number of possible superlattices formed by hard noninteracting spheres. Design of more complex nanoparticle structures, such as dumbbells and hollow nanoparticles, allows extending the number of challenging multicomponent periodic systems. Multifunctional superlattices are presented as a new class of materials with a potentially unlimited library of constituents over a wide range of tunable structures.

April 6, 2007

“Pressure-induced Hydration,” Thomas Vogt, University of South Carolina, hosted by Eric Isaacs

Abstract: We have recently established that in some zeolites (i.e., zeolite Y, zeolite A, natrolite, mesolite, scolecite) a reversible and selective pressure-induced hydration to a "superhydrated phase" occurs at pressures near 1 GPa. Pressure-induced hydration involves a concomitant volume and pore expansion. In some cases, the framework topology permits an auxetic-like behavior responsible for this effect. This talk will present structural models of various systems exhibiting pressure-induced hydration and discuss some of the heuristic rules and potential applications of this effect.

March 28, 2007

“Bioinspired Biomimetic Systems for Advanced Materials,” Elena A. Rozhkova, The University of Chicago, hosted by Tijana Rajh

Abstract: Biologically occurring organometallic supramolecular architectures give priceless lessons for the design and synthesis of sophisticated bio-inspired materials and engineered systems. Oxidoreductases are enzymes found throughout nature that catalyze versatile biologically important reactions, such as oxidation of hydrocarbons, biosynthesis of secondary messengers and hormones, and reversible oxidation of molecular hydrogen (H2). In the first part of my talk, I will discuss some iron-containing systems such as hydroxylases P450, nitric oxide synthase, non-heme AlkB, and multidisciplinary methods of their studying — recombinant DNA/protein technique, synthetic modeling, and chemical substrates probing. Application of modern method — synthetic biology for engineering of bioinspired hydrogen-producing systems on the base of iron-only hydrogenase will be also discussed.

In the second part of this talk, I will focus on bioinorganic nanohybrid materials for biomedical applications. Such nanocomposites combine cells receptors recognition bio-functionality and certain physical property (e.g., magnetic, photosensitivity) for controlled cytotoxic effects. Resulting nano-bio-conjugates are designed to possess synergistically enhanced activity with high potential for combined photo, thermal, and immune cancer therapy.

March 2, 2007

"Magnetic and Structural Properties of Mass-Filtered Three-Dimensional Transition Metal Nanoparticles, " Armin Kleibert, Rostock University

February 26, 2007

““Minima Hopping: An Efficient Way to Optimize Geometry on the Potential Energy Surface and on the Free Energy Surface,” Abdel Kenoufi, University of Basel, hosted by Jeffrey Greeley

Abstract: It is well known that mechanical properties of materials are strongly dependent on the way their geometries have been optimized on the potential energy surface. The study of shear band localization in bulk metallic glasses is one example of this phenomenon. The shear band width depends clearly on the cooling rate that has been defined to decrease the control temperature during the simulated annealing procedure. Therefore, before studying mechanical properties, one has to find a well-cooled geometrical configuration. The global optimization is achieved by minimizing the potential energy in configuration space.

I'll first present the concept and the flowchart of an adapted version of the minima hopping method, which is an efficient way to avoid inconvenient features of simulated annealing methods. The second part will be devoted to numerical comparisons of metallic glasses of minima hopping and simulated annealing methods, performed within the EMT framework. I will show that minima hopping is an efficient way to optimize complex systems such as BMG. In the third part, I'll introduce a version of minima hopping that involves calculations of forces with DFT methods, the dual minima hopping method.

February 21, 2007

"Superconductivity on the Localization Threshold and Superconductor-Insulator Quantum Phase Transition," Tatiana Baturina, Institute of Semiconductor Physics, Novosibirsk, Russia, hosted by Eric Isaacs and Valerii Vinokour

Abstract: The interplay between superconductivity and localization is a phenomenon of fundamental interest. Effects of disorder become critical in two dimensions, and the nature of two-dimensional disordered superconductors is currently the focus of theoretical and experimental attention. The main questions are the possible ground states of two-dimensional electronic systems with Cooper pairing and the structure of the disorder-magnetic-field phase diagram.

I review recent experimental progress and discuss how new experimental findings relate to theories modeling the influence of disorder and/or magnetic field on the superconductor to insulator quantum phase transition. I demonstrate that in the systems near the localization threshold on its superconducting side, applying a perpendicular magnetic field drives the films from a superconducting to an insulating state, with very high values of resistance. Further increase of the magnetic field leads to an exponential decay of the resistance towards the finite value. This value depends on temperature and, in the limit of low temperatures, extrapolates to the universal quantum resistance h/e2. Comparison of studies on different materials indicates that the quantum metallic phase that appears at high magnetic field is a generic property of two-dimensional superconducting systems close to the disorder-driven superconductor-insulator transition.

February 16, 2007

“Nucleic acid sequence is a universal information substrate of all life. Advancement of DNA sequencing technology is central to enabling its utilization,” Viktor Stolc, NASA Ames Research Center, hosted by Kevin White and Eric Isaacs

Abstract: NASA Ames Genome Research Facility is a state-of-the-art research laboratory designed to provide service in large-scale genome research to government, public, and private organizations and to advance the development of single-molecule sensitive biosensors through collaborative projects with academic and industry partners. In addition to the development of faster and less expensive DNA sequencing technologies, advances in the ability to assay functionality of genes and proteins on a genome-wide scale have revolutionized biological sciences.

In partnership with several universities, NASA Ames Genome Research Facility has developed novel applications of high-density DNA oligonucleotide microarrays for probing RNA expression of both protein- and non-protein-coding sequences in the completed genomes of several model organisms and the human genome. Computational methods for the design and analysis of the whole-genome tiling microarrays were developed by using the NASA Ames supercomputer. This work resulted in the confirmation of nearly all previous gene expression results generated with other techniques, and identified thousands of genes and RNA transcripts that were previously undescribed by all other methods.

In partnership with commercial partners, NASA Ames Genome Research Facility also has been developing a solid-state nanopore device for direct reading of DNA sequence from single molecules faster than is currently possible with any other method. Because individual molecules are counted, the output is intrinsically quantitative. The nanopore device will be able to directly sequence single molecules of nucleic acid, DNA, or RNA, without labeling or biochemical manipulation, at a rate of a million bases per second by electrophoresis of the charged polymers through a channel of molecular dimensions. The channel is a solid-state nanopore that can analyze electronic properties of DNA or RNA to obtain a linear composition of each individual genetic polymer molecule. The nanopore-based analysis of nucleic acid polymers is revolutionary because no other technique can determine information content in single molecules of genetic material at the speed of 1 subunit per microsecond. Significant advancement in the realization of this device has been made; currently it is able to measure the length of individual polynucleotides heteropolymers and distinguish the identity of individual subunits (A,C,G,T) in monomer form with single-molecule resolution using nanospectroscopy. Current advances in the nanofabrication process and utility of the solid-state nanopore suggest that in the next few years, ultra-rapid, direct, and single-molecule-sensitive DNA sequencing will radically change life sciences and medicine because no other technique can determine the complete sequence of the genetic information of life.

February 15, 2007

“Electronic Conducting States in Nano- and Mesoscale Molecular Devices,” Nikolai Zhitenev, Lucent Technologies, hosted by Eric Isaacs

Abstract: Organic materials can offer new electronic functionality not available in inorganic devices. However, the integration of organics within nanoscale electronic circuitry poses new challenges for material physics, chemistry, and nanofabrication. I will discuss two very different approaches to designing useful electronic properties in small molecular devices. In the first case, the electronic functionality is to be provided by backbones of short molecules. We have developed a set of fabrication techniques that allow us to build devices with self-assembled monolayers from nearly single-molecule size up to ~300 nm on a side. For the first time, systematic experimenting with the topography, chemical bonding at the metal-molecule interface, and defect generation is performed. Surprisingly, the results consistently demonstrate that the tunneling conductance of common short molecules is 4-6 orders of magnitude smaller than is commonly believed. In the second approach, we build devices with monolayers of macromolecules. The electronic properties are engineered by the composition and by the chemical conversions of the side groups. Voltage-induced reversible switching between low- and high-conductive states is observed in devices fabricated with polyelectrolyte monolayers. In this case, multiple chemical modifications can be performed within completed devices significantly affecting the electrical behavior. We suggest that the switching is caused by ionization of the polymer creating a conducting channel of electronic levels aligned with the contact Fermi level.

February 12, 2007

“Optical Forces and Slow Light in Nanophotonics,” Michelle L. Povinelli, Stanford University, hosted by Larry Curtiss and Gary Wiederrecht

Abstract: Advances in nanofabrication techniques now allow us to pattern materials on a scale smaller than the wavelength of light. I will show how computational simulations can be used to explore novel optical phenomena in nanofabricated devices such as photonic crystals and guide device design. First, I explore the use of optical (or radiation-pressure) forces for reconfiguration and positioning of integrated optical devices. Calculations on waveguide, microsphere, and photonic-crystal systems show that light forces should lead to significant displacements, opening a new route for all-optical control. Second, I describe how dynamically-tuned photonic crystals can be used to slow down the speed of light on-chip, mimicking atomic systems. Thirdly, I describe mechanisms for reducing the propagation losses due to disorder and light leakage in miniaturized nanophotonic waveguides.

February 9, 2007

“Modeling the Metastability and Configurations of 0-D and 2-D Defects in Nanocrystals,” Amanda Barnard, University of Oxford, hosted by Larry Curtiss

Abstract: Although thermodynamically metastable, defects are often observed in polyhedral nanocrystals, nanorods and nanowires, even following annealing. These may include zero-dimensional point defects such as substitutional impurities, or two-dimensional planar defects such as stacking faults and twin planes. For example, many bulk metals have the face-centered cubic structure, but small nanocrystals and nanorods of the same material may exhibit structural modifications such as single or multiple (symmetric) contact twinning, as well as fivefold cyclic twinning resulting in pentagonal nanostructures. Unfortunately such defects are often neglected by most models and computational studies, which consequentially limits theoretical descriptions of nanostructure materials to more idealized (less realistic) approximations. Presented in this talk are examples of how computational and theoretical methods may be used to model the metastability of different configurations of zero-dimensional and two-dimensional defects in faceted nanocrystals, over a range of sizes.

January 30, 2007

“Dynamic Microscopic Patterns at Air/Liquid and Liquid/Liquid Interfaces,” Nathan Ramanathan, Florida State University, hosted by Seth Darling

Abstract: From the striped coats of zebras to the ripples in windblown sand, the natural world abounds with patterns. Such patterns have been of great interest throughout history, and, in the last 20 years, scientists in a wide variety of fields have been studying the patterns formed in well-controlled experiments that yield enormous quantities of high-precision data. The major part of my talk will be focused on the temperature-gradient-driven dynamic flow patterns at air/liquid interfaces, highlighting applications in biomembranes and microfluidics. During the last decade of the 20th Century, physicists and chemists have shown that a neutrally buoyant droplet in a fluid possessing a temperature gradient migrates under the action of thermocapillarity. The drop pole in the high-temperature region has a reduced surface tension. The surface pulls away from this low-tension region, establishing a Marangoni stress that propels the droplet into the warmer fluid. Recently, we have shown a way to generate thermocapillary flow in two-dimensional Langmuir monolayers. Locally irradiating a Langmuir monolayer with an infrared laser opens up a cavitation bubble. The bubble exerts a thermal stress on the adjacent liquid that generates a flow around the bubble that ultimately results in the formation of collapse patterns and vortical flow patterns. The generated thermocapillary flow depends on the magnitude of the applied laser power, surface pressure, temperature-dependent surface tension, and the duration of local heating. At the end of my talk I will discuss some of the magnetic patterns that are formed at the liquid/liquid interface and measurement of femto-Newton range forces.

January 26, 2007

"Mechanical Response of Nanocrystalline Ceramics: Massively Parallel Molecular Dynamics Simulations," Izabela Szlufarska, University of Wisconsin, hosted by Derrick Mancini

Abstract: Silicon carbide is an outstanding material for applications in harsh environments because of its high oxidation resistance and the stability of its properties in high-temperature, high-radiation, and high-frequency conditions. It also has excellent mechanical properties and has recently been explored as potential material for MEMS and NEMS applications. Its mechanical properties can be further improved by decreasing the grains size to the nanometer regime. We employ massively parallel molecular dynamics simulations to study atomistic events at the onset of plasticity in nanocrystalline ceramic thin films. The increased volume fraction of highly disordered intergranular films as compared with nanometals manifests itself in new deformation mechanisms. Our nanoindentation studies of nanocrystalline silicon carbide provide a scenario for the interplay between grain rotation, corporate grain motion, sliding at grain boundaries, and integranular deformation to produce a rich and unique load-displacement response. We predict a crossover from continuous corporate grain response to discrete intergrain plasticity at a critical depth that is a fraction of the grain size. We will also present results of tensile and shear testing in nc-SiC and describe changes in the mechanical response resulting from the reduction of grain size. Understanding the fundamental phenomena that govern elastic and plastic deformations is crucial for design and fabrication of nanocrystalline materials with enhanced mechanical properties. Preliminary results on simulations of diamond nanostructures and implementation of the REBOII potential with long-range interactions into our massively parallel code will also be discussed.

 

January 19, 2007

 

“Nanoimprint Lithography, Nanophotonic Devices and Applications,” Shufeng Bai, Princeton University, hosted by Derrick Mancini

Abstract: Nanoimprint lithography (NIL) is a high-throughput, low-cost, nonconventional lithography method with proven sub-10-nm resolution. It has been listed in theInternational Technology Roadmap for Semiconductors for 32-nm node and is quoted as an engine to nanomanufacturing.

The first part of the talk focuses on nanofabrication technologies. A process was developed to fabricate highly ordered array of nano-rings (as small as 40-nm radius) over large areas. The nanoring array has excellent periodicity, good circularity, and uniformity over wafer scale areas. Concentric double rings were also fabricated, and plasmon resonance in gold nano-rings was observed at infrared wavelength. The potential applications of nanoring arrays include plasmonic devices and magneto-resistive memory, which may replace both computer memory and hard drives in the future. Fabrication and applications of low-cost nanofluidic channels using nanoring lithography will also be discussed. The channels measure 90 nm in cross section and several centimeters in length. Stretching DNA molecules by using the nanochannels was demonstrated.

In the second part of the talk, a novel photonic device called subwavelength resonant grating (SRG) will be introduced. A SRG consists of a single layer of subwavelength surface relief gratings, and it acts as a band stop filter. SRGs are narrow band, ultrathin (< 1 um), highly efficient (~100%), tunable, and suitable for integration. They can be fabricated by using NIL.

By incorporating a SRG with a commercial multimode diode laser, a tunable single mode laser was demonstrated. It operates at 1.5-um wavelength with a side mode repression ratio of 36 dB and wavelength tuning range of 7 nm. Unlike DBR and DFB lasers, strict temperature control is not needed to keep the wavelength stable. A SRG was also used to narrow the spectra and stabilize the wavelengths of high power broad area lasers (BAL). The full-width at half-maximum (FWHM) of a BAL was reduced from several nanometers to less than 0.06 nm, and the wavelength drift against temperature was reduced by a factor of 40. The setup is much simpler than the approaches using conventional diffraction gratings.

Other subwavelength optical elements, such as subwavelength quarter wave plate, may also be discussed if time permits.

2006 Seminars Archive

Date Title

December 21, 2006

"Metal Clusters: Physics on the 1-Nanometer Scale," Karl-Heinz Meiwes-Broer, University of Rostock

Abstract: Metal clusters at surfaces are model systems of nanostructure physics that allow for the study of quantum effects. Exciting material and size-dependent features open the possibility to create novel objects that might serve for future applications ( e.g., in the area of nanoelectronics or quantum information technology). This contribution aims at highlighting few specific features of metal clusters, starting from dynamics in ultracold helium droplets and their interaction with strong femtosecond laser fields. The latter being a playground to study the coupling of strong radiation into matter. In particular, nonstationary plasma effects lead to pronounced dynamics in the optical response. From beam work, it is known that the electron structure of small clusters often has not much to do with the respective bulk. The interaction with a surface, in addition, might change the particular electronic behavior. To investigate electronic properties, we employ the method of tunnelling transport in an STM at low temperatures. The resulting dI/dU curves are distinctly structured, which results from the size-dependent density of states. In addition, the underlying substrate influences the electronic properties, which will be demonstrated with the germanium (100) surface. The magnetic investigations are performed with Kerr effect and absorption with optical and synchrotron radiation. When concentrating onto the ratio of the magnetic orbital to spin moments, a strong cluster size dependence is observed. Even large particles with up to 15 nm show increased magnetic orbital moments.

December 20, 2006

"Vibrational Lifetimes of Hydrogen and Oxygen Defects in Semiconductors," Baozhou Sun, Washington State University, hosted by Matthew Pelton

Abstract: Characterization of defect and impurity reactions, dissociation, and migration in semiconductors requires a detailed understanding of the rates and pathways of vibrational energy flow and of the coupling mechanisms between local modes and the phonon bath of the host material. From time-resolved studies of the lifetimes and dynamics of local vibrational modes, we can obtain the important information on the energy dissipation and decay channels of impurities in semiconductors. The lifetimes of the Si-H stretch modes in silicon are found to be extremely dependent on the local solid-state structures, ranging from a few picoseconds for interstitial-type defects to hundreds of picoseconds for hydrogen-vacancy complexes. The studies of bending modes in semiconductors reveal that the lifetime of bending modes can be explained by energy gap law (i.e, the decay time increases tremendously with increasing decay order). An isotope effect is found in the study of the vibrational lifetimes of interstitial oxygen in silicon. The decay mechanism of interstitial oxygen defects in silicon and germanium is discussed according to their phonon density calculations and the symmetry of their accepting modes. These studies provide a better understanding of the dissociation of Si-H or Si-O bonds and the strong hydrogen and deuterium isotope effect found in H-passivated semiconductor devices.

December 12, 2006

"Pinning and Dynamics of a Magnetic Vortex," Robert L. Compton, University of Minnesota, hosted by Kristen Buchanan

Abstract: A magnetic vortex is often the ground state of micron-diameter soft ferromagnetic disks. Vortex magnetization curls in-plane except at the vortex center, where the magnetization turns sharply out-of-plane, defining a core region with length scale ~10 nm. Like domain walls, the vortex core can be pinned by material defects. But the zero-dimensional nature of a vortex core, compared with the one-dimensional nature of a thin-film domain wall, gives rise to unique pinning behavior. We have used time-resolved Kerr microscopy to investigate the dynamical behavior of micron-diameter disks patterned from sputtered Permalloy films. Broadband spin dynamics include a low-frequency vortex translational mode (vortex mode) that is expected to be nearly independent of field, based on analytical theory and previous experimental work. Instead, when excitation amplitude is small, we find that the translational mode frequency fluctuates with field by a factor of ~2. The quasi-periodic nature of the field dependence points to an origin in a random distribution of pinning defects. Upon increasing the excitation amplitude, the pinning hypothesis is born out by the observation of depinning threshold, accompanied by the complete disappearance of the frequency fluctuations. Finally, by mapping translational mode frequency as a function of orthogonal in-plane fields, we are able to image the distribution of pinning defects in real space with ~20-nm resolution.

December 11, 2006

"Plasmonics: Optics at the Nanoscale," Naomi J. Halas, Rice University, hosted by Gary Wiederrecht

Abstract: In recent years we have shown that certain metallic nanoparticles possess plasmon resonances that depend very sensitively on the shape of the nanostructure. This interesting observation has led to a fundamentally new understanding of plasmon resonances of metallic nanostructures - plasmon hybridization" - where the collective electronic resonances in a metallic nanostructure are understood to be a classical analog of the single electron quantum states of simple atoms and molecules. The plasmon hybridization picture explains the tunability of nanoshells, a dielectric core, metallic shell nanoparticle that is the simplest nanostructure with tunable plasmon resonances. Moreover, this picture provides a nanoscale design principle for predicting the plasmon resonances of an entire new family of plasmonic nanostructures: reduced symmetry nanostructures (nanoeggs and nanorice), multilayer nanoshells (nanomatryushkas), nanoscale dimers, trimers, and N-mers, and a metallic nanosphere adjacent to a thin metallic film, a photonic analog of the spinless Anderson model. Since the plasmon resonances give rise to large local field enhancements on the nanostructure surfaces, a variety of surface enhanced spectroscopies such as surface-enhanced Raman scattering and surface-enhanced infrared absorption can exploit these types of designed metallic nanostructures as tailored, high-performance substrates. In addition, by tuning plasmon resonances into the near infrared region of the spectrum, the physiological "water window" can be accessed, where blood is essentially transparent and light penetrates maximally through human tissue. With bioengineers, we have developed a suite of applications for nanoshells in the human body, such as an all-optical nanoscale pH meter for optical biopsies, and a nanoshell-based approach to cancer therapy.

 

November 9, 2006

"Birck Nanotechnology Center at Purdue," John R. Weaver II, Purdue University, hosted by Derrick Mancini and Judith Yaeger

Abstract: The Birck Nanotechnology Center at Purdue University has some unique capabilities due to a combination of facility design and equipment set. This presentation will to describe the facility and its capabilities and discuss ways that the Center can work with Argonne on nanoscale research projects. This will be an informal presentation with significant time allotted for interaction.

November 8, 2006

 

"Nanoscale Spectroscopy with Optical Antennas," Neil Anderson, University of Rochester, hosted by Gary Wiederrecht

Abstract: Because of diffraction, propagating radiation cannot be localized to dimensions smaller than half the optical wavelength. To overcome this limit, (nanoscale) optical antennas are used to localize radiation to length scales much smaller than the wavelength of light. A laser-irradiated optical antenna, such as a bare metal tip, is placed a few nanometers above a sample surface to establish a localized optical interaction and a spectroscopic response (Raman scattering, fluorescence, absorption, etc.). A high-resolution, hyper-spectral image of the sample surface is recorded by raster-scanning the antenna pixel by pixel over the sample surface and acquiring a spectrum for each image pixel. This type of near-field optical spectroscopy has been used to map the vibrational modes of individual single-walled carbon nanotubes (SWNT) with a resolution of 10nm. The method is able to resolve defects in the nanotube structure as well as interactions with the local environment. Similar studies have recently revealed that electronic states (excitons) in carbon nanotubes are highly localized to defect-rich regions.

October 23, 2006

"Synthesis and Applications of Gold Nanoparticles," Hongwei Liao, Rice University, hosted by Norbert Scherer and Eric Isaacs

October 17, 2006

 

 

"The Localization/Delocalization Dilemma and the Electronic Structure of f-Element Oxides," Richard L. Martin, Los Alamos National Laboratory, hosted by Al Sattelberger

Abstract: The electronic structure of many of the oxides containing d- and f-elements has long been a challenge for theory. For example, the traditional workhorses of density functional theory, the local density approximation (LDA) and the generalized gradient approximations (GGA), predict many of these systems to be metallic, when in fact they are insulators with band gaps of several electron-volts. These problems reflect the localization/ delocalization dilemma faced in systems with weak overlap and seem to be largely overcome by the new generation of hybrid density functionals developed for molecular studies. Only recently has it been possible to apply these functionals to solids, but in the cases studied thus far we find a distinct improvement. The hybrid functionals predict the correct insulating ground state, band gap, lattice constant and magnetic behavior at 0K, where known. I will review the origin of the problem, how hybrid functionals differ from traditional ones, and recent applications to strongly correlated oxides.

October 12, 2006

 

"Synthesis and Assembly of Nanoparticle Into Superlattices and Gels," Christopher M. Sorensen, Kansas State University, hosted by Xiao-Min Lin

Abstract: This talk will give an overview of research the author has been performing over the past several years. Topics will include:

  1. Nanoparticles with narrow size distributioncan be synthesized via a process we call "digestive ripening," which involves heating a suspension of particles in the presence of a surface active ligand, typically alkyl thiols, amines, or phosphines. With time, a polydisperse system will become nearly monodisperse. Another feature of digestive ripening is that mixtures of colloids of different metals will alloy during digestion. Reversible size and shape control can be achieved by changing the ligand.
  2. Nanoparticle suspensions act as solutions and thereby the distinction between suspension and solution blurs. I will show temperature dependent solubility data for nanoparticle solutions that can be made to precipitate to form 2d and 3d superlattices.
  3. Finally I will go to the gas phase and show that nanoparticle aerosols can gel. Timescales for gelation are in a reasonable range only when the system is nano. This aerosol gelation yields very low-density, high-surface-area solids similar to aerogels that may have important technical application.

 

October 5, 2006

"Biofunctionalization and Detection of Magnetic Nanoparticles," Glenn Held, IBM, hosted by G. Brian Stephenson

Abstract: Methods of synthesizing monodisperse, strongly magnetic ferrite nanoparticles have been well documented. However, encapsulation of these particles within an overlayer of biologically active molecules has remained problematic. Such bio-functionalized magnetic nanoparticles would provide the crucial component in ultrasensitive magnetic detection of both proteins and nucleic acids. In addition, such particles could be used to bind and transport proteins and, following introduction into a living organism, they could provide a means of monitoring and influencing cellular processes. In this talk, I will present a method for bio-functionalizatizing manganese ferrite nanoparticles. Following biofunctionalization with DNA or biotin, these particles can be site selectively bound to appropriately patterned silicon oxide substrates. Imaging these substrates with scanning SQUID microscopy provides evidence that these particles retain their magnetic properties. Finally, a novel method of detecting the hybridization of these magnetic nanoparticles to a substrate at room temperature using a biosensor comprised of a protein patterned magnetic tunnel junction situated in orthogonal magnetic fields will be discussed.

September 27, 2006

"Optical Properties of Silicon Clusters and Quantum Dots: Is 'Nano' Really that Different from the Bulk?" Serdar Ogut, University of Illinois Chicago, hosted by Peter Zapol

Abstract: For almost two decades now, there has been an increasing tendency to get excited about any research activity in condensed matter and materials physics with the word "nano" in it. Active research on the optical properties of silicon nanostructures is one good example. In this talk, I will present some of my previous and ongoing research in ab initio modeling of the optical properties of silicon nanostructures, such as hydrogenated silicon quantum dots up to a few nm in size and medium-size atomic Sin (n = 20 – 28) clusters. I will argue, using various examples from these systems, that while "nano" typically presents rather interesting physics, most of this interesting physics can be understood in terms of bulk Si properties with the right boundary conditions.

September 25, 2006

 

"Reduction of Spin Transfer Currents and Low Temperature Anomalies in the Free-layer Nanomagnet Behavior of Nanopillar Spin Valves," Ozhan Ozatay, Cornell University, hosted by Axel Hoffman

Abstract The idea of employing electron spin for information technologies has unique advantages over the conventional charge-based electronics because it potentially enables nonvolatile data storage, improved data processing speed, and more efficient power consumption as well as high integration density. In metallic spintronics, the interaction of the spin of a current-carrying electron and a localized moment of a ferromagnet has two important outcomes: the spin-dependent scattering of the current carrying electrons leading to magnetoresistance effects and to the ability to manipulate the local moment through a mutual spin transfer torque. In this talk, I will present a series of experiments that address issues regarding the latter, spin-transfer phenomenon and that addresses some of the challenges for advancing this phenomenon toward technological applications. In the first part of the talk, I will discuss the nucleation and subsequent depinning of a domain wall driven by a nonuniform spin polarized current injection into a nanomagnet. This is accomplished by defining a 20-to 30-nm-diameter aperture inside a 3.5-nm-thick AlOx in between the Cu spacer and permalloy (Py) free layer of a Py/Cu/Py nanopillar spin valve. The resulting concentrated spin polarized current injection into the free layer nucleates and applies pressure to a domain wall at the contact region. The magnetic reversal is via the propagation of the domain wall driven by spin torque. This mechanism reduces the absolute level of spin transfer switching currents required to achieve magnetization reversal by two orders of magnitude. In the second part of my talk, I will focus on the adverse effects of sidewall oxides in a Py nanomagnet on both field and current driven switching characteristics as a function of temperature. Analytical electron microscopy and surface sensitive x-ray photoemission spectroscopy measurements reveal that the Py surface has NiO, FeO, and Fe2O3 native antiferromagnetic oxides. These adventitious oxides can have a major impact on the efficiency of spin torque switching as well as field driven switching by enhancing magnetic damping as well as causing unstable switching fields due to a rotatable anisotropy. I will show that the passivation of such an oxide layer results in minimal temperature dependence of spin transfer switching currents as well as in stabilizing the switching fields.

September 22, 2006

 

"Design of Biologically Inspired Nanostructured Materials," Szu-Wen Wang, University of California, Irvine, hosted by Eric Isaacs and Lee Makowski

Abstract: The precision of natural protein nanostructures is remarkable, and they can be used as scaffolds upon which to build new functionalities. We are investigating the use of protein assemblies as biomaterials for applications such as dispensing pharmaceutically-active molecules and directing the optical properties of inorganic arrays. Our current work focuses on the in vivo synthesis, self-assembly, and materials characterization of several engineered macromolecular complexes, including nanocapsules, protein polymers, and crystalline arrays. By finely defining architecture at both the molecular and nanoscale levels through genetic engineering, such an approach enables us to tailor unique material properties.

September 20, 2006

"Heterogeneous Nanomaterials: Spanning Supramolecular Templating, TiO2 Surface Defects, and Metal Oxide Morphologies," Bryan M. Rabatic, Chemistry Division, hosted by Tijana Rajh

Abstract: Nanoscale materials comprised of organic and inorganic components are becoming a cornerstone of nanotechnology. Self-assembled organic systems can act as part of such a hybrid material by serving as a template for the synthesis of inorganic structures having features inaccessible with known lithographic techniques. In this regard, peptide-based amphilphilic molecules having an unsymmetrical molecular design are capable of self-ordering in aqueous environments to form one-dimensional scaffolds with 5-nm widths and lengths up to several micrometers. These bioinspired nanoobjects can preferentially complex cadmium ions for the directed precipitation of cadmium sulfide nanocrystals to form a hybrid material having features commensurate with the self-assembled organic template. Furthering this template-based method, we show that the cores of one-dimensional titanium dioxide nanotubes, with lengths up to 300 nm, can serve as templates for the precipitation of silver metal nanowires having diameters of 6-8 nm. We also demonstrate the compliment to the organic template approach; inorganic nanoobjects can serve as templates for organic, biological molecules. In this regard, site-specific defects at the distal tips of ellipsoid-shaped TiO2 nanoparticles, direct the surface functionalization of the nanoobject with the biomolecule dopamine. The defect sites of the inorganic template were identified with high-resolution transmission electron microscopy, and found directly related to the size and shape of the nanoparticle. By templating biotin at the defect sites, tip-to-tip serial self-assembly of these bio-hybrid nanocomposites, via conjugation with the glycoprotein avidin, is shown. Finally, we have been able to produced unusual structures of zirconia using a completely surfactant-free synthetic approach. These materials are synthesized via an aqueous, hydrothermal treatment to form extremely high aspect-ratio nanotube and nanowhip

September 19, 2006

"Evaporation-Induced Self-Assembly of Porous and Composite Thin film Nanostructures, " C. Jeffrey Brinker, University of New Mexico/Sandia National Laboratories, hosted by Eric Isaacs

Abstract: Nature combines hard and soft materials often in hierarchical architectures to get synergistic, optimized properties and combinations of properties with proven, complex functionalities. Emulating such natural material designs in robust engineering materials using efficient processing approaches amenable to manufacturing represents a fundamental challenge to materials scientists and engineers. Currently there is considerable interest in evaporation-driven self-assembly as a means to create porous and composite thin film nanostructures using simple commercial procedures like dip or spin-coating and ink-jet printing. This presentation will first review recent progress on evaporation-induced silica/surfactant self-assembly (EISA) to prepare porous thin film nanostructures of interest for membranes, sensors, and low k dielectrics. Starting with a homogenous solution of surfactant plus hydrophilic oligosilicic acid precursors, solvent evaporation concentrates the depositing film in precursors and surfactant inducing micelle self-assembly and further self-organization into thin film silica/surfactant mesophases. Exploiting the steady, continuous nature of dip-coating, it is possible to spatially resolve the complete evaporation-induced self-assembly pathway (in the coating direction) and interrogate it using spectroscopy and/or grazing incidence SAXS. I will then discuss surfactant self-assembly as a means to organize simultaneously hydrophilic and hydrophobic precursors into hybrid (organic/silica or metal/silica) nanocomposites that are optically or chemically polymerizable, patternable, or adjustable. For example, the co-self-assembly of amphiphilic photoacid generators with silica precursors results in photosensitive thin film mesophases in which the pore size, pore volume, surface area, and refractive index may be continuously varied over a range depending on the UV exposure time. Incorporation of switchable, hydrogel or azobenze moieties provides a means to create nanostructures exhibiting chemo-, thermo- or opto-mechanical actuation. Biocompatible self-assembly, using phospholipids as the structure-directing agents, allows cell immobilization in a robust self-contained, self-sustaining environment of interest for stand-alone cell-based sensors. However, we observe that cells co-opt the EISA process, altering significantly the self-assembly pathway and creating a unique bio/nano interface. As a new direction in self-assembly, we have exploited mechanically-based re-assembly to create superhydrophobic, fractal silica surfaces mimicking those of the Lotus leaf and desert beetle. These surfaces are self-cleaning and fundamentally affect flow, making them of general interest for fluidic-based microsystems.

 

September 8, 2006

"Nanopatterning of Biomolecules," Joseph Kakkassery, Northwestern University, sponsored by Tijana Rajh

Abstract: The emerging field of nanobiotechnology relies on precise patterning of biological molecules on surfaces with nanometer resolution. A few examples include the generation of DNA, protein, virus and cell arrays that have potential applications in the areas of biosensing, proteomics and theranostics. Currently a number of techniques exist for generating nanoscale features of biological molecules. These include electron-beam lithography, dip-pen nanolithography (DPN), nanografting, nanoimprint lithography, nanopipet deposition and contact printing. Each of these techniques has a set of capabilities that differentiate it from the rest, and all possess both strengths and weaknesses with regard to resolution, speed, materials compatibility, complexity, and cost. This talk will focus on the generation of single influenza virus nanoarrays by dip-pen nanolithography and its applications in studying cell infection.

August 28, 2006

"Synthesis and Development of Functional, Biocompatible Nanocomposites," Dolly Batra, Materials Science Division, hosted by Tijana Rajh

Abstract: An important step in the development of functional nanoscale devices is the synthesis of meso- and nanostructured "soft" materials that can be used to incorporate and organize nanoscale features such as biomolecules or nanoparticles. Organic polymers are an attractive class of such soft materials, as their properties can be tuned according to their chemical or biochemical functionalities. Protein-based soft materials, for example, require the synthesis of biocompatible, mesostructured materials that organize biomolecules into highly ordered, functional arrays. To that end, a matrix comprising a two-dimensional hexagonal, mesoporous network of crosslinked polyvinyl alcohol (PVA) has been fabricated that exhibits potential for the integration and organization of soluble and membrane proteins. Several novel polymers based on self-assembled ionic liquids have also been developed, where the liquid crystalline architecture can be controlled via changes in the water content. These soft, nanostructured materials are useful as templates for the in situ synthesis, trapping and ordering of metal (Au) and semiconducting (CdS, PbS) nanoparticle arrays. These composite materials have applications for the fabrication of novel photonic materials and all ‘solid-state’ solar cell devices where the spacing between nanoparticles can be tuned for optimum photovoltaic efficiency.

August 11, 2006

"Advanced DSC Techniques in Mettler-Toledo Thermal Analysis Instrument," Matthias Wagner , Mettler -Toledo, Inc., hosted by Xiao-Min Lin

August 11, 2006

"Charge Transfer and Recombination in Semiconductor Nanostructures Designed for Photovoltaic Applications," Istvan Robel, University of Notre Dame, hosted by Xiao-Min Lin

Abstract: Several approaches for improving the efficiency of nanomaterial-based photovoltaic devices will be discussed in the talk. The use of hybrid assemblies such as type-II semiconductor-semiconductor heterostructures and semiconductor-carbon nanotube composites lead to modified electronic properties beneficial for light harvesting. Photoinduced charge transfer- and recombination dynamics and photoelectrochemical properties will be discussed in two heterostructures (CdSe-TiO2 and CdS-CNT) as well as in semiconductor nanowires (CdSe).

July 25, 2006

"Spin Dynamics in Lateral Thin-Film Nanostructures," Sergio O. Valenzuela, Massachusetts Institute of Technology, hosted by Axel Hoffmann

Abstract: Spintronics aims to replace charge with spin as the main computational element in devices. Much effort is being devoted to understand how the electron spin is transferred through interfaces and to identify fundamental processes that modify the spin polarization or that can be used for spin manipulation. Lateral structures are a unique tool to study these phenomena because of the ease to fabricate them in multi-terminal configurations. This will be illustrated by some of our recent experimental results in thin-film devices, where the output voltage is exclusively determined by the spin degree of freedom, and provides valuable information on spin-flip scattering mechanisms, spin-polarized tunneling, spin-orbit interaction and the spin Hall effect.

July 24, 2006

"Molecular Assembly from Functional Building Blocks," Huisheng Peng, Tulane University, hosted by Seth Darling

Abstract: There is a growing interest in the synthesis of functional materials by supramolecular assembly. Recent attention has been directed toward understanding the assembly mechanism, the incorporation of desired functionalities, and the applications. My research focuses on studying self-assembly of organic/inorganic hybrid molecules (e.g., bridged silsesquioxanes, with a structure of (RO)3Si-R’-Si(OR)3) and polymers. For the self-assembly of bridged silsesquioxane, four functional organic groups, (i.e. polydiacetylene, oligothiophene, perylenediimide, and porphyrin) are readily incorporated into an ordered silica network, and the resultant assemblies show interesting structures and great applications as optoelectronic devices and sensor materials. Polymer assembly is performed in common solvents to produce smart thin films or nanoparticles, and their applications as sensors and controlled drug-delivery vehicles, respectively, have been investigated.

July 14, 2006

"Magnetic and Mechanical Responses of Soft Multiphase Materials," Brian D. Pate, Massachusetts Institute of Technology, hosted by Tijana Rajh

Abstract: The ability of organic matter to undergo reversible structural and electronic reorganization in response to environmental stimuli is directly responsible for the broad utility of soft materials in natural and synthetic systems. In particular, assemblies of molecules or macromolecules engineered to exhibit hard/soft or liquid crystalline phases exhibit a wide range of tunable responses to external electromagnetic and mechanical fields. Recently, the metal-dependent structural reorganization of a series of mesogenic metalloporphyrazines in the presence of applied magnetic fields has been predicted and characterized. A method to magnetically process these liquid crystals to obtain long-range uniaxial orientation of the columnar superstructures has been demonstrated. The alignment of these materials using mechanical fields will also be described, and contrasted with that of two related macromolecular systems, including a novel functionalized polyiptycene and a new series of thermoplastic polyurethanes

July 12, 2006

"Achieving Enzymatic Catalysis in Abiotic Supramolecular Systems," Andrew J. Goshe, CNM Distinguished Postdoctoral Appointee, Chemistry Division, hosted by Tijana Rajh

Enzymes, one of the classes of nanoscaled machines in biology, accomplish a stunning variety of chemical transformations with high specificity and activity. The synthetic replication of the activesites of these enzymes, however, seldom results in catalytically active species. Recent efforts have been directed toward the construction of nanoscaled systems capable of reactivating synthetically derived hydrogenase activesite mimics for the production of hydrogen. The design, synthesis, and properties of such systems will be discussed.

July 12, 2006

"Magnetic Nanoparticle Antibody Conjugates for Potential Cancer Therapies," Dorothy Farrell, London Centre for Nanotechnology, hosted by Seth Darling

Abstract: Numerous biomedical applications for magnetic nanoparticles have been proposed and developed in the past decade. High magnetic susceptibility superparamagnetic nanoparticles are currently being investigated as magnetic hyperthermia and drug delivery agents. In hyperthermia, cancerous cells are destroyed by heat generated in magnetic nanoparticles by an appropriately tuned, externally applied ac magnetic field. If the particles can be confined to the cancerous regions through antigen binding, nearby healthy tissue would be unharmed. Targeting can be further improved using in vivo magnetic actuation of the particles with external magnetic fields. However, up to now the ac power loss profile of particles used in hyperthermia studies has not been sufficient for use in clinical applications. The standard co-precipitation reactions of Fe2+ and Fe3+ salts in alkaline solutions produce non-stoichiometric magnetite 5-15 nm in diameter, with only moderate heating properties.

Along with researchers at the Royal Free and University College Medical School, I am currently developing antibody-nanoparticle conjugates with improved properties for hyperthermia applications. We have conjugated carboxymethyl dextran coated iron oxide nanoparticles to an antibody fragment specific to carcinoembryonic antigen, a protein expressed on many epithelial cancers. Immunoassays studies show that these conjugates maintain reactivity against the target antigen, suggesting that the conjugates can be directed to target tumors within the body. Current work focuses on the preparation of nanoparticles capable of significant heating at the low concentrations (~1mg/cc) attainable in vivo using antigen targeted delivery. To create an optimized hyperthermia agent, iron oxide particles of varying size, shape, phase and crystallinity have been synthesized and their heat generation profiles studied. Using a modified reaction procedure in a biocompatible organic solvent (1,2-propanediol), particles 30-40 nm in diameter have been synthesized. Dispersions of these samples show rises in temperature two times greater than commercially available particles using clinically relevant field conditions.

July 5, 2006

"Understanding the Materials Behavior of Tetrahedral Amorphous Carbon Using MEMS Resonators," David A. Czaplewski, Cornell University, hosted by Leo Ocola

Abstract: Tetrahedral amorphous carbon (ta-C) films have been used to fabricate micro-electromechanical systems (MEMS) with broad applications, such as electronics ( clocks, filters, switches, etc.), sensors (for chemicals, biological agents, pressure, acceleration, etc.), and metrology (scanning probe microscopy). These films have advantageous properties compared to other common MEMS films, such as silicon, polysilicon, silicon nitride, and silicon dioxide. The Youngs’ modulus of ta-C (approximately 80% sp3 bonding) is roughly four times that of the other common films, which can aid in the realization of high-frequency oscillators for filter and other applications. Additionally, the ta-C films are resistant to stiction and auto-adhesion and have an abrupt surface termination, which helps prevent surface-related mechanical dissipation. Understanding dissipation mechanisms that limit the quality factor, Q, in ta-C is essential for realization of components for electronic or sensor applications since the bandwidth for electronic components scales as Q-1 and the sensitivity of sensors scales as Q-½. Additionally, for some devices,, such as a proposed tunable frequency source for space-based electronics, knowledge of the temperature dependence of the elastic constants and Q of ta-C is of primary importance.

In this talk, I will discuss our recent work to understand the fundamental mechanisms that control mechanical dissipation in ta-C and of the experimental measurement of the thermal stability and temperature dependence of the mechanical properties of this material.

June 30, 2006

"The Development of Bio-Inorganic Nanostructures for Device Applications," Brian D. Reiss, Materials Science Division, hosted by Tijana Rajh

Abstract: The integration of biomolecules with inorganic substrates is rapidly generating innovative materials with potential applications ranging from solar power to medical diagnostics. In this presentation two approaches towards the development of biomolecule-based functional materials that may ultimately form the basis of nanoscale devices will be presented. In the first photosynthetic reaction centers from R. Sphaeroides are being investigated for their potential applications in opto-electronic devices. Efforts are currently underway to isolate this protein on inorganic electrodes with controlled orientation, a challenging approach because novel chemistry must be developed to simultaneously link the protein to multiple electrodes. The second system under study uses the technique of phage display offers a way to rapidly identify peptide ligands for any desired material, and such ligands could be used to link biological species to inorganic substrates as desired. Recently, a peptide has been isolated using this approach that selectively binds the ferroelectric material lead zirconium titanate, and this unique system is currently being developed as the basis of a valve for nanofluidic systems.

June 26, 2006

"Tailoring Mesomorphic Structure and Crystalline Morphology in Polymer Films," Raluca Gearba, Institut de Chimie des Surfaces et Interfaces, hosted by Seth Darling

Abstract: Since their discovery, columnar mesophases have become increasingly important in fundamental research and in practical applications because of their peculiar supramolecular architectures, which allow one-dimensional charge transport. Although the most studied columnar phases are formed by disc-shaped molecules, it is now recognized that such phases can also be formed by dendrimers, main- or side-chain polymers with or without mesogenic moieties, phasmids, and board-like molecules. The electronic and optical properties of the liquid crystalline (LC) phases strongly depend on the chemical structure of the molecules and the way there is self-assembly at different scales in bulk and at interfaces. In particular, the organization at the mesoscopic scale, spanning from several nanometers to some hundreds of nanometers, must be tailored to control features such as the size and orientation of the LC mono-domains.

The lecture will show and discuss how the influence of the molecular architecture (degree of flexibility of molecules) and specific interactions such as hydrogen bonding can play on the supramolecular organization. We will demonstrate that using hydrogen bonds to "clamp" the molecules along the columns results in the smallest intermolecular distance (3.18 Å) ever found for columnar mesophases. At the same time, it will be shown how flexible star-shaped molecules self-assemble to give rise to a unique double helical crystal. Interestingly, the growth of the helical crystals can be tailored at the scale of one columnar diameter (2-4 nm) via a monotropic columnar mesophase. This scale is one order of magnitude smaller than the characteristic size of the block-copolymer morphology. By actively playing with the chemical structure, we can identify some of the factors responsible for the structure formation.

June 19, 2006

"Structural Landscapes of Biomimetic Supramolecular Nanomaterials by Solution X-Ray Scattering," Xiaobing Zuo, Chemistry Division, hosted by Tijana Rajh

Abstract: Biomimetic supramolecular nanomaterials are increasingly being designed for applications in solar energy conversion and storage, catalysis, environmental clean-up, and so on. The dynamic features of these molecular materials make in situ structural characterization a critical challenge. Our early studies have demonstrated that wide-angle solution X-ray scattering (WAXS) is a powerful, discriminating, high-throughput technique for in situ supramolecular structural characterization that can be applied with 100 to 1 Å spatial resolution and 100 ps time resolution for mapping structural dynamics along excited state reaction coordinates. This talk will focus on using coordinate-based analyses for wide-angle solution X-ray scattering to in situ characterize the structures and conformational dispersion of supramolecules, from nanocrystals which have rigid and ordered internal structures, to DNA, synthetic molecular squares, and self-folding polymer which is disordered and flexible in conformation. Designs and characterizations of light-induced molecular electronics and machines with time-resolved X-ray scattering will also be discussed.

June 14, 2006

"MicroPIV Measurement of Turbulent and Transitional Flow Characteristics in Microchannels," by Hao (Stephen) Li, Iowa State University

June 9, 2006

"Multiscale Coarse-Grained Modeling of Nanoparticle and Supramolecular Systems," Sergey Izvekov, University of Utah, hosted by Peter Zapol

Abstract: A novel and systematic methodology for the development of accurate coarse-grained (CG) models for simulations of nanoscale and biological systems is described. The method is called the multiscale coarse-graining (MS-CG) method and is based on matching of the effective interactions in the coarse-grained system to an underlying all-atom simulation. The MS-CG models open up the possibility of a dramatic speed up of molecular dynamics simulations of complex condensed-phase, biological, and nanoscale systems while retaining high accuracy in the prediction of structural and often thermodynamic properties. Several past and future applications of the MS-CG methodology will be presented, which include molecular liquids, biological membranes, proteins, and the self-assembly of carbonaceous nanoparticles.

May 30, 2006

"Andreev Reflection at the normal-metal/heavy-fermion superconductor interface: Point contact spectroscopy of CeCoIn5," Laura H. Greene, Swanlund Professor of Physics, University of Illinois at Urbana-Champaign, hosted by Eric Isaacs

Abstract: Point-contact spectroscopy results are obtained with normal-metal gold tips on single crystals of the heavy-fermion superconductor CeCoIn5. Contacts are shown to be in the Sharvin (ballistic) limit. Asymmetry observed in the background conductance starting at T* (~45 K), increasing with decreasing temperature to Tc (2.3 K), signifies the emerging heavy-fermion liquid. Below Tc, the enhancement of the sub-gap conductance arises from Andreev reflection. According to standard theory, the Fermi velocity mismatch between these materials should yield no Andreev reflection. The signal we do observe is several times lower than that observed in conventional superconductors, but consistent with other heavy-fermion superconductor data reported. Data taken in the (001), (110), and (100) orientations provide consistent and reliable spectroscopic evidence of a dx2-y2 superconducting order parameter.

May 29, 2006

"(1) Periodic Calculations with Gaussian Basis Sets" and "(2) First Principles Simuation of Liquid Water near Hydrophobic Surfaces," Konstantin Kudin, Princeton University, hosted by Eric Isaacs

Abstract: In the first part of my talk, I will discuss the implementation of periodic boundary conditions in the Gaussian suite of programs (Gaussian03). The code can carry out efficient density functional (DFT) and Hartree-Fock (HF) calculations for systems periodic in one, two, and three dimensions. I will mention several applications of this computational tool, specifically, studies of pristine and fluorinated carbon nanotubes, BN nanotubes, oxidized graphite, and uranium oxide (UO2) solid.

In the second part I will talk about Car-Parrinello molecular dynamics simulations of liquid water near hydrophobic surfaces. Peculiar properties of water layer near the surface that emerge from these calculations will be discussed.

May 17, 2006

"Electronic and Excitonic Interactions in Molecular and Nanoscale Materials and Devices," Cherie R. Kagan, IBM T. J. Watson Research Center, hosted by Eric Isaacs

Abstract: Molecular and nanoscale materials are being aggressively pursued for a wide range of applications in low-cost, large-area, flexible macroelectronics and optoelectronics and potentially as a post-CMOS alternative to high-density, high-performance nanoelectronics. For these systems to realize their potential, a fundamental understanding of the chemical and physical properties of molecular, supramolecular, and nanostructured assemblies is required. I will describe the synthesis, assembly, and characterization of molecular monolayers, multilayers, and thin films and the intermolecular, intramolecular, and interfacial interactions important to charge transport and exciton transfer and separation. Spectroscopic, microscopic, and electrochemical techniques are used to characterize molecular, supramolecular, and nanostructured assemblies. I will show solution processable, thin films form the active channels of transistors with field-effect mobilities (in micron scale devices) of ~1 cm2/V-sec and ION/IOFF>106, comparable to amorphous silicon TFTs. To probe inter- and intramolecular charge transport in molecular monolayers and multilayers, I will draw on silicon processing to fabricate nanometer scale device test structures and use novel chemical routes to assemble molecular materials at the device interfaces and to bridge the junctions. Integrating molecular assemblies in device test structures provides a platform to probe the underlying physics of charge transport necessary to develop structure-function relationships in molecular materials. Spectroscopic and optoelectronic techniques are used to explore the fate of excitations in molecular and nanoscale assemblies giving rise to energy transfer and charge separation.

May 15, 2006

"Atomic-Scale Catalyst Design from First Principles," Jeffrey P. Greeley, Technical University of Denmark, hosted by Peter Zapol

Abstract: Recent advances in Density Functional Theory (DFT) algorithms, combined with the ever-increasing availability of raw computer power, have put forth the tantalizing possibility that first-principles methods may soon contribute to the efficient, atom-by-atom design of heterogeneous catalysts and other materials. For such computational design efforts to be successful, however, key catalytic parameters for the reactions of interest (binding energies, activation barriers, etc.) must be identified, techniques for assessing the stability of nanoscopic surface structural features in reactive environments must be developed, and an efficient scheme for finding alloys that optimize design criteria for activity and stability must be found.

In this talk, I describe a general methodology for materials design using atomic-scale simulation methods. The method employs DFT calculations to determine important features of catalytic performance, including catalyst activity, structure, and stability, and it is applied to the analysis of hundreds of transition metal alloys for use in two reactions of interest in electrochemistry, the hydrogen evolution and oxygen reduction reactions.

April 28, 2006

"Correlating Atomic Scale Structural and Magnetic Properties by Spin-Polarized STM," Dr. Matthias Bode, Institute of Applied Physics and Microstructure Research Center, Hamburg, Germany, hosted by Eric Isaacs

 

April 27, 2006

"How far can we go? – An Update of Zone Plate Fabrication at Stony Brook," Ming Lu, SUNY at Stony Brook, hosted by Leo Ocola

Abstract: Fresnel phase zone plates are the most important focusing optics for soft X-ray scanning transmission microscopes. In collaboration with NJNC at Bell Labs/Lucent Technologies, the Stony Brook X-ray optics group has been working on zone plate fabrication for more than a decade. In this talk, I will give a survey of our latest progress. Factors that limit zone plate performance under current fabrication flow, as well as our strategies for improvement, will be discussed. For example, a newly discovered effect in e-beam lithography (orientation dependence of linewidth variation, or ODLW) and its correction method will be presented for the first time.

April 25, 2006

"Electron Transport in Artificial Nanosolids," Igor Beloborodov, Fermi Scholar, Materials Science Division, hosted by Peter Zapol

Abstract: Artificial materials composed of metallic nanoparticles have emerged as the next frontier of new materials, where quantum phenomena can be tailored to generate novel bulk materials behavior. These nanosolids can have programmable electronic properties arising from the fact that the interaction strength and degree of disorder in these materials can be controlled by varying the size and composition of the granules. Each building block of these new materials can be viewed as a tiny cluster of atoms of metallic or semiconducting elements. These clusters are not as small as molecules but not as large as macroscopic samples. I will review progress made in the last several years in understanding the properties of artificial nanosolids. In particular, I will discuss the following topics:

  1. Introduction to physics of artificial nanosolids,
  2. Novel transport regimes,
  3. Phase diagram of artificial nanosolids, and
  4. Future opportunities.

April 17, 2006

 

"Nanoscale Theory and Simulation: Light Interactions with Metallic Nanosystems," Tae-Woo Lee, Chemistry Division, hosted by Peter Zapol

Abstract: Materials processing techniques can now engineer materials with nanoscale features. When light interacts with such nanosystems, complex electromagnetic wave phenomena can emerge through strong near-field interactions. For example, surface plasmons (SPs), collective resonances of free electrons in a metal, can be excited in metallic nanosystems. SPs yield intriguing near-field phenomen,a such as highly localized fields and strong intensities. With strong, yet complex, near-field interactions, such systems provide ways of controlling light at the subwavelength scale. First-principles computational modeling tools provide invaluable insights about the complex wave phenomena inherent in light interactions in metallic nanosystems. They also can be used to conduct inexpensive feasibility studies of novel device ideas and allow one to optimize device designs prior to fabrication. First, we address usefulness of numerical approaches in nanophotonic research. Next, three new types of nanosystem are proposed and explored numerically:

  1. A cone-shaped silver nanoparticle interacting with chirped optical pulses. Rigorous numerical simulations reveal how spatio-temporal control of an SP local hot spot can be achieved. The simulations also demonstrate counterintuitive negative group velocity in some situations.
  2. A way to increase surface plasmon polariton (SPP) propagation length and intensity is proposed. (An SPP is a propagating SP excitation.) The underlying mechanism involves reflecting back radiation losses to propagating metal surface region, regenerating SPPs. Extensive finite-difference time-domain simulations, including coupling of external light into the system, demonstrate significant improvements.
  3. Redirecting light propagation with a sharp angle turn is a decades-long problem in photonic integrated-circuit research.

In this study, we discuss light propagating and bending in a slit waveguide. The discussion is based on accurate numerical solutions of Maxwell’s equations. The results, using a realistic model for silver at optical wavelengths, show that good right-angle bending transmission can be achieved for wavelengths greater than 600 nm. The bending efficiency is shown to correlate with a focusing effect at the inner bend corner. Possible experimental realization of these systems is also indicated.

April 14, 2006

"Nanotechnology at Intel Corporation," Dr. Bryan Rice, Intel Corporation, hosted by Ahmed Hassanein

April 14, 2006

"Reactive Molecular Dynamics Simulations of Network-forming Systems with Multiple Coordination States," Liping Huang, University of Michigan, hosted by Peter Zapol

Mar. 31, 2006

"Nanotechnology from the Bottom Up: Light-directed Synthesis of DNA Molecules," Prof. Franco Cerrina, University of Wisconsin – Madison, hosted by Leo Ocola

Abstract: One of the dreams of nanotechnology is to enlist the help of existing organisms as "nanofabricators." This is routinely done today when bacteria are used to produce designer molecules by inserting a specific strand of DNA in a vector. The next step would be to use more advanced organisms, such as diatoms, to generate controlled and user-specified structures. This requires both the knowledge of the genome and the ability to synthesize DNA "on demand," at a reasonable cost and turnaround time.

Indeed, the direct synthesis of DNA constructs in the length of 2,000 to 20,000 base pairs (bp) is at the root of a revolution in genetic engineering. As more and more genomes are decoded, and the function of the genes understood, there is the possibility of actually reprogramming some of the genetic material to achieve specific functions, from medicine to synthetic biology. The well-known base-by-base synthesis of DNA can be greatly enhanced by combinatorial techniques, whereby a large number of single-stranded DNA sub-units (oligonucleotides) are synthesized in parallel and later assembled in longer constructs. Using light-directed synthesis of the oligonucleotides, hundred of thousands of different short sequences (40-70b) can be created in a few hours.

After amplification, these sequences can be assembled in longer units in a hierarchical, multiple stages process. The final product – a synthetic gene – can then be used in a multiplicity of biological applications.

We will review the state of the art of the base-by-base DNA synthesis, with particular emphasis on chip-based methods, and discuss the problem of the errors found in the sequence of synthetic DNA. Many applications require error-free DNA, and this can be guaranteed only by sequencing the final product. Typically, samples extracted from the final product are cloned and sequenced, to find the correct one – an expensive and time consuming process. The number of clones to be sequenced is a strong function of the error rate in the DNA synthesis, so that a rate of less than 1 error per 10,000 bp is necessary to produce a viable process for the synthesis of 2,000 bp genes. We have recently proposed several error-removal methods that can improve the purity of synthesized materials, and produce error-free output material. To achieve this goal it is necessary to combine optimized micro-fabrication techniques in the synthesis and purification of the oligomers, with biological and statistical methods for error removal.

Mar. 22, 2006

"Single Spin Detection Using Magnetic Resonance Force Microscopy," Dr. Raffi Budakian, University of Illinois Urbana-Champaign, hosted by Eric Isaacs

Abstract: Magnetic resonance force microscopy (MRFM) is an emerging technique for direct nondestructive three-dimensional imaging with potential applications to imaging of individual molecules, buried interfaces, nanostructures and inhomogeneous solids. MRFM combines ultrasensitive force detection and magnetic resonance to manipulate and detect subsurface electron or nuclear spins with high sensitivity and spatial resolution.

Recently, we have used MRFM to image a single electron spin with 25-nm lateral resolution located as deep as 100 nm below the surface of a silica sample containing a low concentration of silicon dangling bonds. Achieving this high detection sensitivity has been due in part to a novel spin manipulation protocol that allows us to detect the statistical imbalance in small spin ensembles.

In addition to the detection of single electron spin, we have used this technique to follow the statistical fluctuations in a small ensemble of spins and apply real-time feedback to control the time evolution of the spin orientation. Through the use of feedback, we have demonstrated that spins can be hyperpolarized or "cooled" in the rotating frame of the measurement, transferred and stored in the lab frame and later read out. With modest improvement to the current detection signal-to-noise ratio, MRFM could be used to initialize and readout the quantum state of a single electron spin in real time.

Feb. 28, 2006

"Near-field Optical Scanning Microscopy and Magneto-Optics of Photonic Nanostructures," Alexander Mintairov, University of Notre Dame, hosted by Gary Wiederrecht

Abstract: Experiments that use a near-field scanning optical microscope operating at temperatures 5-300 K and magnetic field strength 0-10 T to study semiconductor quantum dots and photonic crystal structures are presented. The set of experiments includes utilization of nanoindentation to tune the emission properties of a single quantum dot, studying the emission mechanism of blue-green InGaN quantum dot structures, and probing confined optical modes in photonic crystal nanocavities.

Feb. 20, 2006

"Nanostructures with Controlled Shapes, Properties and Applications," Yugang Sun, University of Illinois at Urbana-Champaign, hosted by Derrick Mancini and Gary Wiederrecht

Abstract: This presentation summarizes a number of approaches for generating nanostructures with controlled shapes. "Bottom-up" approaches (e.g., polymer-mediated polyol process) provide route to the large-scale synthesis of silver nanostructures with various well-defined shapes. These silver nanostructures can serve as physical and/or chemical templates to generate core-shell (e.g., nanocables) and hollow structures (e.g., nanoboxes, nanocages, nanotubes, and nanorattles) through surface modifications and galvanic replacement reactions. On the other hand, semiconductor nanowires and ribbons have been fabricated from high-quality, single-crystal, bulk wafers through a "top-down" approach by combining photolithography and anisotropic chemical etching. These nanostructures have well-controlled shapes and exhibit unique properties compared to their bulk materials. In addition, preliminary results indicate they are promising candidates for applications in electronics, optoelectronics, clinical diagnosis, medical therapy, and energy storage/conversion.

Feb. 13, 2006

"Plasmons in Single Gold Nanorods: Ultrafast Nonlinearities and Optical Trapping," Matthew Pelton, University of Chicago, hosted by Gary Wiederrecht

Abstract: The development of functional plasmonic devices will require the ability to construct precisely arranged metallic nanostructures, as well as an understanding of the inherent linear and nonlinear optical properties of the individual elements in the structures. We have therefore measured for the first time nonlinear optical scattering from plasmons in single gold nanorods. Surprisingly, the measured ultrafast nonlinearity does not exhibit any coherent effect associated with plasmon oscillation, indicating a previously unobserved damping of strongly driven plasmons. As well, we have made progress towards constructing ordered arrays of gold nanorods, by optically trapping and orienting individual rods. The optical forces are enhanced by the nanoparticle plasmons, representing the first use of material resonances to trap particles in solution. This result also opens up the possibility of sensitive separation of metal nanoparticles according to their shape, and of three-dimensional plasmon-assisted microscopy in solution.

Feb. 13, 2006

"Directed Self-Assembly of Block Copolymer Blends into Nonregular Device-Orientated Structures," Mark P. Stoykovich, University of Wisconsin-Madison, hosted by Leonidas Ocola

Abstract: The future of many applications at the nanoscale rests upon the ability to produce well-defined patterns with nanometer precision. An emerging approach to nanofabrication is the integration of self-assembling materials into existing manufacturing strategies so as to simultaneously achieve molecular-level process control and the ability to produce useful architectures. Diblock copolymers are promising self-assembling materials that form ordered nanostructures, including spheres, cylinders, and lamellae, whose shape and dimensions depend on the molecular weight and composition of the polymer. Block copolymer lithography refers to the use of these ordered structures in thin films as templates for patterning through selective etching or deposition. Prior applications of block copolymer lithography have been limited to the fabrication of devices that do not require perfect structure ordering and that are formed of periodic arrays of structures, such as flash memory devices, magnetic storage media, silicon capacitors, and quantum dots. Our approach, in comparison, utilizes block copolymer lithography to achieve pattern perfection over macroscopic areas, dimensional control of features within exacting tolerances and margins, and registration and overlay with tailored interfacial interactions. In addition, we have demonstrated that by directing the assembly of blends of block copolymers and homopolymers on chemically nanopatterned substrates, it is possible to pattern nonregular device-oriented structures such as sharp bends. Mean field simulations indicate that the local redistribution of homopolymer within the blend domains greatly facilitates the formation of these nonregular geometries. In the short term, the technological implication of this hybrid top-down bottom-up technique is that the molecular control of structure dimensions afforded by self-assembling block copolymer materials may be harnessed for applications that require patterns significantly more complex than simple periodic arrays.

Feb. 6, 2006

"Ultrafast Meets Ultrasmall: Optically Driven Quantum Gates Based on Single Quantum Dots," Xiaoqin (Elaine) Li, University of Colorado at Boulder, hosted by Gary Wiederrecht

Abstract: Laser pulses as short as 10 femtosecond (10-15 s) have become a routinely available tool in many laboratories. Such laser pulses have a wide range of applications in machining, optical metrology, and probing fast dynamics in chemical, biological, and physical systems. Following a brief introduction of ultrafast science and technology, I will discuss the concept of quantum dots and their general applications. The dynamics of electrons confined in individual quantum dots can be probed directly by using short laser pulses. In addition, I will explain how to manipulate these localized electrons optically to build universal quantum logic gates, the building blocks of quantum computers.

Jan. 31, 2006

 

"Assembling n- and p-type PbSe Quantum Dot Superlattice FETs," Christopher B. Murray, Manager, Nanoscale Materials and Devices, IBM Watson Research Center, hosted by Xiao-Min Lin

 

Jan. 25, 2006

 

"Geometrically Confined Magnets," Kristen Buchanan, Materials Science Division, hosted by Stephen Streiffer

Abstract: Magnetic materials play an important role in a variety of modern devices, for example, computer hard drives, iPods, and electric motors. In general, the magnetic properties of ferromagnets can be understood in terms of competition among the magneto-crystalline, exchange, and magnetostatic energies due to long range dipole-dipole interactions. When the size of a magnet is reduced to the nanoscale, confinement alters the energetics and leads to new magnetic states, for example, vortices. Nanomagnets have great potential for enhancing existing technologies, such as magnetic storage media and magnetic sensors, and they may also find new applications in biomedicine and spintronics, an emerging field that exploits not only the charge of the electron but also its spin. Through advanced patterning and thin-film growth processes, model micromagnetic systems that demonstrate unique behavior in restricted geometries can be fabricated and investigated. My talk will discuss two related avenues of investigation: (1) static properties, in particular the magnetization reversal process in systems relevant to spintronic device design [e.g., layered F/N/F (giant magnetoresistive) and F/AF (exchange-biased) nanomagnets] and (2) spin dynamics, including our recent experimental detection of dynamic vortex interactions in patterned ferromagnetic ellipses. Understanding the static and the dynamic properties of nano-sized magnets is key for future device development.

Jan. 24, 2006

"Coaxing Nanoscale Material Systems to Build Themselves," Seth Darling, Glenn T. Seaborg Distinguished Postdoctoral Fellow, Materials Science Division, hosted by Stephen Streiffer

Abstract: Both top-down and bottom-up approaches to creating nanostructured materials suffer from inherent limitations. Only by combining both methodologies in the form of directed self-assembly can one achieve the full potential of nanotechnology. Lithographic guidance of the orientation of block copolymer domains illustrates the promise of this technique. The value of phase segregated block copolymers to nanoscience derives from the expedient tunability of the size, shape, and periodicity of their self-assembled domains by means of manipulating molecular characteristics. Thin polymer films, by themselves, have limited device applications, but myriad functions can be addressed with hybrid hard/soft matter systems in which the organic layer is used as a scaffold for the nanoscale organization of inorganic materials. This hierarchical approach to create ordered nanostructures removes the linear correlation of size and patterning time associated with traditional lithographic techniques by self-assembling the entire surface in parallel. Applications to magnetic storage media will be discussed in addition to a spectrum of future directions.

Jan. 20, 2006

"Spin-Dependent Transport in Nanoscale Systems," Yi Ji, CNM Distinguished Postdoc, Materials Science Division, hosted by Stephen Streiffer

Abstract: Spintronics is an emerging area of science and technology, where electron spins are utilized to realize new effects and process information. Very rich spintronic phenomena can be generated in nanoscale metallic heterostructures involving ferromagnetic (FM) and nonmagnetic (NM) metals. In this talk, I will describe two examples: nonlocal lateral spin valve and spin-transfer torque effects. A lateral spin valve consists of a NM nanowire connected with two FM electrodes, one as the spin injector and the other as the spin detector. The electrical spin injection is carried out in such a way that the spin current and the charge current are partially separated. A pure spin current without charge flow can be obtained and utilized for new spintronic effects. Spin-transfer torque is the inverse effect of giant magnetoresistance. A spin-polarized current, flowing through a FM/NM/FM trilayer, can transfer spin angular momentum from conduction electrons to the magnetization of the FM layers. The transferred spin angular momentum acts as a torque, and is able to switch the magnetization. We also demonstrated that spin-transfer torque can be generated in a single FM layer, an effect unexpected by the original theoretical prediction.

Jan. 10, 2006

"Plasmonic Materials for Surface-Enhanced Spectroscopy," Xiaoyu Zhang, Northwestern University, hosted by Gary Wiederrecht

Abstract: An update on the fabrication of size-tunable silver nanoparticles using nanosphere lithography (NSL) will be provided. Three examples of new NSL-derived materials will be described: (1) the application of electrochemistry to "fine tune" the structure of silver nanotriangles and the wavelength of its localized surface plasmon resonance (LSPR), (2) the growth of ultrathin protective layers on silver nanoparticles using atomic layer deposition (ALD), and (3) the fabrication of ordered arrays of in-plane, triangular cross-section nanowells with the aid of reactive ion etching (RIE). Furthermore, the highly tunable LSPR of these nanostructures have been explored to establish the first set of optimization conditions for surface-enhanced Raman spectroscopy (SERS). Finally, these optimization conditions have been applied to develop SERS-based sensors for two important target molecules: a Bacillus anthracis biomarker and glucose in a serum protein mixture.