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Center for Nanoscale Materials

CNM Seminar Series

The Center for Nanoscale Materials (CNM) hosts a seminar series to enhance multidisciplinary collaboration.

Date Title

November 9, 2018

11:00 am

Bldg. 440, A105/A106

Directed Self-assembly of Blue Phase Liquid Crystals by Chemically Patterned Surfaces, Xiao Li, Institute for Molecular Engineering, The University of Chicago.  Host:  Daniel Lopez. 

Liquid crystals (LCs) are a state matter intermediate between the solid and liquid phases. The unique properties of LCs, such as inherent ordering as liquid phase, optical anisotropy, the ability to response to an external field, make them be widely used for electronic displays, laser devices, photonics, biosensors, metastructures, etc. Fundamental understanding of the morphology and through-film optical properties of LC system, as well as precisely controlling the orientation of LC molecules towards contacting surfaces, are therefore play the central roles in device design and performance. In this seminar, I will present a generalizable platform based on anchoring contrast from chemically patterned surfaces to directed self-assemble (DSA) LC system. I will concentrate on chiral nematic system to expect more complex liquid crystalline morphologies and behaviors. More specifically, I will focus on blue phase liquid crystals (BPLCs), which exhibit ordered cubic arrangements of topological defects. The highly ordered morphology of BPs gives rise to unusual physical properties, such as Bragg reflection of visible light and fast optical response. However, polycrystalline structures limit their performance in applications. Chemically patterned surfaces are presented for the first time to obtain stable, lattice selective, macroscopic single-crystal BP materials. By studying the chemical pattern assisted heterogeneous crystal nucleation and growth process of BPs, the transformation between BPs is found to be martensitic in nature as the result of the collective behavior of the double- twist-cylinders. I will conclude by discussing some of the potential application of these materials, along with the questions and challenges remaining in the field.

November 2, 2018

11:00 am

Bldg. 440, A105/A106

Bioinspired Micro-Optics and Applications to Imaging Polarimetry, Stanley Pau, University of Arizona, Host: Daniel Lopez

Study of structural colors has led to optical filter designs using liquid crystal polymer that has microscopic structure similar to exoskeleton of many animals. The optical filters are utilized in novel multi-spectral and polarization cameras with applications in medical imaging, remote sensing, surveillance, and metrology.

October 24, 2018

2:00 pm

Bldg. 440, A105/A106

Realizing Resonant Optics with Quantum Electronic Transitions, Zongfu Yu, Department of Electrical and Computer Engineering, University of Wisconsin-Madison, Host:  Dafei Jin

Today’s optical devices are getting smaller and smaller to realize new functionalities and to reduce energy consumption. However, miniaturization becomes more difficult when the size falls below wavelength because of the lack of deep sub-wavelength electromagnetic resonance, an enabling effect for a wide range of applications, from radio-frequency communication, to silicon photonics, metamaterials and metasurfaces.        Quantum electronic transition has the potential to become a new platform to continue the miniaturization of classical optical devices. An electronic transition can resonantly absorb, scatter, and convert photon energy. It has the same scattering matrix as that of classical optical resonators in the single photon régime. Moreover, it has many advantages over classical ones: it is extremely compact, easily tunable by laser, magnetic or electric fields, and can be highly nonlinear.        In this talk, I will start by showing an intriguing function realized by extremely compact resonance. Then, I will discuss how electronic transitions could be used to realize classical functions such as antennas and metasurfaces. Then, I will discuss how electronic transition could rewrite some of the fundamental electromagnetic scattering law when combined with nontrivial topological charge found at Weyl points.

Biography: Zongfu Yu is the Dugald C. Jackson Assistant Professor in the department of electrical and computer engineering at the University of Wisconsin – Madison. His research interests include computational electromagnetics, optics, machine vision and sensing. He is a recipient of Stanford Postdoc Research Awards, DARPA Young Faculty Award (2017), and NSF CAREER Award (2018). He has authored and co-authored over 100 peer-reviewed papers with a total citation over 11,000 and an h-index of 44. He received his Ph.D. in applied physics and M.S. in management science and engineering, both from Stanford University, and a B.S. degree in physics from the University of Science and Technology of China.

October 15, 2018

10:00 am

Bldg. 440, A105/A106

Fine Pitch(<40μm) Integration Platform for Flexible Hybrid Electronics using Fan-Out Wafer-level Packaging, Amir Hanna, University of California Los Angeles

A flexible fan-out wafer-level packaging (FOWLP) process for heterogeneous integration of high performance dies in a flexible and biocompatible elastomeric package (FlexTrateTM) was used to assemble 625 dies with co-planarity and tilt <1µm, average die-shift of 3.28 µm with σ < 2.23 µm. Fine pitch Interconnects (40μm pad pitch) were defined using a novel corrugated topography to mitigate the buckling phenomenon of metal films deposited on elastomeric substrates. Corrugated interconnects were then used to interconnect 200 dies, and then tested for cyclic mechanical bending reliability and have shown less than 7% change in resistance after bending down to 1 mm radius for 1,000 cycles. Two application will be demonstrated: 1) A highly flexible (1 mm bending radius) 7 segment display using 42 high power InGaN LED dies integrated in a 50×40 mm package, and 2) A near field wireless implantable optogenetic implant system on an ultra-flexible (~5mm bending radius) package using commercially available dies showing power transfer efficiency > 15% @ 1cm transmit distance.

October 5, 2018

11:00 am

Bldg. 440, A105/A106

The Birth’, Aging’ and Life-Lengthening of Halide Perovskites, Yuanyuan (Alvin) Zhou, School of Engineering, Brown University.  Host:  Peijun Guo

Halide perovskites have recently emerged as a new family of semiconducting materials that are revolutionizing the field of photovoltaics. The rapid development of perovskite solar cells is being led by the advances in microstructural/compositional engineering of perovskite thin films. In this context, understanding the birth’ (crystallization) and death’ (degradation), and developing new methods for the life-lengthening’ (stabilization) of perovskites are becoming the most significant research directions.

In this talk, first, I will look at fundamental phenomena pertaining to nucleation & grain growth and grain-boundary evolution involved in the thin-film crystallization of perovskites from a materials-science perspective. Established scientific principles that govern these phenomena are invoked in the context of specific examples. Based on these fundamentals, our group have established a set of new synthetic strategies for scalable processing of high-performance large-area perovskite thin films and devices. Second, I will discuss the role of grain boundaries in the degradation processes of perovskites, and show our recent progress in the grain-boundary engineering for enhancing the perovskite stability. Finally, I will discuss the challenges and opportunities in the advanced characterization (e.g. in-situ/operando TEM) of perovskites for not only gaining a deep understanding of defects/microstructures, but also elucidating classical and non-classical phenomena pertaining to the crystallization, degradation, and stabilization of perovskites. The overall goal is to gain a deterministic control over the perovskite thin films with engineered microstructures/compositions for efficient perovskite solar cells that are also highly durable under heat/moisture/light stresses.

Biography: Yuanyuan (Alvin) Zhou is an Assistant Professor (Research) in the School of Engineering at Brown University since June 2016. He received his Ph.D. in Engineering from Brown University in June 2016. He holds a B.S. in Materials Science and Engineering from Xi’an Jiaotong University, and dual M.S. degrees in Materials Science and Engineering from Xi’an Jiaotong University and Chemistry from Korea Research Institute of Chemical Technology. Dr. Zhou’s research focuses on probing the composition-microstructure-property-performance relationships of new-generation functional inorganic materials for energy harvesting, storage and conversion. His research has been funded by NSF, ONR, DURIP and other agencies. He has published 56 journal papers with ~2500 Google citations and 25 H-index.

September 18, 2018

11:00 am

Bldg. 440, A105/A106

Tribochemistry: Shear-Induced Reaction Pathways Explored via Reactive Atomistic Simulation, Ashlie Martini, University of California Merced. Host: Ani Sumant

Low friction in lubricated mechanical components is in part enabled by protective films that form in sliding interfaces during operation. These films, called tribofilms, are formed through chemical reactions between additive molecules in the lubricant and the surfaces, where the reactions are driven by mechanical force exerted by the sliding bodies. Despite the presence of tribofilms in most moving components, the mechanisms of film formation are still poorly understood, primarily because the process occurs inside a moving contact and so cannot be directly interrogated experimentally. Experimental approaches are typically limited to pre- and post-sliding surface analyses. An alternative approach, and one we apply here, is using molecular dynamics simulations to explicitly model the additive molecules and surfaces at the atomic scale. Specifically, we use a reactive force field so the simulation can capture the formation and breaking of covalent bonds that are necessarily part of the tribofilm formation process. We study model systems, including gas phase lubrication of silica surfaces and nanoscale friction at graphene step edges, that can both be explicitly captured in the simulations and for which complementary experiments can be performed to provide partial validation of simulations. Once validated, the atom-scale detail available in the simulations is analyzed to identify the critically important role of shear in the tribofilm formation process. The results indicate that shear not only accelerates reactions but also alters the reaction pathways, enabling the formation of a tribofilm even under relatively low temperature conditions. In general, these findings may form the basis for the design of new boundary lubrication additives based on a better understanding of the tribofilm formation processes.

August 28, 2018

1:30 pm

Bldg. 440, A105/A106

Phonon and Electron Transport Properties of Defected Nanostructured Semiconductors: An Overview, Sanghamitra Neogi, University of Colorado Boulder, Host:  Subramanian Sankaranarayanan

Quantized vibrations in condensed phases, phonons, obey the laws of quantum mechanics in the same way as electrons and photons, that are commonly exploited as energy and/or information carriers. Efforts to control phonons, especially at micro- and nanoscale, have been stimulated by the ever increasing roles that phonons assume via self-interaction and interacting with electrons and photons. Phonon engineering has seen rapid progress through understanding of structure-processing-property relationships that connect nanoscale structures, dictated by methods of fabrication and processing, and vibrational and thermal transport properties. However, a broad range of phonon frequencies needs to be engineered, in contrast with electronic applications, where only energies close to the Fermi level are relevant. The difficulty of working with a broad spectrum of excitations naturally poses major challenges in achieving control over nanoscale phonon transport. Engineered nanoscale features offer remarkable possibilities to manipulate phonons in nanostructures. My research program at CU boulder is focused around the central theme-to tune phonons and their interactions with other quantum particles via engineering of nanostructured materials-in order to enable a broad range of technological applications. However, introduction of structural features impacts the transport of other quantum particles due to increased scattering. Our aim is to devise phonon engineering strategies to produce desired transport of quantum particles in nanostructured materials. In this seminar, I will present an overview of the research activities in my group, in particular, phonon and electron transport in multilayered Si/Ge nanostructures with defected interfaces, electronphonon scattering rates in superlattices, guiding phonons in nanostructured membranes though introduction of local resonances, and statistical/machine learning modeling and prediction of charge transport in multilayered semiconductors.

August 3, 2018

1:30 pm

Bldg. 440, A105/A106

Two-Dimensional Materials under Optical Probes, Shengxi Huang, Host:  Dafei Jin

Two-dimensional (2D) materials have gained increasing attention due to their unique and extraordinary electronic and photonic properties. The realization of the optoelectronic applications of 2D materials still faces several challenges. For example, it is critical to gain clear understandings of (1) the fundamental light-matter interactions in 2D materials, which govern many of the key material properties and are critical for device applications, and (2) the coupling of 2D materials with other nanostructures, which is a required structure for 2D devices and systems. This talk introduces new discoveries and pioneer works using optical spectroscopy techniques on these critical challenges, and novel applications of 2D materials in sensing. The first part of this talk presents the essential properties of 2D materials investigated using spectroscopy, including interlayer coupling of twisted bilayer MoS2 and few-layer black phosphorus, as well as anisotropic light-matter interactions of 2D materials with in-plane anisotropy. The second part of this talk focuses on the interaction of 2D materials with other nanostructures and the related applications. The interactions of 2D materials and selected organic molecules revealed novel enhancement effect of Raman signals for molecules on graphene surface, which offers a new paradigm in chemical and bio sensing. The works presented in this talk are significant in fundamental nanosciences, and offer important guidelines for practical applications of 2D materials in optoelectronics and sensing. The methodologies used here also provide a framework for the future study of many new 2D materials.

July 30, 2018

11:00 am

Bldg. 440, A105/A106

Diffraction and Microscopy with Attosecond Electron Pulses, Yuya Morimoto, Ludwig-Maximillians-Univeristat Munchen-Germany,  Host: Ilke Arslan

Light-matter interaction starts with the motion of charges driven by oscillating light cycles. A full visualization of such electronic motions requires attosecond temporal resolution and nano/atomic-scale spatial resolution. In this presentation, I will introduce attosecond electron microscopy and diffraction [1], which enable the space-time recording of the sub-optical-cycle dynamics. We obtain attosecond electron pulses by temporally modulating a mono-energetic 70 keV electron beam by cycles of a near infrared (1030 nm) laser beam impinged on a dielectric membrane [1,2]. By two proof-of- principle experiments, we show that the attosecond electron pulses are suitable for atomic-scale diffraction and sub-cycle microscopy applications [1]. First, we report Bragg diffraction from a single-crystalline silicon membrane with a signal-to-noise ratio sufficient for time-resolved diffractive imaging. Second, we visualize in real space the oscillating electromagnetic field vectors of an optical wave at a membrane. Our achievements unify the atomic imaging capability of sub-relativistic electron beams with the sub- cycle resolution of attosecond science.

 
References
[1] Y. Morimoto and P. Baum, Nat. Phys. 14, 252 (2018).
[2] Y. Morimoto and P. Baum, Phys. Rev. A 97, 033815 (2018).

July 24, 2018
 
2:00 pm
 
Bldg. 440, A105/A106

Designing and Studying Perovskite Materials for a Renewable Energy Future, Clemens Burda, Department of Chemistry, Case Western Reserve University.  Host:  Tijana Rajh

Over the past decade research in the group of Prof. Burda has focused on the idea to design nanostructured materials with targeted optoelectronic properties. The overarching criterion is that nanoscale materials and interfaces can enhance specific physical properties in ceramics, semiconductors, and metals. In this talk, the synthesis and related excitonic properties of methylammonium lead halide perovskites and their mixed halides are presented with a focus on time-resolved photoluminescence and transient absorption spectroscopy. The substitution of a fraction of bromide with chloride anions leads to a distorted unit cell due to the smaller radius of the chloride anion relative to the bromide ion and thus to decreased symmetry and an increased band gap. Femtosecond laser-induced transient absorption and photoluminescence measurements show that defects contribute to the relaxation processes in photoexcited perovskites. In addition, under two-photon excitation, longer excited state lifetimes could be assigned to the lowest exciton with surprisingly different properties compared to the one-photon created states. Origins and implications of these materials properties will be discussed.

July 23, 2018

11:00 am

Bldg. 440, A105/A106

Engineering of Iron Oxide Nanoparticles for Magnetic Particle Imaging Guided-Hyperthermia (hMPI), Anna C. Samia Department of Chemistry, Case Western Reserve University.  Host:  Tijana Rajh

Iron oxide nanoparticles (IONPs) are investigated due to their chemical tunability and great potential as diagnostic and therapeutic agents. In magnetic particle imaging (MPI), which is an emerging imaging modality that enables the direct mapping of IONP tracers, the signal generation relies heavily on the magnetization reversal of the IONP tracers. As such, it is essential to tune the IONP’s magnetic properties in order to achieve good MPI image resolution. To date, most studies have focused in optimizing spherical magnetite IONPs in MPI applications. In this presentation, a systematic investigation of the effects of chemical doping and shape anisotropy on the MPI performance of IONP tracers will be discussed. Moreover, the demonstration of focused hyperthermia through an MPI-guided approach (hMPI) will be presented. 

July 19, 2018

11:00 am

Bldg. 440, A105/A106

Atomic layer deposition for the synthesis and integration of 2D materials for nanoelectronics and catalysis,  Ageeth Bol, Department of Applied Physics, Eindhoven University of Technology, The Netherlands. Host:  Daniel Lopez
 
Graphene and other layered 2D materials have been the focus of intense research in the last decade due to their unique physical and chemical properties. This presentation will highlight our recent progress on the synthesis and integration of 2D materials for nanoelectronics and catalysis applications using atomic layer deposition (ALD). ALD is a chemical process that is based on self-limiting surface reactions and results in ultrathin films, with sub-nm control over the thickness and wafer-scale uniformity. In the first part of this presentation I will focus on the fabrication of low resistance contacts and ultrathin dielectrics to graphene using atomic layer deposition. In the second part I will show how we use plasma enhanced-ALD to synthesize large-area 2D transition metal dichalcogenides with tuneable functionalities for nanoelectronic and catalysis applications.
 

July 18, 2018

UPDATE: 1:30pm

Bldg. 440, A105/A106

The Nanophone: Sensing Sound with Nanoscale Spider Silk, Jian Zhou, Binghamton University.  Host:  Daniel Lopez

Hundreds of millions of years of evolution resulted in hair-based flow sensors in terrestrial arthropods that stand out among the most sensitive biological sensors known. These tiny sensory hairs can move with a velocity close to that of the surrounding air at frequencies near their mechanical resonance, in spite of the low viscosity and low density of air. No man-made technology to date demonstrates comparable efficiency. Here we show that nanoscale spider silk captures fluctuating airflow with maximum physical efficiency (Vsilk / Vair≈1) from 1 Hz to 50 kHz, providing an effective means for miniaturized flow sensing. Our mathematical model shows excellent agreement with experimental results for silk with various diameters: 500 nm, 1.6 µm, 3 µm. When a fiber is sufficiently thin, it can move with the medium flow perfectly due to the domination of forces applied to it by the medium over those associated with its mechanical properties. While traditional dynamic sensors trade sensitivity for bandwidth – or vice versa, the proposed approach enables the sensitivity of an ideal vibrational sensor without succumbing to the usual bandwidth limitations. By modifying a spider silk to be conductive and transducing its motion using electromagnetic induction, we demonstrate a miniature, directional, broadband, passive, low cost approach to detect fluctuating airflow with almost full fidelity over a frequency bandwidth that easily spans the full range of human hearing, as well as other mammals, birds, amphibians, and reptiles.

July 16, 2018

1:30 pm

Bldg. 440, A105/A106

The Topological Kondo Insulator SmB6: Surface States and Bulk Spin Excitions: Plus…   Laura G. Greene, National MagLab, Florida State University, and Center for Emergent Superconductivity.  Host Daniel Lopez

Samarium hexaboride (SmB6), a well-known Kondo insulator in which the insulating behavior of the bulk arises from strong electron correlations, has recently attracted great attention owing to its possible topological nature. Although there is strong evidence for this, corroborative spectroscopic evidence was lacking; unlike in the weakly correlated counterparts, e.g., Bi2Se3. Our planar tunneling spectroscopy results reveal the linear density of states (DOS) as expected for Dirac cones. The energy and temperature dependence indicate that the topological surface states are not protected above a certain temperature and energy range, and we invoke an inelastic tunneling model involving spin excitons [2.3] that accounts for the observed behavior.

[1] W.K. Park et al., Topological surface states interacting with bulk excitons in the Kondo insulator SmB6 revealed via planar tunneling spectroscopy” PNAS 113, 6599 (2016).
[2] W.T. Fuhrman et al., Interaction driven subgap spin exciton in the Kondo insulator SmB6” Phys. Rev. Lett. 114, 036401 (2015).
[3] G.A. Kapilevich et al. Incomplete protection of the surface Weyl cones of the Kondo insulator SmB6: Spin exciton scattering” Phys. Rev. B 92, 085133 (2015).
 
After this semi-informal talk, we may have informal discussions on any of these topics.
    (PCS = Point Contact Spectroscopy; PTS = Planar Tunneling Spectroscopy)
    Fe-based SCs: PCS detects DoS arising from nematicity, which is explained by orbital fluctuations.
    URu2Si2:        PCS shows hybridization gap is not the hidden order, and more.
    CeCoIn5:       Old PCS work first showing background is a Fano lineshape
 
                Preliminary, undigested PTS work, showing a field-induced pseudogap.

June 21, 2018

1:30pm

Bldg. 440, A105/A106

Engineering the polymer packing structure for intrinsically stretchable electronics, Jie Xu, Stanford University.  Hosts:  Tijana Rajh and Seth Darling.

In the rapidly growing interdisciplinary area of human-integrated and biomimetic electronics, by imparting skin-like mechanical properties (i.e. softness and stretchability) onto electronics, many new functionalities could be achieved. A first step towards this is the development of stretchable electronic materials, especially semiconducting materials. In this talk, I will introduce how we can engineer the polymer packing structure to realize high performance stretchable semiconductors. First, I will talk about the fundamental study of the polymer packing structure and dynamic mobility of nanoconfined soft matter. As an inspiration from this study, I will then move on to the development of a physical approach based on nanoconfinement effect for achieving the first highly stretchable and high-performance semiconductors, which have been further utilized to develop intrinsically stretchable integrated circuits. Further on, I will talk about the unique combination of the nanoconfinement effect and the roll-to-roll printing for simultaneously achieving both enhanced dynamics and multiscale morphological order for conjugated polymers, which are therefore imparted with largely improved stretchability, as well as significantly enhanced electrical performance. At the end, I will talk about how strain deformations influence the polymer packing structures and electrical characteristics in a plasticizer-enabled stretchable semiconducting films.   

June 21, 2018

11:10 am

Bdlg. 402, Room A1100

Quantum Engineering of Superconducting Qubits, William D. Oliver, Department of Physics and Lincoln Laboratory, Massachusetts Institute of Technology.  Host:  Supratik Guha 

Superconducting qubits are coherent artificial atoms assembled from electrical circuit elements. Their lithographic scalability, compatibility with microwave control, and operability at nanosecond time scales all converge to make the superconducting qubit a highly attractive candidate for the constituent logical elements of a quantum information processor. Over the past decade, spectacular improvement in the manufacturing and control of these devices has moved superconducting qubits from the realm of scientific curiosity to the threshold of technical reality. In this talk, we review this progress and our own work at MIT that are creating a future of engineered quantum systems.

June 15, 2018

11:00 am

Bldg. 440, Room A105/A106

The Full Field Diffraction X-ray Microscope on the ID01 beamline ESRF, Tao Zhou, European Synchrotron Radiation Facility (ESRF), Host: Martin Holt.

With the advent of high quality x-ray optics, several techniques have been proposed to exploit the imaging under Bragg conditions at synchrotron sources. Within the framework of the ESRF upgrade, a new dedicated instrument has been implemented on beamline ID01 at The European Synchrotron (ESRF). Since April 2017 this instrument is fully operational and has supplied users with Full Field Diffraction X-ray Microscopy (FFDXM) imaging adapted to various sample environments. Compared to more established scanning diffraction techniques, FFDXM offers fast, spatially resolved images on a large sample area without mechanical motions, perfectly suited for in situ and operando experiments.

The concept of FFDXM will be first demonstrated. A set of objective lens is placed downstream the sample to make a dark field image of the diffracted beam. At 6.5 meters away, the illuminated sample area (Field of View : 200×200 μm^2) is magnified and spatially resolved on a sCMOS camera with a resolution of 100 nm. Essentially an x-ray strain microscope, the FFDXM is capable of probing lattice tilt, strain and grain orientation at surfaces, buried interfaces or inside functioning devices, which is often unreachable for electron microscopy techniques.
Results of several user and in house experiments will be given next, to illustrate the principle of diffraction topography (strained STO), mosaicity (InGaN nano-pyramids) and strain (buried gas cavities in implanted Si wafers) mapping using FFDXM. Typical image acquisition time is around 1 sec; a complete set of measurement takes just a few minutes.
 
Based on these measurement techniques, more complex experiments were conducted. The final part of the talk shall cover preliminary results and outlook from the most recent developments of the microscope, including in situ heating and cryogenic cooling, operando chemistry, sub-ns time resolved and composition sensitive imaging.

June 14, 2018

11:00 am

Bldg. 440, Room A105/A106

Time-Resolved TEM Studies of Nonreversible Processes, Thomas Gage, Chemical Engineering & Materials Science, University of Minnesota.  Host: Ilke Arslan 

Time-resolved in situ TEM studies can offer exclusive insight into dynamic material processes.  High spatial resolution and the ability to perform correlative diffraction and real-space imaging studies make TEM unique as a characterization tool.  While pump-probe techniques can offer picosecond temporal resolution with TEM, they are limited to studying highly reversible processes.  Nonreversible processes, such as crystallization, require all transformation information to be acquired at the rate the phenomenon of interest occurs.  In this talk, I will discuss the unique in situ TEM capabilities we have at the University of Minnesota for studying nonreversible processes. I will focus on the example of laser annealing amorphous yttrium iron garnet films on non-garnet substrates.  The in situ TEM crystallization studies were performed using a high speed camera which is limited to millisecond resolution.  To further push the temporal resolution of in situ TEM studies with our setup, single shot TEM capability in a lightly modified TEM with a small LaB6 cathode was also explored. 

June 11, 2018

1:30 pm

Bldg. 440, Room A105/A106

Fluctuations and nonlinearity in a micromechanical thermal self-oscillator, James Lehto Miller, Kenny Micro Structures & Sensors Lab, Stanford University.  Host:  Daniel Lopez

Microelectromechanical (MEM) resonators are widely used as resonant sensors and oscillators in several areas of science and technology. Present MEM oscillators utilize an external feedback to sustain oscillations. In this presentation, I will discuss a MEM autonomous oscillator whose feedback is mediated by a direct current via the thermal-piezoresistive pumping mechanism. In contrast to traditional oscillators, this self-oscillator operates in its nonlinear régime, where the amplitude is self-limited by nonlinear stiffening and damping. We also study the thermomechanical noise spectrum of our device near the onset for self-oscillations, where we observe non-Lorentzian spectral broadening analogous to the onset of lasing or the ferromagnetic phase transition.

June 8, 2018

11:00 am

Bldg. 440, Room A105/A106

Imaging of Local Structure and Dynamics in Hard and Soft Condensed Matter Systems, Dmitry Karpov, New Mexico State University.  Host:  Martin Holt

With advancement of coherent probes there is a shift from integral studies to highly localized studies in either spatial or temporal domains. Nanostructures and low dimensional phenomena, correlated fluctuations and associated transitions directly benefit from new instrumental capabilities. Studies of ferroelectric and magnetic materials and of their local behavior allow both to test fundamental physics concepts and provide access to technologies with direct practical applications.

Topological phase transitions and topological defects are among the topics that are actively pursued in modern materials science. In recent study [1] conducted by our group we were able to visualize three-dimensional topological vortex structure in a volume of individual ferroelectric nanoparticle of barium titanate under external electric field using Bragg coherent diffractive imaging technique. Among other things we observed: (i) electric field induced structural transition from mixture of tetragonal and monoclinic phases to dominant monoclinic phase; (ii) controllable switching of vortex chirality; (iii) vortex mediated behavior of the nano-domains in the particle; (iv) and that the core of the vortex in the volume behaves as a nanorod of zero ferroelectric polarization which can be rotated by external electric field and can serve as a conducting channel for charge carriers. These findings can be used in the design of novel nanoelectronics devices and for creating artificial states of matter.
 
Better understanding of the materials behavior at the nanoscale requires ways of probing anisotropies of the refractive index. Using polarized laser light, we’ve developed a method [2] termed birefringent coherent diffractive imaging that allows to extract projections of dielectric permittivity tensor in nematic liquid crystal. Further expanding this tool into full-vectorial mode shows that the method can be applied for imaging of magnetic domains, cellular structures, and other samples with different forms of optical anisotropies such as birefringence, depolarization and dichroism. We expect broader impact when the technique is transferred to X-ray régime both from increase in resolution and penetration depth, and from the sensitivity of polarized X-rays to local atomic and ionic displacements and topological chirality.
 
[1] D. Karpov, Z. Liu, T. dos Santos Rolo, R. Harder, P.V. Balachandran, D. Xue, T. Lookman, E. Fohtung, Three-dimensional imaging of vortex structure in a ferroelectric nanoparticle driven by an electric field. Nature Comm. 8 (2017);
 
[2] D. Karpov, T. dos Santos Rolo, H. Rich, Yu. Kryuchkov, B. Kiefer, E. Fohtung, Birefringent coherent diffraction imaging. Proc. of SPIE Vol. 9931 (2016).

June 6, 2018

11:00 am

Bldg. 440, Room A105/A106

Advancing nanoscale materials through the development of coherent x-ray nanobeam scattering techniques, Anastasios Pateras, Department of Materials Science & Engineering, University of Wisconsin-Madison.  Host:  Martin Holt. 

Materials properties dramatically depend on their nanoscale structure. Tightly focused coherent x-ray nanobeams can reveal the atomic structure of crystalline thin films and heterostructures through strain-imaging approaches that solve the phase problem of x-ray crystallography with the use of iterative algorithms. While current modeling approaches are widely based on the kinematical theory of x-ray diffraction are limited to investigating thin layers with thicknesses below the x-ray extinction depth. By considering primary extinction and multiple scattering in the interaction of x-rays with crystals, state-of-the-art strain imaging techniques can be extended to incorporate dynamical diffraction directly inside a phase retrieval algorithm. This opens new opportunities for using coherent x-ray nanobeams for the structural investigation of quantum and energy materials systems that could not be thought before.

April 25, 2018

11:00 am

Bldg. 440, Room A105/A106

Coherent X-ray surface scattering imaging with high-resolution and ptychography, Joon Woo Kim, XSD, ANL, Host:  Martin Holt. 

Lensless coherent diffraction imaging (CDI) has enabled the structure determination of nanomaterials leading to significant scientific discoveries in the field of Materials Science. Coherent surface scattering imaging, which is reflection mode CDI with a grazing incident angle, can image thin nanostructures grown on an opaque substrate, of which the traditional CDI employing transmission or Bragg diffraction geometry is incapable. Since the first demonstration of coherent surface scattering imaging, the efforts have been made to improve spatial resolution with high flux x-ray and to overcome narrow isolated specimen limitations by employing ptychography. I’ll also discuss x-ray radiation pressure effects on nanocrystals during data collection process in Bragg CDI and formation mechanism of five-fold multiply twinned nanoparticle revealed by Bragg CDI.

April 20, 2018

2:00 pm

Bldg. 440, Room A105/A106

Investigating host-guest interactions in two dimensional supramolecular networks, Thomas A. Jung, Paul Scherrer Institute and University of Basel, Switzerland.  Host: Saw Wai Hla

 

Future quantum technologies, for example, rely on the detailed understanding of the interaction between different well-defined electronic states. Surface supported atomic and molecular systems provide a base for such investigations with the particular advantage of addressability. In our work we establish on-surface architectures which exhibit extraordinary local e.g. electronic, magnetic and quantum properties originating from the reduced dimensionality of the self-assembled and atomically precise architectures. Quantum well arrays, for example, can be produced by the interaction of porous on-surface networks with 2D Shockley-type surface states. Interestingly the periodicity of these (lossy) confinements causes band formation by the coupling between the individual quantum well [1]. In our more recent work the quantum wells have been modified by the adsorption / condensation of Xe atoms [2,3]. Localized and delocalized electronic states can be identified across the 2D array as they lead to new, site-specific physical and chemical behavior.

 

Sublattices in 2D checkerboard’ architectures of magnetic molecules on magnetic substrates can be selectively switched by chemical ligation [4]. Also we have observed the first example of 2D ferrimagnetic long-range order and remanence for such a 2D architecture on non-magnetic Au(110) [5]. Uniquely, self-assembled 2D architectures contribute to our understanding of fundamental interactions involved in host-guest systems and allow for the specific operation of quantum states with a partial delocalization delocalized by the supramolecular on-surface architecture.
 
[1] Lobo-Checa, J. et al., Science 325:300 (2009)
[2] Nowakowska, S. et al., Nat. Commun. 6:6071 (2015)
[3] Nowakowska, S. et al., Small 12:3757 (2016)
[4] Ballav N., et al., JPCL 4:2303 (2013)
[5] Girovsky, J. et al., Nat. Commun., DOI: 10.1038/ncomms15388 (2017).
 

April 20, 2018

11:00 am

Bldg. 400, Conf. Rm A105/A106

Data Driven 4-D X-ray Imaging of Nanoscale Dynamics, Mathew J. Cherukara, Advanced Photon Source, Argonne National Laboratory.  Host:  Martin Holt

Observing the dynamic behavior of materials following ultra-fast excitation can reveal insights into the response of materials under non-equilibrium conditions of pressure, temperature and deformation. Such insights into materials response under non-equilibrium is essential to design novel materials for catalysis, low-dimensional heat management, piezoelectrics, and other energy applications. However, material response under such conditions is challenging to characterize especially at the nano to mesoscopic spatiotemporal scales. Time-resolved coherent diffraction imaging (CDI) is a unique technique that enables three-dimensional imaging of lattice structure and strain on sub-ns timescales. In such a pump-probe’ technique, stroboscopic x-ray probes’ are used to image the transient response of a sample following its excitation by a laser pump’. In this talk I will present some of our recent work on imaging and modeling of phonon transport and lattice dynamics in nanomaterials. I will also describe my work in the use of deep neural networks in accelerating the analysis of and increasing the robustness of image recovery from 3D X-ray diffraction data. Once trained, our deep neural networks are thousands of times faster than traditional phase retrieval algorithms used for image reconstruction from 3D diffraction data.

April 16, 2018

11:30 am

Bldg. 440, Conf. Rm A105/A106

Geometric Charges and Kirigami,  Michael Moshe, Host:  Daniel Lopez

Kirigami patterns generate non-trivial three dimensional behavior from perforated sheets, and so offer a promising means for developing mechanical metamaterials. To create a generic account of the mechanical behavior of kirigami, we study the unit cell of a typical kirigami structure: an isolated frame. The mechanical behavior of the entire sheet may then be understood in terms of the coupling of many individual frames.

Recent developments in a geometric formulation of elasticity theory paved the way for a mathematical description of such isolated frames using the concept of geometric charges”. In this approach the mechanical problem of Kirigami and coupled frames is transformed to a simpler problem of interacting geometric charges.
 
In this talk I will present experimental and theoretical results on the relation between Kirigami, the geometric approach to elasticity, and geometric charges. I will show how these results provide  simple rules for designing nontrivial Kirigami patterns.

April 2, 2018

11:00 am

Bldg. 440, Conf. Rm A105/A106

X-ray Studies of the Structure and Properties of Materials During Synthesis and Processing, Matt Highland,  Materials Science Division,  Argonne National Laboratory.  Host:  Martin Holt
 
The properties and functionality of a material depends on its structure as well as its interactions with other materials and its environment. Understanding the nature of these interactions will allows use to create new models and define new methodologies for making materials with desired properties. Gaining this understanding requires experimental techniques that allow us to probe the local structure, phase, and strain of a material system during synthesis and processing, within a larger structure, or under excitation. A variety of x-ray techniques are available to address these challenges. I will describe experiments in which we have used a number of these techniques to probe materials during synthesis, high temperature processing, and ultra-fast excitation. I will discuss how this work provides insight into roles that microstructure and local strain fields play in defining the properties of a material and describe a number of projects motivated by these studies.

March 29, 2018

11:00 am

Bldg. 440, Conf. Rm. A105/A106

Quantum Ordering and Mesoscale Dynamics Unraveled by Focused Coherent X-ray Beams, Qingteng Zhang, XSD, ANL. Host: Martin Holt
 
An ongoing scientific thrust is pushing forward a deeper understanding of the rich correlation between electronic, spin, orbital orderings and atomic lattice in quantum materials. A recent study at the Hard X-ray Nanoprobe (HXN) in Center for Nanoscale Materials (CNM) has shown that quantum ordering can be enhanced in patterned nanostructures [1], providing new venues for the manipulation of quantum structures and exciting opportunities for the design and engineering of functional nanomaterials. One of the science cases is ferroelectric nanodomains in thin atomic layers of complex oxides. Ferroelectric polarization in epitaxial nominal atomic layers often forms into striped nanodomains to minimize the total electrostatic energy of the system. Domain walls provide versatile control of thin film properties because domains are easily reconfigurable and intriguing properties arise at domain walls due to the very large atomic strain caused by abrupt change of polarization direction. In a 100 nm thick PbTiO3/SrTiO3 superlattice, the electric coupling between the ferroelectric PbTiO3 layers is tuned by the SrTiO3 layers and results in nm-periodicity domains with serpentine striped patterns commonly observed in spinodal decomposition systems. This seminar will show that the ferroelectric nanodomains can exhibit thermally-driven equilibrium dynamics [2] similar to the Brownian motions [3] and gelation-induced arrested dynamics of colloidal nanoparticles [4], albeit on a much slower timescale of thousands of seconds. The temperature dependence on the time scale of domain fluctuation can be described using Arrhenius equation yielding an activation energy of 0.35 ± 0.21 eV. This energy level corresponds to the average energy barrier height that separates energetically degenerate domain configurations and implies that the formation and fluctuation of nanodomains may be affected by pinning mechanisms such as oxygen ion vacancies.
 
The seminar will also discuss possible prospective areas of research at the HXN, including a systematic investigation on the size-dependence of quantum orderings in patterned nanostructures which plans to leverage the resources of CNM, and speckle analysis using pattern recognition and deep learning which plans to leverage the computing resources at ALCF.
 
 
References:
[1]. J. Park, J. Mangeri, Q. Zhang et al. Nanoscale 10, 3262 (2018)
[2]. Q. Zhang et al. Phys. Rev. Lett. 118, 097601 (2017)
[3]. Q. Zhang et al. J. Synchrotron. Rad. 63, 679 (2016)
[4]. Q. Zhang et al. Phys. Rev. Lett. 119, 178006 (2017)
 

March 15, 2018

2:00 pm

Bldg. 440, Conf. Rm. A105/A106

Antimicrobial Photodynamic Therapy with Ga-Protoporphyrin Derivatives Against Pathogenic Bacteria, Ana Morales-de-Echegaray, Wei Research Lab, Department of Chemistry, Purdue University.  Host:  Tijana Rajh.

Bacterial pathogens have the ability to acquire hemin through different mechanisms. One mechanism is through cell-surface hemin receptors (CSHRs), which are capable of rapid hemin recognition and make the bacteria vulnerable to antimicrobial photodynamic inactivation (aPDI). The work presented here focuses on gallium protoporphyrin IX (GaPpIX) as a photosensitizer for aPDI against staphylococci. GaPpIX is rapidly uptaken into CSHR-expressing bacteria, and is easily detected within minutes of exposure. Assessment of GaPpIX as a photosensitizer against laboratory strains of Staphylococcus aureus, clinical isolates of methicillin-resistant S. aureus (MRSA), and S. epidermis shows aPDI activity at low micromolar levels, following 15 minutes of exposure to a compact fluorescent light bulb or at nanomolar levels when exposed for 10 seconds with a light emitting diode (LED) light source. Activity also had greater potency when compared against metal-free protoporphyrin (PpIX). These results led to the design of a more potent photosensitizer by incorporating GaPpIX into apohemoglobin (GaPpIXHb) and using the hybrid protein to coat 10-nm silver nanoparticles (AgNPs). The GaPpIXHb-AgNP complexes exhibit remarkable aPDI activity using nanomolar loadings of GaPpIX against clinical MRSA isolates.

March 1, 2018

11:00 am

Bldg. 440, Conf. Rm. A105/A106

Emergent Topology in Artificial Graphenes, Xiao Hu, International Center for Materials Nanoarchitectronics (WPI-MANA), National Institute for Materials Science (NIMS), Tsukuba, Japan.  Host: Ulrich Welp

 

Honeycomb lattice plays an important role in the course of fostering topology physics as known from the Haldane model and the Kane-Mele model [1]. Recently we formulate a new way to achieve topological states exploiting the C6v symmetry of honeycomb structure, which can be applied to various artificial graphenes with tremendous recent interests. As the first example we show how to realize topological electromagnetic transportations in dielectric photonic crystals, which has been proved by recent experiments [2,3,4]. This idea can also be applied to fermionic systems, and especially we find topological electronic states protected by huge energy gaps in order of eV in graphene with regular nano-hole arrays [5,6,7]. Our approach provides a new facet for exploration of novel topological phenomena and functionalities in terms of advanced nanotechnologies.

 References: [1] H.-M. Weng, R. Yu, X. Hu, X. Dai and Z. Fang: Adv. Phys. vol. 64, 227 (2015).  [2] L.-H. Wu and X. Hu: Phys.  Rev. Lett. vol. 114, 223901 (2015).  [3] Y.-T. Yang, J.-H. Jiang, X. Hu and Z.-H. Hang: arXiv.1610.07780.  [4] Y. Li, H. Chen and X. Hu et al.: arXiv:1801.04395.  [5] L.-H. Wu and X. Hu: Sci. Rep. vol. 6, 24347 (2016).  [6] T. Kariyado and X. Hu: Sci. Rep. vol. 7, 16515 (2017).  [7] T. Kariyado, Y.-C. Jiang, H.-X. Yang and X. Hu: arXiv:1801.03115.

Feb. 21, 2018

2:00 pm

Bldg. 440, Room A105/A106

Deep Learning Applied to Simulation of 2d Materials”, Isaac Tamblyn, Security and Discuptive Technologies, National Research Council of Canada. Host:  Pierre Darancet In this talk,

I’ll show how we are using Artificial intelligence as a new tool to improve computer models of physical and chemical processes at the nanoscale. In particular, I’ll discuss how we show how to rapidly solve the Schrödinger Equation [1], predict phase transitions [2], estimate the strength of chemical bonds [3], provide a confidence level for our predictions [4], and achieve a million times speed up in simulating a nanostructured 2d-material [5].

[1] K. Mills, M. Spanner, I. Tamblyn, Deep learning and the Schrödinger equation Phys. Rev. A 96, 042113 (2017), arXiv:1702.01361
 
[2] K. Mills, I. Tamblyn, Deep neural networks for direct, featureless learning through observation: the case of 2d spin models, arXiv:1706.09779
 
[3] K. Ryczko, K. Mills, I. Luchak, C. Homenick, I. Tamblyn, Convolutional neural networks for atomistic systems, arXiv:1706.09496 
 
[4] K. Mills, I. Tamblyn, Phase space sampling and operator confidence with generative adversarial networks, arXiv:1710.08053
 
[5] I. Luchak, K. Mills, K. Ryczko, A. Domurad, I. Tamblyn, Extensive deep neural networks, arXiv:1708.06686
 
 

Feb. 20, 2018

11:00 am

Bldg. 440, Room A105/A106

Scattering Studies of a Micron-sized Gold Particle and Average Nanoparticles”, Milan K. Sanyal,Saha Institute of Nuclear Physics Kolkata, West Bengal, India.  Host:  Martin Holt

Availability of intense synchrotron sources delivering nano-sized beam should be able to provide us structure, composition and strain profiles within a nanoparticle from averaged information obtained over only few such particles and finally may be even from an individual particle. We shall discuss here few evolving x-ray scattering techniques with the help of three recently studied systems, namely distribution of non-FCC phase in a micron-sized gold particle, shape-evolution in gold nanoparticles grown in nano-pores and extraction of compositional profile of an average III-V semiconductor quantum-dot - the size-tunable photonic material.

Feb. 13, 2018

10:30 am

Bldg. 440, Room A105/A106

Materials and Processing for Quantum Computing - Ion Traps and Superconductors”, David P. Pappas, National Institute of Standards and Technology, Boulder.  Host:  Ilke Arslan.

A brief description and history of quantum computing will be presented. Materials topics relevant to ion traps and superconductors will be presented. For the ion traps, the influence of anomalous surface noise on gate operations will discussed. Progress at NIST to study and mitigate these effects will be presented. These include cleaning, surface spectroscopy and scanned probe microscopy as well as a novel stylus trap to measure noise from proximal surfaces. In the second part of the talk similar topics on superconducting transmons will be discussed. In particular, the effects and mitigation techniques of spurious two-level systems at surfaces and interfaces as well as new scalable techniques for fabricating junctions will be presented.

Feb. 2, 2018

2:00 pm

Bldg. 440, Room A105/A106

Flexible Electronics Based on Two-Dimensional Materials and Beyond”, Xu Zhang, Massachusetts Instittue of Technology. Host:  Daniel Lopez

The success in creating atomically thin and mechanically robust two-dimensional (2D) materials has unveiled new possibilities for next generation of flexible and ubiquitous electronics. One critical distinction between 2D crystals and 3D crystals is that 2D crystals are all-surface materials. Therefore, it is essential to understand how 2D materials interact with their environments and how this interaction impacts their electronic properties. A suite of X-ray techniques is used to investigate how the functionalizing dopants impact the electronic and chemical states of graphene. Based on this study, we develop an effective and non-invasive doping method for graphene through plasma-based chlorination. In the second part of this talk, I will focus on system-level applications of 2D materials-based flexible electronics with a special focus on wireless energy harvesting and communication. In particular, we developed a 2D material-based GHz flexible rectifier as an enabling component for both wireless energy harvesting and RF frequency mixing. It is the first flexible rectifier operating up to the X-band and it fully covers the Wi-Fi channels. By integrating with an antenna, the MoS2-enabled rectenna successfully demonstrates direct energy harvesting of electromagnetic (EM) radiation in the Wi-Fi band and lights up a commercial light-emitting diode (LED) with zero external bias (battery-free).

Feb. 1, 2018

2:00 pm

Bldg. 440, Room A105/A106

Novel transport characterizations in anisotropic and disordered”, Lintao Peng, Northwestern University, Electrical Engineering and Computer Science.  Host:  Nathan Guisinger

New electrical transport techniques are introduced for characterization of exfoliated black phosphorous devices. First, an all-electrical conformal-5-contact method is proposed to determine the crystal orientation of an exfoliated flake. Second, the disorder-related switching transient conductivity, and a microscopic DOS model thereof, are discussed within the framework of dispersive diffusion transport and continuous time random walk. Finally, the observation of a disorder-scaling behavior in gate-dependent conductivity is presented and modeled.

Jan. 24, 2018

3:30 pm

Bldg. 440, Room A105/A106

Light- and heat-managing nanomaterials for personal health and energy efficience”, Po-Chun Hsu, Department of Mechanical Engineering, Stanford University.  Host:  Supratik Guha

Energy and health are the two vital necessities for humans. While energy is indispensable, it also produces greenhouse gas emission and climate change. In the US, 12% of total energy is used for maintaining indoor temperatures, which is the fundamental need for human health. Therefore, it is crucial to reduce the building energy consumption while maintaining thermal comfort. In this talk, I will present several nanomaterials that can manage photons and heat transfer to enhance building energy efficiency and personal health. The first part is the personal thermal management by controlling radiation heat transfer, which contributes 50% of the human body heat dissipation. I will demonstrate infrared-reflective nanowires textile for heating, infrared-transparent nanoporous polyethylene for cooling, and asymmetrical emitter to achieve both heating and cooling. The second part is transparent electrodes and electrochromic smart windows for solar heat gain modulation. Fabricated by electrospinning, the metal nanofiber transparent electrodes with superior electrical and optical properties and durability can improve the speed and cycle life of electrochromic windows.

Jan. 11, 2018

11:00 am

Bldg. 440, Room A105/A106

There’s Plenty of Room in Higher Dimensions - Internal Resonance and Decision Mechanisms in Mechanical Resonators”, Axel Eriksson, Chalmers University of Technology, Sweden.  Host:  David Czaplewski. 

To understand how adaptive behavior emerges in living and artificial systems is a major challenge for science. In this talk, I consider something simpler – dead vibrating silicon beams and graphene membranes. I will give a short introduction to nonlinear dynamics of vibrational modes in mechanical resonators. An interesting situation occurs when two vibrational modes have a rational relation between their frequencies – a so called internal resonance. The match in frequency allows for efficient transfer of energy between the two modes. Hence, the internal resonance will strongly affect both the dissipation and the driven response of the resonator. The complex response has similarities with other strongly nonlinear systems such as interacting neurons in the brain. Furthermore, the driven response may exhibit choice mechanisms leading to stochastic switching between different long-term behaviors. In future work, we plan to experimentally control this switching as a means to achieve primitive adaptive behavior in mechanical resonators.