December 16, 2015
11:00 am
Bldg. 440, A105-106

"Quantum Optics of Carbon Nanotubes," Xuedan Ma,Center for Integrated Nanotechnologies Los Alamos National Laboratory and Sandia National Laboratories. Hosted by Gary Wiederrecht

Because of their photoluminescence (PL) emission that spans over the 1.3 - 1.5 μm telecom spectral regime, individual semiconducting single-walled carbon nanotubes (SWCNTs) have been considered as ideal candidates for single photon sources that are critically needed for quantum information processing. However, spectral diffusion, which is often observed in PL spectra of SWCNTs, has been a major issue hampering their application. In this talk, I will first discuss our cryogenic and room temperature single tube PL studies which show that spectral diffusion of SWCNTs is closely related to exciton dimensionality. In further studies on the spectral diffusion behavior of SWCNTs coupled to metallic nanostructures, we find that surface plasmons can localize 1D excitons, therefore indicating possible applications in photon manipulation.

In the second part of this talk, I will discuss about room temperature single photon generation from doped SWCNTs. It has been discovered that low level covalent doping of SWCNTs with oxygen can introduce new bright emitting states promising for room temperature single photon generation. However, SWCNTs doped via prolong exposure to ozone in aqueous suspension typically show strong PL fluctuation and bleaching, making quantum optical experiments challenging. We have developed a novel solid-state doping approach in which undoped SWCNTs are incorporated into SiO₂ matrices by electron-beam deposition. With this method, we are able to create solitary oxygen dopant sites capable of fluctuation-free, room-temperature single photon emission. This finding presents exciting opportunities to the development of electrically driven single-photon sources and integration of these sources into quantum photonic networks.

December 14, 2015

11:00 am

Bldg. 440, A105-106

"Optoelectronic Spin Physics in Quantum Dots and 2D Materials," John R. Schaibley, University of Washington

Electronics is based on manipulating and storing charge in semiconductors and metals. In addition to charge, electrons also have a spin degree of freedom which can be used to store and process information. In this talk, I will discuss several approaches for manipulating spin in low dimensional solid state systems. In particular, I will discuss how spin-photon interfaces based on single quantum dots can be used to store and transfer quantum information, and how novel valley pseudospin degrees of freedom in 2D materials can be used to advance spin based device physics.

December 10, 2015

11:00 am

Bldg. 440, A105-106

"Identifying species in optically excited hematite thin films with transient absorption measurements spanning the near-IR to the hard X-ray regime," Dugan Hayes, Chemical Sciences and Engineering Division, Argonne National Laboratory

Hematite (alpha-Fe2O3) is a remarkably stable and inexpensive heterogeneous catalyst for photochemical and photoelectrochemical water splitting with absorption extending to the near-IR, but its utility is limited by poor hole mobility and an absorbed photon to current efficiency spectrum that drops to zero beyond 2 eV. Efforts to overcome these deficiencies through nanostructuring and doping would greatly benefit from a detailed understanding of the electronic transitions in hematite, but the assignment of the optical bands of this material remains hotly debated. I will present a series of transient absorption measurements of hematite thin films we have performed with excitation wavelengths spanning the optical spectrum with the goal of understanding the wavelength dependence of the photocatalytic activity. By probing the absorption from the near-IR to the hard X-ray regime, we have been able to observe the formation of electron small polarons following band gap excitation and identify similar structural distortions arising from ligand field transitions. Following these observations, we propose that a double-exchange mechanism present in hematite following band gap excitation accounts for the increase in photocurrent measured with blue and near-UV excitation under working conditions. I will also discuss our current effort to extend our ultrafast investigations of hematite and other transition metal oxides into the terahertz regime.

December 10, 2015

2:00 pm

Bldg. 440, A105-106

"Synthetic DNA Devices in Living Systems," Yamuna Krishnan, The University of Chicago, host Tijana Rajh

Due to its nanoscale dimensions and ability to self-assemble via specific base pairing, DNA is rapidly taking on a new aspect where it is finding use as a construction element for architecture on the nanoscale. Structural DNA nanotechnology has yielded architectures of exquisite complexity and functionality in vitro. However, till 2009, the functionality of such synthetic DNA-based devices in living organisms remained elusive. Work from my group has bridged this gap where, we have chosen architecturally simple, DNA-based molecular devices and shown functionality in complex living environments. Using an example from our lab, namely a molecular switch that functions as a fluorescent pH sensor I will illustrate the potential of DNA based molecular devices as unique tools with which to interrogate living systems. We are now exploring the full potential of DNA to create fluorescent sensors for a variety of second messengers and thereby quantitatively image protein activity within living cells and genetic model organisms.

December 8, 2015

11:00 am

Bldg. 440, A105-106

"Sculpting Photocatalysts on the Nano Scale," Lilac Amirov, Israel Institute of Technology, host Elena Shevchenko

The solar-driven photocatalytic splitting of water into hydrogen and oxygen is a potential source of clean and renewable fuels. However, four decades of global research have proven this multi-step reaction to be highly challenging. The design of effective artificial photo- catalytic systems will depend on our ability to correlate the photocatalyst structure, composition, and morphology with its activity.

Here, I will present our strategies, and most recent results, in taking photocatalyst production to new and unexplored frontiers. I will focus on unique design of innovative nano scale particles, which harness nano phenomena for improved activity, and methodologies for the construction of sophisticated heterostructures. I will demonstrate how vital is the ability to characterize our hybrid nanostructures on the atomic level, and how we can benefit from information on the structure-properties relationship for the future design of an efficient photocatalyst for solar-to-fuel energy conversion.

December 4, 2015

11:00 am

Bldg. 440, A105-106

Semiconductor optical waveguides have been the subject of intense study for over two decades due to the promise of unprecedented control of light in a monolithic photonic chip. In this talk I will focus on the nonlinear evolution of intense light pulses in these systems.

Specifically, I will describe experimental efforts utilizing time-resolved measurements to reveal a number of unique physical phenomena arising from the dynamic interaction of light and free carriers. These results are supported by analytic models providing a deeper insight into the physical scaling of these processes. Critically, the ability to independently tune the dispersion and the nonlinearity in a photonic crystal waveguide enables the examination of completely different nonlinear regimes simply by changing the input wavelength.

While the emphasis will be on the physics of nonlinear electro-magnetic waves propagating in an electron plasma, there will also be brief highlights of other nonlinear optical phenomena such as: integrated single photon sources, all-optical switching, and phase-sensitive amplification in silicon.

Looking forward, I describe my recent work developing a new class of hybrid ‘2D+3D’ materials to overcome traditional limitations of nanophotonics. Some example grand challenges will be shown.

November 20, 2015

11:00 am

Bldg. 440, A105-106

Plasmonics nanostructures are becoming remarkably important as tools towards manipulating photons at the nanoscale. They are poised to revolutionize a wide range of applications ranging from integrated optical circuits, photovoltaics, nano-antennas and biosensing.

They enable miniaturization of optical components beyond the “diffraction limit” as they convert optical radiation into highly confined electromagnetic near-fields in the vicinity of sub-wavelength metallic structures due to excitation of surface plasmons (SPs). But do these strong electromagnetic fields generated at the plasmonic “hot spots” raise exciting prospects in terms of driving nonlinear effects in active media?

I shall talk about the design, creation and experimental demonstration of novel hybrid plasmonic nanostructure geometries that combine active materials and nanometallics. Such hybrid nanostructures aim at modulation of light signals at the nanoscale. This not only provides tools for designing active plasmonic devices, but is also a means of re-examining existing conventional rules of light-matter interactions.

Details with respect to working prototypes of passive & active plasmonic devices designed to operate at telecom wavelengths will be presented. Also, insights into the fundamentals of enhanced light-matter interactions in hybrid subwavelength structures with extreme light concentration will be discussed based on ultrafast pump-probe spectroscopy results.

Moreover, I shall present my latest work on how to optically manipulate and arrange metal nanoparticles (MNPs) over large areas on dielectric surfaces, hence seeking to overcome fundamental challenges towards achieving lab- on-chip devices and integrated optical circuitry. I shall demonstrate techniques to achieve controlled deposition of metallic nanorods by tuning their precise alignment and by inducing coupling effects between them via a sortative fringe-based optical trap created by two-beam interferometry.

November 17, 2015

10:30 am

Bldg. 440, A105-106

"APS-U Frontier Experiments for Condensed Matter and Materials Physics," John W. Freeland, X-ray Science Division, Argonne National Laboratory

>The upgrade APS-U will deliver greatly enhanced X-ray coherence and the future experiments will harness this to deliver new insight into scientific problems. In this talk, I will address the gains to be made in area of condensed matter and materials physics, which is based upon the frontier experiments that we articulated in the APS-U first experiments document. The goal of this talk is to motivate discussions for developing the case for the new facilities needed to realize these scientific advances, which is directly connected with the newly released call for white papers for new APS beamlines.

"Nanophotonic Devices, Near-field Interactions, and Plasmonics at the Extreme Nanoscale," John Kohoutek, Northrop Grumman Corporation

This talk will provide an overview of several nanophotonic devices with special consideration given to behind-the-scenes near-field action. Electric field magnitude mapping, as well as optical gradient force and Casimir force measurement techniques, will be reviewed as they relate to the aforementioned devices. A form of extreme nanoplasmonics will be discussed, which includes the probing of surface plasmon resonances in a very small volume and the effect that changes to a very small volume have on a surface plasmon resonance at orders of magnitude greater length scales. Finally, some potential avenues for research related to applied nanophotonics and the study of MEMS will be proposed.

November 3, 2015

3:00 pm

Bldg. 440, A105-106

“Leveraging Advances in Computational Electrodynamics to Enable New Kinds of Nanophotonic Device Design”, Ardavan Oskooi, Simpetus

Advances in computational electrodynamics have the potential to enable fundamentally new kinds of designs in nanophotonic devices which are based principally on complex, non-analytical wave-interference effects. Powerful, flexible, open-source software tools have now been made available for use in large-scale, parallel computations to model the interaction of light with practically any kind of material in any arbitrary geometry. These recent developments in computational capability make possible the investigation of various emergent structures and physical phenomena that were previously beyond the reach of pencil-and-paper analytical methods as well as less versatile and even less accessible commercial software tools. Here, I demonstrate how such advances in finite-difference time-domain (FDTD) methods for computational electromagnetism via an open-source software package known as MEEP can lead to entirely new designs for light trapping in nanostructured thin-film silicon solar cells as well as light extraction from nanostructured organic light-emitting diodes (OLEDs).

In the last part of this seminar, I will provide a live demonstration of launching MEEP simulations on an on-demand high-performance computing (HPC) cluster in the cloud through our startup, Simpetus. Simpetus provides a holistic solution to the three main challenges of using simulations for research and development: 1) no software licenses or installation, 2) no hardware acquisition or maintenance and 3) technical support from the experts. The mission of Simpetus is to propel computational simulations to the forefront of photonics research and development.

"Delineating the Distinct Stages of Mycobacterial Biofilms," Anil Ojha, University of Pittsburgh

Mycobacteria represent a wide range of species, many of which can establish chronic and recalcitrant infections in humans. Tuberculosis, caused by Mycobacterium tuberculosis, is the most devastating mycobacterial pathogen, killing over one million people every year. Our earlier studies have found that mycobacterial species, including M. tuberculosis, can readily form drug-tolerant biofilms, which are genetically programmed assemblage of microbes on surfaces. Given the linkage between biofilm growth and drug tolerance behavior, questions about the genetic requirements for various developmental stages of mycobacterial biofilms open up the possibilities of discovering drug targets for shorter treatment of mycobacterial infections. Evidence for specific genetic factors required for intercellular aggregation, and their relationships with upstream substratum attachment or downstream maturation stages will be discussed in this presentation.

“Quantum design of functional materials: From plasmonics to new materials physics,” Prineha Narang, California Institute of Technology

In this talk I will discuss a multiscale theory approach coupled with spectroscopy aimed at the design of functional materials for active optoelectronic devices.

Despite more than a decade of intensive scientific exploration, new plasmonic phenomena con- tinue to be discovered, including quantum interference of plasmons, observation of quantum coupling of plasmons to single particle excitations, and quantum confinement of plasmons in single-nm scale plasmonic particles. Simultaneously, plasmonic structures find widening applications in integrated nanophotonics, biosensing, photovoltaic devices, single photon transistors and single molecule spec- troscopy. Decay of surface plasmons to hot carriers is a new direction that has attracted considerable fundamental and application interest, yet a theoretical understanding of ultrafast plasmon decay processes and the underlying microscopic mechanisms remain incomplete.

Recently we analyzed the quantum decay of surface plasmon polaritons and found that the prompt distribution of generated carriers is extremely sensitive to the energy band structure of the plasmonic material. A theoretical understanding of plasmon-driven hot carrier generation and relaxation dynamics at femtosecond timescales is presented here. We report the first ab initio calculations of phonon-assisted optical excitations in metals, which are critical to bridging the frequency range between resistive losses at low frequencies and direct interband transitions at high frequencies. We also present calculations of energy-dependent lifetimes and mean free paths of hot carriers, accounting for electron-electron and electron-phonon scattering, lending insight towards transport of plasmonically-generated carriers at the nanoscale. Calculations for multiplasmon and nonlinear processes in the ultrafast regime from the mid-IR to visible and in different geometries will be discussed. Employing a Feynman diagram approach here has been critical to determine the relevant processes.

Another example of theory-directed design of functional materials that will be discussed is the development of Zn-IV nitrides. The commercial prominence in the optoelectronics industry of tunable semiconductor alloy materials based on nitride semiconductor devices, specifically InGaN, motivates the search for earth-abundant alternatives for use in efficient, high-quality optoelectronic devices. II-IV-N2 compounds, which are closely related to the wurtzite-structured III-N semicon- ductors, have similar electronic and optical properties to InGaN namely direct band gaps, high quantum efficiencies and large optical absorption coefficients. The choice of different group II and group IV elements provides chemical diversity that can be exploited to tune the structural and electronic properties through the series of alloys. Here I will describe the first theoretical and experimental investigation of the ZnSnxGe1-xN2 series as a replacement for III-nitrides.

"Strong-Coupled Collective Cyclotron Resonance and Terahertz Cavity Photon in 2D Electron Gases," Qi Zhang

Achieving strong light-matter interaction in low-dimensional solid state systems is essential for both fundamental studies and device applications of cavity quantum electrodynamics (QED). It is particularly interesting to understand and even control the dynamics of collective excitations in solid states, when they are strongly coupled to cavity photons. A Landau-quantized, high-mobility two-dimensional electron gas (2DEG) provides a uniquely clean and tunable semiconductor system in which to explore strong light-matter interaction with many-electron states. In this talk, I will first show how rapidly a superposition of massively degenerate Landau levels loses its coherence in the free space. We observed a collective radiative decay, or superradiance, of cyclotron resonance (CR) in 2DEG with time-domain terahertz magneto-spectroscopy. In the second part, I will demonstrate the strong-coupling between the cyclotron resonance and THz cavity photons. We observed Rabi oscillation in time domain, as well as the collective vacuum Rabi splitting. We significantly suppressed the superradiance decay of CR by the high-Q THz cavity, and resolved an ultra-narrow intrinsic CR linewidth (5 GHz). Our method may also apply to various correlated 2D systems with collective THz excitations. It opens an access to the intriguing physics of THz many-body cavity-QED.

"The Radio & Plasma Waves Investigation on board the JUpiter ICy moons Explorer mission," Kiran Kovi

The JUpiter ICy moons Explorer (JUICE) is the first L-class mission in ESA’s Cosmic Vision programme. Planned to be launched in 2022, JUICE will use Earth-Venus-Earth-Earth gravity assists to arrive at Jupiter in 2030. On arrival, JUICE will perform a tour of the Jupiter system, using gravity assists of the Galilean satellites to shape its trajectory. This tour will include continuous monitoring of Jupiter’s magnetosphere and atmosphere, two targeted Europa flybys, a Callisto flyby phase that includes raising the orbit inclination up to 22°, culminating with the dedicated Ganymede orbital phase with high (5000 km) and medium (500 km) orbits. The focus of JUICE is to characterize the conditions that may have led to the emergence of habitable environments among its three icy and ocean-bearing moons, Europa, Callisto, and Ganymede. Ganymede has been chosen for detailed investigations, since it provides a natural laboratory for analysis of the nature, evolution, and potential habitability of icy worlds in general, but also because of the role it plays within the system of Galilean satellites, and its unique magnetic and plasma interactions with the surrounding Jovian environment. In this presentation we will give an overview of the JUICE mission, with emphasis on the Radio & Plasma Waves Investigation (RPWI), which is one of ten scientific payloads on board.

August 6, 2015

10:00 a.m. - 11:00 a.m.

Bldg. 440, A105-106

"Chirality in flatland: molecular recognition, chiral switches and unidirectional motors at surfaces," Karl-Heinz Ernst, Empa-Swiss Federal Laboratories for Materials Science and Technology, University of Zurich

Many objects in our world have the property that they are incongruent with their mirror image. Such objects are called chiral or enantiomorphous. Examples are quartz crystals, shoes, snail shells, screws, etc. The most significant manifestation of chirality is the appearance of left- and right-handed molecules, so-called enantiomers. Chirality is ubiquitous in the biological world, but handedness comes unbalanced. That is, molecules of life, like sugars, proteins, and their building blocks the amino acids, appear basically in only one handedness. This has dramatic consequences, because the biological and pharmaceutical activity of enantiomers is directly related to their handedness and causes different physiological effects.

After presenting few examples of chirality in the physical and sociological sciences and a brief introduction into the history of molecular chirality and the important role it played for understanding the spatial structure of molecules, various aspects of surface chirality will be discussed:

Molecular recognition among chiral molecules on surfaces is of paramount importance in biomineralization, enantioselective heterogeneous catalysis, and for the separation of chiral molecules into their two mirror-image isomers (enantiomers) via crystallization or chromatography. Understanding the principles of molecular recognition in general, however, is a difficult task and calls for investigation of appropriate model systems. One popular approach is thereby studying intermolecular interactions on well-defined solid surfaces, which allows in particular the use of scanning tunneling microscopy (STM). We present an elucidation of chiral recognition of helical hydrocarbons at the single molecule level, in monolayers and in multi-layers. In a Pasteur-type experiment at the nanoscale, molecules that constitute a dimer are separated with a molecular STM tip and the subsequent determination of their absolute handedness with a metal tip. Moreover, we will present examples of chiral amplification via the so-called 2D ‘sergeant-and-soldiers’ effect, chiral restructuring of a copper surface by prochiral molecules and discuss role of chirality in electrical current-driven molecular machines.

July 29, 2015

4:00 p.m.

Bldg. 440, A105-106

"Surface Engineering of Nanocerias and Their Applications for Catalysis," Qu Yongquan, Frontier Institute of Science and Technology (FIST)

Ceria (CeO₂) is finding prolific industrial applications due to its unique redox properties. Such properties, dominated by structural defects that are primarily oxygen vacancies associated with the Ce³⁺/Ce⁴⁺ redox couple, can be modulated and optimized by controlling the size and morphology of the material, in particular those that are nanostructured. Herein, a novel ceria nanostructure — porous nanorods of ceria (PN-Ceria), is introduced with the controllable surface properties. PN-Ceria has been found to display enhanced reducibility and capacity for oxygen storage as a result of their significantly increased surface area and defects over other forms of nanocerias. Various applications in catalysis have been developed, which are originated from their surface properties.

July 1, 2015

4:00 pm

Bldg. 440, A105-106

June 17, 2015

4:00 pm

Bldg. 440, A105-106

"First Principles Study of Charging and Discharging Mechanism in Alkali Metal-Air Batteries," ShinYoung Kang, Massachusetts Institute of Technology. Host: Maria Chan

Recently, demands on high-energy-density batteries have drawn research interests to non-aqueous metal-air batteries due to their high theoretical specific energies: for example, 3.5 kWh/kg in Li-air batteries (assuming Li2O2 as a discharge product) and 1.6 and 1.1 kWh/kg in Na-air batteries (assuming Na2O2 and NaO2 as a discharge product, respectively). Despite this attention, the performance of metal-air batteries is limited by low power density, poor cyclability, and poor rate capability.

There have been substantial attempts to identify the causes of these shortcomings and to engineer the devices by deploying/replacing components. Especially, we have studied to understand the underlying mechanisms, which is critical to design the technology. This talk will focus on two mechanisms that are of particular importance in each system: i) the charging mechanism in Li-air batteries and ii) the discharging mechanism in Na-air batteries. The charging mechanism in Li-air batteries accompanies high overpotentials and considerable side reactions, resulting in poor battery performance]. In this talk, a metastable topotactic charging mechanism that we first proposed will be introduced, its kinetic accessibility will be demonstrated, and experimental evidence will follow.

On the other hand, the discharge product in Na-air batteries, either Na2O2 or NaO2, had remained a puzzle regarding what controls the formation of each phase. As the battery performance such as discharging overpotential and cyclability is highly influenced by the type of discharge product, understanding and controlling the formation of the discharge products are crucial. In this talk, the thermodynamic stability and nucleation kinetics of each phase will be presented[6], possibly invigorating further interests in the potential of metal-air batteries.

New Energy Storage and Energy Generation Materials from First-Principles Calculations, Anubhav Jain, Lawrence Berkeley National Laboratory

It has now been demonstrated that density functional theory (DFT) calculations can be used to design new materials in several technological areas from first principles. This first part of this talk will cover our efforts in applying DFT calculations towards the design of new materials for next-generation energy storage (Li ion and multivalent ion batteries) and energy generation (thermoelectric materials). The second part of this talk will focus on the Materials Project (MP), a multi-institution effort to compute the fundamental properties of all known inorganic materials and beyond. Currently, the MP web site has registered over 10,000 users (including ~15% from industry) and includes data on over 60,000 compounds. This dataset also includes almost 40,000 band structures and over 1000 full elastic tensors (to our knowledge, the largest such data set). I will discuss the fundamental software infrastructure that makes this effort possible as well as real use cases by the community. Finally, I will discuss upcoming developments such as user data contribution and the possibility to suggest new compounds for computation. Finally, I will discuss opportunities for materials by design and data mining using such large electronic structure databases.

"Joint Density-Functional Theory for Atomically Detailed Structure of the Electrode/Electrolyte Interface," Kendra Letchworth-Weaver, Cornell University

Understanding the complex and inherently multi-scale interface between a charged electrode surface and a fluid electrolyte would inform design of more efficient and less costly electrochemical energy storage and conversion devices. Joint density-functional theory (JDFT)bridges the relevant length-scales by joining a fully ab initio description of the electrode with a highly efficient, yet atomically detailed classical DFT descriptionof the liquid electrolyte structure. First, we introduce a universal functional to couple any quantum-mechanical solute system with a classical DFT for any liquid and present classical density-functionals for both aqueous and non-aqueous fluids. Leveraging the above theoretical innovations and our framework to treat charged systems in periodic boundary conditions,we then predict the voltage-dependent structure and energetics of solvated ions at the interface between graphene and metal electrodes and an aqueous electrolyte. Finally, we discuss how JDFT calculations can determine the surface structure of a trained SrTiO₃ surface under operating conditions for water-splitting and explore why this structure is correlated with higher activity than an untrained surface. We predict the specular X-ray crystal truncation rods for SrTiO₃, finding excellent agreement with experimental measurements from the Cornell High Energy Synchrotron Source (CHESS).

"Spin Dynamics and Transport Studies by Ferromagnetic Resonance (FMR) Based Techniques," Chunhui Du, Ohio State University

Generation and manipulation of spin is of central importance in modern physics. This intense interest is driven in part by exciting new phenomena such as spin Hall effects and spin transfer torque as well as by the growth in new tools enabling microscopic studies. Ferromagnetic resonance (FMR) is a powerful technique to study both macro and nano-scale spin ensembles, and also an effective method to generate pure spin currents. In the first part of my talk, we use FMR spin pumping technique to characterize the spin Hall angles for a series of 3d, 4d, and 5d transition metals with widely varying spin-orbit coupling strengths and demonstrate that both atomic number Z and d-electron count play important roles in spin Hall physics. We have systematically studied spin transport in a series of six Y3Fe5O12/insulator/Pt trilayers where the inserted insulators have different magnetic properties: diamagnetic (one), paramagnetic (one) and antiferromagnetic (AF) (four, having a wide range of magnetic ordering temperatures). We observe remarkably robust spin transport in the AF insulators and a clear linear relationship between the spin decay lengths in the insulators and the damping enhancements in the Y3Fe5O12, suggesting the critical role of magnetic correlations in magnetic insulators for spin transport. I will then describe our experiment using spin wave modes confined into microscopic volumes in a ferromagnetic film by the spatially inhomogeneous magnetic field of a scanned micromagnetic tip of a ferromagnetic resonance force microscope (FMRFM). We have measured local spin transfer from the resonance region to surrounding areas within an insulating ferrimagnetic Y3Fe5O12 thin film, and we image the local magnetic texture variations in patterned ferromagnetic permalloy structures. Micromagnetic simulations accurately reproduce our FMRFM spectra allowing quantitative understanding of the spin dynamics and transport phenomena across various interfaces. I will also show strong coupling of FMR excitation to spins in Nitrogen Vacancy (NV) center in diamond, suggesting NV center is a promising candidate to image the spin dynamics.

"Tunable control over individual impurities in semiconductors with laser illumination and STM manipulation," Anne Benjamin, Ohio State University

Our modern, rapid pace of computing development has so far relied on device miniaturization. As electronic components shrink to the atomic scale, we face new challenges. By understanding and manipulating the electronic properties of single atoms or atomic clusters, we open the door for improved or novel electronic devices. In this talk, I will discuss our studies of individual impurities (Mn, Zn, Er) in GaAs, which add functionality to GaAs ranging from magnetism to infrared optical activity. We perform STM measurements in ultra-high vacuum, at low temperatures, on samples cleaved in vacuum. We tune impurity states with atomic manipulation and laser illumination, and measure these changes with tunneling spectroscopy. For example, we have studied how the proximity of charged defects changes the binding energy of Mn as measured by a shift in the in-gap peak. In addition, we have discovered behavior consistent with a shallow-to-deep transition of Zn impurities, mediated by the presence of other Zn defects and measured as responses of the in-gap peak energy to the electric field of the tip.

More recently, we have studied how laser illumination affects the in-gap peaks of Zn and Er. Above-gap light creates mobile charge carriers whose diffusion modifies the local electrostatic landscape. We see a rich spectrum of impurity peaks associated with subsurface Zn acceptors, which shift, split, and suppress under laser illumination. Surprisingly, we see similar effects with below-gap excitation, which may be due to two-photon absorption creating mobile carriers. We have also studied Er adatoms on GaAs for the first time and find a surprising variety of adsorption states, some of which share an adsorption site and limited switch ability. Different adsorption states exhibit different in-gap peaks and reaction to local electric fields. Above- and below-gap illumination shifts these impurity states, similar to Zn.

March 10, 2015
1:00 p.m.
Bldg. 440, A105-106

"Electronic and optical excitations in TiO2 nano crystals from first principles," Linda Hung, Department of Physics, University of Illinois at Chicago

With advances in theoretical understanding and computing power, first-principles methods can be used to probe the electronic structure and excited state properties of materials at ever-greater accuracy. In particular, time-dependent density-functional theory (TDDFT) and the GW approximation can often simulate excitations from valence states in good agreement with experimental measurements (e.g., from VEELS, IXS, and PES). However, first-principles calculations remain computationally expensive, and limit the size of the material being studied. In this talk, we examine whether the optical and electronic properties of rutile titanium dioxide nanocrystals up to ~1.5 nm in size have approached the bulk limit, and, more generally, how they are affected by quantum confinement. We begin by introducing the methods used in our calculation and reviewing their expected accuracy and applicability We also discuss how expensive GW computations are made feasible by using a real-space implementation. We then report on the size and shape dependence of nanocrystal properties. We find that the largest nanocrystals modeled still exhibit signs of quantum confinement in their quasiparticle levels or optical gaps, but that classical Mie-Gans theory can quite accurately reproduce the line shape of TDDFT absorption spectra.

"The 'K-kit': a Convenient Way for Transmission ElectronMicroscopic Observation of Nanoparticles in Liquid Samples,” Chung-Shi Yang, Institute of Biomedical Engineering and Nanomedicine, National Health Research Institutes, Zhunan, Taiwan

Nanoparticles-based formulation for molecules of theranostic purposes has drawn much attention recently.Electron microscope-based characterization on these nanoparticles, such as size, shape and aggregation/agglomeration while they are present in biological fluids such as blood provides important information related to the ADME (absorption, distribution, metabolism and distribution), yet remains to be a challenging task as conventional EM-based observations are performed under vacuum.We develop a MEMS-based microchip, the “K-kit”, for easy loading of liquid samples that can then be placed on conventional TEM holder to be observed at regular TEM.This K-kit can be applied for the observation of different types of organic and inorganic nanoparticles, including the drug-loaded nanoaprticles, in liquid buffers.

"Enhancement of low-energy electron emission in 2-D radioactive films," Alex M. Pronschinske, Tufts University

Radioactive decay and its accompanying high-energy radiation are well understood and have been utilized for decades. However, the role of low-energy electrons created during irradiation has only recently begun to be appreciated. Low-energy electrons are the most important component of radiation damage in biological environments because they have subcellular ranges and interact destructively with chemical bonds. Their short ranges make them ideal for targeted cancer therapies, yet methods for generating them locally do not exist.

To address this we synthesized one atom thick films of the radioactive isotope I-125 on gold that are stable under ambient conditions. Scanning tunneling microscopy, supported by electronic structure simulations, allowed us to directly observe the nuclear transmutation of individual I-125 atoms into Te-125 atoms, and explain the surprising stability of the film as it underwent radioactive decay. Electron spectroscopy revealed that the interface geometry induces a 500% amplification of low-energy electron emission (< 50 eV) as compared to a bulk emitter. The interface-induced enhancement of the low-energy electron flux arises from high-energy electron scattering within the Au surface, a fundamental process that will persist in a radioisotope/metal nano-structure of any complexity.

These radioactive films offer a platform for understanding the microscopic details of electron-induced processes and provide a route to nano-scale electron emitters. Most significantly, I-125 is commonly used in medical imaging, radiation therapy and biological assays and the I-125/Au sample preparation methods described here are highly compatible with Au nanoparticles. Therefore, this interface enhancement of biologically active low energy electrons will offer nano-scale specificity for highly targeted purposes.

"Models for Coherent and Incoherent Electronic Transport In Organic Semiconductors," Didier Mayou, Institut Neel, CNRS and University Grenoble-Alpes, Grenoble, France

In this talk I present recent models for the analysis of electronic transport in organic semi-conductors. In the first case,, a tight-binding model of coherent electronic transport through molecules allows to derive simple rules for the zero-voltage conductance of nanographenes and Polycyclic Aromatic Hydrocarbons (PAH). One particularly interesting prediction is the vanishing zero-voltage conductance in certain nanographene. Even though these systems are Π conjugated, from the conductance point of view they consist of disconnected parts.

In the second case, I consider electronic transport in bulk organic semiconductors. In that case the electronic transport is sensitive to incoherent mechanisms due to the molecular motion. Using the Kubo formalism I show that the optical conductivity is determined by the thermodynamical average of the quantum diffusion. A simple model for the quantum diffusion is derived which takes in to account the role of scattering by disorder in the spirit of the Drude approach but includes also the effect of Anderson localization due to disorder. This leads to a Drude-Anderson formula for conductivity which depends on elastic mean-free path, inelastic mean-free path and localization length. A fit to experimental data for optical conductivity allows to extract the value of these fundamental lengths and I discuss in particular the case of Rubrene.

"Nanomanufacturing: Is there life beyond Silicon?," J. Alexander Liddle, Center for Nanoscale Science and Technology, National Institute of Standards and Technology

Photolithography applied to the fabrication of integrated circuits in silicon is the preeminent nanomanufacturing technology and has transformed our world. The functionality and value provided per unit area by silicon are extraordinary by any measure. As a consequence, it is economically viable to use very capital-intensive fabrication processes to generate the required nanostructures. The success of silicon has inspired many to contemplate using the IC fabrication toolbox to produce nanoscale products, but the vast majority of other nanotechnology products cannot support the cost of such sophisticated manufacturing methods. Further, the diversity of nanoscale items is so great, that it is only in rare instances that process and design modularity is sufficient to result in the development of a platform manufacturing technology. In this talk I will give examples of how the complexity of the final product, its value and the overall market size dictate what type of nanomanufacturing approach, if any, is viable.

"Fabrication, Properties, and Applications of van der Waals Heterostructures," James Hone, Department of Mechanical Engineering, Columbia University.

Two-dimensional materials such as graphene offer a wide range of outstanding properties but are highly sensitive to disorder from the environment. We have developed techniques to stack 2D materials on top of each other to create "van der Waals Heterostructures with nearly perfect interfaces. Moreover, we can achieve high-quality contacts to the one-dimensional edge of buried layers. This talk will first describe the techniques used to create suchheterostructures. Next, four application areas will be described:

1. Near-ideal performance achieved in graphene through encapsulation in insulating boron nitride (BN);
2. Applications in plasmonics, photonics, and light emission;
3. reatly improved measurements of the electrical transport in semiconducting MoS₂ through BN-encapsulation;
4. Measurements of other 2D materials.

"Electromechanical Properties of Single Molecule Devices," Christopher M. Bruot, Center for Bioelectronics and Biosensing, The Biodesign Institute, Arizona State University

The understanding of charge transport on molecular length scales can be greatly enhanced by probing the interplay between the electrical and mechanical properties of single molecule devices. Here, I will present two studies in which greater understanding of charge transport properties of metal-single molecule-metal devices is achieved by mechanical perturbation with the STM break junction technique. First, the unique conductance behavior of benzendithiol is demonstrated and explained using a combination of spectroscopic techniques. Next, the role of pi-pi overlap between neighboring bases in single DNA molecules is investigated with the tip modulated STM break junction technique.

"Structural Biology of Human Pathogens and Antibiotic Resistance Using Light Sources," Andrzej Joachimiak, Center for Structural Genomics of Infectious Diseases, Structural Biology Center, Biosciences, Argonne National Laboratory, and Computational Institute, University of Chicago

Macromolecular function, including recognition, assembly and catalysis, depend on the 3D structure. X-ray crystallography is the most powerful method capable of providing detailed information on structure and interactions of proteins with small ligands. New light sources and dedicated macromolecular crystallography (MX) beamlines have extended our competence in determining protein structures. Genome sequencing expanded protein sequence space and allows for comprehensive approaches to studies of entire cellular systems, including uncultured organisms. Structural Genomics efforts took advantage of these innovations and contributed a complementary array of highly integrated and cost effective methods in molecular and structural biology and created structure determination. The Midwest Center for Structural Genomics and Center for Structural Genomics of Infectious Diseases pipelines are using the Advanced Protein Characterization Facility for protein and crystal production and the Advanced Photon Source for structure solution.

Antibiotic resistance has been discovered against key antibiotics used in the treatment of many pathogenic strains and poses a major threat worldwide. The continued evolution of a complex array of antibiotic-resistance genes presents a formidable challenge and efforts to develop new antimicrobials have lagged behind. Structure determination pipelines can be applied to emerging diseases and drug resistance. These studies can aid structure-based drug discovery. The New Delhi Metallo-β-lactamase (NDM-1) gene makes multiple pathogenic bacteria resistant to all known β-lactam antibiotics. NDM-1 represents an example of extreme promiscuity - it is capable of efficiently hydrolyzing a wide range of β-lactams, including many "last resort" carbapenems; it can utilize different metal cofactors and seems to exploit alternative mechanisms. The structures of NDM-1 in complex with metal ions and ligands revealed an enlarged and flexible active site capable of accommodating many β-lactam substrates.

The development of new antibiotics that are effective against drug-resistant strains and the discovery of new drug targets are equally important. Recent progress on specific inosine-monophosphate dehydrogenase (IMPDH) inhibitors has prompted a new interest in bacterial IMPDHs as potential drug targets. IMPDH is considered a highly promising target because the protein controls the guanosine monophosphate pool and the gene is often found to be necessary for bacterial survival. Important differences between bacterial and eukaryotic enzymes can be utilized to design species-specific inhibitors. Structural studies of IMPDH in complex with different inhibitors combined with binding studies provide insight to how species-specific inhibitors can be developed.

January 29, 2015
10:00 a.m.
Bldg. 241, C-201

January 22, 2015
3:00 p.m.
Bldg. 440, A105-106

"Engineering Soft Matter for Funational Materials: i) nanocomposite solar cells, (ii) polymer membranes, (iii) active surfaces and (iv) complex fluids," Joao T. Cabral, Imperial College London, UK

I will present an overview of recent work within our group at Imperial College London on soft matter engineering to design and fabricate functional materials. After an introduction to Imperial, my group and sabbatical at IME U Chicago, I will discuss four ongoing projects:

1. Directed assembly of polymer-fullerene nanocomposites for solar cells
   We investigate the thermodynamics and phase separation of polymers and fullerene derivatives in thin films, and employ external fields to direct and tune the assembly process. After establishing the fundamentals with model systems, we implemented this approach on organic solar cells to enhance their lifetime 200 fold.
2. Nanostructure membranes for engineering separations and water
   Employing phase inversion of polymer-solvent ternary mixtures and thin film methods, we design membranes for organic solvent filtration which prevent physical ageing and investigate confinement to engineer optimal performance, e.g. with stiff PIM materials.
3. Facile patterning of active surfaces by lithographic and non-lithographic methods
   Soft matter instabilities provides an exceptional route for the generation of micro/nanostructured and functional surfaces. Non-photolithographic methods are particularly attractive due to their simplicity and accessibility but also surface 3-dimentionality and varied surface chemistry. We exploit a combination of wrinkling instabilities and light-induced wave propagation to pattern structures from 10 nm to several mm, with controlled 3D topography.
4. Complex fluid engineering in microfluidics
   Length and time scales of microflow processing, within m-mm and ms-hours, are naturally commensurate and can be coupled with those of complex or non-Newtonian fluids. Further microfluidics unprecedented control of flow type and magnitude, relevant to continuous manufacturing processes and inherently high-throughput. We demonstrate the engineering of concentrated lamellar suspensions and the rapid encapsulation using phase inversion, with applications in formulations, personal care, food and oil industries.

January 21, 2015
2:00 p.m.
Bldg. 440, A105-106

"Electrical Transport and Energy Application of 2D Layered Materials," Wenzhong Bao, University of Maryland, College Park

Recently, there has been enormous progress in the study of 2D layered materials which can be viewed as individual planes of atomic-scale thickness exfoliated from bulk crystals like graphite, h-BN, several transition metal dichalcogenides (TMD), complex oxides, etc. The unique electronic structures, atomic thickness, mechanical strength and flexibility of these materials offers new opportunities to realize new materials properties with the interplay of electronic, magnetic, mechanical, chemical, and optical phenomena. This presentation will first summarize my previous works in this field, including electrical/thermal transport studies of graphene/MoS2 and the morphology manipulation of suspended membrane via electrostatic and thermal control. Then I will focus on our recent progress of alkali metal intercalation in layered materials, e.g. we measure simultaneous in-situ optical transmittance spectra and electrical transport properties of few-layer graphene (FLG) nanostructures upon electrochemical lithiation/delithiation. Due to the unusual electronic structure of FLG, upon intercalation we observe a simultaneous increase of both optical transmittance and DC conductivity, strikingly different from other materials, and shed light on its application for next generation transparent electrodes. Lastly I will introduce our latest work about using such in-situ microbattery techniques to observe the changes in electrical resistance, optical transmission, and nanoscale structure of MoS2 upon electrochemical lithium insertion, which could guide the design of higher performing Li-MoS 2 coin cell batteries.

January 13, 2015

11:00 a.m.

Bldg. 440, A105-106

"Large Scale Simulation Studies of Metal Oxide Nanostructures," Phuti Ngoepe, Materials Modelling Centre and University of Limpopo, South Africa

The talk will cover large scale simulations studies carried out on metal oxides, mainly using simulated amorphization recrystallization technique, based on atomistic molecular dynamics methods. Simulated synthesis and characterization of binaries such as MnO2, TiO2 and their lithiated form will be discussed. Recent work involving ternaries such as Li2MnO3 and preliminary work on LiMn2O4 will be presented. Electrochemical activity of such metal oxides will be linked to their simulated microstructures.