# CNST Group Seminars: 2011

CNST Nanofabrication Research Group Seminar

## RAMAN CHARACTERIZATION - GE REVISITED

Christian D. Poweleit
Arizona State University, Dept. of Physics.

Thursday, December 15, 2011, 10:30AM, Rm. H107, Bldg. 217

Raman is a continuing growing characterization technique. Its relatively non-destructive process for studying various material properties is well known. Ge was the first transistor material, and the electronic's industry workhorse until the sixties. However, its expense and lack of stable oxide layer made Si the dominant material of choice thereafter. However, as the electronics industry makes its push to smaller devices Ge is making a large contribution to the new electronic devices through strain engineering. Raman spectroscopy is an ideal tool to examine the strain characteristics in these novel devices. Raman allows us to explore existing theories regarding Ge and Ge alloys and their extrapolation into the nano-regime.

For further information contact Renu Sharma, 301-975-2418, renu.sharma@nist.gov

CNST Energy Research Group Seminar

## CARBON NANOTUBES INTERACTIONS: THEORY AND APPLICATIONS

University of South Florida.

Tuesday, November 15, 2011, 10:30AM, Rm.H107, Bldg. 217

Calculations of the pressures on the surfaces of two concentric carbon nanotubes in vacuum are presented. The approach is based on quantizing the electromagnetic field and on the dyadic Green function method. Carbon nanotubes are described as dielectric bodies characterized by a spatially varying permittivity that is a complex function of frequency. The effects of the tubes chiralities on the strength of their mutual interactions are discussed. Furthermore, the results are compared with those obtained with a classical approach, where the carbon nanotubes interaction is described by using a pairwise additive type of interatomic potential. A few practical applications based on the classical approach are also proposed.

For further information contact Paul Haney, 301-975-4025, paul.haney@nist.gov

CNST Electron Physics Group Seminar

## SCANNING TUNNELING MICROSCOPY STUDY OF KXFE2-YSE2 GROWN BY MOLECULAR BEAM EPITAXY

Wei Li
Department of Physics, Tsinghua University.

Tuesday, November 8, 2011, 10:30AM, RM H107, Bldg. 217

The newly discovered alkali-doped iron selenide superconductors not only reach a superconducting transition temperature as high as 32 K, but also exhibit unique characters that are absent in other iron-based superconductors, such as anti-ferromagnetically ordered insulating phases, extremely high Neel transition temperatures, and the presence of Fe vacancies and ordering. These features have generated considerable excitements as well as confusions, regarding the delicate interplay between Fe vacancies, magnetism and superconductivity. In this talk, I will focus on the molecular beam epitaxy (MBE) growth of high-quality KxFe2-ySe2 thin films and in situ low-temperature scanning tunneling microscope (STM) measurement of their atomic and electronic structures. We demonstrate that a KxFe2-ySe2 sample contains two distinct phases: an insulating phase with well-defined check mark5xcheck mark5 order of Fe vacancies, and a superconducting KFe2Se2 phase containing no Fe vacancies. An individual Fe vacancy can locally destroy superconductivity in a similar way as a magnetic impurity in conventional superconductors. The measurement of magnetic field dependence of the Fe-vacancy-induced bound states reveals a magnetically-related bipartite order in the tetragonal iron lattice. These findings elucidate the existing controversies on this new superconductor and provide atomistic information on the interplay between magnetism and superconductivity in iron-based superconductors. Finally I will briefly introduce our recent works on FeTe and topological insulators.

For further information contact Joseph Stroscio, 301-975-3716, joseph.stroscio@nist.gov

CNST Energy Research Group Seminar

## EXPLORING SPIN IN NOVEL MATERIALS AND SYSTEMS

Lei Fang
Department of Physics, the Ohio State University.

Thursday, October 20, 2011, 1:30PM, Rm. H107, Bldg. 217

The principle goal of the emerging field of semiconductor spintronics is to incorporate the spin-based functionality into conventional electronic architectures, enabling both spin-only and multifunctional operation. Toward this goal, it is important to study spin and spin transport in materials with multifunctionality. A principle aim of my research is to integrate the multifunctionalities of the novel materials into spintronics field. In this talk I will present two specific approaches toward the goal: strain-induced intrinsic multiferroic (ferromagnetic/ferroelectric) materials and hybrid organic/inorganic heterostructures. The multiferroic material we studied is strained EuTiO3 film [1]. Magneto Optical Kerr effect is used to probe the magnetic property of the material. Sharp switching to full saturation hysteresis loop is observed. Ferroelectricity is measured by second harmonic generation (SHG) measurement. We confirm strained EuTiO3 exhibits strong ferromagnetism (~ 4 ?B/Eu) and strong ferroelectric moment (~ 10 ?C/cm2) [1]. For the multifunctional heterostructure, an organic-based ferromagnet V[TCNE]x (TCNE: tetracyanoethylene; x~2; TC 400 K) is employed as a spin injector. Electrical spin injection across the organic/inorganic interface is successfully detected in the hybrid spin light emitting diode (spin LED) device [2], which validates the spintronic functionality of organic-based magnets, lays the foundation for a new class of multifunctional hybrid spintronic structures, as well as sets the stage for the first room temperature all-semiconductor spintronic devices.

For further information contact Andrea Centrone, 301-975-8225, andrea.centrone@nist.gov

CNST Nanofabrication Research Group Seminar

## APPLICATION OF NEAR-FIELD MICROWAVE MICROSCOPY TO FERROMAGNETIC RESONANCE SPECTROSCOPY AND ATOMIC RESOLUTION IMAGING

Dr. Christian J. Long
University of Maryland, Dept. of Physics.

Tuesday, October 18, 2011, 10:30AM, Rm. H107, Bldg. 217

Near-field microwave microscopy (NFMM) is a scanning probe technique that is most frequently used to characterize the dielectric properties of bulk and thin film materials at GHz frequencies. It has the advantages of being non-destructive and provides a spatial resolution that is much smaller than the wavelength of the probing radiation. In this talk, we present our work towards expanding the capabilities of NFMM beyond the traditional role of dielectric mapping and into the roles of magnetic property characterization and atomic resolution imaging. First, we explore the possibility of using NFMM to perform magnetic property characterization via scanning ferromagnetic resonance spectroscopy. As an example system, we image the magnetostatic spin wave modes of a single crystal ferrimagnetic disk. We find that the microwave magnetic field around the tip couples to the nodes of the spin wave modes, allowing the positions of the nodes to be mapped across the sample. Second, we push the resolution limits of NFMM to the atomic scale by combining it with scanning tunneling microscopy (STM). Using a custom built hybrid instrument that can simultaneously perform NFMM and STM, we show that NFMM can be used to obtain atomic resolution images of conducting samples. The imaging mechanism in this case is GHz frequency alternating current through the STM tunnel junction. Since the bandwidth of the microwave measurement is much higher than traditional STM, this imaging mode can potentially offer a large improvement in image acquisition time.

For further information contact Rachel Cannara, 301-975-4258, rachel.cannara@nist.gov

CNST Nanofabrication Research Group Seminar

## LAB ON A CHIP INTEGRATION OF MAGNETIC RESONANCE INVESTIGATION AT THE MICROSCALE

University of Freiburg, Department of Microsystems Engineering - IMTEK. Freiburg

Tuesday, September 27, 2011, 10:30AM, Rm. H107, Bldg. 217

Integration of MR-based investigation methods in lab on a chip (LOC) devices for volume- and mass-limited samples needs to address a crucial aspect: a reduction in voxel size from (1 mm)3 to (10 µm)3 results in a signal reduction of 106. The challenge during the past 4 years of our µMRI/NMR group at IMTEK, University of Freiburg, was to recover as much as possible from this signal deficit by focusing on innovative processes and designs of the detection coils. The wirebonding technology for 3D solenoidal microcoils developed at IMTEK combines the advantage of an automatic wirebonder with MEMS integration techniques to obtain large planar arrays of MR detectors. Even if the wirebonding is a serial technique, it is extremely reliable and fast so that the manufacturing of one coil with 10 windings takes approx. 200 ms. Exploiting this technology we have developed an entire toolbox for magnetic resonance imaging (MRI) and spectroscopy (NMR) of microscopic sample as well as lab on a chip integration of detection coils for life sciences and metabolomic applications. We will present: - solenoidal microcoils for magnetic resonance imaging and spectroscopy at the microscale: single cell imaging, coil arrays integrated with CMOS amplifiers; - on-chip probes for wireless NMR via inductive coupling; magic angle coil spinning (MACS) for high resolution, high sensitivity NMR; - 2D phased arrays of microcoils for applications either in solid state NMR (thin films) or in life sciences – biopsies of skin samples.

For further information contact Mihaela Tanase, 301-975-5623, mihaela.tanase@nist.gov

CNST Nanofabrication Research Group Seminar

## BOSE-EINSTEIN CONDENSATION AND POLARITON LASING IN ZNO MICRO-STRUCTURE - A NEW PLATFORM FOR STRONG LIGHT-MATTER INTERACTION STUDIES AT ROOM TEMPERATURE

Xiangshun Lu
Research Associate, Department of Physics, University of Arkansas.

Thursday, September 15, 2011, 10:30AM, Rm. H107, Bldg. 217

Bose-Einstein condensation (BEC) has fascinated scientists for decades and has been observed in atomic gases and solid-state materials. Particularly, the strong exciton-photon coupling in a semiconductor microcavity results in bosonic quasiparticles called exciton-polaritons. Due to its 109 times lighter effective mass than atom, exciton-polaritons provide a new platform for BEC and light-matter interaction studies. In this presentation, I will describe the observations of BEC on both lower polariton branch (LPB) and upper polariton branch (UPB) above a critical pumping threshold at liquid-nitrogen temperature in a tree-like quasi one-dimensional system formed hierarchically by ZnO nanowires from multistep solution-syntheses. The evidences of confirming the BEC include the appearance of interference fringes formed by the long-range spatial spontaneous coherence, a spectroscopic accumulation to the lowest energy state in momentum space, a linear polarization, a nonlinear increase of intensity, and the spatial and spectral narrowing features in the detected optical field. In this solid-state system, upper-polariton BEC, as well as strong polariton lasing and BEC of lower polariton at room temperature involving no extra Bragg mirrors, were demonstrated for the first time, which shed new light on bottom-up nanofabrication of devices for optical computing, information storage and opto-electronics.

For further information contact Gregg Gallatin, 301-975-2140, gregg.gallatin@nist.gov

CNST Nanofabrication Research Group Seminar

## VARIANCE CONTROL: A KEY ENABLER FOR ADVANCED LITHOGRAPHY

Timothy Brunner
IBM SRDC, Hopewell Junction. NY

Wednesday, August 24, 2011, 10:30AM, Rm. H107, Bldg. 217

Process variations are of increasing concern for advanced chip-building processes. The accuracy of computational lithography methods such as OPC, becomes fundamentally limited when the process is not constant over time, across the wafer, from wafer to wafer, from expose tool to expose tool, etc. Many of the root causes of these process variations can be categorized as effective dose variation and effective focus variation. As NAs have increased to 1.35, focus budgets are under particularly intense pressure. Similarly, advanced processes require overlay errors to shrink even faster than feature sizes are shrinking, driven in part by requirements for multiple patterning methods. Successful advanced lithography is enabled by reducing these process fluctuations – dose, focus and overlay errors – to tolerable levels. To address these requirements, we have developed practical metrology methods which can sense sub-1% dose variations, focus variations in the nm range, and sub-nm overlay errors. Our overall infrastructure development includes process-sensitive test targets, dedicated test masks and novel metrology test methods. Our data analysis incorporates knowledge of the step&scan nature of the exposure tool and the detailed exposure routing across the wafer. The combination of the overlay error data (delta X, delta Y) and the focus error (delta Z) give us a detailed picture of errors of the step&scan stage in all 3 dimensions. This presentation will include examples of focus, dose and overlay errors from state-of-the-art immersion exposure tools. The visualization of such errors across the wafer is key to root cause identification and ultimately to process uniformity improvement.

For further information contact Gregg Gallatin, 301-975-2140, gregg.gallatin@nist.gov

CNST Energy Research Group Seminar

## MINIATURIZED PROBES FOR CELL MICROENVIRONMENT: DEVELOPMENT, CHARACTERIZATION, AND

Miguel Acosta
Department of Chemical and Biochemical Engineering, UMBC, Baltimore, MD.

Tuesday, August 23, 2011, 10:30AM, Rm.H107, Bldg. 217

Full Title: Miniaturized probes for cell microenvironment: development, characterization, and application of fluorescent oxygen-sensing microparticles Oxygen concentration is a key parameter in tissue culture and tissue engineering. Additionally, oxygen diffusion through biomaterials plays an important role in maintaining healthy tissues. As such, oxygen is one of the most important cues within the cell microenvironment, playing a role in the regulation of cellular responses that concern such cellular phenomena as cell migration, proliferation, and apoptosis. Oxygen supply has become a limiting factor during the growth of highly metabolic tissues and large tissue masses, mainly as a result of absence of vasculature and the low aqueous solubility of oxygen. In addition, limited oxygen supply has been linked to the propagation of bacterial infections due to bacterial detachment from biofilms within the body. Therefore, gaining an understanding of the cellular response to changes in soluble cues, such as oxygen concentration, through their microenvironment may potentially lead to optimized oxygen delivery within biomaterials, improved methods to control cell behavior in engineered tissues, and improved therapies to treat bacterial infections. However, mapping oxygen concentration and characterizing oxygen transport in three-dimensional culture systems has proven difficult due to the lack of adequate tools. To address this need, we have developed oxygen-sensing microparticles that can be suspended through the volume of a transparent biomaterial and measure oxygen concentration and characterize oxygen transport in a non-invasive manner. These microparticles sense oxygen by fluorescence quenching of the oxygen-sensitive fluorophore tris (4,7-diphenyl-1,10-phenanthroline) ruthenium (II) dichloride, or Ru(Ph2phen3)Cl2, while immobilized onto silica carriers. These microparticles are geared towards applications in both mammalian and bacterial cell culture where oxygen concentration and transport can be directly correlated to cell function. We provide a detailed description of the synthesis processes of these microparticles, their characterization, and calibration. Subsequently, we show that they are suited for their intended applications by demonstrating that they can be suspended through the volume of a biomaterial and are compatible with both mammalian and bacterial culture. Finally, we propose methodologies for the intended applications of the microparticles regarding the correlation cell function to oxygen transport during 3D mammalian cell culture and bacterial biofilm culture. This correlation will mark the first time oxygen concentration is linked to cellular functions that it directly impacts during three-dimensional culture.

For further information contact Veronika Szalai, 301-975-3792, veronika.szalai@nist.gov

CNST Electron Physics Group Seminar

## MAGNETIC VORTEX CORE DYNAMICS PROVED BY HOMODYNE DETECTION, AND INTERACTIONS BETWEEN PROPAGATING SPIN-WAVES AND DOMAIN WALLS

June-Seo Kim
University of Konstanz; Konstanz, Germany.

Friday, August 12, 2011, 10:30AM, Rm H107, Bldg. 217

The magnetic vortex core (VC) dynamics in a ferromagnetic disc is a promising candidate for future non-volatile memory devices. Now, we introduce the VC dynamics on a magnetic disk by using microwave current rectifying effect (Homodyne detection). The Homodyne technique is a sensitive and versatile method to obtain the information about the VC dynamics. By systematic position dependence measurements, we were able to distinguish the polarity of VC and the chirality of vortex state. The study of high resonance frequencies, which are due to the strong pinning effects, allows us to create a three dimensional pinning map on the disc. Since the homodyne signal depends on the phase shift between microwave currents and the anisotropic magnetoresistance response, we have also drawn the phase shift map allowing us to directly distinguish the Oersted field contribution for the VC dynamics. The recent discovery that a propagating spin wave (SW) moves a domain wall (DW) has created a new possibility to manipulate magnetization. Therefore, we numerically investigated interactions between propagating SWs and DWs. Micromagnetic simulations hereby revealed two different physical origins responsible for DW motion: (i) Strong SW reflections due to the DW and (ii) An effective momentum transfer at the certain SW frequencies as the main driving mechanism of the SW induced DW motion. The DW depinning field calculations coincide with two major mechanisms for DW motions.

For further information contact John Unguris, 301-975-3712, john.unguris@nist.gov

CNST Nanofabrication Research Group Seminar

## ULTRA LOW-POWER COMPUTING WITH MULTIFERROIC NANOMAGNETS

Jayasimha Atulasimha
Asst. Prof. Mechanical Eng., Virginia Commonwealth University.

Prof. Electrical Eng., Virginia Commonwealth University

Thursday, July 21, 2011, 1:00PM, Rm. H107, Bldg. 217

We have theoretically shown that multiferroic nanomagnets (consisting of a piezoelectric and a magnetostrictive layer) could be used to perform computing while consuming ~100 kT/bit (Applied Physics Letters 97,173105, 2010). In contrast, today's transistors consume several 100,000 kT/bit. The next question was whether such ultra-low power logic devices could switch at competitive speeds. We therefore solved the LLG equations and showed that such multiferroic nanomagnets could switch ~1GHz, only dissipating ~ few 100 kT of energy/bit (Nanotechnology, 22, 155201, 2011). Our current research focus is in the following areas that will be covered in this seminar: 1. Theoretical study of stress induced magnetization dynamics in multiferroic nanomagnets. 2. Experimental fabrication and of such devices using e-beam lithography to create ~ 100 nm diameter elliptical nanostructures. 3. Simulation of a NAND gate with fan-out to evaluate the use multiferroic nanomagnets as an ultra-low power paradigm for traditional computing. 4. Demonstrating that dipole coupling between such multiferroic nanomagnets could also be elicited to perform logical operations to perform higher order image processing applications such as edge detection and pattern recognition.

For further information contact J. Alex Liddle, 301-975-6050, james.liddle@nist.gov

CNST Energy Research Group Seminar

## DEVELOPMENT OF OPTIMAL SEEBECK COEFFICIENT MEASUREMENT PROTOCOLS

Joshua Martin
Ph.D. Physicist, Material Measurement Laboratory, Ceramics Division , NIST.

Wednesday, July 20, 2011, 10:30AM, Rm.H107, Bldg. 217

Thermoelectric effects enable the interconversion of thermal and electrical energy and are the physical mechanisms for power generation and solid-state refrigeration applications. To evaluate the potential performance of new thermoelectric materials requires a through characterization of their electrical and thermal transport properties. The Seebeck coefficient is one physical property that singularly identifies a material's potential usefulness for thermoelectric application, as it is highly sensitive to the electronic structure. However, researchers employ a variety of measurement techniques, conditions, and probe arrangements. This diversity often results in conflicting materials data, further complicating the interlaboratory confirmation of reported higher efficiency thermoelectric materials. In an effort to identify optimal Seebeck coefficient measurement protocols, we have developed a complimentary strategy to both evaluate and compare these different probe arrangements and measurement methodologies: first, through the design of an improved experimental apparatus, and second, through computational error modeling of Seebeck coefficient measurements using finite element analysis. This talk will include a general overview of thermoelectric metrology, our apparatus design and instrumentation, and a discussion of the metrology simulation results.

For further information contact Fred Sharifi, 301-975-4633, fred.sharifi@nist.gov

CNST Energy Research Group Seminar

## DESIGNING DURABLE SUPERHYDROPHOBIC SURFACES

Molly Gentleman
Texas A&M University, CNST Visiting Fellow.

Monday, July 18, 2011, 10:30AM, Rm. C103-106, Bldg. 215.

Superhydrophobic surfaces have increased in scope and potential uses to include windows, solar cells, and other industrial applications, over the last decade. This is because their water shedding and self-cleaning properties can potentially save energy lost in these systems due to the formation of water films and surface fouling. Current state of the art superhydophobic coatings generally rely on thin organic or polymeric hydrophobic monolayers to impart hydrophobicity to otherwise highly hydrophilic and carefully textured surface. The thin hydrophobic coatings used in most hydrophobic applications have limited life on the surface and their failure can lead to catastrophic wetting of the surface. Additionally, as most hydrophobic surfaces rely of fragile lithographically fabricated textures the potential for mechanical damage to the fine surface features becomes a major risk in the use of surperhydrophobic coatings. As a result the design of robust hydrophobic surfaces is necessary if we are to realize the widespread uses of these systems. In this talk, the design principles for understanding the wettability of industrially relevant oxides will be discussed. Additionally, a model for the selection of hydrophobic oxides will be presented including preliminary data on relevant surface energy modification of these materials.

For further information contact Fred Sharifi, 301-975-4633, fred.sharifi@nist.gov

CNST Nanofabrication Research Group Seminar

## HIERARCHY WITHIN POLYELECTROLYTE MULTILAYERS

Nicole Zacharia
Dept. of Mechanical Engineering, Materials Science and Engineering Program Texas A&M University.

Thursday, July 14, 2011, 10:30AM, Rm. H107, Bldg. 217

Our group works on materials based on the complexation of polyelectrolytes, both bulk complexes and layer-by-layer (LbL) films or coatings. The LbL technique is a way to direct the complexation of polyelectrolytes onto surfaces. We are interested in achieving greater control of the three dimensional structure within these materials, such as creating physical patterns and structured porosity. In this way we are developing methods to create hierarchical structure that may be applicable for use in membranes or biological materials. In line with this notion of hierarchical structure, we are incorporating ionomers into our materials in order to create hierarchies of bonding; phase separated regions of ionic clusters, ionic crosslinks, and finally covalent bonding. As some of these interactions are reversible, they are useful in dissipating energy without destroying the material. With a combination of hierarchical architectures and bonding, we are developing polymeric materials with higher strength.

For further information contact Rachel Cannara, 301-975-4258, rachel.cannara@nist.gov

CNST Energy Research Group Seminar

## A TALE OF TWO CENTERS: REACTION OF MOLECULAR HYDROGEN WITH PARAMAGNETIC FE AND MO COMPLEXES

Monday, July 11, 2011, 10:30AM, Rm.H107, Bldg. 217

The chemistry of molecular hydrogen at transition metal centers connects to a diverse set of fields that ranges from agriculture to alternative energy. Two examples from biology are instructive. The nitrogenase enzyme, which catalytically converts nitrogen into ammonia, is inhibited by molecular hydrogen, but how H2 interacts with the active site Fe7Mo-cofactor is unknown. Hydrogenase enzymes, which catalytically (and reversibly) oxidize molecular hydrogen at both single- and multi-metallic Fe centers, are models for the energy-efficient storage of molecular hydrogen using abundant materials. Significant effort has been put forth to synthesize inorganic complexes that mimic the behavior/structure of these enzymes. The ultimate goal is to understand the enzyme reaction mechanisms and derive similarly efficient inorganic complexes that can perform the same chemistry on an industrial scale. Given the difficulty in characterizing hydrogen ligands by x-ray methods and the challenging technical requirements of neutron diffraction, Electron Nuclear DOuble Resonance (ENDOR) spectroscopy is uniquely suited to studying this chemistry by directly probing the hydrogenous-ligand environment without the interference of other nuclei. To this end we have used ENDOR spectroscopy to study the reaction of molecular hydrogen with two paramagnetic, Jahn-Teller unstable iron and molybdenum complexes. Despite their structural and electronic similarity, the chemistry of molecular hydrogen at each of the metal centers is unique. The electron-nuclear hyperfine coupling, measured by ENDOR spectroscopy, defines these two distinct ligand structures, and in the process reveals the first known example of a paramagnetic metal-dihydrogen complex.

For further information contact Veronika Szalai, 301-975-3792, veronika.szalai@nist.gov

CNST Energy Research Group Seminar

## QUANTUM HALL TRANSPORT IN GRAPHENE AND ITS BILAYER

Yue Zhao
Physics Department, Columbia University.

Monday, July 11, 2011, 1:30PM, Rm. H107, Bldg. 217

The unique chiral nature of the carrier dynamics in single layer graphene (SLG) and bilayer graphene (BLG) results in unevenly spaced Landau levels (LL) including a distinctive level located precisely at the particle-hole degenerate zero energy. As symetry is always at the heart of physics, this presentation will focus on the symmetry breaking ordering of the zero energy LL in both BLG and SLG systems. Results of zero energy quantum hall octet of BLG, and the recent investigation of spin character of the broken symmetry QH state in MLG are presented. And by suspending multi-terminal graphene devices, good access to the energy gap for the one-third fractional quantum hall state is achieved.

For further information contact Nikolai Zhitenev, 301-975-6039, nikolai.zhitenev@nist.gov

CNST Electron Physics Group Seminar

## CHARGE-STATE DEPENDENT ENERGY DEPOSITION BY ION IMPACTS

Russell Lake
Clemson University.

Friday, July 8, 2011, 1:30PM, Rm H107, Bldg. 217

Energy loss in ion-surface collisions determines sputter yields, penetration depths and the formation of defects. However, for highly charged ions (HCIs), the amount of energy deposited in a solid upon impact is poorly understood compared to singly charged ions. For HCIs, energy transfer can be dominated by the inelastic dissipation of potential energy in connection with neutralization. This neutralization energy is the sum of the binding energies of electrons removed during ionization and can be 100 keV. Rapid deposition of this potential energy into a target material initiates a many- body electronic excitation that couples to the lattice and leads to the formation of permanent nanoscale defects. The ability to harness the potential energy from HCIs for new materials processing techniques and to mitigate its role in the erosion of plasma facing materials requires charge dependent measurements sensitive to nanoscale surface modifications. In this talk, I will quantitatively describe the dependence of projectile ion charge-state (Q) in the formation of HCI induced craters formed on thin Al2O3 films. Using the NIST electron beam ion trap (EBIT) facility, tunnel junction devices with ion-irradiated barriers were fabricated and measured in order to detect the charge-state dependent cratering of individual ions through the exponential dependence of tunneling conductance on barrier thickness. By applying a heated spike model, we determine that the total energy required to produce the craters spans from 8 keV to 25 keV over the investigated charge-states of Xe^Q+ (26 ? Q ? 44) with kinetic energies E = (8.1 x Q) keV. Partitioning energy from pre-equilibrium nuclear and electronic stopping as well as neutralization, we find that at least (27 ± 2) % of available ion neutralization energy is required to form the observed craters.

For further information contact Jabez McClelland, 301-975-3721, jabez.mcclelland@nist.gov

CNST Energy Research Group Seminar

## SURFACE-TO-BULK STRUCTURE MANIPULATION AND THE METROLOGY OF ATOMISTIC PROCESSES IN ENERGY RELATED MATERIALS

Faisal M. Alamgir
Georgia Institute of Technology,Materials Science and Engineering.

Friday, July 1, 2011, 2:00PM, Rm.H107, Bldg. 217

We will look at examples of systematic surface-to-bulk composition manipulation together with in-situ (and ex-situ) synchrotron-based experiments, specifically X-ray Absorption Spectroscopy (XAS), in the research of materials for energy storage (Li-ion battery intercalation reactions), energy conversion (surface reactions on fuel-cell catalysts) and energy harvesting (photo-induced water splitting and catalytic H2 production from ethanol). In the case of Li-batteries, we explore the oxygen electrochemistry under operating conditions to identify the release of mechanisms of O2 evolution from Li battery cathodes. O2 evolution is a very important safety concern in batteries for real-world applications. In the area of (electro/photo)catalysis, we investigate ultrathin metal films, consisting of less than 10 monolayers of one metal coating the surface of another, that are fabricated electrochemically, resulting in structures such as core-shell particles or high surface area substrates in which the film provides a conformal coating over a porous support. This study correlates three important aspects of ultrathin metal films: (1) fundamental electron exchange mechanisms (2) structure-dependent electrochemistry including fuel oxidation and desorption reactions, and (3) durability under reaction conditions as a function of layer thickness. The type of overlayer-substrate samples we can create are well suited to exploring electron tunneling and donation modes occurring in the near-surface regime of a bimetallic surface structure. By detecting thickness-dependent shifts in the binding energy and electron orbital occupancies of the overlayer material, we can infer the influence of the buried substrate metal on the electronic structure at the surface. This approach has allowed us to estimate the critical thickness above which a catalytically active ultrathin layer is entirely unaffected by the underlayer in certain catalytically relevant systems.

For further information contact Alec Talin, 301-975-4724, alec.talin@nist.gov

CNST Energy Research Group Seminar

## ENERGY TRANSPORT AND CONVERSION IN SEMICONDUCTOR NANOCRYSTAL SOLIDS

Dong-Kyun Ko
Department of Materials Science and Engineering, University of Pennsylvania.

Tuesday, June 28, 2011, 10:30AM, Rm.H107, Bldg. 217

Solids artificially constructed from semiconductor nanocrystals represent an exciting new form of condensed matter, as they can potentially capture not only the quantum features of the individual building blocks but also novel collective properties through coupling of the nanocrystal components. In this presentation, we report the measurement and interpretation of temperature-dependent thermopower in semiconductor nanocrystal solids, which elucidates the Fermi energy level and the density of states distribution. We utilize this information to monitor doping levels in PbTe nanocrystal solids assembled with different concentrations of "Ag2Te dopant nanocrystals". Combined with temperature-dependent electrical conductivity, these complementary measurements serve as unique and powerful electronic spectroscopy tools to reveal the carrier distribution and dynamics in semiconductor nanocrystal solids. Another scope of this study focuses on the development of solutionprocessable nanocomposites with enhanced thermopower via carrier energy filtering. A demonstration of this enhanced thermopower is provided by nancomposites composed of chemically synthesized Pt nanocrystals embedded in a hydrazine-based solution-processable Sb2Te3 semiconductor. This work highlights the ability to tune composition, size, shape, and concentration of nanocrystals and embedding them either in n- or p-type semiconductor matrices to engineer both carrier energy and phonon spectra with the ease of materials processing.

For further information contact Fred Sharifi, 301-975-4633, fred.sharifi@nist.gov

CNST Nanofabrication Research Group Seminar

## SOLID-LIQUID INTERFACE AND TRANSFORMATIONS IN AL ALLOYS ANALYZED BY IN SITU TRANSMISSION ELECTRON MICROSCOPY

Prakash Palanisamy
Department of Materials Science and Engineering, University of Virginia. Charlottesville, VA

Thursday, June 23, 2011, 10:30AM, Rm. H107, Bldg. 217

Understanding of solid-liquid interfaces and transformations are crucial for crystal growth technology. Three different sets of in situ heating and cooling experiments were conducted in the transmission electron microscope (TEM) to probe the solid-liquid interface and transformations in Al alloy particles. The first set of studies tries to investigate the solid-liquid interface in Al-Si-Cu-Mg alloy particles. The particles were heated in a TEM to 585 ºC. The alloy particles contain two phases, solid Si in contact with liquid Al with Cu and Mg in solution. X-ray spectra were acquired at three different temperatures, say 585 ºC and subsequently cooling it to 565 ºC and 470 ºC in the solid Si, liquid Al and at the solid Si-liquid Al interface. An interesting observation made during the compositional analyses was the Cu segregation at the solid Si-liquid Al interface, when the temperature was decreased from 585 ºC to 470 ºC. This heterogeneous Cu segregation at the solid-liquid interface appears to participate in nucleating a Cu-rich phase at the Si facet and is most probably an Al2Cu phase, correlated in conjunction with calorimetry and thermodynamic calculations. The Cu concentration measured at regular time intervals for 1.5 hr at the solid-liquid interface and in the liquid Al stays almost constant showing that Cu segregation at the interface is not kinetically driven. The second set of studies focus on the solid-liquid transformation and supercooling behavior in pure Al particles. Valence electron energy-loss spectroscopy (VEELS) in a TEM was used to determine the changes in the volume plasmon energy, and hence, the valence electron density during heating and cooling through the melting temperature. While heating the solid Al upto the melting temperature shows a non-linear plasmon energy change due to the phonon anharmonicity, the plasmon energy in liquid Al shows linear temperature dependence. Results show that pure liquid Al particles can be supercooled by 100 ºC prior to their transformation to the solid state and the plasmon energy change during supercooling is not a direct extrapolation from the liquid state. Extended energy-loss fine structure (EXELFS) analysis was carried out during solid-liquid transformation to determine the nearest-neighbor distance change and was compared with the inverse volume plasmon energy results. The third set of experiments was carried out to determine the plasmon at a singular solid Si-liquid Al interface using sub-eV-sub-Å-microscope (SESAM). The free-electron density at the singular interface is different from that of the solid Si and liquid Al as found by rastering the electron probe across the solid-liquid interface. The experimental VEEL spectra results were correlated with the energy-filtered TEM (EFTEM) images acquired using 0.2 eV energy window shows that the plasmon energy at the solid-liquid interface is 15.7 eV that agree with the theoretical non-relativistic calculation. This research was supported by the National Science Foundation under grant DMR-0554792.

For further information contact Renu Sharma, 301-975-2418, renu.sharma@nist.gov

CNST Nanofabrication Research Group Seminar

## GLASS FORMATION BOUNDARY APPROACH TO THE SINTERING OF ALUMINA

Thomas F Lam
Ph.D Graduate in Ceramics from Alfred University. Alfred, NY

Monday, June 20, 2011, 1:30PM, Rm. H107, Bldg. 217

Sintering in alumina has been extensively studied with a wide range of compositions and a correspondingly large variability of reported chemistries and mineralogy in the grain boundaries. Even with recent advances in the understanding kinetics of grain growth and grain boundary structures, only a few studies have attempted to interpret the evolution of the grain boundary phases and chemistries in alumina sintering potentially due to the fact that sintering of ceramics is a decidedly non-equilibrium process. Expanding on a concept used to successfully explain mineralogy of fired porcelain, the glass formation boundary approach is introduced to predict grain boundary evolution in sintered alumina. Microstructural evolution and grain boundary phases were investigated for four CaO:SiO2 ratios in isochronal sintering studies at 1400°C, 1600°C, and 1700°C. The microstructural analysis showed that additive ratios of high silica to calcia ratios yielded amorphous grain boundaries containing anorthite and mullite as secondary phases. A glass formation boundary was applied to explain the formation of mullite without the presence of anorthite. Anorthite found in the samples sintered at 1400°C were proposed to be caused by localized low temperature solid state reactions. A similar argument was used to explain anorthite and gehlenite precipitation at 1400°C at higher CaO ratios. At temperatures above 1600°C amorphous grain boundaries of invert glass compositions and anorthite were found at the grain boundaries and were explainable by an invert glass formation boundary. The glass formation boundary approach adequately provides an explanation for secondary phases reported in the literature and allows for the prediction of grain boundary chemistry in steady-state non-equilibrium conditions experienced when sintering alumina in the presence of a liquid phase (as would be expected in situations with alumina containing silica, alkali, and alkaline earth impurities). The volume of the secondary phases observed correlates with the grain boundary chemistry at the triple points also consistent with the glass formation boundary approach. Furthermore, it is shown that impurities can be viewed as localized concentrations where the volume of secondary phases is directly limited by the concentration of additives. Although this study has addressed CaO and SiO2 as the impurity chemistry, it is expected that this idea can be more globally applied to explain grain boundary evolution in alumina.

For further information contact J. Alexander Liddle, 301-975-6050, james.liddle@nist.gov

CNST Electron Physics Group Seminar

## LOW-ENERGY ION SCATTERING STUDIES OF OXIDES AND SEMICONDUCTORS

Reuben Gann
Dept of Physics/University of California.

Monday, June 20, 2011, 10:30AM, Rm H107, Bldg. 217

Low-energy (500 - 3000 eV) ion scattering is an attractive tool for studying surface structure, chemistry, and electronic properties. Time-of-flight (TOF) measurements in particular measure both the energy and the final charge state of scattered ions simultaneously. Ions that are singly scattered from the surface are guaranteed to do so from only the outer layer of atoms, making the technique very surface sensitive. In these experiments, TOF spectra are gathered from the surfaces of 1. an oxide high-TC superconductor Bi_2Sr_2CaCu_2O_8 (Bi-2212) and 2. clean Si(111) 7x7, in order to determine to what extent the dominant theory of resonant charge transfer can be extended from metals to nonmetals. In the case of Bi-2212, we measured the local electrostatic potential of the clean surface and the surface after adsorbing an alkali (K) and a halogen (I) and compared results to density-function calculations. The Bi-2212 surface was also a fascinating subject to study the effect of ion-beam mixing on a layered surface with low miscibility. Si(111) samples were studied to investigate the effect of dangling-bond passivation and doping (both type and concentration) on the neutralization probability of scattered Li ions on the 7x7 surface, revealing a surprisingly strong effect of doping.

For further information contact Jabez McClelland, 301-975-3721, jabez.mcclelland@nist.gov

CNST Nanofabrication Research Group Seminar

## THEORETICAL AND COMPUTATIONAL ISSUES IN FLUORESCENCE MICROSCOPY BEYOND THE DIFFRACTION LIMIT

Alex Small
Department of Physics, California State Polytechnic University, Pomona.

Friday, June 17, 2011, 10:30AM, Rm. H107, Bldg. 217

Superresolution microscopy techniques enable imaging of live cells with subwavelength resolution. In these techniques, fluorophores are switched on and off, with a sparse subset emitting light at any given time. Consequently, the fluorophores form non-overlapping blurs in the image plane, enabling localization of molecules with subwavelength resolution limited only by noise in photon detection. We used theoretical, statistical, and computational techniques to determine fundamental limits of performance. Using a kinetic model of the fluorophores, we proved the existence of an optimal image acquisition scheme, that maximizes the number of single-molecule images (i.e. no over-lapping blurs). In this scheme, the error rate (ratio of the number of multi-molecule overlap images to the number of images of single molecules) is constant. Interestingly, for fast acquisitions, the scheme is very robust: Deviations from the optimal scheme decrease the number of good images, but decrease the number of bad images (overlaps) to partially compensate. We also developed a formalism for benchmarking algorithms that correct errors by removing overlap images. Only a handful of performance parameters matter for image quality, opening up the possibility of designing fast error correction algorithms based on simple principles. Finally, to optimize the localization procedure, we developed a rapid approximation to the Gaussian Mask technique for least squares fits. Our algorithm significantly reduces the number of function evaluations needed. The results are similar to those obtained with the Gaussian Mask algorithm and images that have undergone noise filtering. This suggests the possibility of doing very fast molecule localization on images represented in a basis where they are sparse.

For further information contact Andrew Berglund, 301-975-2844, andrew.berglund@nist.gov

CNST Nanofabrication Research Group Seminar

## HEAT TRANSPORT IN THERMOELECTRICS

Yaguo Wang
PhD Candidate/School of Mechanical Engineering, Birck Nanotechnology Center, Purdue University.

Tuesday, June 14, 2011, 10:30AM, Rm. H107, Bldg. 217

The quest for economically affordable, sustainable energy resources poses a critical challenge to our society. One promising solution is thermoelectrics, which convert temperature differences to electric voltage and vice versa. Thermoelectrics can be utilized to harvest solar energy through the solar-thermoelectric technique, and also to recover waste heat generated from home heating, automotive exhaust, and various industrial processes. Thermoelectric cooler is of particular interest to the microelectronics industry. High-performance thermoelectric materials should possess high electrical conductivity while low thermal conductivity, simultaneously, which are unfortunately both facilitated by charge carriers. State-of-the-art nanotechnology enables us to create "new" thermoelectric materials with significantly improved properties, such as superlattices (SL) that have been shown to suppress the heat transport without blocking the flow of electrons. Other emerging concepts include quantum dots, filled cage-like structures, nanowires, carbon nanotubes (CNT), nano-pore arrays, and nanocomposites. These developments motivate the study of the fundamental mechanisms in thermoelectrics, which will advance the understanding of underlying physics as well as assist the design and optimization of thermoelectric devices. This talk will demonstrate a comprehensive methodology to study heat transport in thermoelectrics. Principles of the thermoelectric effect and its application in energy related areas will be briefly reviewed. Three experimental / numerical techniques will be introduced, including photo-acoustic analysis to characterize steady-state thermo-physical properties, time-resolved ultrafast laser spectrometer to reveal the ultrafast dynamics of energy carriers occurring on femtosecond (10-15 s) to picosecond (10-12 s) time scales, and high-performance molecular dynamics programs. A case study demonstrating this methodology to the heat transport in Bi2Te3/Sb2Te3 superlattices will be presented. Photo-acoustic technique is used to measure the thermal conductivities in Bi2Te3, Sb2Te3 thin films and Bi2Te3/Sb2Te3 SLs. The mechanisms behind the suppressed heat transport in SLs are examined with ultrafast time-resolved measurements through detecting coherent optical and acoustic phonons. Significantly enhanced scatterings of these phonons in Bi2Te3/Sb2Te3 SLs are revealed, which are attributed to the interfaces of the hetero-structure in SL. Also, decrease of acoustic phonon velocity resulted from folding and flattening of phonons branches is observed. Results show that both interface scattering and the reduced phonon velocity contribute to suppressing the heat transfer process in SLs. Extended Molecular Dynamics models are developed for Bi2Te3 thin films to compute the phonon relaxation time for every single phonon mode. This knowledge is critical to identify which phonon modes dominate and to design most effective scattering channels in superlattices.

For further information contact Rachel Cannara, 301-975-4258, rachel.cannara@nist.gov

CNST Electron Physics Group Seminar

## QUANTUM HALL FERROMAGNETISM IN GRAPHENE ON HEXA-BORON NITRIDE SUBSTRATES

Andrea Young

Thursday, June 9, 2011, 2:00PM, Rm H107, Bldg. 217

In graphene, the structure of the honeycomb lattice endows the wavefunctions with an additional quantum number, termed valley isospin, which, combined with the electron spin, yields four-fold degenerate, approximately SU(4) symmetric LLs. The expanded degenerate Landau level manifold makes a wide variety of symmetry breaking ordered states possible; an outstanding question of fundamental interest is which ones nature chooses, which excitations such states support, and to what extent these states can be manipulated. I will present recent experimental data obtained on high quality graphene devices fabricated on hexagonal Boron Nitride substrates, focusing on the broken symmetry integer quantum Hall regime. In graphene/hBN devices, all integer plateaus are observed at fields of a few tesla. This allows us to probe the transport of spin textured excitations through the application of an in-plane magnetic field, which tunes only the Zeeman energy. I will show that for half-filled quartet Landau levels (filling factors $\nu$ = 4; 8; 12), with the exception of $\nu$=0, the ground state is spin polarized and supports spin-flip excitations, while at $\nu$ = 4, these excitations contain multiple spins, suggesting that charge is carried by Skyrmions. At $\nu$ = 0, in contrast, I will show that the ground state is not spin polarized, and discuss recent progress towards inducing a spin polarized, edge-current carrying state.

CNST Electron Physics Group Seminar

## EXCITATION OF CHAOTIC SPIN WAVES THROUGH THREE-WAVE INTERACTIONS

Mingzhong Wu

Tuesday, June 7, 2011, 1:30PM, Rm H107, Bldg. 217

Nonlinear spin waves in magnetic systems are of both fundamental and technological interest. This presentation will report the excitation of chaotic spin waves in magnetic thin films through three-wave nonlinear processes. The experiments made use of a magnetic yttrium iron garnet (YIG) thin film strip and two microstrip line transducers placed over the YIG strip to excite and detect spin waves. The output signal from the detection transducer was fed back to the excitation transducer through an adjustable microwave attenuator and a linear microwave amplifier. The signal from such a feedback ring was sampled through a directional coupler, with feeds to a spectrum analyzer for frequency analysis and a fast oscilloscope for temporal signal measurements. Experiments were carried out in two regimes. In the first regime, a magnetic field was applied in the plane of the YIG film strip and parallel to the length of the strip, and the excitation of chaotic spin waves was realized through three-wave interactions between backward volume spin waves of different frequencies. In the second regime, a magnetic field was applied in the plane of the YIG strip and perpendicular to the length of the strip. In this case, the chaotic excitation was realized through three-wave interactions between surface and backward volume spin waves. The development of chaotic dynamics with increasing ring gain was studied. The chaotic nature of the measured signals was confirmed by irregular waveforms, broad spectra, finite correlation dimensions, and decaying auto-correlation profiles. The features of the measured chaotic signals for radar applications were also explored.

For further information contact Robert McMichael, 301-975-5121, robert.mcmichael@nist.gov

CNST Nanofabrication Research Group Seminar

## CHALLENGES AND PERSPECTIVES IN MULTI-FREQUENCY ATOMIC FORCE MICROSCOPY COMBINING AMPLITUDE- AND FREQUENCY-MODULATION

Santiago D. Solares
Department of Mechanical Engineering, University of Maryland, College Park.

Thursday, June 2, 2011, 10:30AM, Rm. H107, Bldg. 217

Significant progress has been achieved in atomic force microscopy (AFM) since its invention in 1986. A variety of imaging modes (contact, intermittent-contact, noncontact, etc.) equipped with different types of probes (conventional pyramidal or conical tips, nanotubes, nanowires, etc.) have enabled the acquisition of high-resolution topography and material property images of a wide range of nanoscale samples in liquids, air and vacuum environments. More recently dynamic AFM has been enhanced by incorporating multi-frequency characterization, whereby more than one eigenmode of the microcantilever is excited and controlled simultaneously, such that new characterization channels become available in addition to the fundamental eigenmode response. Since the response variables acquired through these channels (e.g., oscillation frequency, amplitude, and phase) are sensitive to different material properties, multi-frequency operation can effectively increase the amount of information that can be acquired during each scan of the sample. This talk will describe recently proposed techniques that combine amplitude and frequency modulation in bimodal and trimodal AFM operation, and will also present typical computational and experimental results (see Figure 1 [1,2]). The methods will be discussed in terms of their capability, advantages and disadvantages, as well as opportunities for future enhancements that could enable the development of standard procedures and samples. Figure 1. Trimodal AFM images of a SEBS KRATONTM G-1652 thermoplastic rubber triblock co-polymer: (left) second eigenmode phase superimposed on topography, (center) third eigenmode frequency shift superimposed on topography (note that the frequency scale is inverted), and (right) close-up images of the phase and frequency shift. These images were acquired with A1-o = 100 nm, A1-setpoint = 70 nm, A2-o ~ 8.5 nm, A3-o ~ 5.5 nm and scan speed = 5?m/s. The first three eigenmodes of the cantilever were operated in amplitude-modulation, open-loop and phase-locked-loop modes, respectively. [1] S.D. Solares and G. Chawla, J. Appl. Phys. 2010, 108, No. 054901. [2] S.D. Solares and G. Chawla, Meas. Sci. Technol. 2010, 21, No. 125502.

For further information contact Rachel Cannara, 301-975-4258, rachel.cannara@nist.gov

CNST Energy Research Group Seminar

## IN-SITU TEM ELECTROCHEMISTRY OF ANODE MATERIALS IN LITHIUM ION BATTERIES

Jian Huang
Center for Integrated Nanotechnologies, Sandia National Laboratories, Albuquerque, New Mexico.

Friday, May 27, 2011, 1:30PM, Rm.H107, Bldg. 217

We created the first nano-battery inside a transmission electron microscope, allowing for real time atomic scale observations of battery charging and discharging processes. Two types of nano battery cells [1], one ionic liquid based, and the other all solid based, were created. The former consists of a single nanowire anode, an ionic liquid (IL) electrolyte and a bulk LiCoO2 cathode; the latter uses Li2O as a solid electrolyte and metal Li as anode. Four case studies will be presented: 1) Upon charging of SnO2 nanowires in an IL cell, a reaction front propagates progressively along the nanowire, causing the nanowire to swell, elongate, and spiral. The reaction front is a "Medusa zone" containing a high density of mobile dislocations, which are continuously nucleated at the moving front and absorbed from behind. This dislocation cloud indicates large in-plane misfit stresses and is a structural precursor to electrochemically-driven solid-state amorphization. 2) In charging Si nanowires in both the IL cell and the solid electrolyte cell, the nanowires swell rather than elongate. We found unexpectly the highly anisotropic volume expansion in lithiated Si nanowires, resulting in a surprising dumbbell-shaped cross-section which developed due to plastic flow and necking instability. Driven by progressive charging, the stress concentration at the neck region led to cracking, eventually splitting the single nanowire into sub-wires. 3) Carbon coating not only increases rate performance but also alters the lithiation induced strain of SnO2 nanowires. The SnO2 nanowires coated with carbon can be charged about 10 times faster than the non-coated ones. Intriguingly, the radial expansion of the coated nanowires was completely suppressed, resulting in enormously reduced tensile stress at the reaction front, as evidenced by the lack of formation of dislocations. 4) The lithiation process of individual Si nanoparticles was observed in real time in a TEM. A strong size dependent fracture behavior was discovered, i.e., there exists a critical particle size with a diameter of ~ 150 nm, below which the particles neither cracked nor fractured upon lithiation, above which the particles first formed cracks and then fractured due to lithiation induced huge volume expansion. For very large particles with size over 900 nm, electrochemical lithiation induced explosion of Si particles was observed. This strong size-dependent fracture behavior is attributed to the competition between the elastic energy and the surface energy of the nanoparticles. These results highlight the importance of in-situ studies in understanding the fundamental sciences of lithium ion batteries.

For further information contact Alec Talin, 301-975-4724, alec.talin@nist.gov

CNST Nanofabrication Research Group Seminar

## IN-SITU ENVIRONMENTAL TEM STUDIES FOR DEVELOPING STRUCTURE-ACTIVITY RELATIONSHIP IN SUPPORTED METAL CATALYSTS

Santhosh Chenna
School of Mechanical, Aerospace, Chemical and Materials Engineering, Arizona State University. Tempe, AZ

Thursday, May 26, 2011, 10:30AM, Rm. H107, Bldg. 217

Observing the nanostructural evolution in real time can provide insights into fundamental materials processes and mechanisms of transformation, which are often difficult to obtain from ex-situ studies. In-situ transmission electron microscope (TEM) allows for the dynamic observation of nanoscale changes in the presence of external stimulus such as, electrical fields, magnetic fields, gas environments, laser pulses, heating, cooling etc. In the recent years in-situ microscopy has gained a significant importance in the field of heterogeneous catalysis providing fundamental processes taking place during dynamic gas-solid interactions taking place on the surface of the catalyst. Understanding structure-activity relations for heterogeneous catalysts is essential in developing a complete fundamental understanding of the functionality of catalytic materials. During a reaction, the catalyst may undergo several structural and chemical changes due to interactions between the material and the gases in the reactor. Thus to develop structure-activity relationships it is necessary to study the catalyst under working conditions. In-situ environmental transmission electron microscopy (ETEM) is a powerful tool to probe the nanoscale structural and chemical changes taking place in the catalyst under reacting gas conditions. In this presentation, I will present the data of in-situ ETEM studies on nanostructures in parallel with ex-situ reactor studies of conversions and selectivities on Ni/SiO2 and Ru/SiO2 catalysts for partial oxidation of methane reaction (CH4 + ½ O2 to CO + 2H2). Partial oxidation of methane is an important reaction for syngas (CO + H2) production and the product gas ratio (H2/CO = 2) obtained is suitable as an input for Fisher-Tropsch synthesis. I will also present some preliminary data on operand TEM technique, where we can measure the catalytic performance inside the environmental cell using electron energy loss spectroscopy. This technique can allow us to observe the nanostructural changes taking place in the catalyst while simultaneously measuring its activity.

For further information contact Renu Sharma, 301-975-2418, renu.sharma@nist.gov

CNST Electron Physics Group Seminar

## INTERESTING PHYSICS IN MAGNETIC TUNNEL JUNCTIONS

Feng Guo
PhD Candidate/University of Minnesota.

Thursday, May 19, 2011, 10:30AM, Rm H107, Bldg. 217

Though straightforward, tunneling transport measurements often bring us something unanticipated. In this talk, I will discuss a pronounced voltage dependent conductance feature present at nonzero bias in magnetic tunnel junctions. The presence of this feature depends upon the oxidation condition for creating the barrier; it is only present for short and moderate oxidation times. I will show the interfacial nature of this effect and describe how the electronic structure of the chemical bonding at the barrier interface could be responsible for this conductance feature. As a separate part of my talk, I will discuss noise measurements in spin valve systems, both GMR and tunnel junction devices, and discuss how it can open up a new method to understand physical processes.

For further information contact Robert McMichael, 301-975-5121, robert.mcmichael@nist.gov

CNST Electron Physics Group Seminar

## NANOSCALE DOMAIN WALL MOTION IN PERPENDICULAR FERROMAGNETIC LAYERS

Andy Balk
PHD Candidate/Penn State University.

Tuesday, May 17, 2011, 10:30AM, Rm H107, Bldg. 217

We describe measurements of nanoscale magnetic domain wall motion in perpendicularly magnetized GaMnAs. We use the anomalous Hall effect (AHE) as a sensitive local magnetometer, which allows observation of an assortment of novel domain wall properties. First we demonstrate feedback controlled domain wall motion with submicron positioning capability. This feedback technique illustrates the stochastic nature of micron and larger scale domain wall motion. Furthermore we show evidence for another, non-stochastic, adiabatic regime of motion which we identify as a domain wall flexing mode. We analyze the stiffness of this flexing to calculate domain wall pinning site strength and density. We also measure the field driven domain wall mobility in the flexing mode and show it is at least an order of magnitude higher than previously measured creep mobility, an observation which may be important for domain wall logic applications. Finally, our measurements provide evidence for thermally activated domain wall site hopping over distances similar to the characteristic domain wall width. The preprint for this work is located at arXiv:1103.5240at :arXiv:1103.5240

For further information contact John Unguris, 301-975-3712, john.unguris@nist.gov

CNST Nanofabrication Research Group Seminar

## CAPILLARY INTERACTIONS AMONG SPHERICAL PARTICLES AT A CURVED LIQUID INTERFACE

Chuan Zeng
Physics Department, University of Massachusetts Amherst.

Monday, May 16, 2011, 10:30AM, Rm. H107, Bldg. 217

Colloidal particles tend to adsorb on liquid interfaces, where in- plane interactions can arise from a variety of mechanisms. We focus on capillary interactions induced by the curvature of the liquid interface, where particles were assumed to have a constant Young-Laplace contact angle at the three-phase contact line. Whereas spherical particles can adsorb on flat or spherical interfaces without deforming the interface, adsorption on a cylindrical interface deforms the interface because of the lack of azimuthal symmetry around the contact line. We present an analytical model of the interfacial shape and energy upon adsorption of a single particle as well as the interaction between two particles. Based on our result on a cylindrical interface, we propose a general formula for the force on a particle on a curved interface. This study provides an important step toward understanding the interactions among interfacial particles when the interface is distorted by an external field. We acknowledge support from the NSF-supported MRSEC on Polymers at UMass (DMR- 0820506) and NSF CBET-0967620.

For further information contact Andrew Berglund, 301-975-2844, andrew.berglund@nist.gov

CNST Energy Research Seminar

## NANOPATTERNED SUBSTRATES FOR SINGLE-MOLECULE DNA MANIPULATION

Teresa A. Fazio
Department of Applied Physics and Applied Mathematics, Columbia University.

Friday, May 13, 2011, 10:30AM, Rm. H107, Bldg. 217

Single molecule studies of protein-DNA interactions continue to yield new information on numerous DNA processing pathways by enabling real-time observation of proteins as they interact with their DNA substrates. Despite the power of single molecule imaging, the experiments remain technically challenging and are often limited by the difficulty of acquiring statistically significant data sets. To address these issues, we have developed a novel technology called "DNA curtains" in which we utilize a combination of fluid lipid bilayers, nanofabricated barriers to lipid diffusion, and hydrodynamic flow to organize lipid-tethered DNA molecules into defined patterns on the surface of a microfluidic sample chamber. Furthermore, DNA arrays on substrates are an increasingly popular tool for directed self-assembly of nanoscale architectures. One such substrate involves AuPd nanodots, which can be functionalized with oligonucleotides which bind to complementary overhangs on double-stranded DNA. This platform is suitable for directed self-assembly of 200-base pair double-stranded DNA molecules decorated with Au nanoparticles using a PNA-DNA chimera as a linker. In this way, site-selective placement of gold nanoparticles has been achieved.

For further information contact Veronika Szalai, 301-975-3792, veronika.szalai@nist.gov

CNST Electron Physics Group Seminar

## SEMPA INVESTIGATIONS OF THE MAGNETIC MICROSTRUCTURE OF NI(111), SOFT MAGNETIC NANOWIRES, AND VORTEX DOMAIN WALLS

Sebastian Hankemeier
Postdoctoral fellow/Hamburg University.

Thursday, May 12, 2011, 10:30AM, Rm H107, Bldg. 217

I will present some results obtained within the SEMPA project in the group of Prof. H.P. Oepen at Hamburg University. A brief description of the SEMPA technique will be followed by a discussion of the magnetism at the Ni(111) single-crystal surface. In the second part of my talk I will discuss the magnetic fine structure in remanence and the appearance of domain walls in bent nanowires depending on their geometrical properties. Furthermore, I will present a method for controlling the properties of vortex domain walls via magnetic seeding fields. The last part of the talk will then deal with the manipulation of such vortex structures utilizing the spin-transfer torque effect.

For further information contact John Unguris, 301-975-3712, john.unguris@nist.gov

CNST Nanofabrication Research Group Seminar

## A DIRECTLY PATTERNABLE, FULLY INORGANIC HARDMASK FOR HIGH RESOLUTION LITHOGRAPHY

Andrew Grenville
Inpria Corporation.

Thursday, May 12, 2011, 9:30AM, Rm. H107, Bldg. 217

Inpria is developing a directly patternable, fully inorganic hardmask for high resolution lithography. This novel resist platform is based on our solution-deposited metal oxide sulfate dielectric system. The films are atomically smooth, dense and amorphous so are amenable to high resolution with extremely low LWR. The platform has achieved a resolution of 10 nm half-pitch and 1.6 nm LWR at 30 nm half-pitch via e-beam lithography. In addition, as the system does not rely on chemical amplification, it has no acid diffusion and therefore has an especially low resist blur. This is apparent in improved 2-D image fidelity, low LWR and high ultimate resolution. Pattern collapse is also mitigated since an ultrathin (20 nm) imaging layer is possible, and the film itself serves as an inorganic high-selectivity etch mask. We are also developing versions of the material for EUV and 193nm lithography, as well as for spin-on oxide hardmask applications. I this seminar, I will discuss the platform and its application to nanofabrication.

For further information contact James Alex Liddle, 301-975-6050, james.liddle@nist.gov

CNST Nanofabrication Research Group Seminar

## ELECTRONIC AND STRUCTURAL PROPERTIES OF III/V SEMICONDUCTING NANOWIRE HETEROSTRUCTURES

Melodie Fickenscher
Doctoral Candidate in Physics / University of Cincinnati. Cincinnati, OH

Tuesday, May 10, 2011, 10:30AM, Rm. H107, Bldg. 217

Recent developments in the growth of semiconductor nanowires now enable the precise growth of axial and radial heterostructures between almost any two materials. This flexibility provides a unique opportunity where the band structure and electronic wave functions can be tailored to explore the basic physics of one dimensional systems or develop new nanodevices for applications. This talk reviews our work which uses a wide variety of CW and time-resolved spectroscopic techniques to study the electronic properties of these nanowire heterostructures, and correlate these properties using structural characterization by transmission electron microscopy. I will discuss in this talk the particular cases of core/multi-shell GaAs/AlGaAs nanowires where electronic states show evidence of quantum confinement, and lattice mismatched GaAs/GaP nanowires where compressive strain dramatically impacts the band structure of the GaAs core.

For further information contact Renu Sharma, 301-975-2418, renu.sharma@nist.gov

CNST Nanofabrication Research Group Seminar

## COMPOSITIONALLY MODULATED KINETIC TRAPPING: SYNTHETIC AND STRUCTURAL IMPLICATIONS ON THE NANOSCALE

Michael Anderson
Center for Green Materials Chemistry and Materials Science Institute at University of Oregon.

Monday, May 9, 2011, 10:30AM, Rm. H107, Bldg. 217

Synthetic control in solid state systems represents a unique challenge. The majority of solid state synthetic techniques are limited to the most thermodynamically stable product and result in heterogeneous product distributions. As technology is driven to look at metastable compounds for new high performance materials, the ability to synthesize these novel compounds has become the limiting factor. Compositionally modulated kinetic trapping (CMKT) has provided new avenues for generating metastable compounds with a high degree of synthetic control. This control allows us to generate structures that can be tailored to probe the fundamental size-structure-property relationship that is critical for nanoscale technologies. CMKT imparts to the solid state chemist a similar degree of synthetic control as is found in organic syntheses allowing for designed synthesis of compounds while avoiding undesirable reaction byproducts and intermediates. This presentation will provide an overview of the CMKT method and present the results of a series of studies where CMKT was used to explore questions of structure, solid state synthesis, and rational design of metastable compounds that would not have otherwise been possible using conventional synthetic routes.

For further information contact Renu Sharma, 301-975-2418, renu.sharma@nist.gov

CNST Nanofabrication Research Group Seminar

## NANOPLASMONICS AND NANOPHOTONICS WITH ELECTRONS

Mathieu Kociak
Charge de Recherche/de Physique des Solides (UMR CNRS 8502). Orsay, France

Friday, May 6, 2011, 1:30PM, Rm. H107, Bldg. 217

How light behaves and interacts with matter the nanometer scale is a fascinating subject. Indeed, at the nanometer scale both the electromagnetic field and the electron wave functions may be subject to confinement. This is why the optical properties of nano-objects will in general depend drastically on their shape, size and local environment. This the case for surface plasmons on metallic nanoparticles, which can be viewed as classical electromagnetic standing waves, or for the excitons in quantum emitters (such as Quantum Dots), where the confinement now affects the electron wavefunction. Obtaining spectroscopic information at the scale of a nanoparticle, or within the nanoparticle itself is not straightforward because the required spatial resolution can be one or two order of magnitude smaller than the equivalent wavelength of light in the vacuum. Such information is however crucial in many applications (for example biosensors for surface plasmons or photodetectors for excitons). The techniques using photons alone to probe optical properties of nanoparticles thus tend to be very difficult to use. An alternative is to use electrons, taking advantage that the Electron Energy Loss Spectroscopy (EELS) and the Cathodoluminescence (CL) spectroscopy can be roughly viewed as the nanometric analog to the optical absorption and the photoluminescence respectively. In this talk, I will review few results obtained in a Scanning Transmission Electron Microscope (STEM) on the nanometer-scale optical properties of metallic nanoparticles and quantum emitters. In a first part, I will describe how EELS in a STEM can be experimentally used to obtained spatially resolved spectral imaging on metallic nano-objects [1]. I will start from simple, highly crystalline nanoparticles (silver triangles and cubes) to top-down, highly imperfect structures (Split Ring Resonators), and put a special emphasis on the spatial coherence of plasmons in such nanoparticles [2,3]. I will draw the link between the EELS signal and the optical quantity of interest in near-field optical experiments, namely the Electromagnetic Local Density of States [4]. In a second part, I will present a new CL set-up we have developed and show how it can be used to probe optical properties of quantum emitters at the scale of quantum confinement – typically few nanometers. This will be exemplified on recent results on GaN/AlN composite nanowires [5] and metallic nanoparticles. [1] J. Nelayah et al. Nature Physics, 3, 348 (2007) [2] J. Nelayah et al., Nano Letters, 10, 902 (2010) [3] S. Mazzucco, et al., in preparation [4] J. Garcia de Abajo and M. Kociak, Phys. Rev. Lett., 100, 106804 (2008) [5] L. Zagonel et al., Nanoletters ASAP (2010)

For further information contact Renu Sharma, 301-975-2418, renu.sharma@nist.gov

CNST Energy Research Group Seminar

## PLASMONIC ENHANCEMENT ENGINEERING FOR NEAR-GREEN SEMICONDUCTOR LIGHT EMITTERS

John Henson
Postdoctoral Researcher, Boston University.

Thursday, May 5, 2011, 10:30AM, Rm. H107, Bldg. 217

As the development of energy efficient light sources becomes a greater priority for governments, businesses, and consumers, light emitting diodes (LEDs) have become a much sought after technology and one of focused research. It is widely observed that as the emission wavelength of such devices moves into the green part of the visible spectrum, their internal quantum efficiency degrades. LED manufacturers are investing significant resources towards research to improve device efficiency in this green spectral region and throughout the entire UV-visible spectrum. In this work we study the use of plasmonic nanostructures as a method for enhancing the efficiency of light emitting devices. The field of plasmonics has been actively studied in recent years and holds great technological potential for several applications. Once resonantly excited, collective oscillations of the electron gas on the surface of a metal at the interface with a dielectric are known to have several novel optical properties. Surface plasmon polaritons (SPPs) confined to the surface of a planar metal film, and localized surface plasmons (LSPs) confined to the surface of a nanostructure, feature large local optical fields in the near-field zone of the surface and have large modal densities. Plasmonic nanostructures are currently being studied for use in applications such as waveguiding, bio-sensing, surface-enhanced spectroscopy, solid state light emission, and solar cells. It is known that both SPPs and LSPs can enhance the spontaneous emission rate of a nearby radiating dipole, by virtue of their large associated local fields. Effective scattering of plasmons into the radiation continuum can then lead to large enhancements in radiated field intensity. In this work, we study the application of various metallic nanostructures to nitride semiconductor light emitters to enhance their emission efficiency. Computational investigations were conducted to optimize nanostructure geometries for this application and to study their optical properties. Experimentally, we have demonstrated enhancements in collected photo-luminescence intensity and increased emitter recombination rates. Additionally, diffractive effects from carefully designed periodic arrays have been shown to further enhance light extraction and lead to large intensity enhancements.

For further information contact Andrea Centrone, 301-975-8225, andrea.centrone@nist.gov

CNST Electron Physics Group Seminar

## FORMATION OF EPITAXIAL GRAPHENE ON SILICON CARBIDE: COMPARISON OF SI-FACE AND C-FACE

Randall M. Feenstra
Professor/Dept. Physics, Carnegie Mellon University.

Thursday, April 28, 2011, 2:00PM, Rm H107, Bldg. 217

In this talk I will present results on the formation of epitaxial graphene on SiC by heating SiC in vacuum or in various environments. In this process, silicon preferentially leaves the surface due to sublimation, and the carbon left behind self assembles into graphene. High-quality graphene can readily be produced on the Si face [the (0001) surface] in this manner, but graphene formation on the C-face [the (000-1) surface] is more problematic. On the Si-face a well known intermediate layer forms between the SiC and the graphene; this so-called "buffer layer" likely aids in the formation of the graphene, but it is also thought to possibly reduce the mobility of electrons in the graphene. Hence, it is desired to produce graphene on the C-face (where a similar type of intermediate layer is not present). In addition to the formation of graphene in vacuum, inert gas environments have also been studied as a means of allowing independent control of the sample temperature and the Si sublimation rate. Formation of very large, uniform graphene monolayers on the Si-face has been achieved, but again the formation of such layers on the C-face is problematic. Using a combination of low-energy electron microscopy (LEEM) and atomic force microscopy (AFM), the morphology of graphene on these two surfaces of SiC has been studied in detail.

CNST Nanofabrication Research Group Seminar

## WETTING TRANSITIONS ON DESIGNED MICRO-STRUCTURED SURFACES

Carlos E Colosqui
Fuel Cell Research Laboratory, Chemical and Biological Engineering Department Princeton University.

Friday, April 22, 2011, 10:30AM, Rm. H107, Bldg. 217

Nano/micro-structured surfaces can be designed to switch between hydrophobic and hydrophilic conditions under the influence of electric fields, temperature, or electromagnetic radiation. Application of this phenomena is extremely promising for water management in hydrogen fuel cells among many other technologies. While macroscale thermodynamics can predict static contact angles and other equilibrium properties, multiscale approaches are required for understanding the transition between wetting states (i.e. Wenzel and Cassie states), and the associated contact angle hysteresis, which involves processes at sub-micron scales (e.g. pinning of the contact line) and atomic scales (e.g. adhesion hysteresis). Our current research goal is to define micro-structure designs that allow wetting-dewetting transitions with minimal external actuation. For that purpose, we combine direct numerical simulation via microscopic approaches (i.e. lattice Boltzmann simulation) with techniques from applied mathematics (equation free methods) in order to perform pseudo-arclength continuation and bifurcation analysis at macroscopic level. Continuation diagrams expose the effect that diverse geometric features have on the stable (and unstable) steady states observed in simulation and experimental studies.

For further information contact Sukumar Rajauria, 301-975-2160, sukumar.rajauria@nist.gov

CNST Nanofabrication Research Group Seminar

## ADVANCED SURFACE MODIFICATION WITH NANO-COMPOSITE FILMS

Jeff Chinn
Ph.D./Integrated Surface Technologies. Menlo Park, CA

Friday, April 15, 2011, 1:30PM, Rm. H107, Bldg. 217

The functionality and performance of many micro-devices is closely coupled to the control of their microstructure's surface properties. MEMS, micro-fluidics, micro-plates, and ink-jet heads are just some devices which can benefit from surface modification using organic monolayer type films with the desired functional properties. Recently, techniques which allow for the inclusion of inorganic metal oxides have been used to create films, which are called nano-composites. For example, low cost super-hydrophobic coatings can be created by depositing rough metal oxides that are subsequently treated with a low surface energy material. Integrated Surface Technologies (IST) will present its surface engineering technology, which allows for the deposition of organic and inorganic films in a single tool and describe the unique material issues that have been addressed with these films.

For further information contact Sukumar Rajauria, 301-975-2160, sukumar.rajauria@nist.gov

CNST Energy Research Group Seminar

## CHEMICAL IMAGING: AN EMERGING AVENUE FOR MOLECULAR CHARACTERIZATION IN HETEROGENEOUS MATERIALS

Rohit Bhargava
Center for Advanced Study & Beckman Institute for Advanced Science &Technology,University of Ilinois.

Friday, April 15, 2011, 10:30AM, Rm.H107, Bldg. 217

Chemical imaging is an emerging modality that can provide molecular information without dyes, probes or human interpretation. In one implementation of chemical imaging, spectroscopy is used to measure both intrinsic molecular composition and structure of man-made and natural materials. Computer algorithms then convert the rich data into information. Here, we first describe the development of mid-infrared spectroscopic imaging instrumentation, {Anal. Chem., 2010} associated analytical methods and applications of this new technology. Examples of molecular dynamics in heterogeneous polymer systems {Macromolecules 2003} and forensic applications {Anal. Bioanal. Chem., 2009} will be provided. We especially focus on an application that seeks to provide input to the research and clinical efforts in the analysis of human tissues for cancer. Three levels of applications will be discussed for prostate and breast tissue – for the researcher,{Nat. Biotechnol., 2005} for clinical application{Cancer Res., under review} and for predictive medicine. The information can be used as stand-alone diagnostic information or as an adjunct to help pathologists make rapid and efficient decisions. The molecular underpinnings of the spectroscopic information are explored. Next, we describe a new paradigm in making ultrasensitive surface enhanced Raman probes that can result in substantial molecular information to be easily added to biomedical studies or clinical assays. {PNAS, 2010; Opt. Exp., 2010} The development and potential use of these probes for predictive medicine will be discussed in the context of label-free imaging. Finally, we describe how a parallel effort in fundamental theory {Anal. Chem., 2010} and latest advances in instrumentation {Nat. Methods, 2011} are opening of new scientific avenues in computational chemical imaging.

For further information contact Andrea Centrone, 301-975-8225, andrea.centrone@nist.gov

CNST Nanofabrication Research Group Seminar

## UV NANOIMPRINT LITHOGRAPHY STATUS AND APPLICATIONS

S.V. Sreenivasan
Professor and Thornton Centennial Fellow in Engineering at the University of Texas at Austin.

Friday, April 15, 2011, 9:30AM, Rm. H107, Bldg. 217

Nanoimprint lithography techniques are known to possess remarkable replication capability down to sub-5nm resolution. Translating this nano-scale resolution to a commercially viable manufacturing approach requires development of tools, materials, masks and processes that can achieve reliable nano-scale performance at reasonable cost. In recent years, a form of UV imprint lithography known as Jet and Flash Imprint Lithography (J-FIL) has seen significant progress in mask infrastructure, materials, pattern transfer, defect reduction, overlay, and throughput. This progress is creating applications of J-FIL in data storage including patterned media for hard disk drives, and solid state memory at sub-25nm half-pitch nodes. The speaker will present the current state of J-FIL technology in terabit density magnetic storage and advanced solid state memory. He will discuss both stepper as well as whole substrate patterning tools developed using J-FIL. Finally, he will also discuss emerging applications of J-FIL in the biomedical and energy sectors. In addition to the technical presentation, the speaker will include a brief discussion of his experience in commercialization of this technology from a university environment. He will address the challenges involved in raising capital and creating the appropriate team to transition from a technology culture to a product culture.

For further information contact J. Alex Liddle, 301-975-6050, james.liddle@nist.gov

CNST Electron Physics Group Seminar

## ELECTRONS IN HONEYCOMB LATTICES: SURPRISES FROM ELECTRON-ELECTRON INTERACTIONS IN GRAPHENE AND "ARTIFICIAL GRAPHENE"

Marco Polini
Assistant Professor; NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore/Pisa, Italy.

Wednesday, April 13, 2011, 10:30AM, Rm H107, Bldg. 217

Electrons in graphene, a recently isolated one-atom-thick material, move in the presence of a potential created by the periodic arrangement of carbon atoms in a two-dimensional (2D) honeycomb lattice. Periodic potentials with the same crystalline symmetry can also be created artificially, e.g. by nanofabrication applied to an ordinary semiconductor heterostructure that supports a high quality 2D electron gas [1]. In this talk I will review some of the most important electronic properties of these systems, including unusual plasmons [2] and plasmaron satellite bands [3] in graphene and Mott-Hubbard collective modes in "artificial graphene" [4]. References [1] M. Gibertini et al., Phys. Rev. B 79, 241406(R) (2009); C.-H. Park and S.G. Louie, Nano Lett. 9, 1793 (2009); G. De Simoni et al., Appl. Phys. Lett. 97, 132113 (2010). [2] S.H. Abedinpour et al., arXiv:1101.4291. [3] A. Bostwick et al., Science 328, 999 (2010). [4] A. Singha et al., to be published.

For further information contact Joseph Stroscio, 301-975-3716, joseph.stroscio@nist.gov

CNST Nanofabrication Research Group Seminar

## NEW EXPERIMENTAL AND MODELING TECHNIQUES TO SIGNIFICANTLY IMPROVE THE CONFINEMENT OF NANOPARTICLES TO OPTICAL TRAPS

Arvind Balijepalli
Mechanical Metrology Division, Physical Measurement Laboratory, NIST.

Tuesday, April 12, 2011, 10:30AM, Rm. H107, Bldg. 217

The development of complex three-dimensional nanodevices is currently impeded by the absence of effective prototyping tools at the nanoscale. Optical trapping is well established for flexible three-dimensional manipulation of components at the microscale. However, it has so far not been demonstrated to confine nanoparticles for long enough time to be useful in nanoassembly applications. We demonstrate new techniques that successfully extend optical trapping to nanoscale manipulation by increasing trapping lifetimes more than an order of magnitude without correspondingly increasing the average trap power. This is based on fast scanning traps that also enable simultaneous manipulation of multiple particles with complete control (e.g. nanowire manipulation in 5 degrees of freedom). We will present these capabilities and discuss the implications for nanoscale measurement and prototyping.

For further information contact Andrew Berglund, 301-975-2844, andrew.berglund@nist.gov

CNST Nanofabrication Research Group Seminar

## FOUR WAVE MIXING IN HIGHLY RESONANT SYSTEMS: NONLINEAR AND QUANTUM

Postdoctoral Researcher / The French National Center for Scientific Research. Paris, France

Monday, April 4, 2011, 1:30PM, Rm. H107, Bldg. 217

In this talk, I will present some recent results with regards to novel applications of the process of parametric four-wave mixing in highly resonant systems. Two systems will be the focus of the talk: high-Q silica microspheres and 87Rb atomic vapors. In the first part, high-Q silica microspherical cavities are introduced with a special focus on the theory of cavity-mode dispersion. The conditions for parametric four-wave mixing are then analyzed via a simulation based on the split-step Fourier method, capable of handling both the dispersion and nonlinearity of silica microspheres. The results of the simulation are confirmed experimentally, whereby a frequency comb exceeding 250 nm in spectral width is generated through cascaded four-wave mixing. Finally, the quantum theory of four-wave mixing in a silica microsphere is presented. The second part of the talk is dedicated to quantum effects originating from four-wave mixing in an atomic vapor. It is in principle possible to generate pulsed and continuous-wave squeezed vacuum in an atomic vapor through the process of parametric four-wave mixing, which assures the compatibility of the generated squeezed light with atom-based quantum memories. Experimentally, we demonstrate that a simple pass of a pump laser through a 87Rb vapor cell can generate squeezed vacuum with a noise level 1.5 dB below the shot noise limit in a fully-degenerate continuous-wave configuration, and over 1.3 dB of pulsed time-domain squeezing in a non-degenerate parametric amplifier configuration.

For further information contact Kartik Srinivasan, 301-975-5938, kartik.srinivasan@nist.gov

CNST Energy Research Group Seminar

## NANOSCALE ENGINEERING OF STRAIN: FROM ALLOYING IN EPITAXIAL NANOCRYSTALS TO MULTIJUNCTION SOLAR CELLS

Marina S. Leite
The Thomas J. Watson, Sr. Laboratories of Applied Physics, California Institute of Technology.

Friday, April 1, 2011, 10:30AM, Rm. H107, Bldg. 217

Strain engineering at the nanoscale enables the control of a semiconductor material's bandgap energy, which can be used for optoelectronic device applications. Depending on the mechanical strain (elastic energy) between a substrate and an epitaxially grown material, different morphologies can be achieved ranging from strained planar films to 3-dimensional nanocrystals. In the first part of my talk I will show how Ge-Si:Si(001) coherently-strained islands were used to implement an open (closed) system, in which matter is (not) exchanged through surface diffusion. The driving forces and the role played by the different alloying mechanisms, while the system approaches the equilibrium, provide a better understanding of why and how alloying takes place for dome-shaped Ge-Si islands. In the second part of the talk I will discuss a new approach for multijunction solar cells based on direct bandgap III-V semiconductor alloys. Device simulations indicate that efficiency over 50 % can be achieved at 100-suns illumination by using a 4-junction cell formed by InAlAs/InGaP/InGaAsP/InGaAs. For the top subcell, InAlAs, we fabricated wide bandgap solar cells with efficiencies 14 % and Voc = 1 V. The ideal bandgap energy combination corresponds to a lattice parameter of 5.80 Å, which is not available in bulk form. Therefore, we created a "virtual substrate" for epitaxial growth. By relieving 40 nm thick coherently-strained compressed and tensile InxGa1-xAs films from InP substrates, full elastic relaxation occurs preserving the crystalline quality of the films. This method can be implemented to achieve optoelectronic devices with unique properties, including high efficiency solar cells. Bio: Marina Leite received her BS degree in Chemistry, from University of Pernambuco, Brazil, in December 2000. She received both her MS and PhD in Physics from Campinas State University (UNICAMP) in 2003 and 2007, while working at the Brazilian Synchrotron Light Source Laboratory. In her MS program she worked with the synthesis and structural characterization of colloidal nanoparticles. During her PhD, she investigated the growth thermodynamics of self-assembled epitaxial Ge-Si nanocrystals in both the kinetic and the quasi-equilibrium regimes. In 2006 she was a visiting researcher at the Max-Planck Institute for Solid State Physics and the Eindhoven Technical University, in the Netherlands. In 2008 she joined Harry Atwater's group at Caltech as a postdoctoral scholar, working on multijunction solar cells.

For further information contact Nikolai Zhitenev, 301-975-6039, nikolai.zhitenev@nist.gov

CNST Electron Physics Group Seminar

## GRAPHENE: SCRATCHING THE SURFACE

Michael Fuhrer
Professor, Department of Physics/University of Maryland.

Thursday, March 31, 2011, 2:00PM, Rm H107, Bldg. 217

Graphene, a single atom-thick plane of graphite, has recently been isolated and studied experimentally. In this two-dimensional hexagonal lattice of carbon atoms, the electrons obey the Dirac equation for massless particles, complete with a two-component spinor degree of freedom that mimics the spin of a relativistic particle. Graphene is also composed entirely of surface atoms, making the techniques of surface science useful in studying its properties. In this talk, I will first discuss the electronic structure of graphene, and its implications for electronic properties. I will then discuss experiments which combine ultra-high vacuum (UHV) surface science with electronic transport measurements. Surface science techniques can be used to controllably modify graphene's properties: potassium atoms can be deposited to form charged impurity scatterers; ice can be deposited to modify the dielectric environment of graphene and tune the electron-electron interaction strength; and ion irradiation can be used to create atomic vacancies which act as Kondo impurities. Graphene is an extraordinarily sensitive to surface adsorbates, and can be used to detect e.g. the ordering of potassium atoms, or reaction of potassium with water, both at concentrations below 1/1000th of a monolayer.

CNST Energy Research Group Seminar

## CHALLENGES AND OPPORTUNITIES FOR WATER DESALINATION AND REUSE

Todd Anderson
General Electric Global Research, Niskayuna, NY.

Monday, March 28, 2011, 1:30PM, Rm.H107, Bldg. 217

Clean water is a commodity that is becoming increasingly scarce due to the depletion of local natural resources and the demand and associated pollution of increasing populations. As a result, the number of global regions experiencing water stress has been steadily increasing. It is predicted that nearly two thirds of the world's population could be experiencing water stress by 2025. Though water conservation is an obvious and important first step, it is generally not capable of addressing the challenge. Therefore new water sources and increased water recycling are required to support continued population and economic growth. To meet those challenges, there is a significant and growing global R&D effort to deliver new purification technologies both for desalination and water reuse. In this talk I will discuss several of the technologies we are pursuing for robust and lower cost desalination, and wastewater and produced water purification. This discussion will highlight the opportunities and key materials and engineering challenges for reverse osmosis based processes.

For further information contact Fred Sharifi, 301-975-4633, fred.sharifi@nist.gov

CNST NANOFAB SEMINAR

## SUBSTRATE BONDING AND OPTICAL LITHOGRAPHY INNOVATIONS PRESENTED BY SUSS MICROTEC

John E. Edwards
Regional Sales Manager- Suss Microtec.

Tuesday, March 22, 2011, 1:00PM, Rm. H107, Bldg. 217

Of growing importance in 3D packaging is temporary bonding of thinned substrates to carrier substrates. The current state of the art in temporary bonding/de-bonding techniques and materials will be discussed as well as permanent bonding processes. Innovations in optical lithography, including conformal wafer-level nano imprinting and selective surface conditioning with plasma will also be described. New tools developed by SUSS in support of these technologies will be presented.

For further information contact Vincent Luciani, 301-975-2886, Vincent.Luciani@nist.gov

CNST Nanofabrication Research Group Seminar

## ELECTRICALLY PUMPERD, PLASMONIC DFB LASERS

Milan Marell
PhD Candidate, Eindhoven University of Technology. Eindhoven, Netherlands

Monday, March 21, 2011, 10:30AM, Rm. H107, Bldg. 217

Our latest results on the design, fabrication and characterization of metallic coated DFB lasers will be presented. These devices are based on a special form of the metal-insulator-metal waveguides, which support plasmon gap modes. The distributed feedback provides control over the laser's wavelength and its emissive properties. The size of the semiconductor core can be as small as 100 nm, which is well below the diffraction limit of light (for the wavelength of operation). The devices operate in the near-infrared and may eventually be suitable for low-power, high-speed applications.

For further information contact Kartik Srinivasan, 301-975-5938, kartik.srinivasan@nist.gov

CNST Nanofabrication Research Group Seminar

## COLLECTIVE PLASMON MODES IN NANOPARTICLE ASSEMBLIES

Assistant Professor, Dept.of Chemistry, Dept.of Electrical and Computer Engineering, Rice University. Houston, TX

Thursday, March 10, 2011, 10:30AM, Rm. H107, Bldg. 217

In order to incorporate plasmonic nanoparticles into functional devices it is necessary to understand how surface plasmons couple as particles are arranged into ordered structures. Bottom-up assembly of chemically prepared nanoparticles facilities strong plasmon coupling due to short interparticle distances, but also gives to rise to defects in particle size, shape, and ordering. Single particle spectroscopy of plasmonic nanoparticle assemblies, especially when correlated with structural characterization using scanning electron microscopy, allows one to gain a detailed understanding about collective plasmon modes. We have used polarization sensitive dark-field scattering spectroscopy covering a broad spectral range from the visible up to 2000 nm and polarization dependent photothermal imaging to separately investigate radiative and nonradiative coupling in one-dimensional assemblies of plasmonic nanoparticles. For both scattering and absorption, we observed collective plasmon modes that are highly polarized along the main axis of the one-dimensional nanoparticle chain and red-shifted from the plasmon resonance of the individual constituents. These collective plasmon modes are compared to plasmon antenna modes of continuous nanorods with varying length and width. Furthermore, we have developed a fluorescence based method to visualize plasmon propagation in one-dimensional nanostructures.

For further information contact J. Alex Liddle, 301-975-6050, james.liddle@nist.gov

CNST Electron Physics Group Seminar

## ELECTRON-DEFECT AND ELECTRON-ELECTRON INTERACTION IN SINGLE AND BILAYER GRAPHENE

Jun Zhu
Assistant Professor of Physics/Penn State University.

Friday, February 25, 2011, 2:00PM, Rm H107, Bldg. 217

Graphene and its sibling bilayer graphene are two-dimensional electron systems with many unusual physical properties. In this talk, I will present experiments which accurately determine the effective mass of bilayer graphene and its band structure. Our results show that electron-electron interaction strongly renormalizes the bands of bilayer graphene and suppresses the effective mass m*. Its manifestation is different from that in conventional 2D systems. In the second part of the talk, I will describe the remarkable transport and magneto-transport properties of single-layer graphene modified with a dilute coverage of chemisorbed fluorine adatoms. These adatoms are a unique type of atomic defects interacting strongly with graphene. We observe colossal negative magneto-resistance and anomalous phase breaking in these systems. I will discuss the possible origins of the experimental observations.

CNST Nanofabrication Research Group Seminar

## OBSERVATIONS OF FERROELASTIC DOMAIN FORMATION AND MOVEMENT BY RAMAN SPECTROSCOPY

Molly M. Gentleman
Mechanical Engineering Department, Texas A&M University.

Wednesday, February 16, 2011, 10:30AM, Rm. H107, Bldg. 217

The use of ceramic coatings for thermal insulation in high temperature turbine applications has become the industry standard over the past several decades. This is because these thermal barrier coatings (TBCs) are capable of providing large thermal gradients to internally cooled metallic structural components. Although these coatings are consistently used, designers of turbine systems continue to struggle with the failure of these coatings in the form of spallation and erosion at very early stages of life. To overcome these limitations, ceramic materials with increased high temperature toughness must be identified. Current state of the art thermal barrier materials rely on the mechanism of ferroelastic switching to achieve their relatively high fracture toughness at elevated temperatures. To widen the scope of tough materials for applications such as turbine coatings a new technique must be developed that allows for accurate and quick measurements of the presence and magnitude ferroelastic switching. In this talk Raman spectroscopy will be introduced as a new tool capable of not only mapping the affected zones of ferroelastic switching, but also allowing for direct measurements of the coercive stress. These measurements will aid in the selection of thermal barrier materials and accelerate their implementation into engine hardware.

For further information contact Rachel Cannara, 301-975-4258, rachel.cannara@nist.gov

CNST Nanofabrication Research Group Seminar

## CMOS INTEGRATED SILICON NANOPHOTONICS: ENABLING TECHNOLOGY FOR EXASCALE COMPUTATIONAL SYSTEMS

Dr. William Green
Research Staff Member, IBM Thomas J. Watson Research Center, New York.

Tuesday, February 8, 2011, 10:30AM, Rm. H107, Bldg. 217

Today's fastest high-performance supercomputing systems are comprised of tens-of-thousands of individual processors, each containing multiple cores on a single die. Because these vast arrays of discrete processing units require an extremely high-bandwidth, low-latency interconnect network to achieve parallel operation, optical fiber-based interconnects have already replaced copper wires for communication at the rack-to-rack level. Moreover, as the number of cores within each microprocessor continues to scale, additional bandwidth and power consumption challenges emerge, now at the level of global interconnects between cores. One possible solution is to replace conventional electrical global interconnects with an intra-chip optical network, based on silicon nanophotonic integrated circuits. I will review our progress within IBM Research toward achieving this goal, including the recent demonstration of various critical optical components, as well as the development of a monolithic CMOS-integrated silicon nanophotonics technology.

For further information contact Kartik Srinivasan, 301-975-5938, kartik.srinivasan@nist.gov

CNST Energy Research Group Seminar

## GALVANIC DISPLACEMENT FOR THE PREPARATION OF SERS SUBSTRATES

Przemys?aw R. Brejna
Student, Teaching Assistant/ Department of Chemistry, University of Idaho.

Monday, February 7, 2011, 10:30AM, Rm.H107, Bldg. 217

Raman spectroscopy is known to be rather insensitive analytical tool. One method to increase Raman signals is to bind molecules to rough silver or gold surfaces. In this circumstance, the collective motion of the electrons in certain metals that are subjected to an oscillating electric field can interact with molecules bound to the surface of the metal, greatly enhancing their Raman scattering; this effect is known as surface-enhanced Raman scattering (SERS). There are various methods to prepare the substrates for SERS, most of which suffer from irreproducibility and tedious preparation. Some SERS substrates have been manufactured to give reproducible enhancement factors, but these are expensive and give rise to low enhancement factors. This seminar will cover a quest to develop an easy, cost-effective way of preparing the substrates for SERS. The method proposed is based on the galvanic displacement phenomenon, i.e., the spontaneous reduction of silver and gold salts by exposing them to zero-valent materials like germanium or silicon. The method is promising: the substrates are easy to prepare, reproducible, highly enhancing and relatively inexpensive. The large SERS enhancements in certain small regions of the silver or gold substrates are known as "hot spots". Investigating the morphology of hot spots by Raman microspectroscopy is, however, problematic because of its insufficient spatial resolution. The hot-spots are located between closely spaced silver nanoparticles as well as at places where very small nanoparticles merge. Not all such junctions are "hot", however, and an improved knowledge of the nature of the hot particles would allow to further optimize the preparation conditions. Tip-enhanced Raman scattering (TERS), also called inverse SERS, is a mean of obtaining Raman spectra of very small spots. Since galvanic displacement of silver and gold is possible on silicon AFM probes, the feasibility of using this method for the rapid preparation of TERS tips will be presented.

For further information contact Andrea Centrone, 301-975-8225, andrea.centrone@nist.gov

CNST Nanofabrication Research Group Seminar

## OBSERVATION OF QUANTUM PHASE-SLIPS IN JOSEPHSON JUCNTION CHAINS

Ioan-Mihai Pop
PhD Student, Institut Neel, CNRS/UJF Grenoble, France.

Thursday, February 3, 2011, 10:30AM, Rm. H107, Bldg. 217

Josephson junction chains have already been successfully used to create particular electromagnetic environments for the reduction of charge fluctuations. Recently, they have attracted interest as they could provide the basis for the realization of a new type of topologically protected qubit [1] or for the implementation of a new quantum current standard [2]. We present measurements that show clearly the effect of quantum phase-slips on the ground state of a Josephson junction chain. We can tune in situ the strength of the phase-slips and obtain for the first time an excellent quantitative agreement with theory [3]. These phase slips are the result of fluctuations induced by the finite charging energy of each junction in the chain. Our measurements demonstrate that a Josephson junction chain under phase bias behaves in a collective way, very similar to a single macroscopic quantum object [4]. We also show evidence of coherent phase-slip interference, the so called Aharonov-Casher effect. This phenomenon is the dual of the well known Aharonov-Bohm interference. As we sweep the charge capacitively induced on an island in the middle of the chain, the strength of the phase-slips oscillates with a periodicity of 2e. [1] I. M. Pop, I. Protopopov, K. Hasselbach, O. Buisson, W. Guichard and B. Pannetier, Phys. Rev. B, 78, 104504 (2008) [2] W. Guichard and F. Hekking, Phys. Rev. B 81, 064508 (2010) [3] K. A. Matveev, A. I. Larkin, and L. I. Glazman, Phys. Rev. Lett. 89, 096802 (2002) [4] I. M. Pop, I. Protopopov, F. Lecocq, Z. Peng, B. Pannetier, O. Buisson and W. Guichard, Nature Physics, 6, 589-592, (2010).

For further information contact Sukumar Rajauria, 301-975-2160, sukumar.rajauria@nist.gov

CNST Energy Research Group Seminar

## ADATOM ORDERING, BRAGG SCATTERING AND TUNABLE BAND GAP IN FUNCTIONALIZED GRAPHENE

Leonid Levitov
Professor of Physics, MIT.

Thursday, February 3, 2011, 1:30PM, Rm.H107, Bldg. 217

The unique electronic properties of graphene make it an attractive candidate for future nano-electronics applications. However, the gapless character of graphene band structure presents a major obstacle for graphene electronics. This talk will describe a proposal [1] to use controlled chemical adsorption of adatoms or molecules similar to that employed in a recent work on hydrogenated graphene[1], as a tool to open a band gap in this material. The gap is induced by Bragg scattering on a modulation resulting from adatom ordering among the A and B sublattices, which can occur even at small adatom concentration, n 1. [1] DA Abanin, AV Shytov, LSL, Phys. Rev. Lett. 105, 086802 (2010); AV Shytov, DA Abanin, LSL, Phys. Rev. Lett. 103, 016806 (2009)

For further information contact Nikolai Zhitenev, 301-975-6039, nikolai.zhitenev@nist.gov

CNST Nanofabrication Research Group Seminar

## CIRCUIT ANALYSIS IN METAL-OPTICS, THEORY AND APPLICATIONS

Matteo Staffaroni
UC Berkeley.

Friday, January 14, 2011, 10:30AM, Rm. H107, Bldg. 217

A simple circuit model can be used to derive the fundamental electromagnetic properties of metals in the optical regime. The model reveals the possibility of optical voltage transformer action capable of matching large impedances at the nanoscale. Devices exploiting this transformer action have several promising applications such as low power nonlinear optics, mask-less lithography, as means of targeting fluorescent excitation and Surface Enhanced Raman Scattering (SERS) at the single molecule level, and as heating elements for Heat Assisted Magnetic Recording (HAMR). The HAMR application is discussed at length since this will be the first very large scale deployment of a metal-optic device based technology to market (with billions of units shipping each year).

For further information contact Henri Lezec, 301-975-8612, henri.lezec@nist.gov

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