CNST Group Seminars - 2010
CNST Nanofabrication Research Group Seminar
TUNABLE AND ACTIVE OPTICAL NEGATIVE INDEX METAMATERIALS
Shumin Xiao
Graduate Student / Purdue University.
Wednesday, December 22, 2010, 10:30AM, Rm. H107, Bldg. 217
Recent progress in the nanofabrication technologies inspired the demonstration and understanding of negative index materials (NIMs) first in microwave and then in optical ranges. In past few years, this kind of materials has attracted a significant amount of research attention following the prediction of superlensing and cloaking. In this work, we demonstrate our recent progress in design, fabrication, and characterization of optical NIMs (ONIMs). We are focusing on several critical issues in order to push the optical NIMs into real applications. First, we improved the nanofabrication recipes and demonstrated the ONIMs in optical wavelength range, i.e. at 710 nm and 580 nm. Then, we experimentally demonstrated a tunable magnetic response in visible optical range. By covering coupled metallic nanostrips with aligned nematic liquid crystals (NLCs), the magnetic response wavelength of the metamaterial is effectively tuned by changing the refractive index of LC via phase transitions caused by the control of the ambient temperature. With the increasing of ambient temperature from 20?C to 50?C, the wavelength of magnetic response shifts from 650 nm to 632 nm. Numerical simulations confirm our tests and match the experimental observations well. At last, we present our research on the loss, which is inherent in a plasmonic metal structure and is one of the most critical problems of ONIMs. Our idea is using gain materials as host to compensate the losses caused by the metallic structures. We experimentally demonstrated that the incorporation of gain material in the high-local-field areas of a metamaterial could generate extremely low-loss or active optical NIMs. The original loss-limited negative refractive index and the figure of merit (FOM) of the device have been dramatically improved with loss compensation in the visible wavelength range. This study demonstrates conclusively and for the first time an optical metamaterial that is not limited by the inherent loss of its metal constituent. We believe our studies will be very interesting and promising for real applications of NIMs in near future.
For further information contact J. Alex Liddle, 301-975-6050, james.liddle@nist.gov
CNST Energy Research Group Seminar
EMERGENCE OF ELECTRONIC AND MAGNETIC PROPERTIES IN NANOSTRUCTURES
Jay Gupta
Assistant Professor of Physics, Ohio State University.
Wednesday, December 15, 2010, 11:05AM, Rm.C103-106, Bldg.215
We employ a combination of scanning tunneling microscopy and density functional theory to study how electronic and magnetic properties emerge in nanoscale structures. First I will discuss our studies of the electronic properties of 0.5-25 nm2 islands of monolayer-thick Cu2N films. Cu2N is one of a class of ultrathin insulating materials that have attracted recent interest for decoupling adsorbates from surface electron density. Our tunneling spectra reveal two unoccupied surface states at ~2.2 and 3.8 V. Consistent with quantum confinement, the 2V state shifts toward higher voltage as the island size is decreased to ~1.5 nm2. The state is no longer observed for smaller islands, comprising fewer than 50 atoms. In contrast, the 4V surface state does not significantly shift with size, and persists down to the smallest islands studied (12 atoms or ~0.5 nm2). We find good agreement between these observations and DFT calculations of band structure and local density of states as a function of island size. From these comparisons, we conclude that the distinct quantum confinement behaviors of electrons in these two surface states is determined by their proximity to Cu surface states and the corresponding surface band effective masses. We utilize these Cu2N islands to study magnetism and spin transport in organic materials at the single molecule level. I will discuss our measurements of organic charge transfer complexes Co,Fe-[TCNE], which are members of a family of organic magnetic semiconductors with Curie temperatures exceeding room temperature. Despite considerable interest in these materials, the influence of chemical bonding on the magnetic properties is not well understood. We use the atom/molecule manipulation capabilities of the STM to build Co-TCNE and Fe-TCNE complexes on Cu2N. Tunneling spectroscopy shows molecular orbitals and inelastic steps due to various vibrational modes and spin excitations. We find that the net spin on the Co atom in Co[TCNE] complexes depends on the molecular orientation, suggestive of a molecular crystal field splitting due to charge transfer.
For further information contact Alec Talin, 301-975-4724, alec.talin@nist.gov
CNST Nanofabrication Research Group Seminar
HOLEY SHEETS AND CROSSED CONCERTINAS: SCULPTING SILICA WITH ABC BLOCK COPOLYMERS
Gilman Toombes
Post-doctoral Student / Institut Curie, Paris, France.
Monday, December 13, 2010, 10:30AM, Rm. AML, Bldg. 215
In nature, proteins and inorganic precursors self-assemble into complex, hierarchical organic-inorganic hybrid materials with outstanding properties. This process has been mimicked using two-domain AB and ABA block copolymers to direct the assembly of silica and other inorganic materials. However, a large gulf remains between these synthetic composites and biological hybrid materials. Bridging this divide will require the use of structure-directing organic molecules with more complex interactions and phase behavior. One possibility are ABC triblock copolymers, as the addition of a third block produces much richer phase behavior. Using PEP-b-PEO-b-PHMA triblock copolymers, we were able to structure aluminosilica into two complex morphologies not previously achieved using diblock copolymers. These results suggest ABC copolymers may indeed be able to direct the assembly of inorganic materials into a wide range of complex structures.
For further information contact James Alexander Liddle, 301-975-6050, james.liddle@nist.gov
CNST Energy Research Group Seminar
ELECTRIC FIELD DRIVEN TRANSITION AND CONTACT EFFECTS IN MAGNETITE, FE3O4, NANOSTRUCTURES
Alexandra Fursina
Postdoctoral Fellow, Rice University.
Thursday, December 9, 2010, 1:00PM, Rm. H107, Bldg. 217
Nanoscale fabrication methods and measurement techniques enable exploring nanosystems at a previously inaccessible level and revealing new phenomena. One of such examples is newly discovered electric-field driven transition (EFT) in magnetite, Fe3O4, nanostructures. In this talk I will demonstrate the investigation results of this transition and present a nanogap fabrication method developed by me to make the study of EFT possible and effective. Magnetite, Fe3O4, is a strongly electronically correlated system and thus exhibits remarkable electrical and magnetic properties, including the Verwey transition at TV~122 K, which has attracted much attention since its 1939 discovery. By working with 10-20 nm nanogaps produced by self-aligned method (Fursina, et al., Appl. Phys. Lett. 92 (2008) 113102) we have discovered a novel EFD transition in magnetite nanoparticles below TV, from high- to low-resistance states driven by high electric field. The EFD is detected both in Fe3O4 nanoparticles and thin films, is hysteretic in voltage under continuous biasing, and is not caused by self-heating. We first unveil the origin of hysteresis observed in I-V curves. By applying voltage in a pulsed manner with controlled parameters we unambiguously demonstrate that while the transition is field-driven, hysteresis results from Joule heating in the low-resistance state. A simple relaxation-time thermal model captures the essentials of the hysteresis mechanism. Second, by doing multilead electrical measurements, we quantitatively separate the contributions of the Fe3O4 channel and each electrode interfaces and explore the contact effects upon testing several different contact metals. The behavior of the system is consistent with a theoretically predicted transition mechanism of charge gap closure by electric field. Finally, we report measurements of the distribution of switching voltages and its evolution with temperature and magnetic field. These studies demonstrate that nanoscale, nonequilibrium probes can reveal much about the underlying physics of strongly correlated materials.
For further information contact Nikolai Zhitenev, 301-975-6039, nikolai.zhitenev@nist.gov
CNST Electron Physics Group Seminar
ANGLES ON THE HEAD: MOIRE PHYSICS FROM MULTILAYER GRAPHENES
Gene Mele
Dept of Physics/University of Pennsylvania.
Friday, December 3, 2010, 1:00PM, Rm H107, Bldg. 217
Coherent interlayer electronic motion in multilayer graphenes plays a crucial role in determining their low energy electronic behavior. This physics has been well understood for graphenes with stacking sequences in which neighboring crystallographic axes are rotated by multiples of pi/3, including AB (Bernal), AA, ABC stackings and their related polymorphs. A nontrivial extension of this idea to arbitrary commensurate fault angles is stimulated by experimental work suggesting that more general rotational faults can decouple the Dirac points of neighboring layers and lead to effectively two dimensional physics in a family of three dimensional materials. I will present a theory of the low energy electronic spectra for graphene bilayers rotationally faulted at arbitrary (though commensurate) angles, showing that their interlayer coherence leads to unexpectedly rich low energy physics that preempts two dimensional massless Dirac behavior. Importantly, all commensurate rotational faults are classified into two families and a universal family behavior ultimately controls the electronic physics near the charge neutrality point. We use this idea to discuss the low energy electronic spectra of these and other multilayer graphenes and to explore the effects of both applied fields and the possibility of interaction-driven instabilities in a new family of graphene-derived materials.
For further information contact Shaffique Adam, 301-975-6187, shaffique.adam@nist.gov
CNST Energy Research Group Seminar
TUNABLE FIELD-CONTROL OVER THE BINDING ENERGY OF SINGLE DOPANTS BY A CHARGED VACANCY IN GAAS
Donghun Lee
Postdoctoral Research Fellow, Ohio State University.
Tuesday, November 23, 2010, 10:30AM, Rm. H107, Bldg. 217
Local manipulation of electric fields at the atomic scale may enable new methods for quantum transport, and creates new opportunities for field-control of ferromagnetism and spin-based quantum information processing in semiconductors. We used a scanning tunneling microscope to position charged As vacancies in the GaAs (110) surface with atomic precision, thereby tuning the local electrostatic field experienced by single Mn acceptors. The effects of this field are quantified by measuring the shift of an acceptor state within the band gap of GaAs. Experiments with varying tip-induced band bending conditions suggest a large binding energy for surface-layer Mn, which is reduced by direct Coulomb repulsion when the As vacancy is moved nearby.
For further information contact Nikolai Zhitenev, 301-975-6039, nikolai.zhitenev@nist.gov
CNST Energy Research Group Seminar
ELECTRICAL CHARACTERIZATION OF SINGLE GRAIN METAL GATE MOS CAPACITORS
Tao Zheng
Research Assistant, University of Texas at Dallas.
Friday, November 19, 2010, 10:30AM, Rm. H107, Bldg. 217
The orientation dependence of a metal work function could affect the threshold voltage of a MOS metal gate transistor. The electrical characterization of a single grain MOS capacitor is difficult to achieve using an optical microscope based probe station. A Zyvex® Nanoprobe system was used to conduct electrical characterization (C-V, I-V) inside a dual column Focused Ion Beam (FIB) system with a field emission SEM used as the imaging tool. The damage to the dielectric of MOS CAP by e-beam irradiation is evaluated and minimized. C-V measurements of single grain Al/SiO2/Si MOS capacitors at 100 kHz and 1 MHz are presented for Al grains as small as 1.2 ?m2. The flat-band voltage of the micron size single crystal (111) Al gated MOS capacitors are compared with that of polycrystalline Al gated MOS capacitors.
For further information contact Nikolai Zhitenev, 301-975-6039, nikolai.zhitenev@nist.gov
CNST Energy Research Group Seminar
ENHANCED CONVERSION EFFICIENCIES OF HIGH-ASPECT-RATIO SILICON PILLAR ARRAY SOLAR CELLS
Heayoung Yoon
Postdoctoral Researcher, Pennsylvania State University.
Thursday, November 18, 2010, 10:30AM, Rm. H107, Bldg. 217
Significant progress has been made in developing a novel device architecture for further enhancing the performance of solar cells while potentially enabling their large-scale integration with inexpensive materials. Of particular interest are radial junction structures in the form of vertically aligned micro- or nano-pillar arrays, which have been proposed for improving the energy-conversion efficiencies of solar cells fabricated with low-quality materials having short minority carrier diffusion lengths. Unlike planar cells, where the light absorption and carrier collection are in competition, the radial junction architecture offers the advantage of decoupling the processes. This talk will discuss the design, fabrication, and characterization of radial n+-p+ junction solar cells composed of densely-packed c-Si pillar arrays. To understand the measured two-times higher AM 1.5 efficiencies of the pillar array cells compared to planar cells fabricated using the same materials, dark and light-IV characteristics as well as spectral responses are presented for the two structures. The higher pillar array cell efficiencies are due to the larger short-circuit currents from the larger photon absorption thickness and the shorter collection length, with a significant additional contribution from multiple reflection in the structure. The result confirms that the high-aspect-ratio geometry is effective at improving solar cell efficiency for materials with short minority carrier diffusion lengths.
For further information contact Nikolai Zhitenev, 301-975-6039, nikolai.zhitenev@nist.gov
CNST Energy Research Group Seminar
DESIGNING NANOSTRUCTURES FOR ENERGY
Gary W. Rubloff
Director, Nanostructures for Electrical Energy Storage; Director, Maryland NanoCenter.
Tuesday, November 16, 2010, 11:00AM, Rm.H107, Bldg. 217
Current technology for electrical energy storage imposes profound limits on needed advances in energy capture, its efficient utilization, and its impact on the environment. Renewable sources with time-varying output (e.g. solar, wind) require storage mechanisms, while electric vehicles with environmental as well as energy benefits need better storage mechanisms to enable longer distances and faster recharge than expected commercially in the short term. Nanostructures for Electrical Energy Storage (NEES), our DOE-supported Energy Frontier Research Center, is aimed at providing the scientific underpinnings for a new generation of nanostructure solutions to enable EES devices with dramatic improvements in power (10-100X) and energy density (10X). The pathway to these advances is based on design of heterogeneous nanostructures that provide facile, repeatable and bidirectional transport of ions and electrons between high capacity nanostructures (e.g. nanowires) and remote contacts to the external world, while stabilizing efficient charge storage components during charge cycling. These nanostructures are multifunctional in that they must combine efficient charge storage materials (metal oxides, Si) with low-dimensional carbon for accelerated charge transport to storage nanostructures and mechanical robustness during cycling. The NEES research agenda stretches from observing nanoelectrochemistry at individual point defects on single nanowires to studies of massively multifunctional nanostructure arrays. To achieve this, particular emphasis is placed on new processes and combinations for nanostructure synthesis, as well as novel microscopy and MEMS approaches to reveal the behavior and consequences of dynamic nanoelectrochemistry occurring in the nanostructures. While energy storage is the primary driver of this research, most of its features are equally relevant to applications in energy generation (e.g., solar, thermoelectric). The EFRC is led by the University of Maryland in partnership with Sandia and Los Alamos National Laboratories, the University of California Irvine, the University of Florida, and Yale University, in concert with the Maryland NanoCenter, University of Maryland Energy Research Center, and the Center for Integrated Nanotechnologies at Sandia and Los Alamos.
For further information contact Nikolai Zhitenev, 301-975-6039, nikolai.zhitenev@nist.gov
CNST Energy Research Group Seminar
CHARGE TRANSPORT AND QUANTUM CAPACITANCE OF GRAPHENE
Jilin Xia
Graduate Research Assistant, Arizona State University.
Wednesday, November 10, 2010, 10:30AM, Rm. H107, Bldg. 217
Graphene, a one atomic thick planar sheet of carbon atoms, has received much attention due to its unique electronic properties.In this talk, I will illustrate our study on the charge transport of back gated graphene with top high k media systematically, to clarify the reasons of transport properties changing due to high k media. Also, another important quantity, the quantum capacitance, will be described both experimentally and theoretically, for both single and double layer graphene.
For further information contact Nikolai Zhitenev, 301-975-6039, nikolai.zhitenev@nist.gov
CNST Electron Physics Group Seminar
EXPLORING LONG-RANGE INTERACTIONS WITH VARIABLE-DIPOLE RYDBERG STATES
Jennifer Johnson
Physics Dept/University of Maryland.
Friday, November 5, 2010, 1:30PM, Rm H107, Bldg. 217
Quantum phase transitions have fascinated solid state physicists for decades, ever since the discovery of superfluid helium. The discovery of new quantum phases has made the jump from condensed matter into atomic physics, as atom-trapping experiments offer unparalleled control of experimental parameters and impurity levels. I will present theoretical calculations of preparing a Rydberg-dressed state, to create atoms with long lifetimes and longer-range interactions. I will also present experimental results of observed excitation suppression of Rydberg atoms that have a variable dipole moment induced by an external static electric field. By combining these two techniques, we hope to develop a system of atoms with interactions that can be varied over the transitions that have been predicted in recent papers.
For further information contact Jabez McClelland, 301-975-3721, jabez.mcclelland@nist.gov
CNST Electron Physics Group Seminar
PRECISION LIFETIME MEASUREMENTS OF ATOMIC STATES USING ULTRAFAST LASER PULSE EXCITATION AND IONIZATION
Jerry Sell
Laser and Optics Research Center, U.S. Air Force Academy Department of Physics
Friday, October 15, 2010, 10:30AM, Rm. H107, Bldg. 217
Measurements of excited atomic state lifetimes provide a fundamental test of atomic models along with importance in the interpretation of weak interaction experiments such as atomic parity nonconservation. A discussion will be given of our recent measurements of the cesium 6P3/2 state lifetime where we have achieved an improved measurement uncertainty of 0.1%. The method is based upon using the synchronized pulses of a mode-locked Ti:sapphire laser to first excite Cs atoms to the 6P3/2 state, with a subsequent pulse (after amplification and frequency-doubling) ionizing the atoms in this state. This setup results in a high precision time base from the stability of the mode-locked pulses. The 6P3/2 decay curve is obtained by selecting particular excitation pulses with respect to the ionization pulses in time and counting the ions produced. Primary systematic errors such as hyperfine quantum beating will also be discussed.
For further information contact, Jabez McClelland, 301-975-3721, jabez.mcclelland@nist.gov
CNST Nanotechnology Seminar Series
IMPROVED CHARGE COLLECTION IN CONFINED ORGANIC SEMICONDUCTOR BULK HETEROJUNCTION SOLAR CELLS
Charles Black
Group Leader, Center for Functional Nanomaterials; Brookhaven National Laboratory
Wednesday, October 13, 2010, 11:00AM, Rm. C103-106, Bldg. 215
High-performing organic bulk heterojunction active layers form via a self-assembly process of phase separation of blended donor and acceptor materials. Optimizing the device performance is a delicate balance of trapping the blended material in a non-equilibrium configuration. I will describe our experimental efforts to confine both organic semiconductors and semiconductor blends within nanometer-scale volumes to better control material phase separation and understand the effect of geometry on material structure, electronic properties, and photovoltaic performance.
For example, confining blended poly(3-hexylthiophene): [6,6]-phenyl-C61-butyric acid methyl ester organic solar cell active layers within nanometer-scale cylindrical volumes nearly more than doubles the supported photocurrent density compared to equivalent unconfined volumes of the same blend, and increases the poly(3-hexylthiophene) hole mobility in the blend by 1000 times. Grazing incidence x-ray diffraction measurements show that the confining volume disrupts polymer ordering by reducing crystallinity and grain size, as well as changing crystal orientation. Similar confined volumes of single-component poly(3-hexylthiophene) show a 400 times enhancement in hole mobility, while the conductivity of confined [6,6]-phenyl-C61-butyric acid methyl ester decreases by 50 times upon confinement.
For further information contact, Alec Talin, 301-975-4724, alec.talin@nist.gov
CNST Nanofabrication Research Group Seminar
SUBWAVELENGTH-SCALE LIGHT LOCATION IN COMPLETE PHOTONIC BANDGAP MATERIALS
Lingling Tang
PhD, Duke University
Monday, October 4, 2010, 10:30AM, Rm. H107, Bldg. 217
A three-dimensional (3D) photonic crystal is anticipated to be a powerful tool for engineering light propagation and localization within subwavelength scales because of its unique omni-directional Bragg reflection. In the talk, I present an overview of our approaches and major research results in realizing 3D photonic crystals and microcavities at optical wavelengths, including (1) multi-directional etching methods to fabricate woodpile photonic crystals with a variety of crystal orientations and surfaces; (2) mode gap design method for ultra-high-quality factor and small mode volume microcavities, which are also compatible with our fabrication methods; and (3) unit cell modulation design method for 3D photonic crystal waveguides in both lateral and vertical propagation directions.
For further information contact, Kartik Srinivasan, 301-975-5938, kartik.srinivasan@nist.gov
CNST NANOFAB USERS MEETING
Vincent Luciani
CNST NanoFab Manager
Friday, September 17, 2010, 2:00PM, Rm. C103, Bldg. 215
This is the quarterly meeting for users of the CNST NanoFab. The meeting will focus on issues of interest to those that use the facility as well as their supervisors. This is a great way to stay abreast of the latest NanoFab news including; safety, policy changes, new equipment purchases and upgrades, research highlights, and new standard processes. In addition to the general topics listed above every meeting also includes an open discussion to allow users to bring their ideas or suggestions to the attention of the staff. Anyone wishing to have a specific item added to the agenda should contact Vincent Luciani, 301-975-2886, vluciani@nist.gov
For further information contact, Jeff Pasternak, 301-975-4529, jeff.pasternak@nist.gov
CNST Nanofabrication Research Group Seminar
FIBER OPTICAL TWEEZERS FOR MICROSCALE MANIPULATION AND FORCE SENSING
Yuxiang Liu
Research Assistant
Tuesday, September 14, 2010, 10:30AM, Rm. H107, Bldg. 217
Optical tweezers have been an important tool in biology and physics for studying single molecules and colloidal systems. Most of current optical tweezers are built with microscope objectives, which are expensive and bulky. By contrast, optical tweezers built with optical fibers can provide a solution for cost reduction and miniaturization, as well as being integrated in microfluidic systems.
The overall objective of this work is to further the fundamental understanding of fiber optical tweezers, and to develop novel fiber optical tweezers systems to enhance the capability and functionalities of fiber optical tweezers as microscale and nanoscale manipulators/sensors. To achieve this goal, three major research thrusts are carried out. Research Thrust 1: System development, experimental study, and modeling of the 3D trap created with the inclined dual-fiber optical tweezers (DFOTs). Stable three dimensional (3D) optical trapping of a single micron-sized particle has been experimentally demonstrated. This is the first time that the trapping efficiency has been calibrated in the experiments, which enables the system to be used as a picoNewton-level force sensor in addition to a particle manipulator. The influence of system parameters on the trapping performance has been carefully investigated through both experimental and numerical studies. Research Thrust 2: Experimental study and modeling of multiple traps and multiple functionalities realized with the inclined DFOTs. Multiple traps, for the first time, have been experimentally created at different vertical levels with adjustable separations and positions. Moreover, multiple functionalities including particle separation, grouping, stacking, rod alignment, and rod rotation have been experimentally demonstrated for the first time with the inclined DFOTs. The multiple functionalities allow the inclined DFOTs to find applications in the study of interaction forces in colloidal systems as well as parallel particle manipulation in drug delivery systems. Research Thrust 3: Development of fiber-based surface plasmonic (SP) lens to achieve far-field superfocusing effect and study of trapping efficiency enhancement with SP lensed fiber tweezers. Far-field superfocusing effect has been investigated and successfully demonstrated with a fiber-based surface plasmonic (SP) lens for the first time. With the help of the SP lens, the trapping efficiency of optical tweezers has been significantly enhanced, which becomes comparable with that of objective-based optical tweezers. A submicron-sized bacterium has been successfully trapped in three dimensions for the first time with optical tweezers based on single fibers. The fiber-based SP lens can bridge the nanoscale particles/systems and the macroscale power sources/detectors. In addition to optical trapping, the fiber-based SP lens will impact many applications including high-resolution lithography, high-resolution fluorescence detection, and sub-wavelength imaging.
For further information contact, Kartik Srinivasan, 301-975-5938, Kartik.Srinivasan@nist.gov
CNST Energy Research Group Seminar
NANOSTRUCTURED PHOTOELECTRODES FOR DYE SENSITIZED SOLAR CELLS
Jung-Kun Lee
Department of Mechanical Engineering and Materials Science, University of Pittsburgh
Friday, August 20, 2010, 1:30PM, Rm. H107, Bldg. 217
Significant progress has been made in the past few decades on the fabrication of various nanostructured materials. These emerging materials will enable new opportunities for future technological innovation. Possible areas where nanostructured materials will have a unique niche are in photovoltaics. This talk will present the results of recent research on the nanostructured photoelectrodes for dye sensitized solar cells. More recently, the emphasis in the area of solar cells is being shifted to the DSCs with wide band gap nanoparticles serving as a photoelectrode. One of major challenges to improve the energy conversion efficiency of the DSCs is how to efficiently extract photogenerated carriers through the photoelectrode. In fact, the greatest inefficiencies associated with the carrier extraction are traced to the photoelectrodes, which are made out of TiO2 nanoparticles and TCO. The first part of the presentation will be focused on the surface engineering to improve the energy conversion efficiency of dye sensitized solar cells (DSCs). I will show the charge transport characteristics, including the electron diffusion coefficient and the charge recombination behaviors can be significantly improved by modifying the surface of TiO2 nanoparticles. To this end, nanoporous layer or surface adsorbed nitric acid were exploited to suppress the back electron transfer, leading to higher energy conversion efficiency of DSCs. This indicates that controlling the extrinsic parameters such as the specific surface area is very important in improving the energy conversion efficiency of the DSCs. The second part of my talk will present the effect of the aspect ratio on the photovoltaic properties of DSCs. 1-dimensional TiO2 nanorods were synthesized using a combined gel-sol and hydrothermal process. Ellipsoidal TiO2 nanorods of different aspect ratios in the range of 2-10 were prepared by a highly pressurized gel-sol method in the presence of amino acids. Structural analysis shows that the TiO2 nanorods from the gel-sol method have pure and highly crystalline anatase phase, suited for studying the effect of nanoscale architecture. Increase in the aspect ratio of TiO2 nanorods was found to suppress the electron-hole recombination and increase the life time of photogenerated carriers in DSCs, as compared to 0-dimensional TiO2 nanoparticles. This is attributed to the reduced number of grain boundaries and the increased carrier mobility. The physics underlying the effect of shape and grain boundary on the carrier life time and mobility are systematically explored.
For further information contact, Nikolai Zhitenev, 301-975-6039, Nikolai.Zhitenev@nist.gov
CNST Nanofabrication Research Group Seminar
IMAGING BEYOND THE DIFFRACTION LIMIT
Gary Laevsky
Advisor
Wednesday, July 28, 2010, 1:00PM, Rm. H107, Bldg. 217
Until recently optical imaging of biological structure was limited to the diffraction limit as defined by Ernst Abbe. In recent years there has been an explosion of technologies which have broken the resolution limit constrained by diffraction. I will discuss two such technologies being commercialized by Nikon, specifically N-SIM and N-STORM. N-STORM (Stochastic Optical Reconstruction Microscopy) technology enables imaging of interactions within biological structures in multiple colors and three dimensions (3D) by the use of photo-switchable probes and single molecule localization. This technique can achieve resolutions on the scale of tens of nanometers. N-SIM (Structured Illumination Microscopy) utilizes moiré patterns generated by laser interference. Computational analysis of multiple exposures of the specimen illuminated with various orientations of this "structured illumination" can extract specimen information at twice the resolution as limited by diffraction. In addition to exceeding the spatial resolution limit, N-SIM is capable of temporal resolution to study dynamic events in live cells. **A Nikon Motorized TIRF system on a Ti-E Inverted Microscope with Perfect Focus capability will be available for demonstration with your samples on Thursday, July 29th. Please contact Laura Kelehan at LKelehan@nikon.net to reserve a time.
For further information contact, Alex Liddle, 301-975-6050, James.Liddle@nist.gov
CNST Electron Physics Group Seminar
GEOMETRY TUNING AND CLUSTERS IN ARTIFICIAL FRUSTRATED MAGNETS
Jie Li
Research Assistant/Penn State University
Tuesday, July 27, 2010, 10:30AM, Rm. H107, Bldg. 217
Artificial frustrated magnets' are model systems based on geometrically frustrated magnetic materials, consisting of arrays of lithographically fabricated single-domain ferromagnetic islands, arranged in different geometries such that the magnetostatic interactions between the island moments are frustrated. MFM imaging of these arrays allows us to study the accommodation of frustration through the local correlations between the moments as a function of both the strength of the interactions and the geometry of the frustration.
In recent work, we examined different lattice geometries, including triangular, square and hexagonal lattice arrays, as well as a brickwork geometry that combines the anisotropy of the square lattice and the topology of the hexagonal lattice. We find that the hexagonal lattice allows the most optimized minimization of the magnetostatic energy, and that the pair-wise correlations between moments differ qualitatively between hexagonal and brickwork lattices, although they share the same lattice topology. The results indicate that the symmetry of local interactions is more important than overall lattice topology in the accommodation of frustrated interactions. Very recent efforts have focused on the study of small clusters of such islands, investigating the role frustration plays in the moment configuration in small numbers of interacting islands. This has been proven to be very useful in understanding the microscopic foundation of frustration/non-frustration distinction.
For further information contact, John Unguris, 301-975-3712, John.Unguris@nist.gov
CNST Nanofabrication Research Group Seminar
BIOMICROSCOPY AND NANOTOMOGRAPHY FRONTIERS FROM A HERITAGE OF LITHOGRAPHY AND NANOFABRICATION
Michael Goldstein, Ph.D.
Senior Principal Physicist, Intel
Monday, July 26, 2010, 1:30PM, Rm. H107, Bldg. 217
Nanolithography resolution is scaling at a remarkable pace. The first microprocessor was fabricated in 1971 on a 10?m technology and contained just 2300 transistors. Today, leading edge fabrication achieves 32nm feature resolution and products have a budget of up to two billion transistors. The number of contact holes fabricated on a single wafer can now exceed the number of stars in our galaxy. Remarkably, the investments which have been made for nanotechnology development can also be utilized for innovation in biomicroscopy and nanotomography. This presentation will examine the integral role of optics in nanolithography and the fortuitous opportunity to biomedical imaging. The development of 13.5nm wavelength extreme ultra-violet (EUV) lithography has led to improvements in mirror surfacing, interference coatings and compact plasma based light sources. These technologies benefit the development of soft x-ray biomicroscopy. A novel table-top optical design will be presented for label-free molecular resolution imaging in the water window between the 2.3nm oxygen and 4.4nm carbon absorption edges. The intrinsic contrast in this region provides an avenue for unlabeled cellular and organelle research which is otherwise unavailable today. As wavelength is further reduced to the sub-nanometer region, optical components become unnecessary and a tomographic image reconstruction method will be described for volumetric imaging of thick samples with use of electron microscopy staining. These examples demonstrate through simulation how progression in lithographic imaging and nanofabrication can be applied to create a new class of instrumentation for biomedical research.
For further information contact, Gregg Gallatin, 301-975-2140, Gregg.Gallatin@nist.gov
SURF Summer Seminar Series
IMAGING ATOMS AT ULTRA-COLD TEMPERATURES
Joseph Stroscio
Center for Nanoscale Science and Technology, NIST
Wednesday, July 15, 2010, 3:30PM, Green Auditorium, Admin. Building
The scanning tunneling microscope (STM) enables a look into the nanoscale world that is a billion times removed from our everyday senses. The technique is based on the quantum mechanical electron tunneling between a probe tip and a sample surface which achieves atomic resolution measurements. Inherent in the electron tunneling process is sensitivity to the electron states in the sample under investigation, allowing imaging and spectroscopic measurements of electron systems in addition to imaging the atomic structure. In this talk I will describe a new STM instrument recently completed at NIST that operates at ultra-cold temperatures down to 10 mK. I will describe some of the new physics that becomes "visible" with STM measurements at these temperatures in the 2-dimensional carbon system known as "graphene".
For further information contact, Joseph Stroscio, 301-975-3716, Joseph.Stroscio@nist.gov
CNST Electron Physics Group Seminar
SPIN RELAXATION AND SPIN TORQUE TRANSFER EFFECTS IN MAGNETIC NANOSTRUCTURES
Xiaojun Wang
PostDoc/University of Delaware
Wednesday, June 24, 2010, 1:30PM, Rm. H107, Bldg. 217
Spintronics is an emerging field that the spin freedom of an electron is exploited as well as the electrical charge. The advanced lithography techniques enable the fabrication of the devices in the nanometer scale. The properties of spin transport in the magnetic nanostructures are interesting and attract more research attention recently. Nonlocal spin valves provide the ideal system to address the fundamental issues in the lateral transport. The NLSV structure generates a pure spin current and allows for the construction of multiterminal devices. The success of spin injection is characterized by a substantial spin accumulation in the non-magnetic central entity. The figures of merit for achieving this goal are the spin polarization of the injected current (P) and the spin diffusion length (?sf) in the non-magnetic entity. Both Ohmic-junction based and tunnel-junction-based NLSV devices have been fabricated. The value of P and ?sf can be determined by a batch of devices with different separations. The high spin polarized at an elevated bias will be discussed as well as the temporal evolution of spin accumulation in NLSVs. The second topic in my talk is about the spin torque transfer switching of cobalt (Co) nanoparticles. The magnetization reversal of particles induced by spin transfer can be inferred from the dV/dI-I measurements. The current density required for the switching is between 5*108 and 1*109 A/cm2.
For further information contact, Robert McMichael, 301-975-5121, Robert.McMichael@nist.gov
CNST Nanofabrication Research Group Seminar
BEYOND IMAGING: ANALYSIS OF SURFACE PROPERTIES USING ATOMIC FORCE MICROSCOPY
Hendrik Hoelscher
Head of Nano- and Micromechanics Group/Karlsruher Institut fur Technologie
Wednesday, June 23, 2010, 10:30AM, Rm. H107, Bldg. 217
The atomic force microscope (AFM) has developed into the most widespread tool for nanotechnology. This technique was invented more than 20 years ago by Binnig et al. and is nowadays used not only in physical, chemical, biological, and medical research laboratories, but also in many companies for tasks such as product development and routine quality control.
About 10 years ago this technique was extended towards dynamic force spectroscopy (DFS) which is a powerful tool to measure conservative as well as dissipative tip-sample interactions. Even three-dimensional force fields can be measured down to the atomic-scale. Recent research focuses on the application of this technique also in ambient conditions and liquids. In my presentation I will review the theoretical background of dynamic force spectroscopy and present recent experiments focusing on the stretching of chain-like molecules by dynamic force spectroscopy.
For further information contact, Rachel Cannara, 301-975-4258, Rachel.Cannara@nist.gov
CNST Electron Physics Group Seminar
MATERIALS FOR MULTIFUNCTIONAL SPINTRONICS
Ezekiel Johnston-Halperin
Assistant Professor/Ohio State University
Tuesday, June 15, 2010, 10:30AM, Rm. H107, Bldg. 217
The success of solid state electronics over the past sixty years has both driven and been driven by an increasingly sophisticated understanding of the electronic properties condensed matter systems. Modern electronic devices exploit a deep knowledge of charge transport in semiconducting, metallic and organic materials and their various heterointerfaces. The principle goal of the emerging field of spintronics is to incorporate spin-based functionality into these electronic architectures, enabling both spin-only and multifunctional operation. In order to achieve this goal a fundamental understanding of spin in condensed matter systems comparable to our understanding of charge transport is required. A principle aim of our research group is to expand this understanding through the investigation of spin and spin transport in spin-functional materials and heterostructures. For example, the organic-based ferromagnet V[TCNE]x~2 is a promising candidate material due to its room temperature ferromagnetism, semiconducting bandstructure and predicted 100% spin polarization at the Fermi energy. Here we present a recent investigation into the use of V[TCNE]x~2 as a spin injector in a hybrid organic/inorganic spin-light emitting diode (spin-LED) structure. In this study, we detect circular polarization of the electroluminescence that follows the magnetization curve of V[TCNE]x~2. Moreover we observe that the photoluminescence from a V[TCNE]x~2 coated LED shows a dramatic asymmetry in the polarization from light and heavy-hole recombination, in contrast to control measurements of magnetic circular dichroism that show relatively weak and symmetric response. Further, the sign of the optical polarization indicates that the spin current is oriented parallel to the magnetization of the V[TCNE]x~2 layer, consistent with the ferromagnetic ordering in this system. Taken together, these results conclusively demonstrate the first successful transfer of spin from an organic-based magnet into an inorganic semiconductor.
For further information contact, Robert McMichael, 301-975-5121, Robert.McMichael@nist.gov
CNST Electron Physics Group Seminar
CHARACTERIZATION OF NANO-SCALE DIAMOND FIELD EMITTERS
Travis Wade
Vanderbilt University
Monday, June 14, 2010, 10:30AM, Rm. H107, Bldg. 217
Localized electron emission has been demonstrated from cold-cathode diamond nano-emitters fabricated at Vanderbilt University. Ultra-sharp diamond tips with a radius of curvature less than 5 nm have been achieved and show significant improvement in emission characteristics compared to conventional emitters such as silicon. Modification of emission behavior stems primarily from non-idealities in the growth process but inconsistencies are observed between otherwise ideal tips. Under-performing tips are being examined with focus on correlations between the crystalline nature of the tip and its emission profile.
In addition, I will cover our measurements of the electron beam itself (emittance, energy spread) as well as recent measurements utilizing coherent acoustic phonon (CAP) waves for probing sub-surface defects non-destructively.
For further information contact, Jabez McClelland, 301-975-3721, Jabez.McClelland@nist.gov
NANOMANUFACTURING WORKSHOP - ATOMICALLY-PRECISE NANOMANUFACTURING FORUM
Tuesday, May 25, 2010, 12:30PM, Rm. C103-106, Bldg. 215
The Workshop will be held from 12:30 p.m. - 4:30 p.m. on May 25, 2010. Hosted by: The NIST Center for Nanoscale Science and Technology, the NIST Manufacturing Engineering Laboratory, and the APMC Consortium
Forum to discuss atomically-precise nanomanufacturing and the effect it will have on the manufacturing of high-value, nanotechnology-enabled products. Short presentations and discussions will address scanning-probe, focused ion-beam and optical metrology and fabrication methods and efforts to enable the commercialization of these technologies. Globally recognized speakers will include industry and academic leaders from the APMC consortium, DARPA MTO, Texas, and NIST.
Attendees: R&D and industry leaders, researchers, academicians, and entrepreneurs should attend
RSVP: by May 20th to Joyce Waters: joyce.waters@nist.gov
(Please arrive at NIST by noon in order to receive your visitor badge)
For further information contact, Joyce Waters, 301-975-8001, Joyce.Waters@nist.gov
CNST Energy Research Group Seminar
BREAKING THE CHEMICAL AND ENGINEERING BARRIERS TO LIGNOCELLULOSIC BIOFUELS
George W. Huber
Assistant Professor, University of Massachusetts
Monday, May 24, 2010, 10:30AM, Rm. H107, Bldg. 217
Concerns about global warming and national security, combined with the diminishing supply and increased cost of fossil fuels are causing our society to search for new sources of transportation fuels. In this respect plant biomass is the only sustainable feedstock that can be used for production of renewable liquid fuels. Currently cellulosic biomass is significantly cheaper than petroleum (at $15 per barrel of oil energy equivalent) and abundant. However, the chief impediment to the utilization of our biomass resources is the lack of economical conversion processes. In this presentation we will discuss various pyrolysis based approaches for the conversion of lignocellulosic biomass into fuels and chemicals. Pyrolysis is the thermal decomposition of biomass into a mixture of semi-volatile molecules. These pyrolysis vapors can then be condensed into a bio-oil or pyrolysis oil that contains more than 300 compounds. This pyrolysis oil is the cheapest liquid fuel made from biomass. However, this oil is unstable, acidic, insoluble with petroleum based fuels, has a high oxygen content, and polymerizes with time. Alternatively, biomass can be depolymerized by hydrolysis approaches. We will compare these two methods of depolymerizing biomass. The resulting bio-oil can be converted into various fuels and chemicals by aqueous-phase hydrodeoxygenation. Three reaction classes occur in hydrodeoxygenation of biomass: C-C bond cleavage, C-O bond cleavage, and hydrogenation. The key C-C bond cleavage reactions include: retro-aldol condensation and decarbonylation which both occur on metal catalytic sites. Dehydration is the key C-O bond cleavage reaction and occurs on acid catalytic sites. Hydrodeoxygenation of the aqueous phase of bio-oil can produce C1-C6 alkanes, alcohols, and polyols. This research suggests that hydrodeoxygenation chemistry can be tuned to make a wide variety of products from pyrolysis derived feedstocks. Addition of zeolite catalysts into the pyrolysis reactor can directly produce gasoline range aromatics from biomass by an approach we call catalytic fast pyrolysis (CFP). The pyrolysis vapors enter directly into the zeolite pores where they undergo a series of dehydration, decarbonylation and oligomeriation reactions. The shape, pore structure, and active sites of the zeolite catalysts are critical in obtaining high yields of the desired aromatic products. CFP has several advantages compared to other biomass conversion technologies in that a liquid fuel is being produced directly from solid biomass in a single catalytic reactor, short residence times, and inexpensive catalysts are used. We believe that pyrolysis based technologies have a tremendous potential for the conversion of lignocellulosic biomass into renewable fuels and chemicals. As will be demonstrated in this presentation chemistry, chemical catalysis and chemical engineering are critical 21st century needs to help make renewable energy a practical reality.
For further information contact, Renu Sharma, 301-975-2418, Renu.Sharma@nist.gov
CNST Energy Research Group Seminar
IN SITU EVOLUTION OF ENERGY RELATED CATALYTICALLY ACTIVE NANOMATERIALS
Peter Crozier
Professor at Arizona State University
Monday, May 17, 2010, 10:30AM, Rm. H107, Bldg. 217
Catalytically active nanomaterials play a critically important role in modern technology significantly impacting areas in energy including fuel processing, fuel cells and solar fuels. Heterogeneous catalysis relies on the unique ability of highly dispersed forms of material to direct chemical transformations. However, the "active form" of the material may exist only in the unique environment inside a reactor where additional changes in the nanostructure of the catalyst such as phase transformations, shape changes and surface reconstructions may take place. Consequently there is increasing emphasis on developing in situ and operandi characterization methods because only these techniques can probe the catalytic material under reactive gas conditions providing information that may not be obtainable from ex situ methods. We are using in situ environmental transmission electron microscopy (ETEM) to study fundamental questions associated with the synthesis and evolution of catalytic nanomaterials under reactive gas conditions. In the modern ETEM, the powerful combination of atomic resolution imaging and nanospectroscopy provides dynamic information on both the structural and compositional transformations taking place under reactive gas conditions. This presentation will focus on the application of ETEM to the supported metal and oxide catalysts. The nucleation and growth processes taking place during the synthesis of monometallic and bimetallic nanoparticles on high surface-area oxide supports will be discussed. Recent work on cerium-based oxide (CeO2 and ZrxCe1-xO2) demonstrates that the activity of individual nanoparticles can be measured and compared [5-7]. Examples of structural changes taking place during different activation processes will be described for oxide and metal systems.
For further information contact, Renu Sharma, 301-975-2418, Renu.Sharma@nist.gov
CNST Nanofabrication Research Group Seminar
FAST SIMULATION OF PATTERN DEPENDENCIES IN THERMAL NANOIMPRINT LITHOGRAPHY
Hayden Taylor
Postdoctoral Associate/MIT
Thursday, May 13, 2010, 10:30AM, Rm. H107, Bldg. 217
Just as the modeling and simulation of photolithography has enabled optical proximity correction techniques to enter industrial use, the physical simulation of nanoimprint lithography is needed to guide the design of products that will use this emerging process. I present an extremely fast method for simulating thermal nanoimprint lithography. The technique encapsulates the resist material's mechanical behavior using an analytical function for its surface deformation when loaded at a single location. It takes a discretized imprint stamp design and finds resist and stamp deflections. The approach is fast enough to be used iteratively when selecting processing parameters and refining layouts. The technique is also used to derive nanoimprint-aware design rules.
For further information contact, Alex Liddle, 301-975-6050, James.Liddle@nist.gov
CNST Energy Research Group Seminar
SOLUTION PHASE SYNTHESIS OF NANOPARTICLES AND THEIR CATALYTIC APPLICATIONS
Youngmin Lee
Ph.D. in Inorganic Chemistry: Nanomaterials, Brown University
Wednesday, May 12, 2010, 10:30AM, Rm. H107, Bldg. 217
Two of my main research focuses will be discussed: 1) Developing nanocatalysts for fuel cell application, 2) Studying the interaction between Au and oxide in a composite structure. Developing efficient catalysts for fuel cell systems are of great interest due to the demand for high-efficiency energy sources. Pt is widely used as a fuel cell catalyst, however, it is expensive and the surface undergoes poisoning which deteriorates its activity over time. During my doctoral studies, I focused on developing and studying nanocatalysts that are active for the cathode reaction (oxygen reduction) with three different systems: 1) Pt with higher efficiency (cubic Pt), 2) Pt-alloy structure with a lesser amount of Pt (fcc-, fct-FePt), and 3) non-Pt (Au). Cubic Pt nanoparticles (NPs) that have many {100} planes were found to be more active than polyhedral Pt NPs in H2SO4 electrolyte for oxygen reduction. Fct-FePt NPs showed much higher activity and stability than fcc-FePt NPs toward oxygen reduction in H2SO4 because of the intermetallic nature of the crystal structure. Structure- and surface-dependent studies of Au NPs were carried out in KOH electrolyte, where polycrystalline Au NPs showed higher activity than crystalline Au NPs for oxygen reduction. The synthetic methods and characterizations of these nanocatalysts for electrocatalytic applications will be discussed. Great efforts are put on elucidating the interaction between Au NPs and oxide support for catalytic applications (e.g. CO oxidation). However, direct evidence of the enhanced catalytic activity coming from the interaction between Au and oxide support was not previously demonstrated. Dumbbell-like Au-Fe3O4 composite NPs with both components controllable in nanometer-size were synthesized. Also, selective etching method was developed to obtain individual components, Au and Fe3O4, directly from the same Au-Fe3O4 structure. In catalyzing H2O2 reduction in neutral PBS solution, Au-Fe3O4 NPs showed higher activity and stability than its individual component of either Au or Fe3O4, due to a polarization effect coming from the interconnecting area. Here we showed evidence of enhanced catalytic properties from close contact interfaces in Au and Fe3O4.
For further information contact, Alec Talin, 301-975-4724, Alec.Talin@nist.gov
CNST Energy Research Group Seminar
MAGNETIC AND MECHANICAL RESPONSES OF FUNCTIONAL MULTIPHASE MATERIALS
Brian Pate
Adjunct Assistant Professor and Temporary Faculty, Central Michigan University
Friday, May 7, 2010, 10:30AM, Rm. H107, Bldg. 217
The ability of organic matter to undergo reversible structural and electronic reorganization in response to environmental stimuli is directly responsible for the broad utility of soft materials in natural and synthetic systems, including those relevant to energy applications. In particular, assemblies of molecules or macromolecules engineered to exhibit hard/soft or liquid crystalline phases exhibit a wide range of tunable responses to external electromagnetic and mechanical fields. Recently, the metal-dependent structural reorganization of a series of mesogenic metalloporphyrazines in the presence of applied magnetic fields has been predicted and characterized. A method to magnetically process these liquid crystals in thin film and in the bulk to obtain long-range uniaxial orientation of the fiber-like columnar superstructures has been demonstrated. The alignment of these materials using mechanical fields will also be described, and contrasted with that of several macromolecular systems, including a new functionalized polyiptycene and two complementary new series of thermoplastic polyurethanes. Finally, an investigation of potential energy conversion applications will be described.
For further information contact, Alec Talin, 301-975-4724, Alec.Talin@nist.gov
CNST Energy Research Group Seminar
SI WIRE-ARRAY PHOTOVOLTAICS AND HYDROGEN-PRODUCING PHOTOELECTRODES
Shannon Boettcher
Assistant Professor of Chemistry, University of Oregon
Monday, May 3, 2010, 10:30AM, Rm. H107, Bldg. 217
Micron-scale Si wire arrays are three-dimensional semiconductor absorbers that can be used in both photovoltaics and photoelectrochemical water-splitting devices. In principle, the wire-array architecture enables orthogonalization of light absorption and carrier collection and hence allows for the utilization of relatively impure Si in efficient device designs. The wire arrays are grown by a vapor-liquid-solid-catalyzed process on a Si wafer patterned with an array of metal catalyst particles. Following growth, the wires can be embedded in a polymer and peeled from the template growth substrate. The result is an unusual solar cell material: a flexible, bendable, wafer-thickness crystalline Si absorber. In this seminar I will discuss: (1) the growth of high-quality Si wires with controllable doping and the evaluation of their photovoltaic energy-conversion performance using a test electrolyte that forms a rectifying conformal semiconductor-liquid contact, (2) the observation of enhanced absorption in wire arrays exceeding the conventional light trapping limits for planar Si cells of equivalent material thickness, (3) the integration of the Si wire-arrays with electrocatalysts that enable the efficient photocathodic evolution of hydrogen gas from water and (4) single-wire and large-area solid-state Si wire-array solar cell results obtained to date with directions for future cell designs based on optical and device physics.
For further information contact, Nikolai Zhitenev, 301-975-6039, Nikolai.Zhitenev@nist.gov
CNST Energy Research Group Seminar
NANOBIOMATERIALS CREATED THROUGH BIOMOLECULAR SELF-ASSEMBLY
Veronika Szalai
Associate Professor of Chemistry & Biochemistry, University of Maryland
Monday, April 12, 2010, 10:00AM, Rm. H107, Bldg. 217
Self-assembled nanomaterials are an important component of nanotechnology development. Current projects in my group focus on transition metal-containing nanobiomaterials that self-assemble from proteins or nucleic acids. One project focuses on Alzheimer's disease plaques containing fibrils composed of the amyloid-beta peptide. These plaques also contain high concentrations of copper. Our goal is to identify the molecular level details of the copper-binding site in monomeric, oligomeric, and fibrillar amyloid-beta using biophysical methods including electron paramagnetic resonance (EPR) spectroscopy. Another project exploits the interaction of metal complexes with a unique DNA structure called a guanine quadruplex. By including both duplex and quadruplex DNA, we have created synapsable quadruplex wires that can be targeted sitespecifically with metal complexes. Measurements to elucidate the molecular-level details, in particular atom-to-atom connectivities, in these materials are limited because of sample solubilities and heterogeneity. Assessment of these materials' physical properties remain challenging due to difficulties creating interfaces with macroscale measurement devices. Ideas to address both of these issues will be presented.
For further information contact, Nikolai Zhitenev, 301-975-6039, Nikolai.Zhitenev@nist.gov
CNST Electron Physics Group Seminar
THE ROLE OF MOLECULAR BEAM EPITAXY IN OBSERVING COHERENCE IN A QUANTUM HALL INTERFEROMETER
Loren Pfeiffer
Department of Electrical Engineering, Princeton University
Tuesday, March 30, 2010, 10:30AM, Rm. H107, Bldg. 217
The integer Quantum Hall Effect was discovered in 1980 in Silicon MOSFETs. Two years later the Fractional Quantum Hall Effect was discovered in GaAs-AlGaAs heterostructures. Now, recent experiments1 suggest the existence of a third Quantum Hall variety, the Quantum Hall Effect of Quasiparticles obeying Non-abelian Statistics. This apparent discovery of non-abelian quasiparticles makes possible a potential application of the Quantum Hall Effect, that may lead to an elegant topological lock against decoherence of entangled quantum states, and thus would point the way toward building a quantum computer with built-in error correction. We will review how the sequential discoveries of the various levels of the Quantum Hall effect have depended on the gradually improving quality of the semiconductor samples, and how semiconductor perfection still limits current experiments that are exploring the properties of non-abelian quasiparticles.
For further information contact, Joseph Stroscio, 301-975-3716, Joseph.Stroscio@nist.gov
CNST Electron Physics Group Seminar
EXPERIMENTAL DEMONSTRATION OF TOPOLOGICAL SURFACE STATES PROTECTED BY TIME-REVERSAL SYMMETRY
Tong Zhang
Ph.D. Candidate/Tsinghua University
Monday, March 22, 2010, 10:30AM, Rm. H107, Bldg. 217
Topological insulator is a new state of matter which has insulating gap in bulk and gapless states on surface. In this talk, I would report a low temperature scanning tunneling microscope (STM) observation of the standing waves formed by nontrivial surface states of topological insulator Bi2Te3. Molecular beam epitaxy (MBE) was used to grow high quality Bi2Te3 films on Si(111) substrate. By studying the voltage- dependent standing wave patterns around Ag impurities and step edges, we determined the energy dispersion E(k), which conforms the Dirac cone structure of the topological states. We further show that, very different from the conventional surface states, backscattering of the topological states by nonmagnetic impurities is completely suppressed. The absence of backscattering is a spectacular manifestation of the time-reversal symmetry, which offers a direct proof of the topological nature of the surface states.
For further information contact, Joseph Stroscio, 301-975-3716, Joseph.Stroscio@nist.gov
CNST Electron Physics Group Seminar
BISTABILITY AND OSCILLATORY MOTION OF GRAPHENE NANOMEMBRANES STUDIED BY STM
Torge Mashoff
Postdoctoral Candidate/Institute of Physics, RWTH Aachen University, Germany
Friday, March 12, 2010, 10:30AM, Rm. H107, Bldg. 217
The truly two-dimensional material graphene is an ideal candidate for nanoelectromechanics due to its large strength and mobility. Partly freely suspended graphene flakes on SiO2 provide natural nanomembranes of a diameter down to 3 nm within its intrinsic rippling. These membranes can be lifted either reversibly or hysteretically by the tip of a scanning tunneling microscope. This can be explained quantitatively using a clamped membrane model including van-der-Waals and dielectric forces. Exciting the membranes by ac-voltages might lead to a completely novel approach to controlled quantized oscillations or single atom mass detection.
For further information contact, Joseph Stroscio, 301-975-3716, Joseph.Stroscio@nist.gov
CNST Electron Physics Group Seminar
LOCAL CONDUCTANCE VARIATION IN GRAPHENE DEVICES: A SCANNING GATE MICROSCOPE STUDY
Jungseok Chae
Ph.D. Candidate/Seoul National University, South Korea
Thursday, March 11, 2010, 10:30AM, Rm. H107, Bldg. 217
Despite much works have been done on the geometric structures of ripples, defects and edge atoms in a graphene device, there has been no report showing the direct correlation between the structures and the transport property. Unlike scanning tunneling microscopy or other electron microscopes, Scanning Gate Microscope (SGM) is a unique microscopic tool with which the local electronic structure and the transport property of a device can be measured simultaneously. We have performed a transport measurement in nanometer scale using a scanning gate microscope (SGM). We have found the nanoscopic pictures of electron and hole puddles and the role of graphene- device edges in the transport measurements. These experimental findings were successfully explained with a theoretical model.
For further information contact, Joseph Stroscio, 301-975-3716, Joseph.Stroscio@nist.gov
CNST Electron Physics Group Seminar
FERROMAGNETIC RESONANCE IMAGING USING A LOCALIZED SPIN WAVE MODE
Inhee Lee
Ph.D. Candidate/Ohio State University
Wednesday, March 10, 2010, 1:30PM, Rm. H107, Bldg. 217
Nanoscale patterned magnetic structures and multi-component magnetic devices have been studied actively for applications such as highly efficient data storages, non-volatile magnetic memory devices and magnetic sensors. Those studies demand high resolution magnetic imaging tools which can characterize complex, often buried nanoscale structures. Ferromagnetic Resonance (FMR) is a powerful spectroscopic tool which presents the quantitative characterization of magnetic parameters of the sample. FMR using Magnetic Resonance Force Microscopy (MRFM) based on its high sensitivity and high resolution is an excellent tool for the study of ferromagnetic nano-structures. However, for ferromagnetic materials, it is difficult to achieve a spatially well-resolved FMR signal due to the strong spin-spin interactions which lead to collective spin wave excitations, reflecting the global properties of a sample. In this talk, I will present the recent discovery and demonstration of localized FMR modes and their use for FMR imaging. We image the non-uniform demagnetizing field of an individual 5 um Permalloy disk and variation of internal magnetic field in the Permalloy film with high field sensitivity (~ 1 G/Hz1/2). Our estimated highest spatial resolution is ~ 200 nm which is much smaller than the size of the probe magnet (~ 1.2 um) and probe-sample separation (~ 1.3 um). Furthermore, I will discuss other quantitative local magnetic characterization methods such as FMR-MRFM of the suppressed uniform FMR mode and MFM induced by a strong inhomogeneous probe tip field.
For further information contact, Robert McMichael, 301-975-5121, Robert.McMichael@nist.gov
CNST Nanofabrication Research Group Seminar
ENGINEERING AT THE BIOMOLECULAR SCALE
Shalom Wind
Department of Applied Physics and Applied Mathematics, Columbia University. New York, NY
Tuesday, March 9, 2010, 11:00AM, Rm. H107, Bldg. 217
Faithful devotion to Moore's Law has resulted in the scaling of transistor features to only a few tens of nanometers – about the size of large biomolecules and biomolecular complexes. This has created new opportunities where the tools of semiconductor device manufacturing can be applied to fields other than electronics, such as biology and medicine. We are presently exploring the use of traditional and non-traditional micro- and nanofabrication techniques to address questions regarding how external physical cues affect cell function and behavior. Combining advanced nanofabrication and surface chemistry strategies, we fabricate biomimetic surfaces, with which we can simulate specific physical aspects of the extracellular environment, such as mechanical force, rigidity and nanoscale geometry. In this talk, we will describe the fabrication of these surfaces and how different physical configurations elicit different cellular response. For example, by using nanolithographic patterning to control the placement and organization of individual extracellular matrix molecular binding sites, we have recently discovered a minimal cell adhesion unit that supports cell spreading. An understanding of the factors required for a given cellular response will yield insight into the functional complexes involved in specific behaviors and how these functions may be altered. Potential applications range from therapeutic treatments that block metastasis to the rational design of tissue scaffolds that can optimize healing without scarring.
For further information contact, J. Alexander Liddle, 301-975-6050, James.Liddle@nist.gov
CNST Energy Research Group Seminar
ADVANCED USE OF VIBRATIONAL SPECTROSCOPY IN NANOTECHNOLOGY: APPLICATION IN HYDROGEN STORAGE AND CANCER DETECTION
Andrea Centrone
Project Leader Candidate/Dept. of Chemical Engineering
Thursday, February 25, 2010, 10:30AM, Rm. H107, Bldg. 217
The lack of a suitable and cost effective means of storing hydrogen is one of the main unsolved tasks that prevent its use as a fuel on a global scale. Initially, reports of large values of reversible hydrogen absorption on carbon materials attracted great attention, but the non reproducibility of many results stimulated a discussion on possible adsorption mechanisms. To solve this controversy I designed and built a Raman cell that works at low temperature and both in high vacuum or high pressure. The in situ Raman spectra are useful for the understanding the intermolecular interactions responsible for gas sorption in solids and turned out to be fundamentally important for the development of new materials (Metal-Organic Frameworks) with improved hydrogen storage properties.
Despite the improvements in cancer early detection and treatment, cancer is still among the leading causes of death in the USA. Moreover, the collateral effects of traditional cancer therapies are very relevant because just a small fraction of the administered drugs is actually delivered into the tumours. In this talk I will show for the first time that the near-infrared plasmon resonance of gold nanorods (NRs) may be exploited to provide an integrated platform for in vivo multiplexed SERS detection and cancer photothermal heating. Particular emphasis will be given on in vivo SERS imaging and it will be shown how this technology can be integrated with photothermal cancer therapy and in situ drug delivery.
The common theme will between the two topics is the use of vibrational spectroscopy. During the talk I will underline measures and materials challenges that still have to be addressed for enabling the above applications.
For further information contact, Nikolai Zhitenev, 301-975-6039, Nikolai.Zhitenev@nist.gov
CNST NanoFab Seminar
MOLECULAR VAPOR DEPOSITION FOR MULTI-LAYER NANOLAMINATES
Dr. Michael T. Grimes
Sr. Director of R&D, Applied MicroStructures* at www.appliedmst.com
Wednesday, February 24, 2010, 10:30AM, Rm. H107, Bldg. 217
The ability to impart specific surface characteristics or functionality onto a device substrate without altering the bulk material or intrinsic performance is crucial for the successful operation of many modern nanodevices. While self-assembled monolayer (SAM) coatings have demonstrated utility in a variety of surface modification applications to date, additional coating types and layers are required. On many substrate types, traditional SAM precursors exhibit poor adhesion. In other cases the durability of the SAM coating is poor and leads to short device lifetime. Oftentimes, the addition of one or more adhesion layers has expanded the array of materials that can be subsequently coated with SAMs. For example, an adhesion layer allows plastics/polymers to be coated with SAM coatings, usually improving the overall coating durability, in the process. At AMST*, we have developed a variety of low-temperature vapor-deposited techniques that make use of adhesion layers and functional SAM coatings to form highly conformal nanolaminates. Molecular Vapor Deposition (MVD) processing is an ideal way to create these nanolaminates since substrates can be plasma treated and coated with these film stacks within a single chamber. Advantages of using vapor-deposited multi-layer nanolaminate coatings on a variety of different substrates are discussed as well as practical improvements achieved in fields such as MEMS, inkjet printing, barrier layers, and nanoimprint lithography. AMST's MVD® technology is in use at Universities and Institutes worldwide and is used in numerous production applications.
Primary areas of focus have been in: MEMS: Anti-Stiction Semiconductors: NIL & Corrosion Protection Inkjet Printheads: Surface Modification (Hydrophobic/Hydrophilic) Life Sciences: Reactive Coatings & Surface Modification Solar & Displays: Moisture Barrier Films
*Applied Microstructures, Inc. (AMST) is located in San Jose, California. Find more information MVD® is a trademark of Applied MicroStructures
Dr. Michael Grimes has served as the Senior Director of R&D at AMST since April 2006. Dr. Grimes has held a variety of scientific positions during his career in the chromatography, biotechnology, and pharmaceutical industries. Prior to AMST, Dr. Grimes served as a Principal Scientist in the Analytical Sciences Division at Alza Corporation (Johnson & Johnson). Previously, Dr. Grimes worked at both Ciphergen Biosystems and Dionex Corporation where he contributed to the successful commercial release of several products, including polymeric and silica-based chromatographic stationary phases and surface-modified biochips. Dr. Grimes received his Ph.D. in Chemistry from Stanford University where he was an NIH Biotechnology Fellow. Dr. Grimes has multiple patents pending and has published 6 technical papers.
For further information contact, Vincent Luciani, 301-975-2886, Vincent.Luciani@nist.gov
CNST Energy Research Group Seminar
TIO2-BASED PHOTOACTIVE NANOMATERIALS: STRUCTURAL MODIFICATION AND IN SITU SURFACE CHEMISTRY STUDIES
Chuanyi Wang
Visiting Scientist/Department of Chemistry, Tufts University
Monday, February 22, 2010, 10:30AM, Rm. H107, Bldg. 217
Titanium dioxide (TiO2) based nanomaterials have proven to be useful in many fields, especially for energy conversion and environmental remediation. One major direction in this research area is the design and preparation of novel TiO2-based materials possessing high photo activity to satisfy the requirements for practical applications. In this prospect, various nanosized TiO2 including pure TiO2, Fe(III)-doped TiO2 and platinized TiO2 have been synthesized in our laboratories, and their photo-activities have been studied in detail. Experimental observations suggest that factors such as distribution of Fe(III) ions in the TiO2 matrix and/or on the surface, Pt-assisted network formation as well as the dispersity of Pt play vital roles in regulating the photo-activity of these materials. Therefore, molecular level information and mechanistic understanding of the basic principles of photo-activity are of utmost importance toward developing high efficient photoactive materials. To this end, in situ sum frequency generation (SFG) vibrational spectroscopy in conjunction with molecular probe studies have been conducted. On the TiO2 surface, different adsorption behaviors were revealed for three molecular probes, i.e., acetic acid, methanol, and water. Competitive adsorption among the three molecular probes is clearly resolved by the in situ SFG measurements. The adsorption order as well as the difference in response of methanol versus acetic acid adsorption to addition of water has direct implications for understanding TiO2 photocatalysis as well as the surface modifications involved in TiO2 photoelectrochemical solar cells and processes in TiO2 nanomaterial synthesis and assembly.
For further information contact, Nikolai Zhitenev, 301-975-6039, Nikolai.Zhitenev@nist.gov
CNST Energy Research Group Seminar
ENHANCEMENT OF BOILING HEAT TRANSFER BEHAVIOR USING NANOSTRUCTURED SURFACES ON ALUMINUM, COPPER AND SILICON
Terry J. Hendricks
MBI DoD Business Development Manager/SERDP-Army Project Manager,MicroProducts Breakthrough Institute
Tuesday, February 16, 2010, 1:30PM, Rm. H107, Bldg. 217
System energy management and cooling for future advanced lasers, radars, and power electronics is gaining importance, resulting in a search for technologies and design techniques to dissipate ultra-high heat fluxes, reduce system energy usage, and increase system efficiencies. We have reported enhanced pool boiling critical heat fluxes (CHF) at reduced wall superheat on nanostructured Al, Cu and Si substrates which are commonly used in advanced electronics cooling applications. Nanostructuring was realized by using a low temperature nanoparticle deposition process called microreactor-assisted-nanomaterial-deposition (MANDTM). Using this technique we deposited ZnO nano-structures on Al and Cu substrates, and zeolite structures on Si. We varied a number of parameters such as micro-/nano-structure morphologies, pore sizes, densities, and their inter-connectivity to identify optimal boiling morphologies. These surfaces displayed hydrophilic/super-hydrophilic characteristics with measured contact angles as low as 0?. We demonstrated controllability of contact angle from about 58° to near 0° for ZnO on aluminum surfaces and 80° to about 40° for zeolite texturing on silicon surfaces. Average roughness measured using AFM were in the range of 300-600 nm. Pool boiling refers to boiling under natural convection and nucleate boiling conditions, where the heating surface is submerged in a large body of stagnant liquid and the heat transfer is conventionally explained as governed by buoyancy effects, thin-film evaporation at bubble interfaces, and surface bubble dynamics. We have focused to date on water boiling in our experiments, but have future plans for investigating HFE 7100 boiling effects. We observed pool boiling CHF of 80-82.5 W/cm2 for nano-structured ZnO on Al surfaces versus a CHF of 23.2 W/cm2 on a bare Al surface with a wall superheat reduction of 25-38 ?C. These new CHF values on nano-structured surfaces represent a boiling heat coefficient of 24,000 W/m2-K. This represents an increase of almost 4X on nano-textured surfaces, which is contrary to conventional boiling heat transfer theory. This presentation will discuss our current heat transfer data, the behavior differences with conventional boiling theory, heat transfer coefficient comparisons using our nano-textured surfaces, and discuss our results showing critical heat flux dependency on surface wettability (i.e., surface contact angle) on these surfaces. The potential explanations for the CHF dependency with contact angle will be presented and discussed, along with further insights into the boiling heat transfer phenomenon on these nano-structured surfaces.
For further information contact, Fred Sharifi, 301-975-4633, Fred.Sharifi@nist.gov
CNST Electron Physics Group Seminar
NANOMAGNETISM RESEARCH: BENEFIT FROM REDUCED DIMENSIONALITY AND INTERFACES
Jie Wu
Ph.D. Candidate/University of California at Berkeley
Tuesday, February 16, 2010, 10:30AM, Rm. H107, Bldg. 217
Along the effort of intergrating the spin freedom in electronic devices, magnetic structures at nanometer scale are intensely studied because of its importance in both fundamental research and technological applications. Out of the broad topics of nanomagnetism research, I here select several subjects to represent my Ph.D research. Single-crystalline magnetic ultrathin films are synthesized by Molecular Beam Epitaxy (MBE), and measured by state-of-art techniques such as Magneto-Optic Kerr Effect (MOKE), Photoemission Electron Microscopy (PEEM), X-ray Circular and Linear Dichriosm (XMCD and XMLD) Spectroscopy. First, I will present my work on the magnetic long range order in two-dimensional magnetic systems, particularly on the observation of stripe and bubble magnetic phases and the universal laws governing the stripe-to-bubble phase transition. Second, I will present my result on a new type of magnetic anisotropy resulting from the spin frustration at ferromagnetic/antiferromagnetic interfaces. Third, I will revisit the topic of exchange bias and show that the exchange bias actually takes place even before the antiferromagentic spins are frozen. Finally I will discuss our recent observation on vortex state of antiferromagnetic thin disks.
For further information contact, John Unguris, 301-975-3712, John.Unguris@nist.gov
CNST Energy Research Group Seminar
PRECISELY TAILORED NANOSTRUCTURES: MATERIALS CHEMISTRY AND APPLICATIONS
Min Ouyang
Project Leader Candidate
Friday, February 12, 2010, 10:30AM, Rm. H107, Bldg. 217
Nanoscience & Nanotechnology offers opportunity for manipulating and fabricating artificial nanostructures that might not even exist in nature with desired property and functionality. In this talk, I will present a few recent highlights from my research group. I will start from materials standpoint and show how to achieve meticulous control of nanostructures including defects, crystallinity and compositions based on bottom-up chemical synthetic strategy. Enabled by these advances, fundamental physics properties such as photonic, electronic, mechanic and spintronic interactions can be finely tailored at the nanoscale. Uniquely combined with our nanomaterials advancement, different ultrafast optical spectroscopy techniques have been applied to probe fine coupling interactions within these as-synthesized nanostructures. I will further focus on two topics: (1) electron-phonon and phonon-phonon interactions within nanostructures. Role of defects on modifying such fundamental interactions will be discussed, and I will also present how these coupling interactions can be precisely tuned by controlling dielectric confinement of nanostructures. Implications for performance of sensors based on nanoparticles will also be discussed. (2) light-matter-spin interaction at the nanoscale. Semiconductor nanostructures represent promising building blocks for scalable solid-state quantum devices based on electron spin. I will show how quantum confinement can tailor spin properties of nanostructures. Importantly, light-matter interaction can be engineered by artificial nanostructures and thus can be applied to manipulate spin coherence dynamics through ultrafast optical Stark effect at the nanoscale.
BIOGRAPHY Min Ouyang received his B.S. (1996) and M.S. (1997) in Electronics from Peking University, Ph.D in Chemistry from Harvard University in 2001, followed by postdoctoral research in Physics in the University of California at Santa Barbara. Min Ouyang joined the physics department of the University of Maryland as an assistant professor in 2004. Min Ouyang has broad interest in exploring new materials chemistry, physics, and device and technology applications based on the spin and charge degrees of freedom of electrons and nuclei within ordered nano-engineered architectures. Min Ouyang has received Alfred P. Sloan Fellowship (2006), NSF CAREER award (2006), Ralph E. Powe award (2006), ONR Young Investigator award (2007), and Beckman Young Investigator award (2007).
For further information contact, Nikolai Zhitenev, 301-975-6039, Nikolai.Zhitenev@nist.gov
CNST Energy Research Group Seminar
NANOMETER-SIZE ISLANDS ON SEMICONDUCTOR SURFACES: SHAPE, ORDERING, AND QUANTUM SIZE EFFECTS
Ilan Goldfarb
Surface Science Expert/Tel Aviv
Tuesday, February 9, 2010, 10:30AM, Rm. H107, Bldg. 217
In this talk I will survey our ongoing work on self-organization of epitaxial nanoislands on semiconductors surfaces, studied primarily by scanning tunnelling microscopy in ultra-high vacuum. More specifically, the following topics will be discussed. Shape evolution of Ge "hut" clusters on Si(001) from nucleation to elongation, namely peculiar shapes of the sub-critical nuclei, and selection of the elongation direction. Self-organization of cobalt- and titanium-silicide islands in terms of lateral self-ordering along step-bunches on vicinal Si(111) surfaces, and step-bunches as island size-selectors. Quantum size-effect of "electronic growth" in the silicide islands causes the electron energy in the islands to prevail over surface and strain energies and dominate the process of determination of the island shape and height. Finally, metallic nano-contacts on cleaved CdZnTe(110) surface, made of epitaxial indium-telluride and producing Schottky-type contacts, will be discussed.
For further information contact, Alec Talin, 301-975-4724, Alec.Talin@nist.gov
CNST Electron Physics Group Seminar
SINGLE-PHOTON ATOMIC COOLING
Gabriel Price
Postdoctoral Candidate, University of Texas at Austin
Tuesday, January 26, 2010, 10:30AM, Rm. H107, Bldg. 217
This talk details the development and experimental implementation of single-photon atomic cooling. In this scheme atoms are transferred from a large-volume magnetic trap into a small-volume optical trap via a single spontaneous Raman transition that is driven near each atom's classical turning point. This arrangement removes nearly all of an atomic ensemble's kinetic energy in one dimension. This method does not rely on a transfer of momentum from photon to atom to cool. Rather, single-photon atomic cooling achieves a reduction in temperature and an increase in the phase-space density of an atomic ensemble by the direct reduction of the system's entropy. Presented here is the application of this technique to a sample of magnetically trapped 87Rb. Transfer efficiencies between traps of up to 2.2% are demonstrated. It is shown that transfer efficiency can be traded for increased phase-space compression. By doing so, the phase-space density of a magnetically trapped ensemble is increased by a factor of 350 by the single-photon atomic cooling process.
For further information contact, Jabez McClelland, 301-975-3721, Jabez.McClelland@nist.gov
CNST Electron Physics Group Seminar
EXCHANGE BIAS ENHANCEMENT BY Cr ADDITION TO CoO IN A CoO-Co/Pt MULTILAYER SYSTEM
Hans Hug
Director, Nanoscale Materials Science, Swiss Federal Laboratories for Materials Testing and Research
Monday, January 25, 2010, 10:30AM, Rm. H107. Bldg. 217
The main use of exchange bias [1] (EB) in magnetic thin-film systems is for causing a unidirectional anisotropy in a ferromagnetic (F) layer, thus selecting its magnetization direction. This ability is key to enabling a number of sensor and storage technologies [2]. In this work we present data supporting the notion that EB can be increased by reducing the frustration of antiparallel coupling between the antiferromagnetic (AF) uncompensated spins (UCS) and the ferromagnetic (F) spins. We studied EB in magnetron sputtered Si/Pt(5)/{[Co(0.3)Pt(0.7)]9 Co(0.3)}/ Cu(2.2)/ [Co1-x CrxO](1.5)/ [Co(0.3)Pt(0.7)]4 Co(0.3)Pt(2) structures (numbers in parenthesis are thickness in nm). At x=0 the coupling between the antiferromagnetic (AF) CoO layer and the adjacent F-layer results in EB below the blocking temperature of about 200 K. Sputtering at a slightly elevated temperature of 425 K, the addition of Cr in the AF layer (x=20%) increases the EB field by about 74% at 8.2 K. High resolution magnetic force microscopy (MFM) images (1 x 1 um) from films with 20% Cr and without Cr in the AF were obtained from samples cooled in zero field to 8.2K. Ascooled samples display the maze pattern domains of the F. As a field is applied, the unfavorable domains are seen to shrink and then break up, as would be expected. Interestingly, the break-up of the domains occurs at highesr field levels in the sample with Cr. Above saturation, the MFM contrast is due to the uncompensated spins (UCS) of the AF, which are seen to have a granular distribution on a scale of about 20nm. Overlaying the contours of the F-domains on the distribution of UCS shows that the latter are aligned antiparallel to the magnetization of the as-cooled Fdomains, on average, consistent with previous work [3,4]. Moreover, in the sample with Cr in the AF there are fewer spots where the UCS are parallel to the as-cooled F-domain magnetization. This is consistent with our conjecture that Cr contributes to decoupling the AF grains, leading to a reduced frustration of antiparallel coupling, and hence to an improved EB.
References:
[1] W.H. Meiklejohn and C.P. Bean, Phys. Rev. 102 (1956), 1413–1414.
[2] C. Tsang, et al., IEEE Trans. Magn. 30 (1994), 3801–3806 ; S. Parkin, et al., J. Appl. Phys. 85 (1999), 5828–5833, R. Millen, et al., Anal. Chem. 80 (2008), 7940–7946; D. Wood, et al., Sens. Act. A: Phys. 120 (2005), 1-6.
[3] P. Kappenberger, et al., Phys. Rev. Lett. 91 (2003), 26720. [4] I. Schmid, et al., Europhys. Lett. 81 (2008), 17001.
For further information, contact Joseph Stroscio, 301-975-3716, Joseph.Stroscio@nist.gov
CNST Nanofabrication Research Group Seminar
INTRODUCTION TO PRINCIPLES AND APPLICATIONS OF ATOMIC LAYER DEPOSITION
Ganesh M. Sundaram
Cambridge NanoTech Inc.
Friday, January 22, 2010, 1:30PM, Rm. H107, Bldg. 217
The growing adoption of Atomic Layer Deposition (ALD), as a means of producing highly uniform, and conformal thin films, has paved the way for its use in an array of extremely important emergent technologies. In this talk an overview of the ALD deposition process, reaction sequence, fundamentals, and select applications will be presented. Examples of these include the use of ALD for Organic LED (OLED) devices, solar cells, and Li-ion batteries, as well as the use of ALD for low temperature coatings for polymers, conformal coatings of structures with ultra-high aspect ratios, and the growth of nano-laminates.
For further information, contact Henri Lezec, 301-975-8612, Henri.Lezec@nist.gov
CNST Nanofabrication Research Group Seminar
MICRO-MECHANICAL FABRY-PEROT CAVITIES FOR SENSING
Marcel Pruesser, PhD.
Thursday, January 21, 2010, 10:30 AM, Rm. C103-C106, Bldg. 215
In this talk, I will describe our work on micro-opto-mechanical (optical MEMS) chemical vapor sensors. The sensors are based on microbridges coated with sorbent polymers. The microbridges form one reflector in a Fabry-Perot interferometer, such that a read-out laser tuned near a cavity mode sensitively detects microbridge motion and mechanical resonant frequencies. Adsorption of chemical vapors by the sorbent coatings results in a decrease in the microbridge's resonant frequency due to mass loading. In order to improve device performance, we fabricate multiple sensors on a single chip to enhance the detection specificity. The result is an array of in-plane Fabry-Perot microcavities that can be interconnected via integrated waveguides. Finally, I will discuss our recent cavity opto-mechanics experiments, which may enable future all-optical sensors that can be powered and probed from a distance.
For further information, contact Vladimir Aksyuk, 301-975-2867,vladimir.aksyuk@nist.gov
CNST Nanofabrication Research Group Seminar
SHEAR ALIGNMENT OF BLOCK COPOLYMER FILMS AND THEIR APPLICATIONS IN NANOPATTERNING
Richard A. Register
Department of Chemical Engineering and Princeton Center for Complex Materials, Princeton University
Friday, January 15, 2010, 10:00 a.m. Rm. H107, Bldg. 217
Microphase separation in block copolymers is at the heart of their utility as thermoplastic elastomers (melt-processable rubbers), and it is well known that the topology of the nanodomain structure—spheres, cylinders, or lamellae of the hard block—has a profound impact on the mechanical properties, which can range from those of soft rubbers to those of a hard plastic. But the equally well-known facts that these nanodomain structures can be highly regular (a body-centered-cubic packing of near-monodisperse spheres, for example), and that the characteristic dimension of these domains can easily be tuned through the block copolymer molecular weight, are rarely exploited. We use block copolymer thin films as templates, where the block copolymer's nanodomain structure is faithfully reproduced in an inorganic material. For example, we have fabricated dense arrays of 20-40 nm metal or semiconductor particles (dots, from block copolymers which form spherical nanodomains) or lines (wires, from cylinder-formers), all with a size and spacing set through block copolymer molecular weight. The polygrain structure which these nanodomains normally form can be transformed to a single-crystal texture, over macroscopic areas, by a simple shearing process. We have used this approach on cylinder-forming block copolymer monolayer films to fabricate centimeter-scale arrays of parallel metallic nanowires, with 33 nm pitch; due to their fine pitch, such wire grids can polarize an exceptionally broad range of wavelengths extending down into the deep ultraviolet (for 193 nm lithography). Shearing can also align bilayers of a sphere-forming block copolymer, which can be further processed to yield ordered arrays of metal dots. Finally, shear can be used to realign the domain orientation locally in films with an otherwise macroscopic orientation; to create complex orientation patterns on the millimeter scale; and even to transform spheres into cylinders.
For further information contact J. Alexander Liddle 301-975-6050, James.Liddle@nist.gov
CNST Electron Physics Group Seminar
HIGH-TC SUPERCONDUCTIVITY MEETS A 3+3-DIMENSIONAL SPECTROSCOPIC TOOL
Jhinhwan Lee
Asistant Professor, Korea Advanced Institute of Science and Technology
Friday, January 15, 2010, 1:30PM, Rm. H107, Bldg. 217
Using a novel high-precision variable-temperature Fourier-transform scanning tunneling spectroscopy (FTSTS) technique, we observed for the first time (Science 325, 1099 (2009)) the complete set of dispersive octet peaks in the pseudogap phase (up to 1.5 Tc) as well as in the superconducting phase (down to 0.1 Tc) of the underdoped (UD37K) Bi2212. Looking further into the fine structures of the 3D FTSTS data by a novel cross-sectional analysis technique, we could resolve additional signal components that are key to truly quantitative analyses based on the full many-body Green's function. The high-precision measurement of 3D [2D position(nm2), energy(mV)] FTSTS over the entire accessible 3D [T(Kelvin) vs p(doping %) vs B(Tesla)] phase diagram, accompanied by the novel cross-sectional FTSTS analysis based on the full many-body Green's function, will provide one of the most stringent tests for a "complete" many-body theoretical understanding of the high-Tc cuprate superconductivity.
For further information, contact Joseph Stroscio, 301-975-3716, Joseph.Stroscio@nist.gov
