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CNST Group Seminars: 2009



CNST Electron Physics Group Seminar

MAGNETISM IN EPITAXIAL MnSi THIN FlLMS


Theodore Monchesky
Associate Professor, Department of Physics and Atomspheric Science, Dalhousie University

Wednesday, December 9, 2009, 1:30PM, Rm. B145, Bldg. 221

Chirality in magnetic systems remains largely unexplored in spintronics research. A spin-polarized current flowing in a chiral magnetic system will induce a torque that will produce new kinds of magnetic excitation. This spin-transfer torque, which has enable switching of non-chiral magnets, has attracted considerable attention. In a helical magnet, in contrast, spin-transfer torque would produce a continuous rotation of the helix that would offer new opportunities for spin control and manipulation. We are characterizing epitaxial single crystal MnSi layers on Si(111) to determine their suitability for spintronics studies. Bulk MnSi is a weak itinerant-electron helical magnet that has attracted considerable interest due to its pressure induced non-Fermi liquid behavior. In thin films, the 3% lattice mismatch between MnSi(111) and Si(111) produces a positive volume strain in the film, which results in a 50% increase in the Curie temperature. The magnetic properties show departures from the bulk magnetic properties, including glassy magnetic behavior. These measurements suggest a structure more complex than the helical order in bulk.

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


CNST Electron Physics Group Seminar

STABILITY IN A TURBULENT (FERMI) SEA: THE EVER MORE REMARKABLE HIGH TEMPERATURE SUPERCONDUCTORS


Eric Hudson
Professor, Department of Physics, Massachusetts Institute of Technology

Friday, December 4, 2009, 1:30PM, Rm. H107, Bldg. 217

 

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

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

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

CNST Energy Research Group Seminar

NANOIMPRINTED TRANSPARENT METAL ELECTRODES AND THEIR APPLICATIONS IN ORGANIC SOLAR CELLS 


Myung-Gyu Kang
Postdoctoral Candidate

Tuesday, November 17, 2009, 10:30AM, Rm. H107, Bldg. 217

 

Organic solar cells (OSCs) offer a promising alternative to inorganic solar cells due to their low cost, easy fabrication, and compatibility with flexible substrates over a large area. Since their first report, the power conversion efficiency (PCE) of OSCs has steadily increased and now reached up to 4-5 %. However, further enhancement of the PCE together with low-cost fabrication is still required for practical applications. The developed transparent metal electrodes have the characteristics of the high optical transmittance and electrical conductivity, a combination of properties that makes them suitable as a replacement of the expensive indium tin oxide (ITO), a predominant choice as a transparent and conductive electrode (TCE) for organic optoelectronic device applications. Not only do metal electrodes provide excellent optical transmittance and electrical conductivity, but also nanoscale metallic gratings exhibit unique optical properties due to the excitation of surface plasmon resonance (SPR), which can be exploited in specially designed solar cells to achieve enhanced light absorption. For instance, OSCs made with transparent Ag electrode as a TCE outperform the device with conventional ITO electrode due to the surface plasmon enhanced light absorption in organic materials. Photocurrents and external quantum efficiencies (EQE) are enhanced as mush as 43 % and 2.5 fold at a wavelength of 570 nm, respectively, resulting in 35 % enhancement of power conversion efficiency. Therefore, the use of developed transparent metal (e.g. Ag) electrode will help to realize low cost, high performance organic solar cells.

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

CNST Energy Research Group Seminar

SPIN RELAXATION AND QUANTUM INTERFERENCE IN INSB AND INAS BASED HETEROSTRUCTURES 


Ray Kallaher
Postdoctoral Candidate/Dept. of Physics, Virginia Tech

Tuesday, November 10, 2009, 10:30AM, Rm. H107, Bldg. 217

 

Low-temperature quantum-coherent transport in semiconducting systems is sensitive to quantum interference between electron wave functions. The coherence allows identification of spin precession phenomena in magnetotransport measurements. This talk will present magnetotransport measurements in narrow-gap semiconductor systems where strong spin-orbit interactions may lead to avenues for spin manipulation in spintronics devices. At low temperatures Te-doped InSb thin films and quasi-1D wires fabricated from an InSb/InAlSb two dimensional electron systems show antilocalization, occurring as a consequence of the spin-orbit interactions, From the data we can extract spin relaxation times of the itinerant electrons, revealing that increasing dimensional confinement in InSb systems can affect spin decoherence mechanisms. By analyzing the dependence of the spin relaxation time on carrier concentration in films with different Te doping, it is shown that the Elliot-Yafet mechanism is responsible for spin decoherence in doped InSb films at low temperatures. In contrast, spin coherence lengths in the quasi-1D wires are found to be inversely proportional to wire width – consistent with spin decoherence via the D'yakonov-Perel' mechanism. Quantum coherence also leads to pronounced oscillatory intereference phenomena in mesoscopic rings. Magnetotransport across mesoscopic ring arrays fabricated on an InAs/AlGaSb two dimensional electron system show both Aharonov-Bohm oscillations periodic in one flux quantum, _=h/e, as well as Altshuler-Aronov- Spivak oscillations periodic in _=h/2e, affected by the spin degree of freedom. The Fourier spectra of the magnetotransport reveal a splitting of the h/e peak which is attributed to a spinorbit interaction-induced Berry's phase.

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

CNST Electron Physics Group Seminar

SEMICONDUCTOR SPINTRONICS 


Berry Jonker
Senior Scientist/Naval Research Laboratory, Washington, DC

Wednesday, November 4, 2009, 10:30AM, Rm. H107, Bldg. 217

 

This seminar will present a brief overview of two programs on semiconductor spintronics at NRL. First, we describe a simple and efficient way to electrically inject spin-polarized electrons from Fe/Al2O3 and Fe/SiO2 tunnel barrier contacts into silicon, achieving a majority electron spin polarization of at least 30% [1]. We generate both spin-polarized charge currents and pure spin diffusion currents using a non-local spin valve (NLSV) lateral transport structure, and demonstrate that we can manipulate and electrically detect the polarization of the pure spin current [2,3] as required for information processing. This pure spin current produces a net spin polarization and an imbalance in the spin-dependent electrochemical potential, which is detected as a voltage by a second magnetic contact outside of the charge flow path. This voltage is sensitive to the orientation of the contact magnetization relative to the net spin orientation in the Si, which is determined by both the magnetization/bias of the injector contact and spin precession induced by a magnetic field applied normal to the surface (Hanle effect). As the relative orientation of injector and detector contacts changes from parallel to antiparallel, the voltage at the detector contact changes from low to high, respectively. The Hanle field induces precession of the spin in the silicon transport channel, resulting in a modulation of the detected signal. The Hanle measurements yield spin lifetimes of 1-5 ns at 10K for lateral transport in n-doped Si (~ 4x1018 cm-3) [2]. Second, we demonstrate control of the spin population of individual quantum shell states of self-assembled InAs quantum dots (QDs) using a spin-polarized bias current from an Fe thin film contact, and determine the strength of the interaction between spin-polarized electrons in the s, p and d shells [4]. We monitor the shell population and spin polarization by measuring the polarized light emitted as a function of the bias current. As the bias current is increased, the shell states fill, and the electroluminescence (EL) exhibits peaks characteristic of the s-, p-, d-, and f-shell energies. Intershell exchange strongly modifies the optical polarization from that expected for simple models of shell occupation. From a detailed analysis of the EL spectra, we are able to obtain the first experimental measure of the exchange energies between electrons in the s- and p-shells, and between electrons in the p- and d-shells. These energies describe the degree of interaction between these quantum levels.

References: [1] B.T. Jonker et al, Nature Phys. 3 (2007) 542; C. Li et al, APL 95 (2009) 1; G. Kioseoglou et al, APL 94 (2009) 122106. [2] O.M.J. van t' Erve et al, APL 91 (2007) 212109. [3] O.M.J. van t' Erve et al, IEEE Trans. Elec. Devices (Oct 2009). [4] G. Kioseoglou et al, Phys. Rev. Lett. 101, 227203 (28 Nov 2008).

For further information, contact John Unguris, 301-975-4088, John.Unguris@nist.gov

CNST Energy Research Group Seminar

VERTICAL AND HORIZONTAL NANOPOROUSANODIC ALUMINUM OXIDE (AAO) SCAFFOLD FOR REALIZATION OF INTEGRATED SELF-ASSEMBLED DEVICES 


Jihun Oh
Postdoctoral Candidate

Tuesday, November 3, 2009, 1:30PM, Rm. H107, Bldg. 217

 

An ordered array of nanoporous anodic aluminum oxide (AAO) is a nano-structured material that self-orders with domains and can be templated for pore ordering over arbitrarily large areas with controlled symmetry. Thin films of AAO have been used as templates for growth of metallic and semiconducting nanodots, and as both templates and scaffolds for growth of nanowires and nanotubes. To incorporate these nanostructures in electrically active devices and systems, it is necessary to have two electrodes at top and bottom of each nanowire. However, AAO has thin insulating barrier oxide and it is desirable to remove the thin barrier oxide at the base of the pores.

In this talk, I'll present a new method for perforation of the AAO barrier layer based on anodization of Al/W multilayer films on substrates. Using this technique, I will demonstrate that it is possible to perforate OPA barrier layers for porous structures with small-diameter pores at small spacings without changing pore diameter. In addition, I will present the W interlayer process to fabricate through-pore AAO film on any substrate. Using the process, arrays of various metallic nanowires (Ni, Au, Pt, and carbon nanotube) with diameter of 10 ~ 100 nm were grown in an AAO scaffold on electrically connected to conducting substrates by electrochemical and chemical vapor deposition techniques. In addition, fabrication of the horizontal pore arrays will be presented for assembling massively ordered arrays of nanotubes and nanowires in the plane of a substrate for devices such as a field-effect transistor.

For further information, contact Fred Sharifi, 301-975-6433, Fred.Sharifi@nist.gov

CNST Nanofabrication Research Group Seminar

OPTOMECHANICAL CRYSTALS 


Oskar Painter
Associate Professor, Department of Applied Physics, California Institute of Technology

Monday, November 2, 2009, 10:30AM, Rm. H107, Bldg. 217

 

The fact that light carries momentum and can exert a mechanical force was first proposed by Kepler and Newton. The interaction of light with mechanical vibrations, in the form of Brillouin and Raman scattering, has been known since the 1920's and has many practical applications in the fields of spectroscopy and optoelectronics. With the advent of the laser in 1960's, it became possible to manipulate micron-scale dielectric particles using optical "tweezers" as pioneered by Art Ashkin. This was also the beginning of the use of laser beams for the trapping and manipulation of gas-phase atoms, which ultimately led to the demonstration of atomic Bose-Einstein Condensates. More recently, it has been realized that laser light, with its very low intrinsic noise, may be used as an effective method of cooling a macroscopic mechanical resonant element, with hopes of reaching effective temperatures suitable for measuring inherently quantum mechanical behavior. In duality to the cooling effect, it has also been demonstrated that optical amplification from a continuous-wave laser beam can be used to form regenerative mechanical oscillators. With these developments, interest in the new field of cavity-optomechanics has been piqued, with myriad of different materials, devices, and techniques currently being developed. In this talk I will describe some of the on-going work at Caltech to create nano-mechanical structures strongly coupled to internally guided light beams through gradient optical forces. These structures enter physical regimes not possible in more macroscopic devices, with motional mass and effective optomechanical coupling length many orders of magnitude smaller than in Fabry-Perot or whispering-gallery resonators which rely on radiation pressure. I will present recent results on a so-called "zipper" photonic crystal cavity which shows an optical spring effect many times that of the intrinsic mechanical spring, resulting in interesting mechanical mode-mixing and extremely high motion sensitivity. I will also describe efforts to create planar circuits for light and acoustical waves, what we have termed optomechancial crystals. Finally, I will discuss some of the potential applications of these devices to photonics, sensing, and to quantum circuits.

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

CNST Nanofabrication Research Group Seminar

GALLIUM-ARSENIDE DEEP-CENTER LASER 


Janet Pan
Associate Professor and Research Scientist, Yale University

Friday, October 30, 2009, 2:00PM, Rm. H107, Bldg. 217

 

The ongoing quest for semiconductor lasers with low threshold current has led to the development of new materials (e.g., quantum wires and dots) and new optical resonators (e.g., microdisks and photonic bandgap crystals). In a novel approach to ``thresholdless" lasers, we have developed a new growth technique for self-assembled deep-centers in the technologically important semiconductor gallium-arsenide. We recently demonstrated the first gallium-arsenide deep-center laser. These lasers, which intentionally utilize gallium-arsenide deep-center transitions, exhibited a threshold current density of less than 2A/cm2 with electrical injection in continuous-wave mode at room temperature at the important 1.54um fiber-optic wavelength. Moreover, in contrast to conventional semiconductor devices, whose operating wavelengths are fixed by the bandgap energy, the room-temperature stimulated-emission from gallium-arsenide deep-centers can be tuned very widely from the bandgap (about 900nm) to half-the-bandgap (1600nm). We demonstrated laser action at many wavelengths between 1.2um and 1.6um, which includes fiber-optic wavelengths. We explain the physics of gallium-arsenide deep-center lasers.

Biography:

At Yale University, Dr. Janet Pan has been a winner of the NSF Career, ONR Young Investigator, and Sheffield Teaching Awards. Dr. Pan has been an Invited Speaker at the March Meeting of the APS, the International Conference on the Physics of Semiconductors, and Photonics West. Dr.Pan received all her degrees from the Massachusetts Institute of Technology. While at MIT, she won the Hertz, NSF, and Rockwell International Graduate Student Fellowships. She was also a winner of the Associate of MIT Alumnae Highest Academic Achievement Award for best female undergraduate student.

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

CNST Electron Physics Group Seminar

MAGNETOELECTRIC EFFECT IN MULTIFERROIC OXIDES: A PEDAGOGICAL OVERVIEW 


Bhagawan R. Sahu
Research Physicist/Microelectronics Research Center, University of Texas, Austin

Thursday, October 29, 2009, 1:30PM, Rm. H107, Bldg. 217

 

In this talk, I will review the physics of multiferroicity in single phase oxide materials (e.g. BiMeO3 (Me= Fe, Mn) and FeTiO3 and the mechanism of coupling between two order parameters-polarization P and magnetization M -in them. These materials offer an opportunity to study the manipulation of magnetic moments by external voltages. I will then discuss the current understandings and challenges in this field and if time permits, dwell upon another area of multiferroics namely oxide heterostructures where multiferroicity and magnetic-electric coupling occur as an interfacial emergent phenomena.

For further information, contact Mark Stiles, 301-975-3745, Mark.Stiles@nist.gov

CNST Nanofabrication Research Group Seminar

MODEL-BASED WHITE LIGHT INTERFERENCE MICROSCOPY FOR METROLOGY OF TRANSPARENT FILM STACKS AND OPTICALLY-UNRESOLVED STRUCTURES 


Peter de Groot
Director, Research & Development, Zygo Corp. Middlefield, CT

Xavier Colonna de Lega
Senior Research Scientist. Zygo Corp. Middlefield, CT

Tuesday, October 27, 2009, 2:00PM, Rm. H107, Bldg. 217

 

White light interferometry has evolved from a high-precision tool for 3D surface-topography to a multi-functional platform for surface structure analysis. The drivers for this evolution are the increased complexity and shrinking feature size of high-volume production components such as semiconductor wafers, flat panel displays, data storage components and MEMS. The enabling technology is interferometry combined with advanced computer analysis, including detailed instrument modeling, complex reflectivity analysis for transparent films and rigorous coupled wave analysis (RCWA) for optically-unresolved features. I present here the principles and several practical examples of measurements of multi-layer dielectric and metallic film stacks and shape parameters for surface features smaller than 50nm wide using visible-wavelength interferometry. I also show how these data may be combined with 3D surface topography for a complete surface structure analysis.

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

CNST Energy Research Group Seminar

TUNING THE ACTIVITY OF PLATINUM ELECTROCATALYSTS VIA SIZE, SHAPE, AND CAPPING POLYMER 


Ceren Susut
Postdoctoral/Department of Chemistry, Georgetown University

Tuesday, October 20, 2009, 10:30AM, Rm. H107, Bldg. 217

 

The high cost and the low catalytic activity of the anode catalysts are two major obstacles in the development of the direct-methanol fuel cell. Platinum (Pt)-based catalysts are considered the best anode catalysts for methanol electro-oxidation reaction and their catalytic activity is highly dependent on their surface structure. At nanoscale, the major determinants of the surface structure are the shape and size of the catalyst particles. Hence, this talk will focus on the investigation of the shape and size dependent electro-catalytic activities of Pt nanoparticles. Simple synthetic procedures for the concomitant control of the shape and size of the Pt nanoparticles will be described and the trends in the electro-catalytic activity of the synthesized catalysts will be discussed. The findings of a mechanistic investigation based on surface-enhanced infra-red absorption spectroscopy, detailing the intermediate species generated during the methanol electro-oxidation reaction on these catalysts will be presented. Additionally, this talk will illustrate the first evidence on the enhancing effect of the capping polymer polyvinylpyrrolidone on the activity of Pt nanocatalysts for several electrochemical reactions. The results of this overall investigation will be discussed within the context of the development of potential approaches, in fuel-cell related electro-catalysis research, that combine the effect of shape, size and capping polymer to tune the activity of Pt electro-catalysts.

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

CNST Energy Research Group Seminar

METAL-INSULATOR TRANSITION IN THIN FILM VANADIUM DIOXIDE 


Dmitry Ruzmetov
Postdoctoral Fellow in Applied Physics, Harvard University

Tuesday, October 13, 2009, 10:30AM, Rm. H107, Bldg. 217

 

The phenomenon of metal-insulator phase transition in strongly correlated electron systems is one of the focus areas of research in condensed matter physics. The interest is partly motivated by the potential of the materials exhibiting a metal-insulator transition to be used in novel electronics and electro-optic applications as switches or memory elements. There is also considerable interest in understanding the fundamental science behind the correlated electron behavior responsible for striking material property changes such as high temperature superconductivity, metal-insulator transition, and colossal magnetoresistance. Vanadium dioxide has received special attention because of the substantial scale of the metal-insulator transition in this material, the fact that the transition temperature is near room temperature (67°C), and extremely fast optical switching upon the transition (~100 fs).

I will present the results of our comprehensive study of vanadium dioxide (VO2) using a range of photon irradiation and electrical characterization techniques with the focus on the metal-insulator transition (MIT) in this material. Bulk thin film VO2 was investigated by means of synchrotron x-ray absorption and photoemission spectroscopy across the metal-insulator transition (MIT). The manifestation of MIT is observed in the unoccupied (x-ray absorption spectra) and occupied (photoemission spectra) density of states near the Fermi level. The energy band structure measurements are directly correlated to electron transport data for a set of vanadium oxide films with varying V-O stoichiometry. The optical studies of VO2 films revealed record high switching of the mid-infrared reflectance upon MIT and provided the evidence of the percolative nature of the phase transition. Our Hall effect experiments allowed determining the carrier density and electron mobility across the MIT – important parameters in the Mott theory of MIT. Our recent experiments on VO2 nano-junctions showed the scaling of the MIT effect by voltage triggering down to 200nm devices. Possible applications in electronics and our current experiments with VO2 devices will be outlined.

For further information, contact Albert Talin, 301-975-4724, Albert.Talin@nist.gov

CNST Electron Physics Group Seminar

SPIN TRANSFER TORQUE INDUCED LOW TEMPERATURE MAGNETIZATION DYNAMICS: A CASE STUDY 


Jacques Miltat
CNST Visiting Fellow/Laboratoire de Physique des Solides, France

Friday, October 2, 2009, 1:30PM, Rm. H107, Bldg. 217

 

Unambiguous evidence for the switching of sub-micron size spin-valves elements under the action of spin transfer torques was gained in year 2000 [1], i.e. some three years after the publication of John Slonczewski 's seminal patent [2]. Another key theoretical prediction is the existence of stable precession states under suitable field and dc current conditions [2]. Sustained precession gives rise to an rf GMR signal in the few GHz range, the frequency of which may be tuned by the amplitude of the dc current. A few GHz agility has been demonstrated in nano-contact devices [3] or GMR-type nanopillars [4,5] . Although the very existence of precessional states is understood in broad terms, fine features of the dispersion relations clearly call for an analysis beyond the single spin approximation. In spite, however, of the highly predictive power of micromagnetics, a fine comparison between theory and the most appealing experimental results has remained elusive. Rather than attempting to correlate experimental data with simulations based on assumed sample properties, it may well seem more appropriate to imagine which sample properties may lead to a given experimental response. It turns out that even a rather poor answer truly proves challenging.

[1] F. J. Albert et al., Appl. Phys. Lett. 77 (2000) 3809 [2] J. C. Slonczewski, US Patent 5 695 864 (1997) [3] W.H. Rippard et al., Phys. Rev. Lett. 92 (2004) 027201 [4] I. N. Krivorotov et al., SCIENCE 307 (2005) 228 [5] I.N. Krivorotov et al., Phys. Rev. B76 (2007) 024418

For further information, contact Mark Stiles, 301-975-3745, Mark.Stiles@nist.gov

CNST Electron Physics Group Seminar

ENGINEERED NANOSTRUCTURES OF ANTIGEN PROVIDE ALTERNATIVE AND SUPERIOR MEANS FOR INVESTIGATING AND ACTIVATING MAST CELLS 


Zhao Deng
Graduate Student

Tuesday, September 22, 2009, 10:30AM, Rm. H107, Bldg. 217

 

The high-resolution imaging and nanofabrication capabilities of AFM were exploited to unravel the signaling processes involved in the activation of mast cells, a key cell type of the immune system. AFM imaging in buffer revealed rich membrane structures associated with the activation of mast cells with remarkable details. These high-resolution surface characteristics were further correlated with cytoskeletal arrangement and intracellular organelles using a combined atomic force and laser scanning confocal microscope, which enabled the disclosure of detailed degranulation mechanisms for mast cells. Ligand nanostructures that mimic multivalent antigens in vivo were fabricated on surfaces using AFM-based nanografting, and served as cell-stimulating platforms. Upon changing geometrical parameters these engineered nanostructures exhibited regulatory effects on both cell adhesion and activation. These investigations demonstrate the revealing and regulatory power of AFM on the hypersensitive reactions of mast cells, and pave the way for the development of new therapies for treating allergic diseases.


CNST Energy Research Group Seminar

ELECTROCHEMICAL STUDIES ON PT-MODIFIED METAL (M) BIMETALLIC ELECTROCATALYSTS 


Bingchen Du
Postdoctoral Fellow, Georgetown University

Monday, September 21, 2009, 10:30AM, Rm. H107, Bldg. 217

 

Electrocatalytic activities of Pt-modified M (M = Ru, Au) bimetallic catalysts were prepared in terms of a surface modification strategy were investigated towards methanol (MeOH) electro-oxidation, carbon monoxide (CO) oxidation and oxygen reduction reaction (ORR). By experimentally controlling the Pt coverage on the metal substrates via a spontaneous deposition method, the resulting Pt-modified Ru or Au substrates indicated Pt coverage-dependent electrochemistry. Most importantly, it was observed that the inactivity of Pt towards MeOH oxidation with very low coverage and, the emerging and increasing activity with increasing coverage coincided with the phenomena predicted by the ensemble effect, a hypothesis that has not yet supported directly by experimental evidence. Later a one-pot wet chemistry method was developed to prepare Pt-decorated Ru nanoparticles with a submonolayer of Pt. The electrochemical characterization of the whole series of samples provided experimental evidence that strongly supported a bifunctional mechanism, rather than an electronic effect as the dominant factor contributing to the enhanced CO tolerance. Finally, using a core(Au)/shell(Pt) model, a detailed investigation of electrocatalytic properties of Au@Pt nanoparticles was performed as a function of the Pt shell packing density and Au core size. It was observed that the electrochemical behavior of Pt quite much deviated from its bulk counterpart especially at low coverage. The data obtained so far indicated that the future of PtAu as an anode electrocatalyst for MOR is questionable.

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

CNST Electron Physics Group Seminar

MANIPULATION OF ULTRA COLD ION BUNCHES WITH TIME DEPENDENT FIELDS 


Merijn P. Reijnders
Doctoral candidate/Eindhoven University of Technology, Netherlands

Friday, September 18, 2009, 1:30PM, Rm. H107, Bldg. 217

 

Many state-of-the art applications that use ion sources, like focused ion beam systems designed to drill and mill on the nanometer level, are limited by the energy spread of existing ion sources. We are working on a new source concept[1][2], based on near-threshold ionization of laser cooled atoms inside a magneto optical trap (MOT), to improve this. We have achieved much lower longitudinal energy spreads (0.02 eV) compared the current industry standard Gallium liquid-metal ion sources [3].

Due to the very low initial temperature, extracting at voltages down to several volts is possible. This makes it feasible to manipulate the ions bunches with time dependent electric fields while they are still in the accelerator. We will present measurements done with different kinds of time dependent electric fields that show they can be used to reduce the energy spread even more. Additionally we show they can be used to create a focusing lens.

[1] J.L. Hanssen et al, Phys. Rev. A 74, 063416 (2006). [2] S. B. van der Geer et al, J. Appl. Phys. 102, 094312 (2007) [3] M. P. Reijnders et al, PRL 102, 034802 (2009)

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

CNST Energy Research Group Seminar

FUNCTIONAL NANOMATERIALS FOR RENEWABLE ENERGY APPLICATIONS 


Susanta Mohapatra
Postdoctoral Fellow, Chemical and Materials Engineering, University of Nevada Reno, NV

Wednesday, September 16, 2009, 10:30AM, Rm. H107, Bldg. 217

 

Recently, the major concern in the United States (U.S.) is the ever rising fuel price, unemployment and global warming. Extensive research is going on to find alternative green fuel sources so that U.S. dependence on imported oil can be reduced. The major hopes to satisfy our day-to-day fuel demand come from hydrogen, biofuel, photovoltaic and fuel cell research. Water is a renewable resource and covers almost 75% of planet earth and each molecule of water yields one molecule of hydrogen. It is demonstrated that hydrogen can replace our fossil fuel needs. This is also only one energy source which is sustainable and non-carbon fuel. The other promising quick solutions are to get biofuel from waste materials, biomass, converting sugars into liquid fuels and algal biofuel. In addition to direct production of fuel we also can save fuels by using photovoltaic and advanced battery. As the fuel demand is too high not a single technology can solve the energy problem. We need to bring breakthrough researches in each and every streams of renewable energy. In the mean time we also have to make sure that our environment is not affected by the introduction of these new technologies. So, there is an urgent need to develop new environmentally friendly energy sources and improving energy efficiency in many technologies and processes. This talk targets the development of Energy Materials four major promising areas within energy science: (i) Photoelectrochemical and catalytic hydrogen production, (ii) hydrogen storage materials, (iii) Li-ion battery and (iv) Biofuel production from CO2 and non-food sources. Fabrication and study of functional nanoscale materials, with an emphasis on atomic-level tailoring using electrochemical methods to achieve desired properties and functions will be discussed. The flexibility in electrochemical methods for manipulation and structuring of desired materials at the nanoscale level opens up new possibility for revolutionary energy materials.

References: S.K. Mohapatra, M. Misra, V.K. Mahajan, K.S. Raja J. Catal. 246 (2007) 362; S.K. Mohapatra, K.S. Raja, M. Misra, V.K. Mahajan, M. Ahmadian, Electrochimica Acta 53 (2007) 590; S.K. Mohapatra, M. Misra J. Phys. Chem. C 111 (2007) 11506; A. Mishra, S. Banerjee, S.K. Mohapatra, M. Misra, Nanotechnology 19 (2008) 445607; S.K. Mohapatra, K.S. Raja, V.K. Mahajan, M. Misra J. Phys. Chem. C 112 (2008) 11007 ; S.K. Mohapatra, S.E. John, S. Banerjee, M. Misra, Chem. Mater. 21 (2009) 3048; N. Kondamudi, J. Strull, M. Misra S.K. Mohapatra Journal of Agriculture & Food Chemistry, 57 (2009) 6163.

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

Nanofabrication Research Group Seminar

FLUORESCENT NANODIAMONDS: TOWARDS SMALLER AND BRIGHTER

Daniel Gruber
Postdoctoral Research Fellow

Thursday, September 10, 2009, 1:30PM, Rm. H107, Bldg. 217

The fluorescent nitrogen-vacancy (NV) defect center in nanodiamond has become a popular tool for a wide range of applications like biological labelling, super-resolution microscopy or sensitive magnetic field measurements on the nanoscale. For most of these applications, the diamonds used should be as small and bright as possible.

In this talk, I will first give an overview of the properties of fluorescent nanodiamond, show some applications, and then concentrate on research done in our group to reduce the size of nanodiamonds while retaining the fluorescence properties.

Two different approaches will be discussed: 1. using small 5nm diameter detonation-type nanodiamond as starting material and 2. reducing the size of larger nanodiamond by oxidation. Finally,I will explain why small diamonds may be hard to cool down and how to use them as temperature sensors for the nanoscale. For further information contact Andrew Berglund, 301-975-2844, Andrew.Berglund@nist.gov

CNST Electron Physics Group Seminar

GRAPHENE TRANSPORT PROPERTIES 


Shaffique Adam
Center for Nanoscale Science and Technology, National Institute of Standards and Technology

Thursday, September 10, 2009, 10:30AM, Rm. H107, Bldg. 217

 

Arguably, one of the most intriguing properties of graphene transport is the non-vanishing ``minimum conductivity" at the Dirac point. The carrier density in these single monatomic sheets of carbon can be continuously tuned from electron-like carriers for large positive gate bias to hole-like carriers for negative bias. The physics close to zero carrier density (also called the intrinsic or Dirac region), is now understood to be dominated by the inhomogeneous situation where the local potential fluctuates around zero, breaking the landscape into puddles of electrons and holes. In this talk I will first briefly review (from a theorist's perspective) the competing effects of disorder, electron-electron interactions and quantum interference on graphene's transport properties. I will then compare a fully quantum-mechanical numerical calculation of the conductivity to a semi-classical Boltzmann transport theory and find that while the two theories are incompatible at weak disorder, they are compatible for strong disorder [1]. This result elucidates why the semi-classical self-consistent Boltzmann Random-Phase-Approximation theory for graphene transport [2] is in remarkable agreement with recent experiments [3-4].

[1] Adam, Brouwer, and Das Sarma "Crossover from quantum to Boltzmann transport in graphene" Phys. Rev. B Rapid Communications 79, 201404 (2009). [2] Adam, Hwang, Galitski, and Das Sarma "A self-consistent theory for graphene transport" Proc. Nat. Acad. Sci. USA 104, 18392 (2007). [3] Tan, Zhang, Bolotin, Zhao, Adam, Hwang, Das Sarma, Stormer, and Kim "Measurement of scattering rate and minimum conductivity in graphene" Phys. Rev. Lett. 99, 246803 (2007). [4] Chen, Jang, Adam, Fuhrer, Williams, and Ishigami "Charged-impurity scattering in graphene" Nature Physics 4, 377 (2008).

For further information contact mark Stiles, 301-975-3745, Mark.Stiles@nist.gov

CNST Nanofabrication Research Group Seminar

NANOPOSITIONING SINGLE QUANTUM DOTS 


Edo Waks
Assistant Professor, Department of Electrical and Computer Engineering, University of Maryland

Monday, August 31, 2009, 1:30PM, Rm. H107, Bldg. 217

 

Quantum dots (QDs) are stable, bright, semiconductor based light emitters that exhibit a quantized energy spectrum. For these reasons they have been considered as excellent candidates for development of nonlinear optoelectronic components, as well as basic building blocks for future quantum information technology. Many of these applications rely on the resonant interactions of QDs with nanophotonic structures such as microcavities or plasmonic nanoparticles. To reliably implement these resonant interactions requires the nanometer scale positioning of single QDs with the correct emission wavelength. Such positioning has proved extremely challenging due to both spatial randomness of QD growth locations and spectral randomness of QD emission (inhomogeneous broadening). In this talk I will present a novel technique for positioning single QDs with nanometer scale precision using electroosmotic flow control (EOFC). EOFC enables us to select single QDs inside a microfluidic chamber that have the correct radiative properties, and move them to a desired position. I will present our latest experimental results on QD positioning, and discuss our effort to positioning a single QD inside a photonic crystal cavity. Applications of these capabilities for optical computation and quantum information processing will also be addressed.

Biography - Edo Waks is a professor in the Department of Electrical and Computer Engineering at the University of Maryland, College Park. He is also a member of the Joint Quantum Institute (JQI), a collaborative effort between the University of Maryland and NIST, Gaithersburg, dedicated to the study of quantum coherence. Waks received his B.S. and M.S. from Johns Hopkins University, and his Ph.D. from Stanford University. He was awarded the prestigious NSF CAREER award as well as an ARO Young Investigator Award for the investigation of interactions between quantum dots and nanophotonic structures. His current work focuses coherent control and manipulation semiconductor quantum dots, and their interactions with photonic crystal devices for creating strong atom-photon interactions.

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

CNST Electron Physics Group Seminar

EXPLORING THE LIMITS OF SCANNING-PROBE MICROSCOPY - FROM FEMTOAMP STM TO FUNCTIONAL AFM 


Colm Durkan
University Lecturer, Head of Nanoscience group, Fellow of Girton College, University of Cambridge, UK

Tuesday, August 25, 2009, 1:30PM, Rm. H107, Bldg. 217

 

Recently, we have been attempting to push the current sensitivity of the scanning tunneling microscope. We will present our work on molecular imaging using femtoampere tunneling currents, and explore the possibility of imaging weakly conducting systems that this represents. We will also look at our work in the opposite regime, where the STM tip actively perturbs the system under study - using STM to locally alter the coupling between layers in HOPG. We will then move on to describe our recent activities in functional AFM - using the AFM to explore the magnetic phase diagram of permalloy nanodots. The main topic will then be on functional imaging of ferroeelctrics - we have developed a technique enabling us to simultaneously image and manipulate both ferroelectric and ferroelastic domains in ferroelectric thin films. We will explore the intimate interplay between ferroelectricity and ferroelasticity and how this knowledge can be used to create novel device structures.

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

CNST Energy Research Group Seminar

APPLICATIONS OF METAL-ORGANIC FRAMEWORKS BEYOND HYDROGEN STORAGE: WAY BEYOND... 


Mark Allendorf
Sandia National Labs, Livermore, CA 94550

Wednesday, August 19, 2009, 10:00AM, Rm. C103-106, Bldg. 215

 

The unique properties of the novel nanoporous materials known as metal-organic frameworks (MOFs) are attracting much interest from communities concerned with storage of hydrogen and other gases, and also for chemical separations. However, the ordered crystalline structures of MOFs and their unique, structurally flexible, nature create opportunities for their use in technically challenging arenas, such as chemical sensing, radiation detection, nanoparticle synthesis, and nanoscale tuning of properties. This presentation will provide an overview of MOF-related research activities at Sandia National Laboratories and will include recent work in the following areas: 1) MOF adaptation to the surfaces of microcantilevers to create a rapid, reversible chemical sensor; 2) synthesis of MOFs with luminescent linkers to create new scintillators; 3) infiltration of MOFs with metal hydrides to create nanoscale hydrogen storage materials; and 4) Ag@MOF nanocomposites with enhanced Raman scattering.

Mark D. Allendorf (Ph.D., inorganic chemistry, Stanford University) is a Distinguished Member of the Technical Staff at Sandia/CA, a Fellow of The Electrochemical Society, and formerly that organization's president. He currently leads efforts at Sandia to develop both the fundamental science and applications of MOF compounds. His research interests include chemical sensing, radiation detection, nanoparticle synthesis, and heterostructures for nanoscale electronics. He has published over 100 articles in peer-reviewed journals and conference proceedings.

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

CNST Electron Physics Group Seminar

INDIVIDUAL ATOMS AND MOLECULES ON INSULATING FILMS STUDIED WITH NONCONTACT AFM 


Leo Gross
Postdoctoral Fellow/IBM Research, Zurich

Wednesday, August 19, 2009, 10:30AM, Rm. H107, Bldg. 217

 

We investigated the charge state switching of individual gold and silver adatoms on ultrathin NaCl films on Cu(111) using a qPlus tuning fork atomic force microscope (AFM) operated at 5 Kelvin with oscillation amplitudes in the sub-Ångstrom regime. Charging of a gold adatom by one electron charge increased the force on the AFM tip by a few piconewtons. Employing Kelvin probe force microscopy (KPFM) we also measured the local contact potential difference (LCPD). We observed that the LCPD is shifted depending on the sign of the charge and allows the discrimination of positively charged, neutral, and negatively charged atoms.

Furthermore, we modified AFM tips by means of vertical manipulation techniques, i.e. deliberately picking up known adsorbates, to increase spatial resolution. To study the effect of the atomic tip termination we used different well defined tip terminations to image individual pentacene molecules. We compare our experimental results with density functional theory (DFT) calculations to gain insight on the physical origin of contrast formation on the atomic scale.

for further information contact Rachel Cannara, 301-975-4258, Rachel.Cannara@nist.gov

CNST Nanofabrication Research Group Seminar

HIGH INDEX CONTRAST SILICON-ON-INSULATOR PHOTONICS: FROM PRACTICAL LIMITATIONS TO NEW OPPORTUNITIES 


Shayan Mookherjea
Associate Professor, University of California at San Diego, ECE Department

Tuesday, August 18, 2009, 2:00PM, Rm. H107, Bldg. 217

 

I will discuss my group's recent work on silicon on insulator (SOI) photonics for on-chip lightwave circuits. Part of the talk will discuss the novelty and future prospects for silicon photonics applications and research from a university researcher's perspective who collaborates with industrial partners in this work. In this work, we show that it is important to consider the effects of disorder which inevitably arises from the limited tolerances of lithography. Disorder effects are much more severe for high index contrast, sub micron scale devices, such as SOI photonics, than in any previous generation of integrated optics. Consequently, we have shown that some proposed applications, such as slow light, are severely impacted. On the other hand, disorder in SOI photonics can also enable the realization of phenomena such as light localization, which may offer new approaches to achieve desired functionality in spite of challenging fabrication and design requirements.

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

CNST Nanofabrication Research Group Seminar

DETERMINING THE HYDRODYNAMIC SIZE AND SHAPE OF FLUORESCENT BIOMOLECULES BY PROBING THEIR SINGLE-MOLECULE BROWNIAN MOTION

 

Sandeep Pallikkuth
Postdoctoral

Wednesday, August 12, 2009, 2:00PM, Rm. H107, Bldg. 217

 

Monitoring the Brownian motion of a fluorescent biomolecule in solution renders information regarding its hydrodynamic shape and size under physiological conditions. In contrast to the translational diffusion of a fluorescent biomolecule that typically occurs on the micro- to millisecond time scale, its size is more sensitive to its rotational diffusion dynamics occurring on the pico- and nanosecond time scale. While the former is conveniently obtained from a conventional fluorescence correlation spectroscopy experiment, the latter is generally obtained from a time-resolved fluorescence anisotropy experiment upon pulsed excitation, which is inherently limited to the measurement of rotational correlation times not exceeding the fluorescence lifetime of the fluorophore.

To circumvent this problem and to provide an accurate measurement of the rotational diffusion time of a biological macromolecule, which is typically in the order of tens of nanoseconds, we apply a recently developed photon counting technology for the measurement of fluorescence correlation from picoseconds to seconds by registering distinct photon arrival times with picosecond resolution. Utilization of this technique in a polarization-sensitive manner along with an exact theoretical analysis in terms of the second-order correlation function allows us to probe simultaneously the translational and rotational diffusion of fluorescent biomolecules. We demonstrate the application of this novel single-molecule methodology for the determination of the hydrodynamic size and shape of small dye molecules (with sizes below 10 Å) as well as of fluorescent proteins.

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

CNST NanoFab Seminar

COMBINED SCANNING PROBE MICROSCOPY AND MICRO/NANO RAMAN STUDIES OF MODERN NANOSTRUCTURES

 

Pavel Sergeevich Dorozhkin
General Manager, Optics & Spectroscopy products
Oleg Gennadievich Butyaev and John Janzer

Monday, August 3, 2009, 1:30PM, Rm. H107, Bldg. 217

 

We will demonstrate various applications of confocal Raman/fluorescence microscope integrated with Atomic Force Microscope (AFM) to investigate modern nanostructures. First, we report on "classical" applications of such combination, when 2D AFM and confocal Raman maps are acquired simultaneously from the same part of the sample, but "independently" one from another. Physical characterization and modification capabilities of AFM merge with chemical resolution of confocal Raman microscope and general capabilities of optical microscope to provide complete information about sample investigated. Diffraction limited resolution of 2D Raman maps is 200 nm. We demonstrate results on various promising nanoelectronics materials: grapheme flakes, carbon nanotubes, semiconductor nanowires etc.

The ultimate goal of integrating AFM with Raman/fluorescence spectroscopy is to break diffraction limit and to bring spatial resolution of optical methods down to resolution of AFM (a few nm). We present results of Tip Enhanced Raman Spectroscopy (TERS) mapping experiments realized using integrated AFM-Raman system. Measurements are realized in two different excitation configurations: Inverted (for transparent samples) and Upright (reflected light configuration, for opaque samples). In both geometries we demonstrate near field Raman enhancement effect due to resonant interaction of light with localized surface plasmon at the apex of a metal AFM probe. Various samples are studied by TERS technique: thin metal oxide layers, fullerenes, strained silicon, carbon nanotubes, and grapheme. Actual plasmonic and near field nature of the Raman enhancement is proven by a number of ways: dependence of the enhancement on the excitation wavelength and polarization, enhancement versus tip-sample distance curves, observation of selective enhancement of Raman signal from thin surface layers of the sample etc. Finally, the ultimate performance of TERS is demonstrated by measuring Raman 2D maps with sub wavelength resolution – determined not by the wavelength of light, but by the localization area of the surface plasmon electromagnetic field.

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

CNST NanoFab Seminar

NANOFAB USERS MEETING 


Vincent Luciani
NanoFab Group Leader

Friday, July 31, 2009, 2:00PM, Rm. C103-C106, Bldg. 215

 

Agenda items will include

  • Update on new tool installation
  • Discussion of new tools desired
  • Last meeting's action items
  • Research Participant growth rate stats
  • Improved safety rules
  • Outreach efforts
  • NanoFab User Committee


  • There will be prizes, open discussions and a surprise guest!
For further information contact Vincent Luciani, 301-975-2886, Vincent.Luciani@nist.gov

CNST Energy Research Group Seminar

I/F NOISE CHARACTERIZATION OF N- AND P-TYPE POLYCRYSTALLINE SILICON THIN FILM TRANSISTORS 


Mahdokht Behravan
Post Doctoral Candidate

Thursday, July 30, 2009, 10:30AM, Rm. C103-106, Bldg. 215

 

Polycrystalline silicon has drawn attention from researchers due to its higher mobilities compared to amorphous silicon (a-Si), which is currently used in the majority of thin film transistor (TFT) sensor arrays. Higher mobilities of poly-Si TFTs allow faster switching and higher transistor drive capabilities compared with a-Si TFTs, enabling build of more complex sensor arrays with smaller pixel sizes while maintaining sufficient gain. A limiting factor in the performance of TFT sensor arrays is the high level of 1/f noise from individual transistors incorporated in each pixel. This talk will discuss the low frequency noise behavior of poly-Si TFTs. Several factors contribute to the noise characteristics of these devices, including carrier number, trap density, and strong coulomb interactions. The data is compared to existing models that provide a theoretical framework for these observations.

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

CNST Outreach Series

MEL INTRODUCTION TO NIST'S CENTER FOR NANOSCALE SCIENCE AND TECHNOLOGY AND THE NANOFAB 


Robert Celotta, CNST
Alex Liddle and Vincent Luciani

Monday, July 20, 2009, 2:00PM, Rm. C103-106, Bldg. 215

 

This meeting with the Manufacturing Engineering Laboratory is part of a series of presentations to introduce the staff to NIST's newest operating unit, the Center for Nanoscale Science and Technology (CNST). An overview of the CNST will be presented which will provide a brief description of CNST's structure, which consists of both a research program and the NanoFab, a shared-use nanofabrication and nanoscale measurement facility. A strong bias toward collaborative work being among CNST's prime attributes, the overview will describe how NIST staff can go about collaborating with scientists in the research program or make use of the NanoFab. The NanoFab, which provides economical access to a wide variety of advanced lithography and microscopy tools, will be described. Examples of recent nanofabrication projects will be used to illustrate our capabilities. Finally, the process for becoming a NanoFab user or having a nanostructure made or measured for you will be outlined. The laboratory by laboratory series of presentations has been designed to allow significant time to answer questions and tours will be arranged.

For further information contact Lloyd Whitman, 301-975-8002, Lloyd.Whitman@nist.gov

CNST Outreach Series

CSTL INTRODUCTION TO NIST'S CENTER FOR NANOSCALE SCIENCE AND TECHNOLOGY AND THE NANOFAB 


Robert Celotta, CNST
Alex Liddle and Vincent Luciani

Thursday, July 16, 2009, 2:00PM, Rm. C103-106, Bldg. 215

 

This meeting with the Chemical Science and Technology Laboratory is part of a series of presentations to introduce the staff to NIST's newest operating unit, the Center for Nanoscale Science and Technology (CNST). An overview of the CNST will be presented which will provide a brief description of CNST's structure, which consists of both a research program and the NanoFab, a shared-use nanofabrication and nanoscale measurement facility. A strong bias toward collaborative work being among CNST's prime attributes, the overview will describe how NIST staff can go about collaborating with scientists in the research program or make use of the NanoFab. The NanoFab, which provides economical access to a wide variety of advanced lithography and microscopy tools, will be described. Examples of recent nanofabrication projects will be used to illustrate our capabilities. Finally, the process for becoming a NanoFab user or having a nanostructure made or measured for you will be outlined. The laboratory by laboratory series of presentations has been designed to allow significant time to answer questions and tours will be arranged.

For further information contact Lloyd Whitman, 301-975-8002, Lloyd.Whitman@nist.gov


CNST Electron Physics Group Seminar

ENABLERS FOR PROBE-BASED NANOMANUFACTURING AND NANOMETROLOGY

 

Harish Bhaskaran
Postdoctoral Fellow/IBM Zurich Research Laboratory

Wednesday, July 15, 2009, 10:30AM, Rm. H107, Bldg. 217

 

Of all the nanomechanical systems used, probes are perhaps the simplest, yet most indispensable tools used in the nanoscale research and development world today. At the nanoscale, quick and easy characterization tools are urgently needed to be able to deliver many technologies from their languid presence in the basement to the real world. Probe-based techniques are gaining prominence because they can be used to effectively probe both the surface, as well as the electrical characteristics at the nanoscale. In addition the same probe can be used to manipulate structures, and then re-image the manipulated region. Thus, any nanomanufacturing scheme will have to use probe-technologies at some level.

In this talk, I will give an overview of my work within IBM in tackling some of these interesting issues. A brief introduction to probe-based data storage will be given, since this application embodies many of the challenges facing probe-based technologies. Some of my work on platinum silicide tips and "encapsulated" tips for conduction-mode probe-based technologies will also be presented. The performance of the encapsulated conducting tips in sliding is shown to be several times better than commercial conducting probes. Both these technologies have enabled us to perform effective nanoscale phase transformations in chalcogenide-based phase change materials - a proof of concept that probe-based nanometrology can be robust.

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

CNST Outreach Series

MSEL INTRODUCTION TO NIST'S CENTER FOR NANOSCALE SCIENCE AND TECHNOLOGY AND THE NANOFAB 


Robert Celotta, CNST
Alex Liddle and Vincent Luciani

Tuesday, July 14, 2009, 1:30PM, Rm. C103-106, Bldg. 215

 

This meeting with the Materials Science and Engineering Laboratory is part of a series of presentations to introduce the staff to NIST's newest operating unit, the Center for Nanoscale Science and Technology (CNST). An overview of the CNST will be presented which will provide a brief description of CNST's structure, which consists of both a research program and the NanoFab, a shared-use nanofabrication and nanoscale measurement facility. A strong bias toward collaborative work being among CNST's prime attributes, the overview will describe how NIST staff can go about collaborating with scientists in the research program or make use of the NanoFab. The NanoFab, which provides economical access to a wide variety of advanced lithography and microscopy tools, will be described. Examples of recent nanofabrication projects will be used to illustrate our capabilities. Finally, the process for becoming a NanoFab user or having a nanostructure made or measured for you will be outlined. The laboratory by laboratory series of presentations has been designed to allow significant time to answer questions and tours will be arranged.

For further information contact Lloyd Whitman, 301-975-8002, Lloyd.Whitman@nist.gov


CNST Nanofabrication Research Group Seminar

INTRODUCTION OF FUNCTIONALITIES INTO DNA NANOSTRUCTURES

 

Seung-Hyeon (Sarah) Ko
Department of Chemistry, Purdue University

Friday, July 10, 2009, 10:30AM, Rm. H107, Bldg. 217

 

DNA has been intensively explored as a building block for nanoconstruction based on rational design and self-assembly. DNA nanostructures have been continuously evolved and there have been remarkable achievements. However, it remains challenging to introduce functionalities into such DNA nanostructures.

DNA is potentially a good candidate for biomedical applications because it is biodegradable and a natural component of life systems. Recently our group has developed a DNA nanotube (DNA-NT) system with a single component, a 52-base-long DNA single strand.2 I have explored the use of DNA-NTs as drug carriers for cellular delivery.3 Functional agents (folate, a cancer cell target agent, and Cy3, model drug and imaging agent) are conjugated with DNA-NTs. The folate-conjugated DNA-NTs are effectively and selectively taken up by cancer cells because folate receptors are over-expressed on the cell surfaces of various cancer cells.

RNA molecules are structurally close to DNA. Different from DNA, RNA has very rich chemical, structural, and functional diversities. I have developed a novel strategy to design and construct RNA nanostructures.4 This strategy is generally applicable and has been demonstrated by assembly of RNA into various well-defined nanomotifs, which can further assemble into extended or discrete large structures. I expect that this strategy will allow us to assemble various nanostructures with multi-functional RNA modalities.

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

CNST Outreach Series

EEEL INTRODUCTION TO NIST'S CENTER FOR NANOSCALE SCIENCE AND TECHNOLOGY AND THE NANOFAB 


Robert Celotta, CNST
Alex Liddle and Vincent Luciani

Thursday, July 9, 2009, 2:00PM, Rm. C103-106, Bldg. 215

 

This meeting with the Electronics and Electrical Engineering Laboratory is part of a series of presentations to introduce the staff to NIST's newest operating unit, the Center for Nanoscale Science and Technology (CNST). An overview of the CNST will be presented which will provide a brief description of CNST's structure, which consists of both a research program and the NanoFab, a shared-use nanofabrication and nanoscale measurement facility. A strong bias toward collaborative work being among CNST's prime attributes, the overview will describe how NIST staff can go about collaborating with scientists in the research program or make use of the NanoFab. The NanoFab, which provides economical access to a wide variety of advanced lithography and microscopy tools, will be described. Examples of recent nanofabrication projects will be used to illustrate our capabilities. Finally, the process for becoming a NanoFab user or having a nanostructure made or measured for you will be outlined. The laboratory by laboratory series of presentations has been designed to allow significant time to answer questions and tours will be arranged.

For further information contact Lloyd Whitman, 301-975-8002, Lloyd.Whitman@nist.gov

CNST NanoFab Seminar

NANO-SCALE OPTICAL MICROSCOPE & HYPERSPECTRAL IMAGING SYSTEM 


Byron Cheatham & James Beach
CytoVita Technical Specialists

Tuesday, July 7, 2009, 1:00PM, Rm. H107, Bldg. 217

 

Byron Cheatham and James Beach will give an overview of the CytoVivaTM nano-scale optical microscopy & integrated hyperspectral imaging system and list CytoViva example applications supported (over 150 plus current research clients) including Nano-drug delivery, Nano-toxicology, and Nano-materials development . There will also be an overview on the system components including High S/N Optical Microscope-images nano-scale samples interacting and VNIR Hyperspectral Imaging-pixel level spectral quantification of nano-particles and sub-cellular components, 25nm pixel size and 1.25nm spectral resolution.

For further information contact Eileen Sparks, 301-975-8065, Eileen.Sparks@nist.gov


CNST Outreach Series

TS, TIP, MEP, AND THE CFO INTRODUCTION TO NIST'S CENTER FOR NANOSCALE SCIENCE AND TECHNOLOGY AND THE NANOFAB

 

Robert, Celotta, CNST
Alex Liddle and Vincent Luciani

Tuesday, June 30, 2009, 2:00PM, Rm. C103, Bldg. 215

 

This meeting is part of a series of presentations to introduce the staff to NIST's newest operating unit, the Center for Nanoscale Science and Technology (CNST). An overview of the CNST will be presented which will provide a brief description of CNST's structure, which consists of both a research program and the NanoFab, a shared-use nanofabrication and nanoscale measurement facility. A strong bias toward collaborative work being among CNST's prime attributes, the overview will describe how the CNST fulfills its mission of enabling nanotechnology through collaboration with scientists within its research program and by providing easy access to the NanoFab. The NanoFab, which provides economical access to a wide variety of advanced lithography and microscopy tools, will be described. Examples of recent nanofabrication projects will be used to illustrate our capabilities. Finally, the process for becoming a NanoFab user or having a nanostructure made or measured will be outlined. The laboratory by laboratory series of presentations has been designed to allow significant time to answer questions and tours will be arranged.

For further information contact Lloyd Whitman, 301-975-8002, Lloyd.Whitman@nist.gov


CNST Electron Physics Group Seminar

NANOSCALE TEMPERATURE RISE AND MELTING AT A RUBBING INTERFACE

 

Benjamin D. Dawson
Ph.D. Candidate, North Carolina State University

Friday, June 26, 2009, 11:00AM, Rm. H107, Bldg. 217

 

Temperature rise, and the associated effects of softening and/or melting, of a sliding asperity contact impacts a broad range of fundamental and applied topics--from nano- and micro-electromechanical systems to frictional behavior at geological faults. Despite great importance, however, a fundamental understanding of the interfacial and chemical processes that occur in such contacts is lacking. By utilizing the unique capabilities of a combined scanning tunneling microscope and quartz crystal microbalance, the velocity dependent morphology of a single asperity contact is able to be probed. The results give intriguing evidence for a velocity dependent transition from a solid interface to a liquid-like interface, the first such observation for a sliding asperity contact.

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


CNST Electron Physics Group Seminar

CATALYTIC CVD GROWTH OF CARBON NANOTUBES AND THEIR APPLICATION AS CHEMICAL SENSORS

 

Navdeep Bajwa
Postdoctoral Fellow, The US Naval Research Laboratory

Monday, June 22, 2009, 10:30AM, Rm. H107, Bldg. 217

 

Carbon based materials come in a variety of different forms that depend on how their atoms link together, such as zero-dimensional fullerenes, one-dimensional nanotubes, two-dimensional (2-D) graphene and three-dimensional (3-D) graphite. The properties of these carbon based materials can be tailored by irradiation and chemical functionalization to use them for various applications. In recent years, carbon nanotubes (CNTs) have been a subject of increased interest especially because of their exceptional thermal, electrical and mechanical properties which far exceed those of most bulk materials. However inspite of considerable progress in the synthesis of CNTs there still exist significant challenges like production of nanotube materials with controlled diameter, length, orientation, location and microstructure. Thus there is a need to understand the growth mechanisms of both multiwalled and singlewalled carbon nanotubes in order to synthesize them in a controlled manner. The high electrical conductivity and surface area of CNTs is motivating their application as chemical sensors. We present here a systematic study of molecular adsorption on SWNTs by measurements of the conductivity response of single walled carbon nanotube (SWNT) arrays to trace vapors for a range of linear chain and aromatic molecules. Ab initio calculations were performed with density functional theory methods to investigate the molecular adsorption of these molecules on SWNTs. Both conductance measurements and Ab initio calculations show that the adsorption energies of linear alkane, alcohol and ketone molecules increase linearly with the length of the molecule. These results indicate that the initial adsorption and conductivity response occurs with molecules predominantly lying flat on the defect-free nanotube side walls and the long time response is dominated by adsorption at defects. The difference in the conductivity responses for polar and non polar adsorbates is attributed to changes in scattering due to adsorbates. Further experiments with random arrays of carbon nanotubes reveal a strong conductivity response after exposure to aromatic molecules containing nitro functional groups, such as nitrobenzene and trinitrotoluene. Ab initio calculations also show a strong increase in adsorption energy with the addition of each nitro group to a molecule (around 100 meV) and a gradual increase with nanotube size, in agreement with preliminary experimental results. Finally, these calculations are compared with results for the adsorption at oxidation defects.

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


CNST Outreach Series

PL INTRODUCTION TO NIST'S CENTER FOR NANOSCALE SCIENCE AND TECHNOLOGY AND THE NANOFAB

 

Robert Celotta
Alex Liddle, and Vincent Luciani

Friday, June 19, 2009, 2:30PM, Rm. C103, Bldg. 215

 

This meeting with the Physics Laboratory is part of a series of presentations to introduce the staff to NIST's newest operating unit, the Center for Nanoscale Science and Technology (CNST). An overview of the CNST will be presented which will provide a brief description of CNST's structure, which consists of both a research program and the NanoFab, a shared-use nanofabrication and nanoscale measurement facility. A strong bias toward collaborative work being among CNST's prime attributes, the overview will describe how NIST staff can go about collaborating with scientists in the research program or make use of the NanoFab. The NanoFab, which provides economical access to a wide variety of advanced lithography and microscopy tools, will be described. Examples of recent nanofabrication projects will be used to illustrate our capabilities. Finally, the process for becoming a NanoFab user or having a nanostructure made or measured for you will be outlined. The laboratory by laboratory series of presentations has been designed to allow significant time to answer questions and tours will be arranged.

For further information contact Lloyd Whitman, 301-975-8002, Lloyd.Whitman@nist.gov


CNST Electron Physics Group Seminar

APPLYING NANOTRIBOLOGY TO MICRO AND NANOMECHANICAL DEVICES

 

Robert W. Carpick
Director, The Nanotechnology Institute, University of Pennsylvania

Thursday, June 18, 2009, 10:30AM, Rm. H107, Bldg. 217

 

The reduced length scale of contacts in micro- and nano-electromechanical systems (M/NEMS) and atomic force microscopy (AFM)-based applications leads to tremendous increases in contact stresses, adhesive interactions, friction, tribochemical reactions, and wear. These phenomena are yet to be well-understood or controlled, creating a critical scientific challenge for the development and commercialization of these micro- and nano-technologies. I will discuss specific applications where these factors are critical, including nanomanufacturing, nanomechanical data storage, and MEMS and NEMS switches. I will then discuss experimental methodologies for measuring and understanding nanoscale tribology through combinations of AFM, other microscopies, and surface spectroscopic techniques. I will then highlight recent measurements that demonstrate how nanotribological phenomena are related to surface atomic bonding and environmental conditions. Particular emphasis will be placed on how the use of materials with excellent macroscopic tribo-mechanical properties, including diamond and diamond-like films, can provide dramatic improvements compared with silicon-based materials which are more commonly used in nanoscale applications currently.

For further information contact Rachel Cannara, 201-975-4258, Rachel.Cannara@nist.gov


CNST Outreach Series

BFRL INTRODUCTION TO NIST'S CENTER FOR NANOSCALE SCIENCE AND TECHNOLOGY AND THE NANOFAB

 

Robert Celotta, Director of CNST.
Alex Liddle and Vincent Luciani of CNST

Monday June 8, 2009, 2:00PM, Rm. B245, Bldg. 224

 

This meeting with the Building and Fire Research Laboratory is part of a series of presentations to introduce the staff to NIST's newest operating unit, the Center for Nanoscale Science and Technology (CNST). An overview of the CNST will be presented which will provide a brief description of CNST's structure, which consists of both a research program and the NanoFab, a shared-use nanofabrication and nanoscale measurement facility. A strong bias toward collaborative work being among CNST's prime attributes, the overview will describe how NIST staff can go about collaborating with scientists in the research program or make use of the NanoFab. The NanoFab, which provides economical access to a wide variety of advanced lithography and microscopy tools, will be described. Examples of recent nanofabrication projects will be used to illustrate our capabilities. Finally, the process for becoming a NanoFab user or having a nanostructure made or measured for you will be outlined. The Laboratory by laboratory series of presentations has been designed to allow significant time to answer questions and tours will be arranged.

For further information contact Lloyd Whitman, 301-975-8002, Lloyd.Whitman@nist.gov


CNST Nanofabrication Research Group Seminar

3D NANOSCOPY WITH A DOUBLE-HELIX MICROSCOPE


Sri Rama Prasanna Pavani
Dept. of Electrical and Computer Engineering, University of Colorado at Boulder

Friday, June 5, 2009, 3:00PM, Rm. H107, Bldg. 217

 

Abstract: Double-helix point spread function (DH-PSF) is an engineered three-dimensional (3D) PSF specifically designed for 3D position estimation and imaging. It exhibits two lobes that rotate continuously around the optical axis with propagation. An information theoretical analysis shows that the DH-PSF carries higher and more uniform Fisher Information about a particle's 3D position than the PSF of traditional imaging systems. Experiments with DH-PSF demonstrate nanometer scale 3D position localization precisions. Further, a variety of two-dimensional microscope modalities such as bright-field, dark-field, and fluorescence can be directly transformed into their 3D counterparts by placing a DH-PSF phase mask in their imaging paths. Using photoactivatable fluorophores with a DH-PSF microscope opens up avenues for improving 3D imaging resolution beyond the optical diffraction limit.

Bio: Sri Rama "Prasanna" Pavani is a doctoral student in the department of Electrical and Computer Engineering at the University of Colorado - Boulder, where he is a CDM Optics fellow and a COSI Associate fellow. Prasanna's primary research interest is in developing computational optical sensing and imaging (COSI) systems to capture information that is normally lost in traditional imaging systems. In the last few years, he has applied the COSI paradigm to applications like quantitative phase imaging, 3D PSF engineering, 3D tracking / velocimetry, and recently to 3D superresolution imaging. His doctoral research has been recognized with an OSA outstanding paper award, a SPIE optical science and engineering scholarship, and two Colorado Photonics Industry Association best poster awards. More information on Prasanna's research can be found here: http://eces.colorado.edu/~pavani/

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


CNST Electron Physics Group Seminar

DEVELOPMENT OF A SCANNING TUNNELING POTENTIOMETRY SYSTEM FOR MEASUREMENT OF ELECTRONIC TRANSPORT AT SHORT LENGTH SCALES

 

Michael Rozler
Ph.D. Candidate / Stanford University

Thursday, May 28, 2009, 10:30AM, Rm. H107, Bldg. 217

 

It is clear that complete understanding of macroscopic properties of materials is impossible without a thorough knowledge of behavior at the smallest length scales. While the past 25 years have witnessed major advances in a variety of techniques that probe the nanoscale properties of matter, electrical transport measurements – the heart of condensed matter research – have lagged behind, rarely progressing beyond bulk measurements. This thesis describes a scanning tunneling potentiometry (STP) system developed to simultaneously map the transport-related electrochemical potential distribution of a biased sample along with its surface topography, extending electronic transport measurements to the nanoscale. Combining a novel sample biasing technique with a continuous current-nulling feedback scheme pushes the noise performance of the measurement to its fundamental limit - the Johnson noise of the STM tunnel junction. The resulting 130 nV voltage sensitivity allows us to spatially resolve local potentials at scales down to 2 nm, while maintaining atomic scale STM imaging, all at scan sizes of up to 15 microns. A mm-range two-dimensional coarse positioning stage and the ability to operate from liquid helium to room temperature with a fast turn-around time greatly expand the versatility of the instrument. Use of carefully selected model materials, combined with excellent topographic and voltage resolution has allowed us to distinguish measurement artifacts caused by surface roughness from true potentiometric features, a major problem in previous STP measurements. The measurements demonstrate that STP can produce physically meaningful results for homogeneous transport as well as non-uniform conduction dominated by material microstructures. The results establish scanning tunneling potentiometry as a useful tool for physics and materials science.

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


CNST Nanofabrication Research Group Seminar

VERTICAL MOLECULAR TRANSITORS

 

Shachar E. Richter
School of Chemistry and University Center for Nanoscience and Nanotechnology, Tel Aviv University

Tuesday, May 26, 2009, 10:30AM, Rm. H107, Bldg. 217

 

We demonstrate a universal method in which a new type of nanometer-sized, ambipolar, vertical molecular transistor is fabricated in parallel fashion. This Central-Gate Molecular Vertical Transistor (C-Gate MolVeT) is fabricated by a combination of conventional micro-lithography techniques and self-assembly methods. Here we will show several examples which utilize this device to investigate transport phenomena on the molecular scale.

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


CNST Nanofabrication Research Group Seminar

DEVELOPMENT OF MATERIALS FOR USE IN DOUBLE EXPOSURE LITHOGRAPHY

 

Adam J. Berro
Department of Chemistry and Biochemistry, The University of Texas at Austin. Austin, TX

Thursday, May 21, 2009, 10:30AM, Rm. H107, Bldg. 217

 

Optical lithography has been the standard method for production of microelectronic devices for several decades, however, there are no techniques for extending present technology beyond the 32 nm fabrication node. One potential solution is Double Exposure Lithography (DEL), that requires the development of materials that have a nonlinear response to exposure dose. While there are several possible methods for achieving this goal, Intermediate-State Two Photon Photoacid Generators (ISTP) and Optical Threshold Layer (OTL) approaches will be discussed.

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

 


CNST Nanofabrication Research Group Seminar

MATERIALS CHALLENGES IN NANOSTRUCTURED ZNO-CONJUGATED POLYMER PHOTOVOLTAIC DEVICES

 

Julia W. P. Hsu
Sandia National Laboratories

Thursday, April 30, 2009, 10:30AM, Rm. H107, Bldg. 217

It has been widely recognized that increasing the sources of clean energy is absolutely critical for maintaining living standards while halting environmental degradation. Solar energy holds a great promise as a clean energy source, but current technologies are too expensive for wide usage. In addition to traditional semiconductor solar cells, organic photovoltaics (OPVs) have been targeted for inexpensive, lightweight applications, such as consumer electronics and field deployable sensors. A subset of OPVs, called hybrid solar cells, uses a wide bandgap oxide semiconductor as the electron acceptor. They take advantage of the environmental stability and high electron mobilities of metal oxide semiconductors, while largely retaining the solution-based processing available to organic semiconductor devices. In addition, the use of ordered nanostructures increases the area of the heterojunction, resulting in increased dissociation of photogenerated excitons and collection of charges. We focus on nanostructured ZnO – polythiophene (P3HT) heterojuctions. The challenges are to form oxide nanostructures with spacings that match the exciton diffusion length in conjugated polymers (~ 10 nm), to infiltrate high-molecular weight polymer in the dense oxide matrix, and to achieve efficient charge transfer at the heterojunction interface. In this talk, I will discuss progress made on each of the challenges and discuss future directions.

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




CNST NANOFAB USERS MEETING

 

Friday, April 3, 2009, 2:00PM, Rm. C103, Bldg. 215

The first quarterly NanoFab users meeting will be held on April 3rd. The NanoFab will be closed on this day due to the previously scheduled semi-annual maintenance so let's make good use of the time. The meeting will include an open forum for our users as well as a discussion of the following topics of mutual interest:

  • Safety Update
  • Sunray cards
  • Locker rooms
  • Metals restrictions
  • User committee
  • New equipment status; 3d software, Rotor, Heidelburg lens, Nano, Pumps, Stepper.
  • Desired equipment
  • Equipment reservations and scheduling

  • Please let me know if you have any suggestions for agenda items. Send them to Vincent.luciani@nist.gov Feel free to bring along anyone interested in becoming a NanoFab user as well
    Thanks,
    Vince Luciani
    NanoFab Operations Group Leader, Center for Nanoscale Science and Technology
  • For further information contact Vincent Luciani,
    301-975-4529, vincent.luciani@nist.gov

DC REGIONAL MEETING OF THE AVD MID-ATLANTIC CHAPTER AND OPEN HOUSE OF THE NIST CENTER FOR NANOSCALE SCIENCE AND TECHNOLOGY

 

Wednesday, April 1, 2009, 9:00AM, Rm. C103, Bldg. 215

NIST staff, AVS members, potential members, and students and postdocs who are working in nanoscience are invited to a joint regional meeting of the Mid-Atlantic Chapter of the AVS and an Open House of the NIST Center for Nanoscale Science and Technology (CNST). The meeting will feature invited speakers on local nanoscience research, information on how to become a facilities user at CNST, a tour of the NIST Nanofabrication Facilities, and a poster session for students and postdocs working in nanoscience. www2.avs.org/chapters/midatlantic For furter information contact Terrence Jach, 301-975-2362, Terrence.Jach@nist.gov




CNST Nanofabrication Research Group Seminar

NEAR-FIELF CHARACTERIZATION OF THE NANOPHOTONIC DEVICES

 

Maxim Abashin
Ph.D. Candidate (graduate student)/Research Assistant

Friday, March 27, 2009, 10:30AM, Rm. H107, Bldg. 217

 

The field of nanophotonics is rapidly growing and has a lot of promises in the all-optical signal processing and data transmission as well as in biological and chemical applications such as sensing and material analysis. Experimental characterization of nanophotonic components and devices is an important step in concept verification and fabrication validation. Subwavelength resolution and access to evanescent fields delivered by Near-field Scanning Optical Microscopy (NSOM) will be indispensable for such characterization.

NSOM combined with heterodyne detection (HNSOM) has the capability to measure both optical amplitude and phase distributions and thus provides more detailed characterization of the nanodevices. In this talk, several examples of near-field characterization of nanophotonic devices based on the Photonic Crystal and metamaterial concepts will be presented. Also HNSOM technique with spectrally broad sources allowing characterization of the dispersive properties (group refractive index) will be described.

 

For further information contact James Alexander Liddle,
301-975-6050, James.Liddle@nist.gov 




CNST Nanofabrication Research Group Seminar

MEASURING AND UNDERSTANDING REACTION KINETICS AT NANO SCALE

 

Renu Sharma
Senior Research Scientist and Director of Industrial Associates Program, Arizona State University

Friday, March 13, 2009, 1:30PM, Rm. H107, Bldg. 217

 

The world of nanomaterials has become the 'real world' for most of the applications in the area of nanotechnology. As post-synthesis handling of materials at a nanoscale is not practical, nanomaterials often need to be synthesized directly as part of a device or circuit. In situ synthesis of nanomaterials requires optimization of reaction kinetics. A clear understanding of the structure, chemistry, and properties of individual naonaparticle is essential to fabricate individual components for nanotechnology. This demand posted by nanotechnology has led to the modifications in the design of transmission electron microscopes that permit us to perform in situ synthesis and characterization concurrently, such environmental transmission electron microscope (E(S)TEM). A modern E(S)TEM, equipped with a field-emission gun (FEG), energy filter or electron energy loss spectrometer, scanning transmission electron microscopy (STEM) coils, and bright and dark field detectors, is a versatile tool for understanding and measuring chemical processes at nanometer level. Its applications range from in situ measurements of the reaction steps such as oxidation-reduction or corrosion, to in situ synthesis of nanomaterials such as quantum dots, carbon nanotubes, Si, or GaN nanowires. Examples of measuring reaction kinetics of individual naoparticles (e.g. CNT, Si nanowires) and structural modifications during functioning of nanomaterials (catalyst) will be used elucidate the applications of the E(S)TEM.

 

For further information contact James Alexander Liddle,
301-975-6050, James.Liddle@nist.gov 




CNST Nanofabrication Research Group Seminar

CHARACTERIZATION OF ELECTRONIC FUNCTIONALITY IN NANOSCALE STRUCTURES

 

Philip E. Batson
IBM Thomas J. Watson Research Center. Yorktown Heights, NY

Thursday, March 12, 2009, 10:30AM, Rm. H107, Bldg. 217

 

During the 1990's, work with Spatially Resolved Electron Energy Loss Spectroscopy in the electron microscope showed that electronic structure at the 70-200meV level, relevent to the operation of semiconductors, can be obtained from nanometer-sized particles, single defects, and Si and Si-Ge quantum wells. It became apparent during this work that the available spatial resolution of about 2 Angstroms was not adequate to address the growing need to characterize semiconductor devices for local compositon, atomic structure and electronic structure. Thus, correction of aberrations within the electron microscope, an unattained dream for the first 50 years of electron microscopy, became a necessary capability for development of present and future semiconductor products. Addition of aberration correction produced a sub-Angstrom electron probe for the first time, revealing a dynamic landscape of individual atoms on surfaces and within the bulk. As it becomes easier to precisely control the microscope electron optical system, it will soon be possible to extend the spectroscopy to 10-30 meV energies, making accessible phonons, structural transitions, bandgaps in nanotubes, carrier plasmons, low frequency dielectric constants and possibly carrier transport channels in single molecules -- all with sub-Angstrom spatial resolution. These excitations will likely exhibit unforseen behavior, resulting from the physical confinement in nanometer-sized systems.

 

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




CNST Nanofabrication Research Group Seminar

MEMBRANE STACKING TECHNOLOGY FOR THE FABRICATION OF 3D PHOTONIC CRYSTALS

 

Amil Patel
Doctoral Candidate, The Massachusetts Institute of Technology, Cambridge, MA

Tuesday, March 10, 2009, 10:30AM, Rm. H107, Bldg. 217

 

Three-dimensional photonic crystals (3DPCs) are nanostructured metamaterials that have the potential to revolutionize integrated photonics with their inherent ability to confine optical modes to volumes on the order of a wavelength.

In a 3DPC, an omnidirectional bandgap is created by a periodic modulation of high contrast dielectric materials[1]. This means that specific optical modes cannot propagate through the medium. Devices that allow modes to exist, such as waveguides and resonators, can be embedded within the crystal by disrupting the perfect periodicity of the structure.

The difficulty in fabricating these structures emanates from: its multilevel nature (up to 20 layers with sub 50nm overlay), sub 100nm features, and the large area required (10 mm x 10mm). Previously, we reported the fabrication of a 3DPC using traditional planar fabrication processes following cycles of deposition, pattern, etch and planarization [2]. However, this method suffered from low yields, small areas and long lead times.

In order to surmount past shortcomings, we are exploring a novel method of multilayer nanofabrication by which membranes etched with 2D photonic structures are stacked [3]. My research develops this platform by addressing three umbrella challenges. First, I develop processes to generate free-standing membranes etched with photonic structures. Second, I explore nanoimprint lithography and coherent diffraction lithography as two methods of patterning large-area 2DPCs with registration. Finally, I present solutions to the specific stacking hurdles of particle contamination, alignment [4] and membrane detachment.

 

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




CNST Nanofabrication Research Group Seminar

NANOSCALE CHARACTERIZATION: MOVING FROM HIGH-RESOLUTION 2D OVER 3D TOMOGRAPHY TO 4D TIME-RESOLVED ELECTRON MICROSCOPY

 

Alexander Ziegler
Ph.D., Max-Planck Institute for Extraterrestrial Physics

Monday, March 9, 2009, 10:30AM, Rm. H107, Bldg. 217

 

In recent years there have been many developments in electron microscopy that have pushed the spatial resolution and sensitivity to the single atom level for imaging, diffraction and spectroscopy. These capabilities have significantly extended our understanding of materials properties, particularly in the realm of nanoscale materials. 2-dimensional high resolution TEM for example, has produced astonishing images of atomic arrangements in advanced materials, while the experimental tools for 3-dimensional tomographic reconstructions are most advanced in the life sciences. The burgeoning field of nanotechnology ensures that electron microscopy will be a scientific method at the forefront of materials science for the foreseeable future. However, throughout these rapid advancements in technology, and all the insights that have resulted from them, one area that has remained largely untapped has been the ability to measure the atomic scale properties of materials and biological specimen on very short timescales (10-9-10-15s). The experimental range that could conceivably be reached by a transmission electron microscope (TEM) operating using very short pulse durations and a high repetition rate, could be used for such important materials research areas as reaction dynamics related to catalysis and surface adsorption, atomic re-arrangements relevant to phase transformations and structural changes occurring upon heating, and domain switching in ferroelectrics. The experimental opportunities for the life sciences are different and will require special instrumental developments.

The challenges encountered while advancing from 2-dimensional towards 4-dimensional electron microscopy are described here by showing a variety of specific examples from the materials and the life sciences. Furthermore, the present limitations and capabilities of the current state-of-the-art 4D-TEM (or Dynamic TEM: DTEM) and the outlook for future experimental capabilities will be discussed

 

For furter information contact James Liddle,
301-975-6050, James.Liddle@nist.gov 




CNST Electron Physics Group Seminar

DYNAMICAL MEASUREMENTS WITH A NUCLEAR MAGNETIC RESONANCE FORCE MICROSCOPE

 

Hang-Jong Chia
Graduate Research Assistant, University of Texas at Austin

Monday, March 2, 2009, 10:30AM, Rm. H107, Bldg. 217

 

Nuclear Magnetic Resonance Force Microscopy (NMRFM) is a technique that combines the fine resolution of scanning probe microscopy with the spin sensitivity of nuclear magnetic resonance (NMR) to yield highly detailed spin information. NMRFM provides resolution that is several orders of magnitude finer than conventional NMR, thus enabling measurements of samples previously inaccessible by conventional NMR, such as thin films and nanostrucstures. In this talk I will discuss the principle behind NMRFM operation and the construction as well as experiments we have performed with our He-3 NMRFM. Room temperature measurements were taken on ammonium sulfate to yield micron scale 1-D images and a spin echo as well as the demonstration of spin nutation. I will also discuss future applications of this instrument toward relaxation measurements of single crystal magnesium diboride at low temperatures as well as other experiments that increase the sensitivity of this technique.

 

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




CNST Electron Physics Group and Quantum Electrical Metrology Division Seminar

QUANTUM EFFECTS IN THE CONDUCTIVITY OF HIGH-MOBILITY SI MOSFET AT ULTRA-LOW TEMPERATURES

 

Nikolai Klimov
Ph.D./Rutgers University, Department of Physics and Astronomy

Thursday, February 19, 2009, 10:30AM, Rm. H107, Bldg. 217

 

We have measured the conductivity of high-mobility (001) Si metal-oxide-semiconductor field effect transistors over wide ranges of electron densities n=(1.8–15)x10^11 cm^-2, temperatures T=30mK–4.2K, and in-plane magnetic fields B=0–5T. The experimental data have been analyzed using the theory of interaction effects in the conductivity of disordered two-dimensional (2D) systems. The parameters essential for comparison with the theory, such as the intervalley scattering time and valley splitting, have been measured in independent experiments. The observed behavior of the conductivity, including the quasi-linear increase with decreasing T down to ~0.4K and its downturn at lower temperatures, is in agreement with the theory. The values of the Fermi-liquid parameter F_0^\sigma, obtained from the comparison agree with the corresponding values extracted from the analysis of Shubnikov–de Haas oscillations based on the theory of magneto-oscillations in interacting 2D systems.

 

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




CNST Nanofabrication Research Group Seminar

NANOPARTICLE ASSEMBLY, MANIPULATION, AND METROLOGY

 

Samuel Stavis
National Research Council Research Associate

Thursday, February 5, 2009, 10:30AM, Rm. H107, Bldg. 217

 

The novel properties of nanoparticles are driving the rapid growth of nanotechnology in the global market while simultaneously provoking concern about nanometer scale Environmental, Health and Safety (EHS) issues. The abilities of the private sector to capitalize on these opportunities and the public sector to address these challenges remain limited by conventional methods of nanoparticle synthesis and characterization. The concurrent need for increased analytical ability in the life sciences and the drive to elucidate nanoscale and single molecule phenomena are spurring the development of fluidic devices with critical dimensions that enhance control over interactions with nanoscale analytes. Almost all nanofluidic devices remain limited in form and function by planar microfabrication and nanofabrication processes developed by the semiconductor electronics industry. In this presentation, I will describe our efforts to solve several related problems at the convergence of these trends via the development of enabling fluidic devices for the assembly, manipulation and metrology of nanoparticles. Soft matter nanobioparticles have significant potential for therapeutic applications including drug delivery and gene therapy. I will present the results of our investigation of the microfluidic environment that determines the characteristics of self-assembled nanoscale lipid vesicles and the use of these liposomes as nanoscale templates for the formation of derivative hydrogel nanoparticles. I will then describe our advances in fluorescence fluctuation analysis for the accurate characterization of the encapsulation and confinement of single biomolecules in nanoscale liposomes for biophysical investigations. I will also present our development of next generation nanofluidic structures with complex and curving surfaces for the enhanced manipulation and metrology of nanoscale analytes, with an emphasis on single molecule analysis and nanoparticle sorting applications.

 

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




CNST Nanotechnology Seminar Series

UNDERSTANDING NANOSTRUCTURE NUCLEATION, GROWTH AND GROWTH TERMINATION THROUGH REAL TIME TEM OBSERVATIONS

 

Eric A. Stach
Director, Purdue Electron Microscopy Consortium

Thursday, January 29, 2009, 10:30AM, Rm. C103-C106, Bldg. 215

 

In order for nanostructure materials to find application in real technologies, we must have a thorough understanding of how to create reproducible materials. I will detail our work using environmental and ultra-high vacuum transmission electron microscopy methods to image nanostructure nucleation and growth as it happens, thereby allowing unique insights into both growth mechanisms and kinetics. In particular, I will describe in detail the kinetics of the vapor-liquid-solid growth of silicon nanowires, with a focus on the kinetics of both Au dissolution in the AuSi eutectic liquid, and on the nucleation of Si from this same liquid at higher saturations. Careful quantification of the images and correlation with a simple model of the process indicates that the nucleation process is highly repeatable down to very small scales (of order 10 nm), and that we can extract information regarding the critical supersaturations required for nucleation. I will also discuss our latest results concerning growth termination during the creation of carbon nanotube 'carpets', wherein we correlate the end of growth with an Ostwald ripening of the catalysts require to mediate the conversion of hydrocarbon source gases to carbon nanotubes. Throughout, I will try to demonstrate the power of the in-situ TEM technique to visualize how things happen during nanostructure creation.

 

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




CNST Electron Physics Group Seminar

CORRELATION OF MICROSTRUCTURE AND MAGNETOTRANSPORT IN ORGANIC SEMICONDUCTOR SPIN VALVE STRUCTURES

 

Yaohua Liu
Ph.D. Candidate, Department of Physics and Astronomy, Johns Hopkins University

Thursday, January, 15, 2009, 10:30AM Rm. H107, Bldg. 217

 

There is currently a rapidly increasing interest in spin-dependent electronic transport in organic semiconductors (OSC). At its heart, this is based on the expectation that weak spin-orbit coupling in these light-element-based materials will lead to long spin relaxation times and long spin coherence lengths that may ultimately enable their use in magnetoelectronic devices. However, while there are several reports of observation of magnetotransport effects in multilayer OSC spin valve structures, the origins are still under debate, and both spin polarized tunneling and spin-coherent diffusive transport mechanisms have been invoked to explain the observed results. We have studied magnetotransport in several Co/OSC/Fe systems, using Alq3, CuPc, PTCDA and CF3-NTCDI as the spin transport layers. Magnetoresistance (MR) was observed up to room temperature in Alq3 and CuPc based devices. Focusing on the Alq3 system, we studied the devices' microstructure by X-ray reflectometry, Auger electron spectroscopy, and polarized neutron reflectometry. Our study shows evidence for spin-coherent diffusive transport and reveals the correlation between microstructure and magnetotransport in these organic devices. In particular, larger MR effects are associated with smaller average roughness at both the Alq3/Co and Fe/Alq3 interfaces. The PNR results show that the chemical and magnetic scattering length depth (SLD) profiles are different at the Alq3/Fe interface. The sample with larger MR has a relatively sharp magnetic interface, indicating there is a better separation between the bulk Fe layer (with bulk-like magnetization) and the interfacial Fe/Alq3 mixed layer (with significantly reduced magnetization). Our studies indicate the importance of detailed control and understanding of interfaces in these systems.

 

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




CNST Electron Physics Group Seminar

EXTENSIONS OF ATOMIC FORCE MICROSCOPY: DATA STORAGE, TRIBOLOGY, AND OFF-CONTACT IMAGING

 

Rachel Cannara
Postdoctoral Scholar, IBM Zürich Research Laboratory, Switzerland

Friday, January 9, 2009, 11:00AM, Rm. H107, Bldg. 217

 

I will discuss my activities as a postdoctoral fellow in the memory and probe technologies group at IBM Research. First, I will describe my work toward achieving high speed writing for probe-based data storage in polymers (the "Millipede" concept). In addition, I studied the pressure dependence of friction between silicon probe tips and polymer surfaces. The pressure-dependent component of the shear stress helps reduce the activation energy for atom-by-atom removal of tip material. Another aspect of my work is the discovery of a new surface interrogation method that employs thermoelectric cantilevers for off-contact thermal imaging. The integrated heaters in these cantilevers provide a useful alternative to other imaging methods for handling challenging topographies, limiting tip wear in high speed applications, and enabling combined imaging and manipulation schemes. Finally, I will briefly summarize my current investigations using conductive probes to characterize chalcogenide phase change materials for emerging memory devices.

 

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

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