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Birck and NCN Publications

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Articles 301 - 330 of 353

Full-Text Articles in Nanoscience and Nanotechnology

Thermionic Emission Energy Distribution From Nanocrystalline Diamond Films For Direct Thermal-Electrical Energy Conversion Applications, Kishore Uppireddi, Tyler Westover, Timothy Fisher, Brad Weiner, Gerardo Morell Aug 2009

Thermionic Emission Energy Distribution From Nanocrystalline Diamond Films For Direct Thermal-Electrical Energy Conversion Applications, Kishore Uppireddi, Tyler Westover, Timothy Fisher, Brad Weiner, Gerardo Morell

Birck and NCN Publications

In the ongoing quest for energy production by nonconventional methods, energy conversion by vacuum and solid-state thermionic emission devices is one of the potentially efficient pathways for converting thermal energy directly into electrical power. The realization of practical of thermionic energy conversion devices strongly depends on achieving low work function materials, which is thus far a limiting factor. In an attempt to develop a new low work function thermionic material, this work reports thermionic emission energy distributions (TEEDs) from nanocrystalline diamond (NCD) films in the temperature range from 700 to 900 °C that reveal a consistent effective work function of …

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Modeling Of Subcontinuum Thermal Transport Across Semiconductor-Gas Interfaces, Druv Singh, Xiaohui Guo, Alina Alexeenko, Jayathi Y. Murthy, Timothy Fisher Jul 2009

Modeling Of Subcontinuum Thermal Transport Across Semiconductor-Gas Interfaces, Druv Singh, Xiaohui Guo, Alina Alexeenko, Jayathi Y. Murthy, Timothy Fisher

Birck and NCN Publications

A physically rigorous computational algorithm is developed and applied to calculate subcontinuum thermal transport in structures containing semiconductor-gas interfaces. The solution is based on a finite volume discretization of the Boltzmann equation for gas molecules (in the gas phase) and phonons (in the semiconductor). A partial equilibrium is assumed between gas molecules and phonons at the interface of the two media, and the degree of this equilibrium is determined by the accommodation coefficients of gas molecules and phonons on either side of the interface. Energy balance is imposed to obtain a value of the interface temperature. The classic problem of …

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Tunable Magnetic Response Of Metamaterials, Shumin Xiao, Uday K. Chettiar, Alexander V. Kildishev, V. Drachev, I C. Khoo, V. M. Shalaev Jul 2009

Tunable Magnetic Response Of Metamaterials, Shumin Xiao, Uday K. Chettiar, Alexander V. Kildishev, V. Drachev, I C. Khoo, V. M. Shalaev

Birck and NCN Publications

We demonstrate a thermally tunable optical metamaterial with negative permeability working in the visible range. By covering coupled metallic nanostrips with aligned nematic liquid crystals (NLCs), the magnetic response wavelength of the metamaterial is effectively tuned through control of the ambient temperature, changing the refractive index of LC via phase transitions. By increasing the ambient temperature from 20 to 50 degrees C, the magnetic response wavelength shifts from 650 to 632 nm. Numerical simulations confirm our tests and match the experimental observations well.

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Translation Of Nanoantenna Hot Spots By A Metal-Dielectric Composite Superlens, Zhengtong Liu, Mark D. Thoreson, Alexander V. Kildishev, V. M. Shalaev Jul 2009

Translation Of Nanoantenna Hot Spots By A Metal-Dielectric Composite Superlens, Zhengtong Liu, Mark D. Thoreson, Alexander V. Kildishev, V. M. Shalaev

Birck and NCN Publications

We employ numerical simulations to show that highly localized, enhanced electromagnetic fields, also known as "hot spots," produced by a periodic array of silver nanoantennas can be spatially translated to the other side of a metal-dielectric composite superlens. The proposed translation of the hot spots enables surface-enhanced optical spectroscopy without the undesirable contact of molecules with metal, and thus it broadens and reinforces the potential applications of sensing based on field-enhanced fluorescence and surface-enhanced Raman scattering.

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Translation Of Nanoantenna Hot Spots By A Metal-Dielectric Composite Superlens, Zhengtong Liu, Mark D. Thoreson, Alexander V. Kildishev, V. M. Shalaev Jul 2009

Translation Of Nanoantenna Hot Spots By A Metal-Dielectric Composite Superlens, Zhengtong Liu, Mark D. Thoreson, Alexander V. Kildishev, V. M. Shalaev

Birck and NCN Publications

We employ numerical simulations to show that highly localized, enhanced electromagnetic fields, also known as "hot spots," produced by a periodic array of silver nanoantennas can be spatially translated to the other side of a metal-dielectric composite superlens. The proposed translation of the hot spots enables surface-enhanced optical spectroscopy without the undesirable contact of molecules with metal, and thus it broadens and reinforces the potential applications of sensing based on field-enhanced fluorescence and surface-enhanced Raman scattering.

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Simplified Model For Periodic Nanoantennae: Linear Model And Inverse Design, Joshua Borneman, Kuo-Ping Chen, Alexander V. Kildishev, V. M. Shalaev Jul 2009

Simplified Model For Periodic Nanoantennae: Linear Model And Inverse Design, Joshua Borneman, Kuo-Ping Chen, Alexander V. Kildishev, V. M. Shalaev

Birck and NCN Publications

We determine and use a minimal set of numerical simulations to create a simplified model for the spectral response of nanoantennae with respect to their geometric and modeling parameters. The simplified model is then used to rapidly obtain best-fit modeling parameters to match experimental results, accurately predict the spectral response for various geometries, and inversely design antennae to have a desired performance. This method is structure and model independent, and is applied here to both nanoantenna pair arrays and strips modeled using a 3D finite-element method and 2D spatial harmonic analysis, respectively. Typical numerical simulations may need hours per model, …

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Ultrasensitive Protein Detection In Blood Serum Using Gold Nanoparticle Probes By Single Molecule Spectroscopy, Jiji Chen, Chungang Wang, Joseph Irudayaraj Jul 2009

Ultrasensitive Protein Detection In Blood Serum Using Gold Nanoparticle Probes By Single Molecule Spectroscopy, Jiji Chen, Chungang Wang, Joseph Irudayaraj

Birck and NCN Publications

A one-step rapid and ultrasensitive immunoassay capable of detecting proteins in blood serum is developed using gold nanoprobes and fluorescence correlation spectroscopy (FCS). In this approach we take advantage of the inherent photoluminescence property of gold nanoparticles (GNPs) to develop a fluorophore-free assay to observe binding entities by monitoring the diffusion of bound versus unbound molecules in a limited confocal volume. 40-nm GNPs conjugated separately with rabbit anti-IgG (Fc) and goat anti-IgG (Fab) when incubated in blood serum containing IgG forms a sandwich structure constituting dimers and oligomers that can be differentiated by to detect IgG in blood serum at …

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Pseudomorphic Stabilization Of Rocksalt Gan In Tin/Gan Multilayers And Superlattices, Vijay Rawat, Dmitri Zakharov, E A. Stach, Timothy D. Sands Jul 2009

Pseudomorphic Stabilization Of Rocksalt Gan In Tin/Gan Multilayers And Superlattices, Vijay Rawat, Dmitri Zakharov, E A. Stach, Timothy D. Sands

Birck and NCN Publications

Gallium nitride (GaN) in its stable wurtzite phase has proven its utility in light-emitting diodes and diode lasers as well as high-temperature and high-power electronic devices. In addition to its equilibrium wurtzite phase, GaN exhibits two cubic polymorphs, a zinc-blende phase and a high-pressure rocksalt phase. Here, we report the pseudomorphic stabilization of the high-pressure rocksalt phase of GaN within TiN/GaN multilayers as verified using x-ray diffraction and high-resolution transmission electron microscopy. High-resolution lattice imaging confirmed that the lattice parameter of the rocksalt GaN phase is 0.41 nm. The critical thickness of the GaN film that can be pseudomophically stabilized …

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Temperature Dependence Of Hot-Carrier Relaxation In Pbse Nanocrystals: An Ab Initio Study, Hua Bao, Bradley F. Habenicht, Oleg V. Prezhdo, X Ruan Jun 2009

Temperature Dependence Of Hot-Carrier Relaxation In Pbse Nanocrystals: An Ab Initio Study, Hua Bao, Bradley F. Habenicht, Oleg V. Prezhdo, X Ruan

Birck and NCN Publications

Temperature-dependent dynamics of phonon-assisted relaxation of hot carriers, both electrons and holes, is studied in a PbSe nanocrystal using ab initio time-domain density-functional theory. The electronic structure is first calculated, showing that the hole states are denser than the electron states. Fourier transforms of the time-resolved energy levels show that the hot carriers couple to both acoustic and optical phonons. At higher temperature, more phonon modes in the high-frequency range participate in the relaxation process due to their increased occupation number. The phonon-assisted hot-carrier relaxation time is predicted using nonadiabatic molecular dynamics, and the results clearly show a temperature-activation behavior. …

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Thermal Conductivity Of Bismuth Telluride Nanowire Array-Epoxy Composite, Kalapi G. Biswas, Timothy D. Sands, Baratunde Cola, Xianfan Xu Jun 2009

Thermal Conductivity Of Bismuth Telluride Nanowire Array-Epoxy Composite, Kalapi G. Biswas, Timothy D. Sands, Baratunde Cola, Xianfan Xu

Birck and NCN Publications

Electrodeposition of nanowire array in porous anodic alumina (PAA) templates combine the performance benefits offered by crystallographic texture control, lattice thermal conductivity suppression through boundary scattering of phonons, elastic relaxation of misfit strain, and scalablity essential for high efficiency thermoelectric devices. The template material, however, can serve as a thermal shunt thereby reducing the effective thermoelectric performance. Here, we demonstrate a process of minimizing the parasitic thermal conduction by replacing the PAA matrix with SU-8 (kappa similar to 0.2 W/m K). We report a reduction in the performance penalty from 27% for Bi2Te3/PAA to similar to 5% for Bi2Te3/SU-8 nanocomposite …

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Demonstration Of Quadrature-Squeezed Surface Plasmons In A Gold Waveguide, Alexander Huck, Stephan Smolka, Peter Lodahl, Anders S. Sorensen, Alexandra Boltasseva, Jiri Janousek, Ulrik Andersen Jun 2009

Demonstration Of Quadrature-Squeezed Surface Plasmons In A Gold Waveguide, Alexander Huck, Stephan Smolka, Peter Lodahl, Anders S. Sorensen, Alexandra Boltasseva, Jiri Janousek, Ulrik Andersen

Birck and NCN Publications

We report on the efficient generation, propagation, and reemission of squeezed long-range surface-plasmon polaritons in a gold waveguide. Squeezed light is used to excite the nonclassical surface-plasmon polaritons, and the reemitted quantum state is fully characterized by complete quantum tomographic reconstruction of the density matrix. We find that the plasmon-assisted transmission of nonclassical light in metallic waveguides can be described by a beam splitter relation. This result is explained theoretically.

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Performance Analysis Of Statistical Samples Of Graphene Nanoribbon Tunneling Transistors With Line Edge Roughness, Mathieu Luisier, Gerhard Klimeck Jun 2009

Performance Analysis Of Statistical Samples Of Graphene Nanoribbon Tunneling Transistors With Line Edge Roughness, Mathieu Luisier, Gerhard Klimeck

Birck and NCN Publications

Using a three-dimensional, atomistic quantum transport simulator based on the tight-binding method, we investigate statistical samples of single-gate graphene nanoribbon (GNR) tunneling field-effect transistors (TFETs) with different line edge roughness probabilities. We find that as the nanoribbon edges become rougher, the device OFF-current drastically increases due to a reduction of the graphene band gap and an enhancement of source-to-drain tunneling leakage through the gate potential barrier. At the same time, the ON-current remains almost constant. This leads to a deterioration of the transistor subthreshold slopes and to unacceptably low ON/OFF current ratios limiting the switching performances of GNR TFETs.

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Demonstration Of Quadrature-Squeezed Surface Plasmons In A Gold Waveguide, Alexander Huck, Stephan Smolka, Peter Lodahl, Anders S. Sorensen, Alexandra Boltasseva, Jiri Janousek, Ulrik Andersen Jun 2009

Demonstration Of Quadrature-Squeezed Surface Plasmons In A Gold Waveguide, Alexander Huck, Stephan Smolka, Peter Lodahl, Anders S. Sorensen, Alexandra Boltasseva, Jiri Janousek, Ulrik Andersen

Birck and NCN Publications

We report on the efficient generation, propagation, and reemission of squeezed long-range surface-plasmon polaritons in a gold waveguide. Squeezed light is used to excite the nonclassical surface-plasmon polaritons, and the reemitted quantum state is fully characterized by complete quantum tomographic reconstruction of the density matrix. We find that the plasmon-assisted transmission of nonclassical light in metallic waveguides can be described by a beam splitter relation. This result is explained theoretically.

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Anisotropic Metamaterials Emulated By Tapered Waveguides: Application To Optical Cloaking, Igor I. Smolyaninov, Vera N. Smolyaninova, Alexander V. Kildishev, V. M. Shalaev May 2009

Anisotropic Metamaterials Emulated By Tapered Waveguides: Application To Optical Cloaking, Igor I. Smolyaninov, Vera N. Smolyaninova, Alexander V. Kildishev, V. M. Shalaev

Birck and NCN Publications

We demonstrate that metamaterial devices requiring anisotropic dielectric permittivity and magnetic permeability may be emulated by specially designed tapered waveguides. This approach leads to low-loss, broadband performance. Based on this technique, we demonstrate broadband electromagnetic cloaking in the visible frequency range on a scale similar to 100 times larger than the wavelength.

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Metal-Oxide-Semiconductor Field-Effect Transistors On Gaas (111)A Surface With Atomic-Layer-Deposited Al2o3 As Gate Dielectrics, Xu M, Y Q. Wu, O Koybasi, T Shen, P. D. Ye May 2009

Metal-Oxide-Semiconductor Field-Effect Transistors On Gaas (111)A Surface With Atomic-Layer-Deposited Al2o3 As Gate Dielectrics, Xu M, Y Q. Wu, O Koybasi, T Shen, P. D. Ye

Birck and NCN Publications

GaAs inversion-mode metal-oxide-semiconductor field-effect transistors (MOSFETs) with atomic-layer-deposited Al2O3 as gate dielectrics are fabricated on (111)A and (100) surfaces. With the same channel length of 0.75 mu m, the maximum drain current of 15 mA/mm on n-channel MOSFET is obtained on (111)A surface, in great contrast to only 1 mu A/mm on (100) surface. For p-channel MOSFETs, maximum drain currents of 0.17 mA/mm and 0.8 mA/mm are obtained on (111)A and (100) surfaces, respectively. An empirical model is proposed to correlate the experimental observation with the existing III-V MOS theories.

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Device Considerations For Development Of Conductance-Based Biosensors, Kangho Lee, Pradeep R. Nair, Adina Scott, Muhammad A. Alam, David B. Janes May 2009

Device Considerations For Development Of Conductance-Based Biosensors, Kangho Lee, Pradeep R. Nair, Adina Scott, Muhammad A. Alam, David B. Janes

Birck and NCN Publications

Design and fabrication of electronic biosensors based on field-effect-transistor (FET) devices require understanding of interactions between semiconductor surfaces and organic biomolecules. From this perspective, we review practical considerations for electronic biosensors with emphasis on molecular passivation effects on FET device characteristics upon immobilization of organic molecules and an electrostatic model for FET-based biosensors.

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High Efficiency Excitation Of Plasmonic Waveguides With Vertically Integrated Resonant Bowtie Apertures, Edward C. Kinzel, Xianfan Xu May 2009

High Efficiency Excitation Of Plasmonic Waveguides With Vertically Integrated Resonant Bowtie Apertures, Edward C. Kinzel, Xianfan Xu

Birck and NCN Publications

In recent years, many nanophotonic devices have been developed. Much attention has been given to the waveguides carrying surface plasmon polariton modes with subwavelength confinement and long propagation length. However, coupling far field light into a nano structure is a significant challenge. In this work, we present an architecture that enables high efficiency excitation of nanoscale waveguides in the direction normal to the waveguide. Our approach employs a bowtie aperture to provide both field confinement and high transmission efficiency. More than six times the power incident on the open area of the bowtie aperture can be coupled into the waveguide. …

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Resonant Oscillation Of Misch-Metal Atoms In Filled Skutterudites, Yaguo Wang, Xianfan Xu, Jihui Yang May 2009

Resonant Oscillation Of Misch-Metal Atoms In Filled Skutterudites, Yaguo Wang, Xianfan Xu, Jihui Yang

Birck and NCN Publications

We investigate vibrational behaviors in misch-metal filled antimony skutterudites in the time domain. At higher filling ratios of guest atoms, the vibration frequency approaches that of the cage structure and the amplitude becomes stronger. Furthermore, the reduction of lattice thermal conductivity over a wide temperature range can be explained using the measured resonant vibrational frequency. These findings reveal that the reduction of the lattice thermal conductivity is a result of scattering of acoustic phonons due to the resonant interaction between guest atoms and lattice phonons.

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Real Space First-Principles Derived Semiempirical Pseudopotentials Applied To Tunneling Magnetoresistance, Kirk Huw Bevan, Tony Low, H Guo May 2009

Real Space First-Principles Derived Semiempirical Pseudopotentials Applied To Tunneling Magnetoresistance, Kirk Huw Bevan, Tony Low, H Guo

Birck and NCN Publications

We present a real space density functional theory localized basis set semiempirical pseudopotential (SEP) approach. The method is applied to iron and magnesium oxide, where bulk SEP and local spin density approximation band structure calculations are shown to agree within approximately 0.1 eV. Subsequently we investigate the qualitative transferability of bulk derived SEPs to Fe/MgO/Fe tunnel junctions. We find that the SEP method is particularly well suited to address the tight binding transferability problem because the transferability error at the interface can be characterized not only in orbital space (via the interface local density of states) but also in real …

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Rarefied Gas Flow In Microtubes At Different Inlet-Outlet Pressure Ratios, Z Yang, Suresh Garimella May 2009

Rarefied Gas Flow In Microtubes At Different Inlet-Outlet Pressure Ratios, Z Yang, Suresh Garimella

Birck and NCN Publications

A model is developed for rarefied gas flow in long microtubes with different inlet-outlet pressure ratios at low Mach numbers. The model accounts for significant changes in Knudsen number along the length of the tube and is therefore applicable to gas flow in long tubes encountering different flow regimes along the flow length. Predictions from the model show good agreement with experimental measurements of mass flow rate, pressure drop, and inferred streamwise pressure distribution obtained under different flow conditions and offer a better match with experiments than do those from a conventional slip flow model.

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Efficient Unidirectional Ridge Excitation Of Surface Plasmons, I P. Radko, S I. Bozhevolnyi, G Brucoli, L Mart´In-Moreno, F J. Garc´Ia-Vidal, A Boltasseva Apr 2009

Efficient Unidirectional Ridge Excitation Of Surface Plasmons, I P. Radko, S I. Bozhevolnyi, G Brucoli, L Mart´In-Moreno, F J. Garc´Ia-Vidal, A Boltasseva

Birck and NCN Publications

Using leakage-radiation microscopy, we characterize the efficiency of unidirectional surface-plasmon excitation with periodic (800 nm) arrays of 130-nm-high and 330-nm-wide gold ridges on a thin gold film illuminated with a focused (5-mu m-wide) laser beam. We demonstrate that, at the resonant wavelength of 816 nm, the excitation efficiency of > 0.4 can be obtained with >= 5 ridges by adjusting the beam position. Conducting numerical simulations, we account for the experimental results and calculate the electric-field enhancement achieved near the gold surface.

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Characterization Of Electrochemically Grafted Molecular Layers On Silicon For Electronic Device Applications, Adina Scott, David B. Janes Apr 2009

Characterization Of Electrochemically Grafted Molecular Layers On Silicon For Electronic Device Applications, Adina Scott, David B. Janes

Birck and NCN Publications

Recently, there has been considerable interest in developing organically functionalized silicon surfaces for a variety of applications including sensing and nanoelectronics. In this study, a series of as-deposited, para-substituted aryl-diazonium molecular layers covalently grafted to < 111 >-orientation silicon are characterized using a variety of surface analysis techniques. Collectively, these measurements suggest that relatively ideal molecular layers can be achieved with a variety of headgroups. Submonolayer amounts of silicon oxide are detected on all modified surfaces and the extent of silicon oxidation depends on the molecular substituent. For electronic device applications, it is necessary to apply contacts to molecular layers while maintaining …

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Toward Surround Gates On Vertical Single-Walled Carbon Nanotube Devices, Aaron D. Franklin, Robert A. Sayer, Timothy D. Sands, Timothy Fisher, David B. Janes Mar 2009

Toward Surround Gates On Vertical Single-Walled Carbon Nanotube Devices, Aaron D. Franklin, Robert A. Sayer, Timothy D. Sands, Timothy Fisher, David B. Janes

Birck and NCN Publications

The one-dimensional, cylindrical nature of single-walled carbon nanotubes (SWCNTs) suggests that the ideal gating geometry for nanotube field-effect transistors (FETs) is a surround gate (SG). Using vertical SWCNTs templated in porous anodic alumina, SGs are formed using top-down processes for the dielectric/metal depositions and definition of the channel length. Surround gates allow aggressive scaling of the channel to 25% of the length attainable with a bottom-gate geometry without incurring short-channel effects. The process demonstrated here for forming SGs on vertical SWCNTs is amenable for large-scale fabrication of multinanotube FETs.

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Insights Into Few-Layer Epitaxial Graphene Growth On 4h-Sic(000(1)Over-Bar Substrates From Stm Studies, Laura B. Biedermann, Michael L. Bolen, Michael A. Capano, Dmitry Zemlyanov, R. Reifenberger Mar 2009

Insights Into Few-Layer Epitaxial Graphene Growth On 4h-Sic(000(1)Over-Bar Substrates From Stm Studies, Laura B. Biedermann, Michael L. Bolen, Michael A. Capano, Dmitry Zemlyanov, R. Reifenberger

Birck and NCN Publications

Epitaxial carbon was grown by heating (000 (1) over bar) silicon carbide (SiC) to high temperatures (1450-1600 degrees C) in vacuum. A continuous graphene surface layer was formed at temperatures above 1475 degrees C. X-ray photo-electron spectroscopy (XPS) and scanning tunneling microscopy (STM) were extensively used to characterize the quality of the few-layer graphene (FLG) surface. The XPS studies were useful in confirming the graphitic composition and measuring the thickness of the FLG samples. STM studies revealed a wide variety of nanometer-scale features that include sharp carbon-rich ridges, moire superlattices, one-dimensional line defects, and grain boundaries. By imaging these features …

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Theoretical Basis Of Parametric-Resonance-Based Atomic Force Microscopy, G Prakash, S Hu, Arvind Raman, R. Reifenberger Mar 2009

Theoretical Basis Of Parametric-Resonance-Based Atomic Force Microscopy, G Prakash, S Hu, Arvind Raman, R. Reifenberger

Birck and NCN Publications

Parametric resonance underpins the physics of swings, resonant surface waves, and particle traps. There is increasing interest in its potential applications in atomic force microscopy (AFM). In this paper, the dynamics of parametrically resonant microcantilevers for high sensitivity imaging and force spectroscopy applications is investigated theoretically. Detailed numerical parametric-resonance simulations are performed to understand how the microcantilever amplitude varies with tip-sample separation, the tip-sample interaction, and the scanning dynamics of a microcantilever probe. We find three key advantages of a parametrically resonant microcantilever for AFM applications: (a) the reduction in ringing effects near feature edges that occur for high-Q microcantilevers; …

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A Ph-Tunable Hydrogel Microlens Array With Temperature-Actuated Light-Switching Capability, Zhenwen Deng, Babak Ziaie Feb 2009

A Ph-Tunable Hydrogel Microlens Array With Temperature-Actuated Light-Switching Capability, Zhenwen Deng, Babak Ziaie

Birck and NCN Publications

In this letter, we demonstrate a two step casting process to fabricate a bifunctional hydrogel-based microlens array, which responds to both temperature (becomes opaque above certain temperature) and pH (changes its focal length at different pH levels), and can be operated in air for an extended period of time. Each lens in the array is 1 mm in diameter and its focal length changes from 4.5 to 55 mm when the environmental pH is varied between 2.0 and 5.0. The light-switching capability is measured to be similar to 92% when temperature increases from 25 to 35 degrees C.

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Compositional Contrast Of Biological Materials In Liquids Using The Momentary Excitation Of Higher Eigenmodes In Dynamic Atomic Force Microscopy, Xin Xu, John Melcher, Sudipta Basak, R. Reifenberger, Arvind Raman Feb 2009

Compositional Contrast Of Biological Materials In Liquids Using The Momentary Excitation Of Higher Eigenmodes In Dynamic Atomic Force Microscopy, Xin Xu, John Melcher, Sudipta Basak, R. Reifenberger, Arvind Raman

Birck and NCN Publications

Atomic Force microscope (AFM) cantilevers commonly used for imaging soft biological samples in liquids experience a momentary excitation of the higher eigenmodes at each tap. This transient response is very sensitive to the local sample elasticity under gentle imaging conditions because the higher eigenmode time period is comparable to the tip-sample contact time. By mapping the momentary excitation response, we demonstrate a new scanning probe spectroscopy capable of resolving with high sensitivity the variations in the elasticity of soft biological materials in liquids.

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Materializing A Binary Hyperlens Design, Alexander V. Kildishev, Uday K. Chettiar, Zubin Jacob, V. M. Shalaev, Evgenii Narimanov Feb 2009

Materializing A Binary Hyperlens Design, Alexander V. Kildishev, Uday K. Chettiar, Zubin Jacob, V. M. Shalaev, Evgenii Narimanov

Birck and NCN Publications

We present a design of cylindrical hyperlens made of a layered binary material. The design approach uses an improved effective medium theory to take account of radius-dependent effects due to curvature of material interfaces resulting in nonperiodically distributed thicknesses of the lens layers. The performance of this lens is compared versus the designs with periodically thick layers, which we showed in earlier papers. Detailed quantitative results analyzed for the lenses with the same number and starting order of layers prove better functioning of the lens designed with this approach.

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Influence Of Dimensionality On Thermoelectric Device Performance, Raseong Kim, Supriyo Datta, Mark S. Lundstrom Feb 2009

Influence Of Dimensionality On Thermoelectric Device Performance, Raseong Kim, Supriyo Datta, Mark S. Lundstrom

Birck and NCN Publications

The role of dimensionality on the electronic performance of thermoelectric devices is clarified using the Landauer formalism, which shows that the thermoelectric coefficients are related to the transmission, T(E), and how the conducting channels, M(E), are distributed in energy. The Landauer formalism applies from the ballistic to diffusive limits and provides a clear way to compare performance in different dimensions. It also provides a physical interpretation of the "transport distribution," a quantity that arises in the Boltzmann transport equation approach. Quantitative comparison of thermoelectric coefficients in one, two, and three dimensions shows that the channels are utilized more effectively in …

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Valley Degeneracies In (111) Silicon Quantum Wells, Neerav Kharche, Seongmin Kim, Timothy B. Boykin, Gerhard Klimeck Jan 2009

Valley Degeneracies In (111) Silicon Quantum Wells, Neerav Kharche, Seongmin Kim, Timothy B. Boykin, Gerhard Klimeck

Birck and NCN Publications

(111) silicon quantum wells have been studied extensively, yet no convincing explanation exists for the experimentally observed breaking of sixfold valley degeneracy into two- and fourfold degeneracies. Here, systematic sp(3)d(5)s(*) tight-binding and effective mass calculations are presented to show that a typical miscut modulates the energy levels, which leads to breaking of sixfold valley degeneracy into two lower and four raised valleys. An effective mass based valley-projection model is used to determine the directions of valley minima in tight-binding calculations of large supercells. Tight-binding calculations are in better agreement with experiments compared to effective mass calculations.

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