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Birck and NCN Publications

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Articles 181 - 210 of 353

Full-Text Articles in Nanoscience and Nanotechnology

Amorphous Interface Layer In Thin Graphite Films Grown On The Carbon Face Of Sic, R. Colby, M. L. Bolen, Michael A. Capano, E. A. Stach Sep 2011

Amorphous Interface Layer In Thin Graphite Films Grown On The Carbon Face Of Sic, R. Colby, M. L. Bolen, Michael A. Capano, E. A. Stach

Birck and NCN Publications

Cross-sectional transmission electron microscopy (TEM) is used to characterize an amorphous layer observed at the interface in graphite and graphene films grown via thermal decomposition of C-face 4H-SiC. The amorphous layer does not cover the entire interface, but uniform contiguous regions span microns of cross-sectional interface. Scanning transmission electron microscopy (STEM) images and electron energy loss spectroscopy (EELS) demonstrate that the amorphous layer is a carbon-rich composition of Si/C. The amorphous layer is clearly observed in samples grown at 1600 degrees C for a range of growth pressures in argon, but not at 1500 degrees C, suggesting a temperature-dependent formation …

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Design Of A Gainp/Gaas Tandem Solar Cell For Maximum Daily, Monthly, And Yearly Energy Output, Alexander W. Haas, John R. Wilcox, Jeffery L. Gray, Richard J. Schwartz Sep 2011

Design Of A Gainp/Gaas Tandem Solar Cell For Maximum Daily, Monthly, And Yearly Energy Output, Alexander W. Haas, John R. Wilcox, Jeffery L. Gray, Richard J. Schwartz

Birck and NCN Publications

Solar concentrator cells are typically designed for maximum efficiency under the AM1.5d standard spectrum. While this methodology does allow for a direct comparison of cells produced by various laboratories, it does not guarantee maximum daily, monthly, or yearly energy production, as the relative distribution of spectral energy changes throughout the day and year. It has been suggested that achieving this goal requires designing under a nonstandard spectrum. In this work, a GaInP/GaAs tandem solar cell is designed for maximum energy production by optimizing for a set of geographically-dependent solar spectra using detailed numerical models. The optimization procedure focuses on finding …

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Role Of Surface Orientation On Atomic Layer Deposited Al2o3/Gaas Interface Structure And Fermi Level Pinning: A Density Functional Theory Study, Ganesh Hegde, Gerhard Klimeck, Alejandro Strachan Sep 2011

Role Of Surface Orientation On Atomic Layer Deposited Al2o3/Gaas Interface Structure And Fermi Level Pinning: A Density Functional Theory Study, Ganesh Hegde, Gerhard Klimeck, Alejandro Strachan

Birck and NCN Publications

We investigate the initial surface reaction pathways in the atomic layer deposition (ALD) of Al2O3 on GaAs (111)A and (111)B substrates using precursors trimethylaluminum (TMA) and water to ascertain the effect of surface orientation on device performance. We find that the condition of the respective substrates prior to deposition of TMA and water has a major impact on the surface reactions that follow and on the resulting interface structure. The simulations explain the atomistic mechanism of the interfacial self-cleaning effect in ALD that preferentially removes As oxides. The electronic structure of the resulting atomic configurations indicates states throughout the bandgap …

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Strain Effects On The Phonon Thermal Properties Of Ultra-Scaled Si Nanowires, Abhijeet Paul, Gerhard Klimeck Aug 2011

Strain Effects On The Phonon Thermal Properties Of Ultra-Scaled Si Nanowires, Abhijeet Paul, Gerhard Klimeck

Birck and NCN Publications

The impact of uniaxial and hydrostatic stress on the ballistic thermal conductance (jl) and the specific heat (Cv) of [100] and [110] Si nanowires are explored using a Modified Valence Force Field phonon model. An anisotropic behavior of jl and isotropic nature of Cv under strain are predicted for the two wire orientations. Compressive (tensile) strain decreases (increases) Cv. The Cv trend with strain is controlled by the high energy phonon sub-bands. Dominant contribution of the low/mid (low/high) energy bands in [100] ([110]) wire and their variation under strain governs thebehaviorofjl.VC 2011AmericanInstituteofPhysics.

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Mechanism Of Thermal Conductivity Reduction In Few-Layer Graphene, Druv Singh, Jayathi Y. Murthy, Timothy S. Fisher Aug 2011

Mechanism Of Thermal Conductivity Reduction In Few-Layer Graphene, Druv Singh, Jayathi Y. Murthy, Timothy S. Fisher

Birck and NCN Publications

Using the linearized Boltzmann transport equation and perturbation theory, we analyze the reduction in the intrinsic thermal conductivity of few-layer graphene sheets accounting for all possible three-phonon scattering events. Even with weak coupling between layers, a significant reduction in the thermal conductivity of the out-of-plane acoustic modes is apparent. The main effect of this weak coupling is to open many new three-phonon scattering channels that are otherwise absent in graphene. However, reflection symmetry is only weakly broken with the addition of multiple layers, and out-of-plane acoustic phonons still dominate thermal conductivity. We also find that reduction in thermal conductivity is …

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Relaxation Of Optically Excited Carriers In Graphene, Raseong Kim, Vasili Perebeinos, Phaedon Avouris Aug 2011

Relaxation Of Optically Excited Carriers In Graphene, Raseong Kim, Vasili Perebeinos, Phaedon Avouris

Birck and NCN Publications

We explore the relaxation of photoexcited graphene by solving a transient Boltzmann transport equation with electron-phonon (e-ph) and electron-electron (e-e) scattering. Simulations show that when the excited carriers are relaxed by e-ph scattering only, a population inversion can be achieved at energies determined by the photon energy. However, e-e scattering quickly thermalizes the carrier energy distributions washing out the negative optical conductivity peaks. The relaxation rates and carrier multiplication effects are presented as a function of photon energy, graphene doping, and dielectric constant.

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Entanglement Dynamics Of One-Dimensional Driven Spin Systems In Time-Varying Magnetic Fields, Bedoor Alkurtass, Gehad Sadiek, Sabre Kais Aug 2011

Entanglement Dynamics Of One-Dimensional Driven Spin Systems In Time-Varying Magnetic Fields, Bedoor Alkurtass, Gehad Sadiek, Sabre Kais

Birck and NCN Publications

We study the dynamics of nearest-neighbor entanglement for a one-dimensional spin chain with a nearest-neighbor time-dependent Heisenberg coupling J(t) between the spins in the presence of a time-dependent external magnetic field h(t) at zero and finite temperatures. We consider different forms of time dependence for the coupling and magnetic field: exponential, hyperbolic, and periodic. Solving the system numerically, we examined the system-size effect on the entanglement asymptotic value. It was found that, for a small system size, the entanglement starts to fluctuate within a short period of time after applying the time-dependent coupling. The period of time increases as the …

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Anti-Stokes Fluorescence Imaging Of Microscale Thermal Fields In Thin Films, A. N. Kuzmin, A. Baev, A. V. Kachynski, Timothy S. Fisher, Ali Shakouri, P. N. Prasad Aug 2011

Anti-Stokes Fluorescence Imaging Of Microscale Thermal Fields In Thin Films, A. N. Kuzmin, A. Baev, A. V. Kachynski, Timothy S. Fisher, Ali Shakouri, P. N. Prasad

Birck and NCN Publications

We demonstrate that the in-plane thin film heat transport can be accurately mapped via confocal anti-Stokes fluorescence imaging using fluorescent dye probes and nanoheaters. We employ 3D finite elements analysis to evaluate the thermal conductivity of a control sample and to assess the validity of a point heat source approximation. We have found that this approximation is adequate with use of a tightly focused laser beam, providing a robust means for determining the thermal conductivity of a sample under investigation. (C) 2011 American Institute of Physics. [doi:10.1063/1.3606429]

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Computational Study Of The Seebeck Coefficient Of One-Dimensional Composite Nano-Structures, Raseong Kim, Mark S. Lundstrom Aug 2011

Computational Study Of The Seebeck Coefficient Of One-Dimensional Composite Nano-Structures, Raseong Kim, Mark S. Lundstrom

Birck and NCN Publications

The Seebeck coefficient (S) of composite nano-structures is theoretically explored within a self-consistent electro-thermal transport simulation framework using the non-equilibrium Green's function method and a heat diffusion equation. Seebeck coefficients are determined using numerical techniques that mimic experimental measurements. Simulation results show that, without energy relaxing scattering, the overall S of a composite structure is determined by the highest barrier within the device. For a diffusive, composite structure with energy relaxation due to electron-phonon scattering, however, the measured S is an average of the position-dependent values with the weighting factor being the lattice temperature gradient. The results stress the importance …

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Observation Of Nonclassical Scaling Laws In The Quality Factors Of Cantilevered Carbon Nanotube Resonators, Ajit Vallabhaneni, Jeff Rhoads, Jayathi Y. Murthy, Xiulin Ruan Aug 2011

Observation Of Nonclassical Scaling Laws In The Quality Factors Of Cantilevered Carbon Nanotube Resonators, Ajit Vallabhaneni, Jeff Rhoads, Jayathi Y. Murthy, Xiulin Ruan

Birck and NCN Publications

This work examines the quality factors (Q factors) of resonance associated with the axial and transverse vibrations of single-wall carbon nanotube (SWCNT) resonators through the use of molecular dynamics (MD) simulation. Specifically, the work investigates the effect of device length, diameter, and chirality, as well as temperature, on the resonant frequency and quality factor of these devices and benchmarks the results of MD simulations against classical theories of energy dissipation. The quality factor (Q) associated with transverse vibration is found to increase with increasing device length (Q similar to L(theta), where 0.8 < theta < 1.4) and decrease with increasing device diameter (Q similar to D(-mu), where 1.4 < mu < 1.6), while the Q associated with axial vibration is almost independent of length and diameter. We show that to accurately predict temperature dependence of Q, the external and internal energies need to be properly decomposed, and temperature quantum correction should be performed. For both vibrational modes, Q shows a temperature dependence Q similar to T(-alpha), where alpha > 1 when below Debye temperature due to quantum …

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Atomic-Layer-Deposited Al2o3 On Bi2te3 For Topological Insulator Field-Effect Transistors, Han Liu, Peide D. Ye Aug 2011

Atomic-Layer-Deposited Al2o3 On Bi2te3 For Topological Insulator Field-Effect Transistors, Han Liu, Peide D. Ye

Birck and NCN Publications

We report dual-gate modulation of topological insulator field-effect transistors (TI FETs) made on Bi2Te3 thin flakes with integration of atomic-layer-deposited (ALD) Al2O3 high-k dielectric. Atomic force microscopy study shows that ALD Al2O3 is uniformly grown on this layer-structured channel material. Electrical characterization reveals that the right selection of ALD precursors and the related surface chemistry play a critical role in device performance of Bi2Te3 based TI FETs. We realize both top-gate and bottom-gate control on these devices, and the highest modulation rate of 76.1% is achieved by using simultaneous dual gate control. (C) 2011 American Institute of Physics. [doi:10.1063/1.3622306]

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Dislocation Pinning Effects Induced By Nano-Precipitates During Warm Laser Shock Peening: Dislocation Dynamic Simulation And Experiments, Yiliang Liao, Chang Ye, Huang Gao, Bong-Joong Kim, Sergey Suslov, Eric A. Stach, Gary J. Cheng Jul 2011

Dislocation Pinning Effects Induced By Nano-Precipitates During Warm Laser Shock Peening: Dislocation Dynamic Simulation And Experiments, Yiliang Liao, Chang Ye, Huang Gao, Bong-Joong Kim, Sergey Suslov, Eric A. Stach, Gary J. Cheng

Birck and NCN Publications

Warm laser shock peening (WLSP) is a new high strain rate surface strengthening process that has been demonstrated to significantly improve the fatigue performance of metallic components. This improvement is mainly due to the interaction of dislocations with highly dense nanoscale precipitates, which are generated by dynamic precipitation during the WLSP process. In this paper, the dislocation pinning effects induced by the nanoscale precipitates during WLSP are systematically studied. Aluminum alloy 6061 and AISI 4140 steel are selected as the materials with which to conduct WLSP experiments. Multiscale discrete dislocation dynamics (MDDD) simulation is conducted in order to investigate the …

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Periodically Changing Morphology Of The Growth Interface In Si, Ge, And Gap Nanowires, C-Y Wen, J. Tersoff, K. Hillerich, M.C. Reuter, J. H. Park, S. Kodambaka, Eric Stach, F.M. Ross Jul 2011

Periodically Changing Morphology Of The Growth Interface In Si, Ge, And Gap Nanowires, C-Y Wen, J. Tersoff, K. Hillerich, M.C. Reuter, J. H. Park, S. Kodambaka, Eric Stach, F.M. Ross

Birck and NCN Publications

Nanowire growth in the standard < 111 > direction is assumed to occur at a planar catalyst-nanowire interface, but recent reports contradict this picture. Here we show that a nonplanar growth interface is, in fact, a general phenomenon. Both III-V and group IV nanowires show a distinct region at the trijunction with a different orientation whose size oscillates during growth, synchronized with step flow. We develop an explicit model for this structure that agrees well with experiment and shows that the oscillations provide a direct visualization of catalyst supersaturation. We discuss the implications for wire growth and structure.

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Direct Simulation Monte Carlo Study Of Effects Of Thermal Nonuniformities In Electron-Beam Physical Vapor Deposition, A. Venkattraman, Alina A. Alexeenko Jul 2011

Direct Simulation Monte Carlo Study Of Effects Of Thermal Nonuniformities In Electron-Beam Physical Vapor Deposition, A. Venkattraman, Alina A. Alexeenko

Birck and NCN Publications

In a typical electron-beam physical vapor deposition system, there is limited control over how the high-power electron beam heats the metal surface. This leads to thermal nonuniformities at the melt. Three-dimensional direct simulation Monte Carlo simulations were performed with the aim of quantifying the effect of such spatial variations of source temperature in thin film depositions using an electron-beam physical vapor deposition system. The source temperature distribution from a typical deposition process was used in the direct simulation Monte Carlo simulations performed for various mass flow rates. The use of an area-averaged temperature is insufficient for all mass flow rates …

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Schottky-Barrier Height Modulation Of Metal/In0.53ga0.47as Interfaces By Insertion Of Atomic-Layer Deposited Ultrathin Al2o3, Runsheng Wang, Min Xu, Peide D. Ye, Ru Huang Jul 2011

Schottky-Barrier Height Modulation Of Metal/In0.53ga0.47as Interfaces By Insertion Of Atomic-Layer Deposited Ultrathin Al2o3, Runsheng Wang, Min Xu, Peide D. Ye, Ru Huang

Birck and NCN Publications

The improvement of the metal/InGaAs interface is essential for the future application of InGaAs metal source/drain Schottky-barrier metal-oxide-semiconductor field-effect-transistors. In this article, on In0.53Ga0.47As, the authors examine the recently proposed method of inserting an ultrathin insulator to modulate the effective Schottky-barrier height (SBH) at the metal/semiconductor interface. Both n-type and p-type In0.53Ga0.47As are investigated by inserting an atomic-layer deposited Al2O3 interlayer. The results indicate that SBH modulation is more effective at the n-InGaAs interface than the p-InGaAs interface for the same Al2O3 thickness. However, the Fermi level at the metal/InGaAs interface is still weakly pinned even after inserting 2 nm …

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Numerical Modeling Of Plasmonic Nanoantennas With Realistic 3d Roughness And Distortion, Alexander V. Kildishev, Joshua D. Borneman, Kuo-Ping Chen, Vladimir P. Drachev Jul 2011

Numerical Modeling Of Plasmonic Nanoantennas With Realistic 3d Roughness And Distortion, Alexander V. Kildishev, Joshua D. Borneman, Kuo-Ping Chen, Vladimir P. Drachev

Birck and NCN Publications

Nanostructured plasmonic metamaterials, including optical nanoantenna arrays, are important for advanced optical sensing and imaging applications including surface-enhanced fluorescence, chemiluminescence, and Raman scattering. Although designs typically use ideally smooth geometries, realistic nanoantennas have nonzero roughness, which typically results in a modified enhancement factor that should be involved in their design. Herein we aim to treat roughness by introducing a realistic roughened geometry into the finite element (FE) model. Even if the roughness does not result in significant loss, it does result in a spectral shift and inhomogeneous broadening of the resonance, which could be critical when fitting the FE simulations …

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Scattering Mechanisms In A High-Mobility Low-Density Carbon-Doped (100) Gaas Two-Dimensional Hole System, J. D. Watson, S. Mondal, G. A. Csathy, M. J. Manfra, E. H. Hwang, S. Das Sarma, L. N. Pfeiffer, K. W. West Jun 2011

Scattering Mechanisms In A High-Mobility Low-Density Carbon-Doped (100) Gaas Two-Dimensional Hole System, J. D. Watson, S. Mondal, G. A. Csathy, M. J. Manfra, E. H. Hwang, S. Das Sarma, L. N. Pfeiffer, K. W. West

Birck and NCN Publications

We report on a systematic study of the density dependence of mobility in a low-density carbon-doped (100) GaAs two-dimensional hole system (2DHS). At T = 50 mK, a mobility of 2.6 x 10(6) cm(2)/Vs at a density p = 6.2 x 10(10)cm(-2) was measured. This is the highest mobility reported for a 2DHS to date. Using a backgated sample geometry, the density dependence of mobility was studied from 2.8 x 10(10) cm(-2) to 1 x 10(11) cm(-2). The mobility vs density cannot be fit to a power law dependence of the form alpha similar to p(alpha) using a single exponent …

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Supersymmetry Identifies Molecular Stark States Whose Eigenproperties Can Be Obtained Analytically, Mikhail Lemeshko, Mustafa Mustafa, Sabre Kais, Bretislav Friedrich Jun 2011

Supersymmetry Identifies Molecular Stark States Whose Eigenproperties Can Be Obtained Analytically, Mikhail Lemeshko, Mustafa Mustafa, Sabre Kais, Bretislav Friedrich

Birck and NCN Publications

We made use of supersymmetric (SUSY) quantum mechanics to find the condition under which the Stark effect problem for a polar and polarizable closed-shell diatomic molecule subjected to collinear electrostatic and nonresonant radiative fields becomes exactly solvable. The condition Delta omega = omega(2)/4(m+1)(2) connects values of the dimensionless parameters omega and Delta omega that characterize the strengths of the permanent and induced dipole interactions of the molecule with the respective fields. The exact solutions are obtained for the vertical bar(J) over tilde = m, m; omega, Delta omega > family of 'stretched' states. The field-free and strong-field limits of the combined-fields …

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Room Temperature Device Performance Of Electrodeposited Insb Nanowire Field Effect Transistors, Suprem Das, Collin J. Delker, Dmitri Zakharov, Yong P. Chen, Timothy D. Sands, David B. Janes Jun 2011

Room Temperature Device Performance Of Electrodeposited Insb Nanowire Field Effect Transistors, Suprem Das, Collin J. Delker, Dmitri Zakharov, Yong P. Chen, Timothy D. Sands, David B. Janes

Birck and NCN Publications

InSb nanowires have been formed by electrodeposition in porous anodic alumina templates and employed as transistor channels. The 100 nm diameter nanowires had a zinc blende crystal structure. Single-nanowire field-effect transistors (NW-FETs) with a channel length of 500 nm exhibited on-currents of similar to 40 mu A, on/off ratios of similar to 16-20, drain conductances of similar to 71 mu S and field-effect electron mobility of similar to 1200 cm(2) V(-1) s(-1). Compared with reported NW-FETs, the on-current is large and the current saturation occurs at low source-drain voltages. These characteristics can be understood in terms of velocity saturation effects …

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Dynamics Of Entanglement In A Two-Dimensional Spin System, Qing Xu, Gehad Sadiek, Sabre Kais Jun 2011

Dynamics Of Entanglement In A Two-Dimensional Spin System, Qing Xu, Gehad Sadiek, Sabre Kais

Birck and NCN Publications

We consider the time evolution of entanglement in a finite two-dimensional transverse Ising model. The model consists of a set of seven localized spin-1/2 particles in a two-dimensional triangular lattice coupled through nearest-neighbor exchange interaction in the presence of an external time-dependent magnetic field. The magnetic field is applied in different function forms: step, exponential, hyperbolic, and periodic. We found that the time evolution of the entanglement shows an ergodic behavior under the effect of the time-dependent magnetic fields. Also, we found that while the step magnetic field causes great disturbance to the system, creating rapid oscillations, the system shows …

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Comparison Of Photothermal And Piezoacoustic Excitation Methods For Frequency And Phase Modulation Atomic Force Microscopy In Liquid Environments, A. Labuda, K. Kobayashi, Daniel Kiracofe, K. Suzuki, P. H. Gruetter, H. Yamada Jun 2011

Comparison Of Photothermal And Piezoacoustic Excitation Methods For Frequency And Phase Modulation Atomic Force Microscopy In Liquid Environments, A. Labuda, K. Kobayashi, Daniel Kiracofe, K. Suzuki, P. H. Gruetter, H. Yamada

Birck and NCN Publications

In attempting to perform frequency modulation atomic force microscopy (FM-AFM) in liquids, a non-flat phase transfer function in the self-excitation system prevents proper tracking of the cantilever natural frequency. This results in frequency-and-phase modulation atomic force microscopy (FPM-AFM) which lies in between phase modulation atomic force microscopy (PM-AFM) and FM-AFM. We derive the theory necessary to recover the conservative force and damping in such a situation, where standard FM-AFM theory no longer applies. Although our recovery procedure applies to all cantilever excitation methods in principle, its practical implementation may be difficult, or even impossible, if the cantilever is driven piezoacoustically. …

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Formation Of Silicon Nanodots Via Ion Beam Sputtering Of Ultrathin Gold Thin Film Coatings On Si, Osman El-Atwani, Sami Ortoleva, Alex Cimaroli, Jean Paul Allain May 2011

Formation Of Silicon Nanodots Via Ion Beam Sputtering Of Ultrathin Gold Thin Film Coatings On Si, Osman El-Atwani, Sami Ortoleva, Alex Cimaroli, Jean Paul Allain

Birck and NCN Publications

Ion beam sputtering of ultrathin film Au coatings used as a physical catalyst for self-organization of Si nanostructures has been achieved by tuning the incident particle energy. This approach holds promise as a scalable nanomanufacturing parallel processing alternative to candidate nanolithography techniques. Structures of 11- to 14-nm Si nanodots are formed with normal incidence low-energy Ar ions of 200 eV and fluences above 2 x 10(17) cm(-2). In situ surface characterization during ion irradiation elucidates early stage ion mixing migration mechanism for nanodot self-organization. In particular, the evolution from gold film islands to the formation of ion-induced metastable gold silicide …

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Improving Near-Field Confinement Of A Bowtie Aperture Using Surface Plasmon Polaritons, Pornsak Srisungsitthisunti, Okan Ersoy, Xianfan Xu May 2011

Improving Near-Field Confinement Of A Bowtie Aperture Using Surface Plasmon Polaritons, Pornsak Srisungsitthisunti, Okan Ersoy, Xianfan Xu

Birck and NCN Publications

Bowtie aperture is known to produce subdiffraction-limited optical spot with high intensity. In this work, we investigate integrating a bowtie aperture with circular grooves to reduce the divergence of the near-field produced by the bowtie aperture. Numerical results indicate that surface waves reflected from circular grooves improve the field confinement of a bowtie aperture along the polarization axis. These circular grooves with period near half the wavelength of surface plasmon polaritons reduce the spot size by as much as 40% at distances between 20 and 100 nm from the surface and create a more symmetrical optical spot. (C) 2011 American …

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Chaos-Assisted Emission From Asymmetric Resonant Cavity Microlasers, Susumu Shinohara, Takahisa Harayama, Takehiro Fukushima, Martina Hentschel, Satoshi Sunada, Evgenii Narimanov May 2011

Chaos-Assisted Emission From Asymmetric Resonant Cavity Microlasers, Susumu Shinohara, Takahisa Harayama, Takehiro Fukushima, Martina Hentschel, Satoshi Sunada, Evgenii Narimanov

Birck and NCN Publications

We study emission from quasi-one-dimensional modes of an asymmetric resonant cavity that are associated with a stable periodic ray orbit confined inside the cavity by total internal reflection. It is numerically demonstrated that such modes exhibit directional emission, which is explained by chaos-assisted emission induced by dynamical tunneling. Fabricating semiconductor microlasers with an asymmetric resonant cavity, we experimentally demonstrate the selective excitation of the quasi-one-dimensional modes by employing the device structure to preferentially inject currents to these modes and observe directional emission in good accordance with the theoretical prediction based on chaos-assisted emission.

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Engineered Valley-Orbit Splittings In Quantum-Confined Nanostructures In Silicon, Rajib Rahman, J. Verdujin, Neerav Kharche, Gabriel Lansbergen, Purdue University Gerhard Klimeck, Lloyd Hollenberg, Sven Rogge May 2011

Engineered Valley-Orbit Splittings In Quantum-Confined Nanostructures In Silicon, Rajib Rahman, J. Verdujin, Neerav Kharche, Gabriel Lansbergen, Purdue University Gerhard Klimeck, Lloyd Hollenberg, Sven Rogge

Birck and NCN Publications

An important challenge in silicon quantum electronics in the few electron regime is the poten- tially small energy gap between the ground and excited orbital states in 3D quantum confined nanostructures due to the multiple valley degeneracies of the conduction band present in silicon. Understanding the “valley-orbit” (VO) gap is essential for silicon qubits, as a large VO gap prevents leakage of the qubit states into a higher dimensional Hilbert space. The VO gap varies considerably depending on quantum confinement, and can be engineered by external electric fields. In this work we investigate VO splitting experimentally and theoretically in a …

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Fabrication And Realistic Modeling Of Three-Dimensional Metal-Dielectric Composites, Mark D. Thoreson, Jieran R. Fang, Alexander V. Kildishev, Ludmila J. Prokopeva, Piotr Nyga, Uday K. Chettiar, Vladimir M. Shalaev, Vladimir P. Drachev May 2011

Fabrication And Realistic Modeling Of Three-Dimensional Metal-Dielectric Composites, Mark D. Thoreson, Jieran R. Fang, Alexander V. Kildishev, Ludmila J. Prokopeva, Piotr Nyga, Uday K. Chettiar, Vladimir M. Shalaev, Vladimir P. Drachev

Birck and NCN Publications

Historically, the methods used to describe the electromagnetic response of random, three-dimensional (3D), metal-dielectric composites (MDCs) have been limited to approximations such as effective-medium theories that employ easily-obtained, macroscopic parameters. Full-wave numerical simulations such as finite-difference time domain (FDTD) calculations are difficult for random MDCs due to the fact that the nanoscale geometry of a random composite is generally difficult to ascertain after fabrication. We have developed a fabrication method for creating semicontinuous metal films with arbitrary thicknesses and a modeling technique for such films using realistic geometries. We extended our two-dimensional simulation method to obtain realistic geometries of 3D …

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Particle-Hole Asymmetry Of Fractional Quantum Hall States In The Second Landau Level Of A Two-Dimensional Hole System, A. Kumar, N. Samkharadze, Gabor A. Csathy, Michael J. Manfra, L. N. Pfeiffer, K. W. West May 2011

Particle-Hole Asymmetry Of Fractional Quantum Hall States In The Second Landau Level Of A Two-Dimensional Hole System, A. Kumar, N. Samkharadze, Gabor A. Csathy, Michael J. Manfra, L. N. Pfeiffer, K. W. West

Birck and NCN Publications

We report the unambiguous observation of a fractional quantum Hall state in the Landau level of a two-dimensional-hole sample at the filling factor v = 8/3. We identified this state by a quantized Hall resistance and an activated temperature dependence of the longitudinal resistance and found an energy gap of 40 mK. Notably, the particle-hole conjugate state at filling factor v = 7/3 in our sample did not develop down to 6.9 mK. This observation is contrary to that in electron samples, in which the 7/3 state is typically more stable than the 8/3 state. We present evidence that the …

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Atomistic Approach To Alloy Scattering In Si(1-X)Ge(X), Saumitra R. Mehrotra, Abhijeet Paul, Gerhard Klimeck Apr 2011

Atomistic Approach To Alloy Scattering In Si(1-X)Ge(X), Saumitra R. Mehrotra, Abhijeet Paul, Gerhard Klimeck

Birck and NCN Publications

SiGe alloy scattering is of significant importance with the introduction of strained layers and SiGe channels into complementary metal-oxide semiconductor technology. However, alloy scattering has till now been treated in an empirical fashion with a fitting parameter. We present a theoretical model within the atomistic tight-binding representation for treating alloy scattering in SiGe. This approach puts the scattering model on a solid atomistic footing with physical insights. The approach is shown to inherently capture the bulk alloy scattering potential parameters for both n-type and p-type
carriers and matches experimental mobility data.

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First-Principles Analysis Of Zrn/Scn Metal/Semiconductor Superlattices For Thermoelectric Energy Conversion, Bivas Saha, Timothy D. Sands, Umesh V. Waghmare Apr 2011

First-Principles Analysis Of Zrn/Scn Metal/Semiconductor Superlattices For Thermoelectric Energy Conversion, Bivas Saha, Timothy D. Sands, Umesh V. Waghmare

Birck and NCN Publications

We present a first-principles density functional theory-based analysis of the electronic structure, vibrational spectra, and transport properties of ZrN/ScN metal/semiconductor superlattices aiming to understand its potential and suitability for thermoelectric applications. We demonstrate (a) the presence of Schottky barriers of 0.34 eV at the metal/semiconductor interface and (b) a large asymmetry in the electronic densities of states and flattening of electronic bands along the cross-plane directions near the Fermi energy of these superlattices, desirable for high Seebeck coefficient. The vibrational spectra of these superlattices show softening of transverse acoustic phonon modes along the growth direction and localization of ScN phonons …

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Decomposition Of Unitary Matrices For Finding Quantum Circuits: Application To Molecular Hamiltonians, Anmer Daskin, Sabre Kais Apr 2011

Decomposition Of Unitary Matrices For Finding Quantum Circuits: Application To Molecular Hamiltonians, Anmer Daskin, Sabre Kais

Birck and NCN Publications

Constructing appropriate unitary matrix operators for new quantum algorithms and finding the minimum cost gate sequences for the implementation of these unitary operators is of fundamental importance in the field of quantum information and quantum computation. Evolution of quantum circuits faces two major challenges: complex and huge search space and the high costs of simulating quantum circuits on classical computers. Here, we use the group leaders optimization algorithm to decompose a given unitary matrix into a proper-minimum cost quantum gate sequence. We test the method on the known decompositions of Toffoli gate, the amplification step of the Grover search algorithm, …

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