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Articles 211 - 240 of 541

Full-Text Articles in Nanoscience and Nanotechnology

Conductivity Of An Atomically Defined Metallic Interface, David J. Oliver, Jesse Maassen, Mehdi El Ouali, William Paul, Till Hagedorn, Yoichi Miyahara, Yue Qi, Hong Guo, Peter Gruetter Nov 2012

Conductivity Of An Atomically Defined Metallic Interface, David J. Oliver, Jesse Maassen, Mehdi El Ouali, William Paul, Till Hagedorn, Yoichi Miyahara, Yue Qi, Hong Guo, Peter Gruetter

Birck and NCN Publications

A mechanically formed electrical nanocontact between gold and tungsten is a prototypical junction between metals with dissimilar electronic structure. Through atomically characterized nanoindentation experiments and first-principles quantum transport calculations, we find that the ballistic conduction across this intermetallic interface is drastically reduced because of the fundamental mismatch between swave-likemodes of electron conduction in the gold and d wave-like modes in the tungsten. The mechanical formation of the junction introduces defects and disorder, which act as an additional source of conduction losses and increase junction resistance by up to an order of magnitude. These findings apply to nanoelectronics and semiconductor device …

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Nonlinear Dynamics Of The Atomic Force Microscope At The Liquid-Solid Interface, Daniel Kiracofe, Arvind Raman Nov 2012

Nonlinear Dynamics Of The Atomic Force Microscope At The Liquid-Solid Interface, Daniel Kiracofe, Arvind Raman

Birck and NCN Publications

The measurement of intermolecular forces at the liquid-solid interface is key to many studies of electrochemistry, wetting, catalysis, biochemistry, and mechanobiology. The atomic force microscope (AFM) is unique in its ability to measure and map these forces with nanometer resolution using the oscillating sharp tip of an AFM cantilever. These surface forces are only measured by observing the changes they induce in the dynamics of the resonant AFM probe. However, AFM cantilever dynamics at this interface can be significantly different when compared to air/vacuum environments due to the nature of nanoscale forces at the interface and the low-quality factors in …

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Nanobarcoding: Detecting Nanoparticles In Biological Samples Using In Situ Polymerase Chain Reaction, Trisha Eustaquio, James F. Leary Nov 2012

Nanobarcoding: Detecting Nanoparticles In Biological Samples Using In Situ Polymerase Chain Reaction, Trisha Eustaquio, James F. Leary

Birck and NCN Publications

Background: Determination of the fate of nanoparticles (NPs) in a biological system, or NP biodistribution, is critical in evaluating an NP formulation for nanomedicine. Current methods to determine NP biodistribution are greatly inadequate, due to their limited detection thresholds. Herein, proof of concept of a novel method for improved NP detection based on in situ polymerase chain reaction (ISPCR), coined "nanobarcoding," is demonstrated. Methods: Nanobarcoded superparamagnetic iron oxide nanoparticles (NB-SPIONs) were characterized by dynamic light scattering, zeta potential, and hyperspectral imaging - measurements. Cellular uptake of Cy5-labeled NB-SPIONs (Cy5-NB-SPIONs) was imaged by confocal microscopy. The feasibility of the nanobarcoding method …

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Topological Insulator Bi2te3 Films Synthesized By Metal Organic Chemical Vapor Deposition, Helin Cao, Rama Venkatasubramanian, Chang Liu, Jonathan Pierce, Haoran Yang, M. Zahid Hasan, Yue Wu, Yong P. Chen Oct 2012

Topological Insulator Bi2te3 Films Synthesized By Metal Organic Chemical Vapor Deposition, Helin Cao, Rama Venkatasubramanian, Chang Liu, Jonathan Pierce, Haoran Yang, M. Zahid Hasan, Yue Wu, Yong P. Chen

Birck and NCN Publications

Topological insulator (TI) materials such as Bi2Te3 and Bi2Se3 have attracted strong recent interests. Large scale, high quality TI thin films are important for developing TI-based device applications. In this work, structural and electronic properties of Bi2Te3 thin films deposited by metal organic chemical vapor deposition (MOCVD) on GaAs (001) substrates were characterized via x-ray diffraction (XRD), Raman spectroscopy, angle-resolved photoemission spectroscopy (ARPES), and electronic transport measurements. The characteristic topological surface states with a single Dirac cone have been clearly revealed in the electronic band structure measured by ARPES, confirming the TI nature of the MOCVD Bi2Te3 films. Resistivity and …

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A Band-Pass Filter Approach Within Molecular Dynamics For The Prediction Of Intrinsic Quality Factors Of Nanoresonators, Ajit K. Vallabhaneni, Xiulin Ruan, Jeff F. Rhoads, Jayathi Murthy Oct 2012

A Band-Pass Filter Approach Within Molecular Dynamics For The Prediction Of Intrinsic Quality Factors Of Nanoresonators, Ajit K. Vallabhaneni, Xiulin Ruan, Jeff F. Rhoads, Jayathi Murthy

Birck and NCN Publications

The temperature and frequency dependence of the flexural mode quality factors (Q) of doubly clamped single wall carbon nanotube resonators are calculated using classical molecular dynamics simulations. The validity of the various methods available in the literature for calculating Q based on the temporal response of the system during ring-down is discussed and the discrepancies associated with the methods are explained. A new approach based on band-pass filtering is proposed for calculating Q, which reveals classical temperature dependence (Q similar to T-1) in contrast to the previously reported results (Q similar to T-beta, 0 < beta < 1). It is shown that the Q estimated from the temporal response is in good agreement with the Q estimated from frequency response. This work also demonstrates that the proposed method is particularly advantageous when multiple modes are simultaneously excited within the linear regime. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4754450]

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Cu2o And Au/Cu2o Particles: Surface Properties And Applications In Glucose Sensing, Yu-Ho Won, Lia A. Stanciu Oct 2012

Cu2o And Au/Cu2o Particles: Surface Properties And Applications In Glucose Sensing, Yu-Ho Won, Lia A. Stanciu

Birck and NCN Publications

In this work we investigated the surface and facet-dependent catalytic properties of metal oxide particles as well as noble metal/metal oxide heterogeneous structures, with cuprous oxide (Cu2O) and Au/Cu2O being selected as model systems. As an example of application, we explored the potential of these materials in developing electrocatalytic devices. Cu2O particles were synthesized in various shapes, then used for testing their morphology-dependent electrochemical properties applied to the detection of glucose. While we did not attempt to obtain the best detection limit reported to date, the octahedral and hexapod Cu2O particles showed reasonable detection limits of 0.51 and 0.60 mM, …

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Cross-Plane Electronic And Thermal Transport Properties Of P-Type La0.67sr0.33mno3/Lamno3 Perovskite Oxide Metal/Semiconductor Superlattices, Pankaj Jha, Timothy D. Sands, Laura Cassels, Philip Jackson, Tela Favaloro, Benjamin Kirk, Joshua Zide, Xianfan Xu, Ali Shakouri Sep 2012

Cross-Plane Electronic And Thermal Transport Properties Of P-Type La0.67sr0.33mno3/Lamno3 Perovskite Oxide Metal/Semiconductor Superlattices, Pankaj Jha, Timothy D. Sands, Laura Cassels, Philip Jackson, Tela Favaloro, Benjamin Kirk, Joshua Zide, Xianfan Xu, Ali Shakouri

Birck and NCN Publications

Lanthanum strontium manganate (La0.67Sr0.33MnO3, i.e., LSMO)/lanthanum manganate (LaMnO3, i.e., LMO) perovskite oxide metal/semiconductor superlattices were investigated as a potential p-type thermoelectric material. Growth was performed using pulsed laser deposition to achieve epitaxial LSMO (metal)/LMO (p-type semiconductor) superlattices on (100)-strontium titanate (STO) substrates. The magnitude of the in-plane Seebeck coefficient of LSMO thin films (/K) is consistent with metallic behavior, while LMO thin films were p-type with a room temperature Seebeck coefficient of 140 mu V/K. Thermal conductivity measurements via the photo-acoustic (PA) technique showed that LSMO/LMO superlattices exhibit a room temperature cross-plane thermal conductivity (0.89 W/m.K) that is significantly lower …

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Improvement Of Near-Infrared Absorption Linewidth In Algan/Gan Superlattices By Optimization Of Delta-Doping Location, C. Edmunds, L. Tang, J. Shao, D. Li, M. Cervantes, G. Gardner, Dmitri Zakharov, Michael J. Manfra, O. Malis Sep 2012

Improvement Of Near-Infrared Absorption Linewidth In Algan/Gan Superlattices By Optimization Of Delta-Doping Location, C. Edmunds, L. Tang, J. Shao, D. Li, M. Cervantes, G. Gardner, Dmitri Zakharov, Michael J. Manfra, O. Malis

Birck and NCN Publications

We report a systematic study of the near-infrared intersubband absorption in AlGaN/GaN superlattices grown by plasma-assisted molecular-beam epitaxy as a function of Si-doping profile with and without delta-doping. The transition energies are in agreement with theoretical calculations including many-body effects. A dramatic reduction of the intersubband absorption linewidth is observed when the delta-doping is placed at the end of the quantum well. This reduction is attributed to the improvement of interface roughness. The linewidth dependence on interface roughness is well reproduced by a model that considers the distribution of well widths measured with transmission electron microscopy. (C) 2012 American Institute …

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Role Of Nanostructure On Reaction And Transport In Ni/Al Intermolecular Reactive Composites, Mathew J. Cherukara, Karthik Guda Vishnu, Alejandro Strachan Aug 2012

Role Of Nanostructure On Reaction And Transport In Ni/Al Intermolecular Reactive Composites, Mathew J. Cherukara, Karthik Guda Vishnu, Alejandro Strachan

Birck and NCN Publications

We use molecular dynamics to characterize the exothermic chemistry of Ni/Al nanolaminates for various temperatures, periodic lengths, and in the presence of extended defects. We show that the reaction is mass diffusion controlled for bulk nanolaminates, with the overall reaction time scaling with the square of the mean transport distance. The presence of voids or free surfaces not only leads to a significant decrease in reaction time (by as much as a factor of 5), but fundamentally changes the nature of the reaction. Free surfaces and voids running across several periods provide a mechanism for ballistic mass transport and change …

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Population And Coherence Dynamics In Light Harvesting Complex Ii (Lh2), Shu-Hao Yeh, Jing Zhu, Sabre Kais Aug 2012

Population And Coherence Dynamics In Light Harvesting Complex Ii (Lh2), Shu-Hao Yeh, Jing Zhu, Sabre Kais

Birck and NCN Publications

The electronic excitation population and coherence dynamics in the chromophores of the photosynthetic light harvesting complex 2 (LH2) B850 ring from purple bacteria (Rhodopseudomonas acidophila) have been studied theoretically at both physiological and cryogenic temperatures. Similar to the well-studied Fenna-Matthews-Olson (FMO) protein, oscillations of the excitation population and coherence in the site basis are observed in LH2 by using a scaled hierarchical equation of motion approach. However, this oscillation time (300 fs) is much shorter compared to the FMO protein (650 fs) at cryogenic temperature. Both environment and high temperature are found to enhance the propagation speed of the exciton …

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Direct Writing Of Au Nanoneedles Array On Glass By Confined Laser Spinning, Yingling Yang, Dong Lin, Gary J. Cheng Aug 2012

Direct Writing Of Au Nanoneedles Array On Glass By Confined Laser Spinning, Yingling Yang, Dong Lin, Gary J. Cheng

Birck and NCN Publications

Generation of gold nanoneedles on glass by confined laser spinning was explored by using a nanosecond pulsed laser. When the coated Au thin film was irradiated under the confinement of glass, gold nanoneedles were formed by spreading the molten liquid of gold under high pressure. The mechanism of the confined laser spinning process is studied. The maximum velocity and instability of molten liquid during confined laser spinning were estimated. The diameter of nanoneedles can be controlled by changing the thickness of coated gold thin film. Large scale of gold nanoneedles can be formed by this direct writing method and collected …

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Control Of Reflectance And Transmittance In Scattering And Curvilinear Hyperbolic Metamaterials, T. U. Tumkur, J. K. Kitur, B. Chu, Lei Gu, V. A. Podolskiy, Evgenii E. Narimanov, M. A. Noginov Aug 2012

Control Of Reflectance And Transmittance In Scattering And Curvilinear Hyperbolic Metamaterials, T. U. Tumkur, J. K. Kitur, B. Chu, Lei Gu, V. A. Podolskiy, Evgenii E. Narimanov, M. A. Noginov

Birck and NCN Publications

We demonstrate reduced reflectance in curvilinear lamellar hyperbolic metamaterials as well as planar hyperbolic metamaterials consisting of metal/dielectric multilayers, with scatterers deposited on the top. The reduced reflectance is accompanied by a significant enhancement in transmission along with non-reciprocity of transmittance in forward and backward propagating directions. The observed experimental behavior is qualitatively similar to the results of numerical solutions of Maxwell equations. The findings of this study pave the way to a variety of important applications, including broadband enhancement of light trapping in photovoltaic devices. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4746387]

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Multipartite Quantum Entanglement Evolution In Photosynthetic Complexes, Jing Zhu, Sabre Kais, Alan Aspuru-Guzik, Sam Rodriques, Ben Brock, Peter J. Love Aug 2012

Multipartite Quantum Entanglement Evolution In Photosynthetic Complexes, Jing Zhu, Sabre Kais, Alan Aspuru-Guzik, Sam Rodriques, Ben Brock, Peter J. Love

Birck and NCN Publications

We investigate the evolution of entanglement in the Fenna-Matthew-Olson (FMO) complex based on simulations using the scaled hierarchical equations of motion approach. We examine the role of entanglement in the FMO complex by direct computation of the convex roof. We use monogamy to give a lower bound for entanglement and obtain an upper bound from the evaluation of the convex roof. Examination of bipartite measures for all possible bipartitions provides a complete picture of the multipartite entanglement. Our results support the hypothesis that entanglement is maximum primary along the two distinct electronic energy transfer pathways. In addition, we note that …

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Electron Band Alignment At The Interface Of (100)Insb With Atomic-Layer Deposited Al2o3, H.Y. Chou, V. V. Afanas'ev, M. Houssa, A. Stesmans, Lin Dong, Peide Ye Aug 2012

Electron Band Alignment At The Interface Of (100)Insb With Atomic-Layer Deposited Al2o3, H.Y. Chou, V. V. Afanas'ev, M. Houssa, A. Stesmans, Lin Dong, Peide Ye

Birck and NCN Publications

From experiments on internal photoemission of electrons at the (100)InSb/Al2O3 interface, the top of the InSb valence band is found to be 3.05 +/- 0.10 eV below the oxide conduction band and corresponds to a conduction band offset of 2.9 +/- 0.1 eV. These results indicate that the top of valence band in InSb lies energetically at the same level as in GaSb and above the valence bands in InxGa1-xAs (0

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Size-Dependent Hardness Of Nanoscale Metallic Contacts From Molecular Dynamics Simulations, Hojin Kim, Alejandro Strachan Aug 2012

Size-Dependent Hardness Of Nanoscale Metallic Contacts From Molecular Dynamics Simulations, Hojin Kim, Alejandro Strachan

Birck and NCN Publications

We characterize how size and shape affects the hardness of nanoscale metallic contacts using large-scale molecular dynamics (MD) simulations. High-aspect-ratio contacts continue the experimentally observed trend of hardening with decreasing contact size down to the sub-10-nm regime. However, we find that this effect is shape dependent and the rate of hardening with decreasing contact size diminishes as the aspect ratio of the asperities becomes smaller. Interestingly, low-aspect-ratio asperities that can support simple dislocation glide exhibit softening with decreasing size. A detailed analysis of the MD trajectories reveals the dislocation mechanisms that govern these complex size effects.

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Nanoscale Contacts Between Semiconducting Nanowires And Metallic Graphenes, Seongmin Kim, David B. Janes, Sung-Yool Choi, Sanghyun Ju Jul 2012

Nanoscale Contacts Between Semiconducting Nanowires And Metallic Graphenes, Seongmin Kim, David B. Janes, Sung-Yool Choi, Sanghyun Ju

Birck and NCN Publications

Metal–semiconductor (M–S) junctions are important components in many semiconductor devices, and there is growing interest in realizing high quality M–S contacts that are optically transparent. In this paper, we present our investigations into the characteristics of M–S junction in a semiconducting ZnO nanowire that was directly grown on a multilayer graphene film (MGF). The synthesized nanowires were fabricated into two-terminal devices with MGF as one contact and Al as the other contact. By comparison with devices employing Al contacts at both ends, the nanowire resistivity and specific contact resistivity of the MGF–nanowire contact can be extracted. The extracted specific contact …

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Near Field Enhancement In Silver Nanoantenna-Superlens Systems, Zhengtong Liu, Erping Li, Vladimir M. Shalaev, Alexander V. Kildishev Jul 2012

Near Field Enhancement In Silver Nanoantenna-Superlens Systems, Zhengtong Liu, Erping Li, Vladimir M. Shalaev, Alexander V. Kildishev

Birck and NCN Publications

We demonstrate near field enhancement generation in silver nanoantenna-superlens systems via numerical modeling. Using near-field interference and global optimization algorithms, we can design nanoantenna-superlens systems with mismatched permittivities, whose performance can match those with matched permittivities. The systems studied here may find broad applications in the fields of sensing, such as field-enhanced fluorescence and surface-enhanced Raman scattering, and the methodology used here can be applied to the designing and optimization of other devices, such as two-dimensional near field focusing lens. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4732793]

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A Thermophone On Porous Polymeric Substrate, Girish Chitnis, Albert Kim, Seung Hyun Song, A. M. Jessop, J. S. Bolton, Babak Ziaie Jul 2012

A Thermophone On Porous Polymeric Substrate, Girish Chitnis, Albert Kim, Seung Hyun Song, A. M. Jessop, J. S. Bolton, Babak Ziaie

Birck and NCN Publications

In this Letter, we present a simple, low-temperature method for fabricating a wide-band (>80 kHz) thermo-acoustic sound generator on a porous polymeric substrate. We were able to achieve up to 80 dB of sound pressure level with an input power of 0.511 W. No significant surface temperature increase was observed in the device even at an input power level of 2.5 W. Wide-band ultrasonic performance, simplicity of structure, and scalability of the fabrication process make this device suitable for many ranging and imaging applications. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4737005]

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Cooling Of Photoexcited Carriers In Graphene By Internal And Substrate Phonons, Tony Low, Vasili Perebeinos, Raseong Kim, Marcus Freitag, Phaedon Avouris Jul 2012

Cooling Of Photoexcited Carriers In Graphene By Internal And Substrate Phonons, Tony Low, Vasili Perebeinos, Raseong Kim, Marcus Freitag, Phaedon Avouris

Birck and NCN Publications

We investigate the energy relaxation of hot carriers produced by photoexcitation of graphene through coupling to both intrinsic and remote ( substrate) surface polar phonons using the Boltzmann equation approach. We find that the energy relaxation of hot photocarriers in graphene on commonly used polar substrates, under most conditions, is dominated by remote surface polar phonons. We also calculate key characteristics of the energy relaxation process, such as the transient cooling time and steady-state carrier temperatures and photocarrier densities, which determine the thermoelectric and photovoltaic photoresponse, respectively. Substrate engineering can be a promising route to efficient optoelectronic devices driven by …

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Does The Low Hole Transport Mass In <110> And <111> Si Nanowires Lead To Mobility Enhancements At High Field And Stress: A Self-Consistent Tight-Binding Study, R. L. Kotlyar, T. D. Linton, R. Rios, M. D. Giles, S. M. Cea, K. J. Kuhn, Michael Povolotskyi, Tillmann Kubis, Gerhard Klimeck Jun 2012

Does The Low Hole Transport Mass In <110> And <111> Si Nanowires Lead To Mobility Enhancements At High Field And Stress: A Self-Consistent Tight-Binding Study, R. L. Kotlyar, T. D. Linton, R. Rios, M. D. Giles, S. M. Cea, K. J. Kuhn, Michael Povolotskyi, Tillmann Kubis, Gerhard Klimeck

Birck and NCN Publications

The hole surface roughness and phonon limited mobility in the silicon h100i, h110i, and h111i square nanowires under the technologically important conditions of applied gate bias and stress are studied with the self-consistent Poisson-sp3d5s*-SO tight-binding bandstructure method. Under an applied gate field, the hole carriers in a wire undergo a volume to surface inversion transition diminishing the positive effects of the high h110i and h111i valence band nonparabolicities, which are known to lead to the large gains of the phonon limited mobility at a zero field in narrow wires. Nonetheless, the hole mobility in the unstressed wires down to the …

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Repeatable Low-Temperature Negative-Differential Resistance From Al0.18ga0.82n/Gan Resonant Tunneling Diodes Grown By Molecular-Beam Epitaxy On Free-Standing Gan Substrates, D. Li, L. Tang, C. Edmunds, J. Shao, G. Gardner, Michael J. Manfra, O. Malis Jun 2012

Repeatable Low-Temperature Negative-Differential Resistance From Al0.18ga0.82n/Gan Resonant Tunneling Diodes Grown By Molecular-Beam Epitaxy On Free-Standing Gan Substrates, D. Li, L. Tang, C. Edmunds, J. Shao, G. Gardner, Michael J. Manfra, O. Malis

Birck and NCN Publications

Low-aluminum composition AlGaN/GaN double-barrier resonant tunneling structures were grown by plasma-assisted molecular-beam-epitaxy on free-standing c-plane GaN substrates grown by hydride-vapor phase epitaxy. Clear, exactly reproducible, negative-differential resistance signatures were observed from 4 x 4 mu m(2) devices at 1.5V and 1.7V at 77K. The relatively small value of the maximum peak-to-valley ratio (1.03) and the area dependence of the electrical characteristics suggest that charge transport is affected by leakage paths through dislocations. However, the reproducibility of the data indicates that electrical traps play no significant role in the charge transport in resonant tunneling diodes grown by molecular-beam-epitaxy under Ga-rich conditions …

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Single-Molecule Tools Elucidate H2a.Z Nucleosome Composition, Jiji Chen, Andrew Miller, Ann L. Kirchmaier, Joseph M.K. Irudayaraj Jun 2012

Single-Molecule Tools Elucidate H2a.Z Nucleosome Composition, Jiji Chen, Andrew Miller, Ann L. Kirchmaier, Joseph M.K. Irudayaraj

Birck and NCN Publications

Although distinct epigenetic marks correlate with different chromatin states, how they are integrated within single nucleosomes to generate combinatorial signals remains largely unknown. We report the successful implementation of single molecule tools constituting fluorescence correlation spectroscopy (FCS), pulse interleave excitation-based Forster resonance energy transfer (PIE-FRET) and fluorescence lifetime imaging-based FRET (FLIM-FRET) to elucidate the composition of single nucleosomes containing histone variant H2A.Z (Htz1p in yeast) in vitro and in vivo. We demonstrate that yeast nucleosomes containing Htz1p are primarily composed of H4 K12ac and H3 K4me3 but not H3 K36me3 and that these patterns are conserved in mammalian cells. Quantification …

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Analysis Of Thermal Conductance Of Ballistic Point Contacts, Changwook Jeong, Mark S. Lundstrom Jun 2012

Analysis Of Thermal Conductance Of Ballistic Point Contacts, Changwook Jeong, Mark S. Lundstrom

Birck and NCN Publications

Substantial reduction of thermal conductance (K-ph) was recently reported for air gap heterostructures (AGHs) in which two bulk layers were connected by low-density nanopillars. We analyze K-ph using a full phonon dispersion and including important phonon scattering. We find a transition from ballistic at low temperatures to quasi-ballistic transport near room temperature and explain the slow roll-off in K-ph that occurs near room temperature. We show that the density of nanopillars deduced from the analysis depends strongly on the phonon dispersion assumed. Our model provides a good agreement with experiment that will be necessary to design AGHs for thermoelectric applications. …

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The Effects Of Diameter And Chirality On The Thermal Transport In Free-Standing And Supported Carbon-Nanotubes, Bo Qiu, Yan Wang, Xiulin Ruan, Qing Zhao Jun 2012

The Effects Of Diameter And Chirality On The Thermal Transport In Free-Standing And Supported Carbon-Nanotubes, Bo Qiu, Yan Wang, Xiulin Ruan, Qing Zhao

Birck and NCN Publications

We use molecular dynamics simulations to explore the lattice thermal transport in free-standing and supported single-wall carbon-nanotube (SWCNT) in comparison to that in graphene nanoribbon and graphene sheet. For free-standing SWCNT, the lattice thermal conductivity increases with diameter and approaches that of graphene, partly due to the curvature. Supported SWCNT thermal conductivity is reduced by 34%-41% compared to the free-standing case, which is less than that in supported graphene. Also, it shows an evident chirality dependence by varying about 10%, which we attribute to chirality-dependent interfacial phonon scattering. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4725194]

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On The Best Bandstructure For Thermoelectric Performance: A Landauer Perspective, Changwook Jeong, Raseong Kim, Mark S. Lundstrom Jun 2012

On The Best Bandstructure For Thermoelectric Performance: A Landauer Perspective, Changwook Jeong, Raseong Kim, Mark S. Lundstrom

Birck and NCN Publications

The question of what bandstructure produces the best thermoelectric device performance is revisited from a Landauer perspective. We find that a delta-function transport distribution function (TDF) results in operation at the Mahan-Sofo upper limit for the thermoelectric figure-of-merit, ZT. We show, however, the Mahan-Sofo upper limit itself depends on the bandwidth (BW) of the dispersion, and therefore, a finite BW dispersion produces a higher ZT when the lattice thermal conductivity is finite. Including a realistic model for scattering profoundly changes the results. Instead of a narrow band, we find that a broad BW is best. The prospects of increasing ZT …

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Parametric Noise Squeezing And Parametric Resonance Of Microcantilevers In Air And Liquid Environments, Gyan Prakash, Arvind Raman, Jeff F. Rhoads, Ronald G. Reifenberger Jun 2012

Parametric Noise Squeezing And Parametric Resonance Of Microcantilevers In Air And Liquid Environments, Gyan Prakash, Arvind Raman, Jeff F. Rhoads, Ronald G. Reifenberger

Birck and NCN Publications

In this work, parametric noise squeezing and parametric resonance are realized through the use of an electronic feedback circuit to excite a microcantilever with a signal proportional to the product of the microcantilever's displacement and a harmonic signal. The cantilever's displacement is monitored using an optical lever technique. By adjusting the gain of an amplifier in the feedback circuit, regimes of parametric noise squeezing/amplification and the principal and secondary parametric resonances of fundamental and higher order eigenmodes can be easily accessed. The exceptionally symmetric amplitude response of the microcantilever in the narrow frequency bandwidth is traced to a nonlinear parametric …

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Quantized Hall Effect And Shubnikov-De Haas Oscillations In Highly Doped Bi2se3: Evidence For Layered Transport Of Bulk Carriers, Helin Cao, Jifa Tian, Ireneusz Miotkowski, Tian Shen, Jiuning Hu, Shan Qiao, Yong P. Chen May 2012

Quantized Hall Effect And Shubnikov-De Haas Oscillations In Highly Doped Bi2se3: Evidence For Layered Transport Of Bulk Carriers, Helin Cao, Jifa Tian, Ireneusz Miotkowski, Tian Shen, Jiuning Hu, Shan Qiao, Yong P. Chen

Birck and NCN Publications

Bi2Se3 is an important semiconductor thermoelectric material and a prototype topological insulator. Here we report observation of Shubnikov-de Hass oscillations accompanied by quantized Hall resistances (R-xy) in highly doped n-type Bi2Se3 with bulk carrier concentrations of few 10(19) cm(-3). Measurements under tilted magnetic fields show that the magnetotransport is 2D-like, where only the c-axis component of the magnetic field controls the Landau level formation. The quantized step size in 1/R-xy is found to scale with the sample thickness, and average similar to e(2)/h per quintuple layer. We show that the observed magnetotransport features do not come from the sample surface, …

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Amorphous Ni/Al Nanoscale Laminates As High-Energy Intermolecular Reactive Composites, Karthik Guda Vishnu, Mathew Cherukara, Hojin Kim, Alejandro Strachan May 2012

Amorphous Ni/Al Nanoscale Laminates As High-Energy Intermolecular Reactive Composites, Karthik Guda Vishnu, Mathew Cherukara, Hojin Kim, Alejandro Strachan

Birck and NCN Publications

We use molecular dynamics simulations to explore the potential use of amorphous metals in intermolecular reactive composites. Our simulations show that amorphous Ni/Al nanolaminates lead to an increase in temperature of up to 260 K over their crystalline counterparts; this increase corresponds to over 20% of the heat of fusion and can be explained in terms of the amorphization energy. The reactions are diffusion controlled and crystallization is observed in laminates with relatively long periods where high temperatures are experienced for sufficiently long times prior to intermixing; the effect of this process on the energetics and time involved in the …

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Two-Temperature Nonequilibrium Molecular Dynamics Simulation Of Thermal Transport Across Metal-Nonmetal Interfaces, Yan Wang, Xiulin Ruan, Ajit K. Roy May 2012

Two-Temperature Nonequilibrium Molecular Dynamics Simulation Of Thermal Transport Across Metal-Nonmetal Interfaces, Yan Wang, Xiulin Ruan, Ajit K. Roy

Birck and NCN Publications

We have used a two-temperature nonequilibrium molecular dynamics method for predicting interfacial thermal resistance across metal-nonmetal interfaces. This method is an extension of the conventional nonequilibrium molecular dynamics for the dielectric-dielectric interface, where a temperature bias is imposed and the heat current is derived. We have included the electron degree of freedom for the interfacial thermal transport problem by treating the electron-phonon coupling with the two-temperature model. The method is demonstrated on two model systems, that is, silicon-copper interface and carbon-nanotube-copper interface. Temperature nonequilibrium between electrons and phonons in the metal side is quantitatively predicted, and a temperature drop across …

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Reduction Of Spectral Phonon Relaxation Times From Suspended To Supported Graphene, Bo Qiu, Xiulin Ruan May 2012

Reduction Of Spectral Phonon Relaxation Times From Suspended To Supported Graphene, Bo Qiu, Xiulin Ruan

Birck and NCN Publications

We have performed molecular dynamics simulations with phonon spectral analysis to predict the mode-wise phonon relaxation times (RT) of suspended and supported graphene at room temperature, and the findings are consistent with recent optical measurements. For acoustic phonons, RTs reduce from up to 50 ps to less than 5 ps when graphene is put on silicon dioxide substrate. Similarly, optical phonon RTs reduce by half when supported. Stronger interfacial bonding is found to result in more RT reduction. Our results provide a fundamental understanding at the spectral phonon property level for the observed thermal conductivity reduction in supported graphene. (C) …

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