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  • American Institute of Physics (AIP)  (21)
  • 2015-2019  (17)
  • 1990-1994  (4)
  • 2016  (17)
  • 1993  (4)
  • 1
    Electronic Resource
    Electronic Resource
    Simulations of hydrogen deposition processes in a-Si:H film growth (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 3295-3298 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Molecular dynamics simulations of the deposition of atomic H on both c-Si and a-Si:H substrates are performed to understand the physical processes occurring in the presence of an atomic H flux during growth. The absorption probability, and dynamical behavior of the H are studied as a function of the incident H energy. Both hydrogen absorption and backscattering events are observed. The hydrogen reflection probability has a maximum around 50 eV and decreases at higher incident kinetic energies. In the hydrogen backscattering events a substantial subsurface penetration and energy transfer through collisions are observed. Hydrogen absorption events have been closely analyzed and a surface hydrogen release event was observed during an absorption event.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352977
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Path integral description of polymers using fractional Brownian walks (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 9230-9236 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The statistical properties of fractional Brownian walks are used to construct a path integral representation of the conformations of polymers with different degrees of bond correlation. We specifically derive an expression for the distribution function of the chains' end-to-end distance, and evaluate it by several independent methods, including direct evaluation of the discrete limit of the path integral, decomposition into normal modes, and solution of a partial differential equation. The distribution function is found to be Gaussian in the spatial coordinates of the monomer positions, as in the random walk description of the chain, but the contour variables, which specify the location of the monomer along the chain backbone, now depend on an index h, the degree of correlation of the fractional Brownian walk. The special case of h=1/2 corresponds to the random walk. In constructing the normal mode picture of the chain, we conjecture the existence of a theorem regarding the zeros of the Bessel function.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465539
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Si3N4/Si/n-GaAs capacitor with minimum interface density in the 1010 eV−1 cm−2 range (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 2977-2979 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report significant improvements in the electrical characteristics of Si3N4/Si/GaAs capacitors with the assistance of atomic hydrogen during the in situ growth of Si on GaAs. Si3N4/Si/GaAs capacitors have shown a minimum interface state density as low as 3×1010 eV−1 cm−2 as determined by the low-frequency capacitance method. The hysteresis and frequency dispersion in the GaAs metal-insulator-semiconductor capacitor are very small (200 and 100 meV, respectively). These results represent significant advances over previous reports.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.109162
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Si3N4/Si/In0.53Ga0.47As depletion-mode metal-insulator-semiconductor field-effect transistors with improved stability (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 3291-3293 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on the electrical characteristics of in situ deposited Si3N4/Si/In0.53Ga0.47As depletion-mode metal-insulator-semiconductor field-effect transistors (MISFETs). MISFETs with 2.2-μm gate lengths fabricated by a self-aligned gate process exhibited extrinsic transconductances of over 200 mS/mm. The drain current drifted by only 1% during the first 10 h of operation. This small shift is attributed to the reduction of traps at the interface by a pseudomorphic Si layer, incorporated at the interface between the dielectric and the In0.53Ga0.47As channel.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.109075
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  • 5
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    Effect of superheat and electric field on saturated film boiling (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-05-11
    Description: The objective of this investigation is to study the influence of superheat temperature and applied uniform electric field across the liquid-vapor interface during film boiling using a coupled level set and volume of fluid algorithm. The hydrodynamics of bubble growth, detachment, and its morphological variation with electrohydrodynamic forces are studied considering the medium to be incompressible, viscous, and perfectly dielectric at near critical pressure. The transition in interfacial instability behavior occurs with increase in superheat, the bubble release being periodic both in space and time. Discrete bubble growth occurs at a smaller superheat whereas vapor columns form at the higher superheat values. Destabilization of interfacial motion due to applied electric field results in decrease in bubble separation distance and increase in bubble release rate culminating in enhanced heat transfer rate. A comparison of maximum bubble height owing to application of different intensities of electric field is performed at a smaller superheat. The change in dynamics of bubble growth due to increasing superheat at a high intensity of electric field is studied. The effect of increasing intensity of electric field on the heat transfer rate at different superheats is determined. The boiling characteristic is found to be influenced significantly only above a minimum critical intensity of the electric field.
    Print ISSN: 1070-6631
    Electronic ISSN: 1089-7666
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 6
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    Effect of potassium doping on electronic structure and thermoelectric properties of topological crystalline insulator (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-05-10
    Description: Topological crystalline insulator (TCI), Pb 0.6 Sn 0.4 Te, exhibits metallic surface states protected by crystal mirror symmetry with negligibly small band gap. Enhancement of its thermoelectric performances needs tuning of its electronic structure particularly through engineering of its band gap. While physical perturbations tune the electronic structure of TCI by breaking of the crystal mirror symmetry, chemical means such as doping have been more attractive recently as they result in better thermoelectric performance in TCIs. Here, we demonstrate that K doping in TCI, Pb 0.6 Sn 0.4 Te, breaks the crystal mirror symmetry locally and widens electronic band gap, which is confirmed by direct electronic absorption spectroscopy and electronic structure calculations. K doping in Pb 0.6 Sn 0.4 Te increases p -type carrier concentration and suppresses the bipolar conduction via widening a band gap, which collectively boosts the thermoelectric figure of merit (ZT) to 1 at 708 K.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 7
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    Interface structure in nanoscale multilayers near continuous-to-discontinuous regime (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-07-28
    Description: Interfacial atomic diffusion, reaction, and formation of microstructure in nanoscale level are investigated in W/B 4 C multilayer (ML) system as functions of thickness in ultrathin limit. Hard x-ray reflectivity (XRR) and x-ray diffuse scattering in conjunction with x-ray absorption near edge spectroscopy (XANES) in soft x-ray and hard x-ray regimes and depth profiling x-ray photoelectron spectroscopy (XPS) have been used to precisely evaluate detailed interfacial structure by systematically varying the individual layer thickness from continuous-to-discontinuous regime. It is observed that the interfacial morphology undergoes an unexpected significant modification as the layer thickness varies from continuous-to-discontinuous regime. The interfacial atomic diffusion increases, the physical density of W layer decreases and that of B 4 C layer increases, and further more interestingly the in-plane correlation length decreases substantially as the layer thickness varies from continuous-to-discontinuous regime. This is corroborated using combined XRR and x-ray diffused scattering analysis. XANES and XPS results show formation of more and more tungsten compounds at the interfaces as the layer thickness decreases below the percolation threshold due to increase in the contact area between the elements. The formation of compound enhances to minimize certain degree of disorder at the interfaces in the discontinuous region that enables to maintain the periodic structure in ML. The degree of interfacial atomic diffusion, interlayer interaction, and microstructure is correlated as a function of layer thickness during early stage of film growth.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 8
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    Structural anomaly and dynamic heterogeneity in cycloether/water binary mixtures: Signatures from composition dependent dynamic fluorescence measurements and computer simulations (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-03-25
    Description: We have performed steady state UV-visible absorption and time-resolved fluorescence measurements and computer simulations to explore the cosolvent mole fraction induced changes in structural and dynamical properties of water/dioxane (Diox) and water/tetrahydrofuran (THF) binary mixtures. Diox is a quadrupolar solvent whereas THF is a dipolar one although both are cyclic molecules and represent cycloethers. The focus here is on whether these cycloethers can induce stiffening and transition of water H-bond network structure and, if they do, whether such structural modification differentiates the chemical nature (dipolar or quadrupolar) of the cosolvent molecules. Composition dependent measured fluorescence lifetimes and rotation times of a dissolved dipolar solute (Coumarin 153, C153) suggest cycloether mole-fraction (X THF/Diox ) induced structural transition for both of these aqueous binary mixtures in the 0.1 ≤ X THF/Diox ≤ 0.2 regime with no specific dependence on the chemical nature. Interestingly, absorption measurements reveal stiffening of water H-bond structure in the presence of both the cycloethers at a nearly equal mole-fraction, X THF/Diox ∼ 0.05. Measurements near the critical solution temperature or concentration indicate no role for the solution criticality on the anomalous structural changes. Evidences for cycloether aggregation at very dilute concentrations have been found. Simulated radial distribution functions reflect abrupt changes in respective peak heights at those mixture compositions around which fluorescence measurements revealed structural transition. Simulated water coordination numbers (for a dissolved C153) and number of H-bonds also exhibit minima around these cosolvent concentrations. In addition, several dynamic heterogeneity parameters have been simulated for both the mixtures to explore the effects of structural transition and chemical nature of cosolvent on heterogeneous dynamics of these systems. Simulated four-point dynamic susceptibility suggests formation of clusters inducing local heterogeneity in the solution structure.
    Print ISSN: 0021-9606
    Electronic ISSN: 1089-7690
    Topics: Chemistry and Pharmacology , Physics
    Published by American Institute of Physics (AIP)
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  • 9
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    Collective dynamic dipole moment and orientation fluctuations, cooperative hydrogen bond relaxations, and their connections to dielectric relaxation in ionic acetamide deep eutectics: Microscopic insight from simulations (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-08-31
    Description: The paper reports a detailed simulation study on collective reorientational relaxation, cooperative hydrogen bond (H-bond) fluctuations, and their connections to dielectric relaxation (DR) in deep eutectic solvents made of acetamide and three uni-univalent electrolytes, lithium nitrate (LiNO 3 ), lithium bromide (LiBr), and lithium perchlorate (LiClO 4 ). Because cooperative H-bond fluctuations and ion migration complicate the straightforward interpretation of measured DR timescales in terms of molecular dipolar rotations for these conducting media which support extensive intra- and inter-species H-bonding, one needs to separate out the individual components from the overall relaxation for examining the microscopic origin of various timescales. The present study does so and finds that reorientation of ion-complexed acetamide molecules generates relaxation timescales that are in sub-nanosecond to nanosecond range. This explains in molecular terms the nanosecond timescales reported by recent giga-Hertz DR measurements. Interestingly, the simulated survival timescale for the acetamide-Li + complex has been found to be a few tens of nanosecond, suggesting such a cation-complexed species may be responsible for a similar timescale reported by mega-Hertz DR measurements of acetamide/potassium thiocyanate deep eutectics near room temperature. The issue of collective versus single particle relaxation is discussed, and jump waiting time distributions are determined. Dependence on anion-identity in each of the cases has been examined. In short, the present study demonstrates that assumption of nano-sized domain formation is not required for explaining the DR detected nanosecond and longer timescales in these media.
    Print ISSN: 0021-9606
    Electronic ISSN: 1089-7690
    Topics: Chemistry and Pharmacology , Physics
    Published by American Institute of Physics (AIP)
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  • 10
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    Solvent organization around the perfluoro group of coumarin 153 governs its photophysical properties: An experimental and simulation study of coumarin dyes in ethanol as well as fluorinated ethanol solvents (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-05-13
    Description: The self-aggregation property of the perfluoro group containing molecules makes it important in the research fields of biology and polymer and organic synthesis. In the quest of understanding the role of the perfluoro group on the photophysical properties of perfluoro-containing molecules in biologically important fluoroethanol solvents, we have applied photophysical as well as molecular dynamics simulation techniques to explore the properties of perfluoro groups containing molecule coumarin-153 (C153) in ethanol (ETH), monofluoroethanol (MFE), difluoroethanol (DFE), and trifluoroethanol (TFE) and compared them with the molecules without perfluoro moiety, namely coumarin-6H (C6H) and coumarin-480 (C480). In contrast to C6H and C480, the excited state lifetime of C153 in fluorinated ETHs is not monotonic. The excited state lifetime of C153 decreases in MFE and DFE as compared to ETH, whereas in TFE, it increases as compared to MFE and DFE. Molecular dynamics simulation reveals that the carbon terminal away from the OH group of fluorinated ETHs has a preferential orientation near the perfluoro (CF 3 ) group of C153. In MFE and DFE, the CF 3 group of C153 prefers to have a CF 2 —F⋯H —(CHF) type of electrostatic interaction over CF 2 —F⋯F —(CH 2 ) kind of dispersion interaction which increases the rate of nonradiative decay, probably due to the electrostatic nature of the CF 2 —F⋯H —(CHF) hydrogen bond. On the other hand, in TFE, C—F⋯ F—C type of dispersion interaction, also known as fluorous interaction, takes place between the CF 3 groups of C153 and TFE which decreases the rate of nonradiative rate as compared to MFE and DFE, leading to the increased lifetime of C153 in TFE. Photophysical and MD simulation studies clearly depict that the structural organization of solvents and their interaction with the fluorocarbon group are crucial factors for the photophysical behavior of the fluorocarbon containing molecules.
    Print ISSN: 0021-9606
    Electronic ISSN: 1089-7690
    Topics: Chemistry and Pharmacology , Physics
    Published by American Institute of Physics (AIP)
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