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  • Articles  (39,767)
  • 2010-2014  (37,560)
  • 1955-1959  (2,207)
  • Journal of Applied Physics  (15,963)
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  • Articles  (39,767)
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  • 1
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    A molecular dynamics study of tilt grain boundary resistance to slip and heat transfer in nanocrystalline silicon (2014)
    American Institute of Physics (AIP)
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    Publication Date: 2014-12-31
    Description: We present a molecular dynamics study of grain boundary (GB) resistance to dislocation-mediated slip transfer and phonon-mediated heat transfer in nanocrystalline silicon bicrystal. Three most stable ⟨110⟩ tilt GBs in silicon are investigated. Under mechanical loading, the nucleation and growth of hexagonal-shaped shuffle dislocation loops are reproduced. The resistances of different GBs to slip transfer are quantified through their constitutive responses. Results show that the Σ3 coherent twin boundary (CTB) in silicon exhibits significantly higher resistance to dislocation motion than the Σ9 GB in glide symmetry and the Σ19 GB in mirror symmetry. The distinct GB strengths are explained by the atomistic details of the dislocation-GB interaction. Under thermal loading, based on a thermostat-induced heat pulse model, the resistances of the GBs to transient heat conduction in ballistic-diffusive regime are characterized. In contrast to the trend found in the dislocation-GB interaction in bicrystal models with different GBs, the resistances of the same three GBs to heat transfer are strikingly different. The strongest dislocation barrier Σ3 CTB is almost transparent to heat conduction, while the dislocation-permeable Σ9 and Σ19 GBs exhibit larger resistance to heat transfer. In addition, simulation results suggest that the GB thermal resistance not only depends on the GB energy but also on the detailed atomic structure along the GBs.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
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  • 2
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    Si doping effects on (In,Ga)N nanowires (2014)
    American Institute of Physics (AIP)
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    Publication Date: 2014-12-31
    Description: Si doped (In,Ga)N nanowires (In content up to 0.4) are grown on Si(111) substrates by plasma-assisted molecular beam epitaxy. By increasing the Si doping level, coalescence between nanowires is reduced and a more uniform morphology is obtained. The Raman spectra from highly doped samples show a characteristic broad band in the optical phonon frequency range, which became more prominent at higher doping levels. This Raman band can be explained by plasmon-phonon scattering from a free electron gas with strong wave-vector nonconservation, providing evidence for successful n-type doping. The measured plasmon-phonon modes are explained by lineshape simulations taking into account the simultaneous contribution of both the charge-density fluctuation and the impurity induced Fröhlich scattering mechanisms. The according lineshape analysis allows for an estimate of the carrier concentration.
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  • 3
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    Enhanced power factor of higher manganese silicide via melt spin synthesis method (2014)
    American Institute of Physics (AIP)
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    Publication Date: 2014-12-31
    Description: We report on the thermoelectric properties of the higher manganese silicide MnSi 1.75 synthesized by means of a one-step non-equilibrium method. The ultrahigh cooling rate generated from the melt-spin technique is found to be effective in reducing second phases, which are inevitable during the traditional solid state diffusion processes. Aside from being detrimental to thermoelectric properties, second phases skew the revealing of the intrinsic properties of this class of materials, for example, the optimal level of carrier concentration. With this melt-spin sample, we are able to formulate a simple model based on a single parabolic band that can well describe the carrier concentration dependence of the Seebeck coefficient and power factor of the data reported in the literature. An optimal carrier concentration around 5 × 10 20  cm −3 at 300 K is predicted according to this model. The phase-pure melt-spin sample shows the largest power factor at high temperature, resulting in the highest zT value among the three samples in this paper.
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  • 4
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    Strong correlation between oxygen vacancy and ferromagnetism in Yb-doped ZnO thin films (2014)
    American Institute of Physics (AIP)
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    Publication Date: 2014-12-31
    Description: Zn 1−x Yb x O (0 ≤ x ≤ 0.02) thin films have been prepared by inductively coupled plasma enhanced physical vapor deposition method. All the Yb-doped ZnO thin films show room-temperature ferromagnetism. The correlation between oxygen vacancy and magnetism in Yb-doped ZnO thin films is studied. It is found that Yb irons initially substitute for Zn sites when x ≤ 0.01 and then enter the interstitial sites of ZnO with increasing Yb concentration of x 〉 0.01. The ferromagnetism is induced by the coexistence of oxygen vacancy and Yb point defects. A strong correlation between oxygen vacancy and saturation magnetization is observed.
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  • 5
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    A two-parameter nondiffusive heat conduction model for data analysis in pump-probe experiments (2014)
    American Institute of Physics (AIP)
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    Publication Date: 2014-12-31
    Description: Nondiffusive heat transfer has attracted intensive research interests in last 50 years because of its importance in fundamental physics and engineering applications. It has unique features that cannot be described by the Fourier law. However, current studies of nondiffusive heat transfer still focus on studying the effective thermal conductivity within the framework of the Fourier law due to a lack of a well-accepted replacement. Here, we show that nondiffusive heat conduction can be characterized by two inherent material properties: a diffusive thermal conductivity and a ballistic transport length. We also present a two-parameter heat conduction model and demonstrate its validity in different hotspot-size-dependent heat transfer experiments. This model not only offers new insights of nondiffusive heat conduction but also opens up new avenues for the studies of nondiffusive heat transfer outside the framework of the Fourier law.
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  • 6
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    The origin of 2.7 eV blue luminescence band in zirconium oxide (2014)
    American Institute of Physics (AIP)
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    Publication Date: 2014-12-31
    Description: The luminescence spectra of non-stoichiometric zirconium oxide film series with different oxygen vacancies' concentrations show the blue photoluminescence band centered near a 2.7 eV peak. There is a broad band at 5.2 eV in the luminescence excitation spectrum for blue emission. The ab-initio quantum-chemical calculation gives a peak in the optical absorption at 5.1 eV for the oxygen vacancy in cubic ZrO 2 . It was concluded that the 2.7 eV blue luminescence excited near 5.2 eV in a zirconium oxide film is associated with the oxygen vacancy.
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  • 7
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    Geometric treatment of conduction electron scattering by crystal lattice strains and dislocations (2014)
    American Institute of Physics (AIP)
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    Publication Date: 2014-12-31
    Description: The problem of conduction electron scattering by inhomogeneous crystal lattice strains is addressed using a tight-binding formalism and the differential geometric treatment of deformations in solids. In this approach, the relative positions of neighboring atoms in a strained lattice are naturally taken into account, even in the presence of crystal dislocations, resulting in a fully covariant Schrödinger equation in the continuum limit. Unlike previous work, the developed formalism is applicable to cases involving purely elastic strains as well as discrete and continuous distributions of dislocations—in the latter two cases, it clearly demarcates the effects of the dislocation strain field and core. It also differentiates between elastic and plastic strain contributions, respectively. The electrical resistivity due to the strain field of edge dislocations is then evaluated and the resulting numerical estimate for Cu shows good agreement with reported experimental values. This indicates that the electrical resistivity of edge dislocations in metals is not entirely due to the core, contrary to current models. Application to the study of strain effects in constrained quantum systems is also discussed.
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  • 8
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    Preferred orientations of laterally grown silicon films over amorphous substrates using the vapor–liquid–solid technique (2014)
    American Institute of Physics (AIP)
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    Publication Date: 2014-12-31
    Description: A novel method has been optimized so that adhesion layers are no longer needed to reliably deposit patterned gold structures on amorphous substrates. Using this technique allows for the fabrication of amorphous oxide templates known as micro-crucibles, which confine a vapor–liquid–solid (VLS) catalyst of nominally pure gold to a specific geometry. Within these confined templates of amorphous materials, faceted silicon crystals have been grown laterally. The novel deposition technique, which enables the nominally pure gold catalyst, involves the undercutting of an initial chromium adhesion layer. Using electron backscatter diffraction it was found that silicon nucleated in these micro-crucibles were 30% single crystals, 45% potentially twinned crystals and 25% polycrystals for the experimental conditions used. Single, potentially twinned, and polycrystals all had an aversion to growth with the {1 0 0} surface parallel to the amorphous substrate. Closer analysis of grain boundaries of potentially twinned and polycrystalline samples revealed that the overwhelming majority of them were of the 60° Σ3 coherent twin boundary type. The large amount of coherent twin boundaries present in the grown, two-dimensional silicon crystals suggest that lateral VLS growth occurs very close to thermodynamic equilibrium. It is suggested that free energy fluctuations during growth or cooling, and impurities were the causes for this twinning.
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  • 9
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    Low- and high-order harmonic generation in the extended plasmas produced by laser ablation of zinc and manganese targets (2014)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2014-12-31
    Description: The systematic studies of the harmonic generation of ultrashort laser pulses in the 5-mm-long Zn and Mn plasmas (i.e., application of nanosecond, picosecond, and femtosecond pulses for ablation, comparison of harmonic generation from atomic, ionic, and cluster-contained species of plasma, variation of plasma length, two-color pump of plasmas, etc.) are presented. The conversion efficiency of the 11th–19th harmonics generated in the Zn plasma was ∼5 × 10 −5 . The role of the ionic resonances of Zn near the 9th and 10th harmonics on the enhancement of harmonics is discussed. The enhancement of harmonics was also analyzed using the two-color pump of extended plasmas, which showed similar intensities of the odd and even harmonics along the whole range of generation. The harmonics up to the 107th order were demonstrated in the case of manganese plasma. The comparison of harmonic generation in the 5-mm-long and commonly used short (≤0.5 mm) plasma plumes showed the advanced properties of extended media.
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  • 10
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    Single molecule transistor based nanopore for the detection of nicotine (2014)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2014-12-31
    Description: A nanopore based detection methodology was proposed and investigated for the detection of Nicotine. This technique uses a Single Molecular Transistor working as a nanopore operational in the Coulomb Blockade regime. When the Nicotine molecule is pulled through the nanopore area surrounded by the Source(S), Drain (D), and Gate electrodes, the charge stability diagram can detect the presence of the molecule and is unique for a specific molecular structure. Due to the weak coupling between the different electrodes which is set by the nanopore size, the molecular energy states stay almost unaffected by the electrostatic environment that can be realised from the charge stability diagram. Identification of different orientation and position of the Nicotine molecule within the nanopore area can be made from specific regions of overlap between different charge states on the stability diagram that could be used as an electronic fingerprint for detection. This method could be advantageous and useful to detect the presence of Nicotine in smoke which is usually performed using chemical chromatography techniques.
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