The creation of supra-thermal densities of high-energy phonons in He II
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Phonon scattering
Phonon scattering
Surface phonon
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As nanostructured devices become prevalent, interfaces often play an important role in thermal transport phenomena. However, interfacial thermal transport remains poorly understood due to complex physics across a wide range of length scales from atomistic to microscale. Past studies on interfacial thermal resistance have focused on interface-phonon scattering at the atomistic scale but overlooked the complex interplay of phonon-interface and phonon-phonon scattering at microscale. Here, we use the Peierls-Boltzmann transport equation to show that the resistance from the phonon-phonon scattering of non-equilibrium phonons near a Si-Ge interface is much larger than that directly caused by the interface scattering. We report that non-equilibrium in phonon distribution leads to significant entropy generation and thermal resistance upon three-phonon scattering by the Boltzmann's H-theorem. The physical origin of non-equilibrium phonons in Ge is explained with the mismatch of phonon dispersion, density-of-states, and group velocity, which serve as general guidance for estimating the non-equilibrium effect on interfacial thermal resistance. Our study bridges a gap between atomistic scale and less studied microscale phenomena, providing comprehensive understanding of overall interfacial thermal transport and the significant role of phonon-phonon scattering.
Phonon scattering
Microscale chemistry
Interfacial thermal resistance
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Phonon bandgap typically has a significant effect on phonon–phonon scattering process. In this work, the effects of mass modified phonon bandgap in θ -phase TaN are systemically investigated by the means of first-principles calculations with linearized Boltzmann transport equation. Through detailed calculations, we find that phonon bandgap has a significant effect on three-phonon process while exhibits a much weaker effect on four-phonon process. The reason for the ultrahigh thermal conductivity of θ -phase TaN is the long lifetime of phonons including both three-phonon and four-phonon processes, which originates from the weak phonon anharmonicity and large phonon bandgap-induced small phonon–phonon scattering phase space. This work advances the understanding of phonon bandgap effects on phonon transport.
Phonon scattering
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In most materials the electron–phonon (e-p) scattering is far weaker than phonon–phonon (p-p) scattering, and the e-p scattering is usually proportional to the e-p coupling strength. Here, we report strong e-p scattering but low e-p coupling strength in two-dimensional(2D) Nb2C by first-principles calculations. Moreover, the intensity of e-p scattering is close to that of p-p scattering at 300 K in sharp contrast to normal cases. This abnormal e-p scattering is understood by a specific feature that the energy difference between occupied and empty electron states near the Fermi level is in the order of the characteristic phonon energy. By calculating the phonon transport property of 2D Nb2C, we show that this strong e-p scattering can result in great reduction in the lattice thermal conductivity.Our work also highlights a new way for searching novel 2D materials with low lattice thermal conductivity.
Phonon scattering
Lattice (music)
Electron scattering
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A theoretical model has been developed to investigate the effect of nonequilibrium phonons or hot phonons on the energy-loss rate of hot carriers in semiconductors in the extreme quantum limit at low temperatures. The acoustic-phonon scattering via the deformation potential and piezoelectric scattering are assumed to be the dominant scattering mechanisms at low temperatures. The model includes band nonparabolicity, energy nonequipartition of phonons, Landau-level broadening, and classical free-carrier screening. The energy-loss rates of hot electrons with nonequilibrium phonons as well as the thermal phonon distribution have been calculated using the above-mentioned model for n-type InSb. These theoretical results have also been compared with experimental results for n-type InSb at B=3 T and ${\mathit{T}}_{\mathit{L}}$=4.2 K. The energy-loss rate with the thermal phonon distribution is found to be much higher than the experimental result. The energy-loss rate of hot electrons calculated with use of the nonequilibrium phonon distribution with phonon boundary scattering is reduced compared with the values of the energy-loss rate obtained with use of the equilibrium phonon distribution. The incorporation of nonequilibrium phonons brings the theoretical results into agreement with the experimental data, giving a reasonable value for the phonon lifetime. However, the phonon lifetime required to fit the experimental data is found to be much higher than the values obtained from phonon boundary scattering. This discrepancy may be attributed to the acoustic-phonon mismatch factor.
Scattering rate
Phonon scattering
Surface phonon
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Abstract This chapter discusses major scattering processes found in semiconductors, including phonon scattering (deformation scattering, piezoelectric scattering, polar scattering and non-polar scattering), scattering arising from impurities (charged, so a Coulomb scattering, and charge neutral) and scattering arising in compositional randomness, from carrier-carrier events and due to coupled-particle interactions. The discussion starts by making connections between the classical scattering cross-section and its quantum-mechanical origins through the matrix elements for scattering. The ability to write the matrix element is employed for describing scattering by phonons in its various forms, for impurities and their various levels of accuracy of the description. Umklapp processes are described. When multiple scattering processes are present, the resulting transport manifests the processes’ independence and dependence. With an understanding of the scattering, observed behavior in semiconductors of interest is summarized to show their relative importance. The chapter concludes by discussing frequency and high field behavior manifested by electron ensembles.
Mott scattering
Phonon scattering
Biological small-angle scattering
Quasielastic scattering
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A scattering theory of one-dimensional electron gas formed in a narrow channel GaAs-AlGaAs high electron mobility transistor has been developed. The mobility values for the different scattering mechanisms have been computed and their variation with temperature has been presented. The various scattering processes include acoustic phonon scattering for both deformation potential and piezoelectric scattering mechanisms, impurity scattering, and surface roughness scattering at lower temperatures and polar optic phonon scattering at higher temperatures. The effect of dynamic screening has also been included. Finally, the temperature variation of thermopower for different 1D electron concentrations has been shown and attempts have been made to interpret the results obtained.
Phonon scattering
Electron Mobility
Electron scattering
Mott scattering
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Phonon scattering
Microscale chemistry
Interfacial thermal resistance
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Measurements have been obtained of the diffuse scattering of X-rays from an aluminium crystal over the temperature range 100-500 K. It is found that the scattering from transverse modes is as expected from the known phonon frequencies; neither anharmonicity nor atomic deformation with displacement from equilibrium position modifies this scattering. The scattering from longitudinal modes at medium values of the scattering vector is adequately represented by including the lowest order anharmonic process, but at high scattering vectors the next order anharmonic term must be included. At very low scattering vectors an additional contribution is found in the total intensity from longitudinal scattering vectors an additional contribution is found in the total intensity from longitudinal modes. The extra scattering is not associated with anharmonic behaviour although it is temperature dependent. It may be due to atomic deformation or electron-phonon interaction.
Phonon scattering
Mott scattering
Biological small-angle scattering
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Phonon scattering
Scattering rate
Strain (injury)
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