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Mean free path

About: Mean free path is a research topic. Over the lifetime, 4412 publications have been published within this topic receiving 114418 citations.


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TL;DR: In this article, the phonon dispersion and phonon lifetime of single layer graphene were extracted from a molecular dynamics simulation and the mode dependent thermal conductivity was calculated from phonon kinetic theory, showing that the relative contribution of different mode phonons is not sensitive to the grain size of graphene.
Abstract: Molecular dynamics simulation is performed to extract the phonon dispersion and phonon lifetime of single layer graphene. The mode dependent thermal conductivity is calculated from the phonon kinetic theory. The predicted thermal conductivity at room temperature exhibits important quantum effects due to the high Debye temperature of graphene. But the quantum effects are reduced significantly when the simulated temperature is as high as 1000 K. Our calculations show that out-of-plane modes contribute about 41.1% to the total thermal conductivity at room temperature. The relative contribution of out-of-plane modes has a little decrease with the increase of temperature. Contact with substrate can reduce both the total thermal conductivity of graphene and the relative contribution of out-of-plane modes, in agreement with previous experiments and theories. Increasing the coupling strength between graphene and substrate can further reduce the relative contribution of out-of-plane modes. The present investigations also show that the relative contribution of different mode phonons is not sensitive to the grain size of graphene. The obtained phonon relaxation time provides useful insight for understanding the phonon mean free path and the size effects in graphene.

70 citations

Journal ArticleDOI
TL;DR: An extension of the well-known coherent-potential approximation is developed for the study of various properties of random arrangements of spherical dielectric scatterers and suggests that the positions of the band gaps in periodic dielectic structures are closely related with the range of localized states in random dielectrics media.
Abstract: An extension of the well-known coherent-potential approximation is developed for the study of various properties of random arrangements of spherical dielectric scatterers. Some of the short-range order is taken into account by considering a coated sphere as the basic scattering unit. A generalization of the energy-transport velocity is obtained. The validity of our approach is checked by comparison with experimental results, as well as with numerical calculations. Results for the long-wavelength effective dielectric constant, phase velocity, energy-transport velocity, mean free path, and diffusion coefficient are presented and compared with experiments on scattering from dielectric spheres. In addition, our findings suggest that the positions of the band gaps in periodic dielectric structures are closely related with the range of localized states in random dielectric media.

70 citations

Journal ArticleDOI
TL;DR: The results of this paper verify that the authors have an excellent understanding of the SRD algorithm at the kinetic level and that analytic expressions for the transport coefficients derived elsewhere do indeed provide a very accurate description of theSRD fluid.
Abstract: The dynamic structure factor, vorticity and entropy density dynamic correlation functions are measured for stochastic rotation dynamics (SRD), a particle based algorithm for fluctuating fluids. This allows us to obtain unbiased values for the longitudinal transport coefficients such as thermal diffusivity and bulk viscosity. The results are in good agreement with earlier numerical and theoretical results, and it is shown for the first time that the bulk viscosity is indeed zero for this algorithm. In addition, corrections to the self-diffusion coefficient and shear viscosity arising from the breakdown of the molecular chaos approximation at small mean free paths are analyzed. In addition to deriving the form of the leading correlation corrections to these transport coefficients, the probabilities that two and three particles remain collision partners for consecutive time steps are derived analytically in the limit of small mean free path. The results of this paper verify that we have an excellent understanding of the SRD algorithm at the kinetic level and that analytic expressions for the transport coefficients derived elsewhere do indeed provide a very accurate description of the SRD fluid.

69 citations

Journal ArticleDOI
TL;DR: In this paper, the attenuation parameter (AP) was calculated for 45 elements (Be, C, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Sr, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, Ba, La, Hf, Ta, W, Re, Os, Ir, Pt, Au, Pb) and
Abstract: The attenuation parameter (AP), which quantitatively describes the influence of elastic electron scattering on the electron spectroscopies, has been calculated for 45 elements (Be, C, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Sr, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, Ba, La, Hf, Ta, W, Re, Os, Ir, Pt, Au, Pb) and for energies of 250, 500, 1000 and 1500 eV. The calculations were performed with a Monte Carlo algorithm in which elastic scattering is modelled by use of the partial wave expansion method. The results show a linear relationship between the AP and the inelastic mean free path (IMFP), and a linear least-squares fit of the data provides a simple formula to calculate the AP for a given material and energy. The depth distribution function (DDF), which in the most general sense discribes the attenuation properties of signal electrons, can be calculated analytically using this AP. The possibility of using the calculated AP values in combination with this DDF to extract IMFP data from an overlayer experiment has also been explored. Evidence is found, and discussed, that the presentedalgorithm can be used to convert IMFPs to attenuation lengths (AL).

69 citations

Journal ArticleDOI
TL;DR: The electrical resistivity and the Seebeck coefficient of thermally evaporated thin bismuth films of thicknesses from 300 to 1900 A\r{} have been measured and the latter is negative and its magnitude is found to increase initially with increasing temperature, reach a maximum, and then decrease with a further rise in temperature.
Abstract: The electrical resistivity and the Seebeck coefficient of thermally evaporated thin bismuth films of thicknesses from 300 to 1900 A\r{} have been measured in the temperature range 300--470 K. The latter is negative and its magnitude is found to increase initially with increasing temperature, reach a maximum, and then decrease with a further rise in temperature. The temperature at which the Seebeck coefficient is maximum is found to be thickness dependent, decreasing with increasing thickness. The observed dependence is explained by considering that the Fermi energy is temperature dependent. Bismuth films show a negative temperature coefficient of resistivity. The thickness dependence of the electrical resistivity and the Seebeck coefficient of simultaneously prepared films are analyzed using the newer effective mean-free-path model. From the analysis, important material constants like the mean free path, the electron concentration, and the effective mass of electrons have been evaluated.

69 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202375
2022207
2021134
2020114
2019113
201887