Topic
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.
Papers published on a yearly basis
Papers
More filters
••
TL;DR: In this article, thermal conductivity measurements of thin Si membranes spanning a wide thickness range were used to characterize how bulk thermal conductivities are distributed over phonon mean free paths, and a noncontact transient thermal grating technique was used to measure the thermal conductive of suspended Si membranes ranging from 15-1500 nm in thickness.
Abstract: Knowledge of the mean-free-path distribution of heat-carrying phonons is key to understanding phonon-mediated thermal transport. We demonstrate that thermal conductivity measurements of thin membranes spanning a wide thickness range can be used to characterize how bulk thermal conductivity is distributed over phonon mean free paths. A noncontact transient thermal grating technique was used to measure the thermal conductivity of suspended Si membranes ranging from 15--1500 nm in thickness. A decrease in the thermal conductivity from 74--13% of the bulk value is observed over this thickness range, which is attributed to diffuse phonon boundary scattering. Due to the well-defined relation between the membrane thickness and phonon mean-free-path suppression, combined with the range and accuracy of the measurements, we can reconstruct the bulk thermal conductivity accumulation vs. phonon mean free path, and compare with theoretical models.
125 citations
••
TL;DR: In this article, it was shown that dislocations in germanium act as rows of closely spaced acceptor centres, and the mobility normal to the dislocation will be reduced because of the space charge cylinders deflecting electrons and scatter the electron momentum normal.
Abstract: Experiments suggest that dislocations in germanium act as rows of closely spaced acceptor centres. In n-type material a dislocation accepts electrons and becomes a line of negative charge surrounded by a cylindrical region of fixed positive space charge. An array of parallel dislocations will have relatively little effect on electron mobility parallel to the dislocations. The mobility normal to the dislocations will be reduced because: (1) The space charge cylinders deflect electrons and scatter the electron momentum normal to the dislocations; this reduces mean free time. Dislocation scattering is characterized by a mean free path that depends on direction. (2) Even when the dislocations are far enough apart that the mean free time is not affected, the macroscopic mobility may be reduced because the electrons cannot drift parallel to the applied field; instead they follow curved paths winding between the space charge cylinders (which in typical cases are the order of a micron in diameter). This ...
125 citations
••
TL;DR: In this paper, the upper critical field as a function of impurity concentration and temperature is calculated, and it is shown that the specific heat at the transition point in the presence of a field is a function only and does not depend on the magnetic-impurity concentration.
Abstract: We have studied in detail and extended the recent theory of Gor'kov and Rusinov which describes superconductors with ferromagnetically aligned impurities, under the assumption that the electron mean free path due to spin-orbit interaction is small as compared with the coherence distance. We show that all usually considered physical quantities of such a system are identical to those of a superconductor containing magnetic impurities with randomly oriented spins, and point out those vertices for which differences should arise. In addition, we investigate the magnetic properties of such systems. The upper critical field as a function of impurity concentration and temperature is calculated, and it is shown that the specific heat at the transition point in the presence of a field is a function of temperature only and does not depend on the magnetic-impurity concentration. The last results can explain the recent experimental findings by Finnemore et al.
125 citations
••
TL;DR: In this article, the thermal conductivities of pyrolytic graphite have been measured over the temperature range 100-900°K using the semi-continuum model of Komatsu and Nagamiya and an expression is derived for the phonon mean free path due to Umklapp scattering.
Abstract: The thermal conductivities of three specimens of well-oriented, annealed pyrolytic graphite have been measured over the temperature range 100–900°K The conductivity parallel to the deposition plane is analysed in terms of mean free paths using the semi-continuum model of Komatsu and Nagamiya An expression is derived for the phonon mean free path due to Umklapp scattering A temperature independent phonon mean free path results from boundary scattering The conductivity perpendicular to the deposition plane has been fitted to the Leibfried-Schlomann equation
125 citations
••
TL;DR: An implementation of a nanoscale thermal conductivity spectroscopy technique that allows for the study of mean free path distributions in optically absorbing materials with relatively simple fabrication and a straightforward analysis scheme.
Abstract: Heat conduction in semiconductors and dielectrics depends upon their phonon mean free paths that describe the average travelling distance between two consecutive phonon scattering events. Nondiffusive phonon transport is being exploited to extract phonon mean free path distributions. Here, we describe an implementation of a nanoscale thermal conductivity spectroscopy technique that allows for the study of mean free path distributions in optically absorbing materials with relatively simple fabrication and a straightforward analysis scheme. We pattern 1D metallic grating of various line widths but fixed gap size on sample surfaces. The metal lines serve as both heaters and thermometers in time-domain thermoreflectance measurements and simultaneously act as wire-grid polarizers that protect the underlying substrate from direct optical excitation and heating. We demonstrate the viability of this technique by studying length-dependent thermal conductivities of silicon at various temperatures. The thermal conductivities measured with different metal line widths are analyzed using suppression functions calculated from the Boltzmann transport equation to extract the phonon mean free path distributions with no calibration required. This table-top ultrafast thermal transport spectroscopy technique enables the study of mean free path spectra in a wide range of technologically important materials.
124 citations