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.

Heat transfer and density distribution measurements between parallel plates in the transition regime

Abstract: The heat conduction and density distributions were experimentally determined for rarefied gases at rest contained between two unequally heated parallel plates Both argon and nitrogen were used as test gases Particular attention was focused on obtaining measurements in the transition regime where the ratio of plate spacing to mean free path was between 1 and 20 The gas density distribution was measured by observing the luminescence produced by a high‐energy electron beam traversed between the plates The experimental results for argon were compared with the analytical results of Wang Chang and Uhlenbeck, Gross and Ziering, and Lees In computing these results the thermal accommodation coefficient measured in the free‐molecule regime was used with the assumption that its value remained constant over the entire pressure range The average agreement between the heat conduction data and the results of the four‐moment methods of Lees and Gross‐Ziering was about 2%, while the measured density profiles agreed with the results of these analyses within 3% Both the heat conduction and density distribution data differ by ∼10‐20% from the results of Gross‐Ziering's eight‐moment method

Molecular-dynamics simulation of flow in a two-dimensional channel with atomically rough walls.

Abstract: Fluid flows in a two-dimensional channel with atomically rough walls were studied by molecular-dynamics simulations. Both sinusoidally and randomly roughened walls with various roughness amplitudes A were used. It was found that the no-slip condition arises when the molecular mean free path l is comparable with A. Therefore the ratio l/A should be employed to validate the no-slip condition, rather than the traditionally used ratio of the mean free path to the channel or tube diameter (Knudsen number).

Resistivity size effect in epitaxial Ru(0001) layers

Abstract: Epitaxial Ru(0001) layers are sputter deposited onto Al2O3(0001) substrates and their resistivity ρ measured both in situ and ex situ as a function of thickness d = 5–80 nm in order to quantify the resistivity scaling associated with electron-surface scattering. All layers have smooth surfaces with a root-mean-square roughness <0.4 nm, exhibit an epitaxial relationship with the substrate: Ru[0001]||Al2O3[0001] and Ru [101¯0]||Al2O3 [112¯0], and show no resistance change upon air exposure, suggesting negligible resistivity contributions from geometric surface roughness and grain boundary scattering and negligible changes in the surface scattering specularity p upon oxygen exposure. The room temperature ρ vs d data are well described by the semiclassical Fuchs-Sondheimer (FS) model, indicating a bulk electron mean free path λ = 6.7 ± 0.3 nm. However, the measured ρo × λ product at 77 K is 43% lower than at 295 K, suggesting a breakdown of the FS model and/or a thickness-dependent electron-phonon coupling and/or a temperature- or environment-dependent p. Transport simulations employing the ruthenium electronic structure determined from first-principles and a constant relaxation time approximation indicate that ρ is strongly (by a factor of two) affected by both the transport direction and the terminating surfaces. This is quantified with a room temperature effective mean free path λ*, which is relatively small for transport along the hexagonal axis independent of layer orientation (λ* = 4.3 nm) and for (0001) terminating surfaces independent of transport direction (λ* = 4.5 nm), but increases, for example, to λ* = 8.8 nm for (112¯0) surfaces and transport along [11¯00]. Direct experiment-simulation comparisons show a 12% and 49% higher λ from experiment at 77 and 295 K, respectively, confirming the limitations of the semi-classical transport simulations despite correct accounting of Fermi surface and Fermi velocity anisotropies. The overall results demonstrate a low resistivity scaling for Ru, suggesting that 10 nm half-pitch Ru interconnect lines are approximately 2 times more conductive than comparable Cu lines.