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.

Universal phonon mean free path spectra in crystalline semiconductors at high temperature

Abstract: Thermal conductivity in non-metallic crystalline materials results from cumulative contributions of phonons that have a broad range of mean free paths. Here we use high frequency surface temperature modulation that generates non-diffusive phonon transport to probe the phonon mean free path spectra of GaAs, GaN, AlN, and 4H-SiC at temperatures near 80 K, 150 K, 300 K, and 400 K. We find that phonons with MFPs greater than 230 ± 120 nm, 1000 ± 200 nm, 2500 ± 800 nm, and 4200 ± 850 nm contribute 50% of the bulk thermal conductivity of GaAs, GaN, AlN, and 4H-SiC near room temperature. By non-dimensionalizing the data based on Umklapp scattering rates of phonons, we identified a universal phonon mean free path spectrum in small unit cell crystalline semiconductors at high temperature.

Linear magnetoresistance in topological insulator thin films: Quantum phase coherence effects at high temperatures

Abstract: In addition to the weak antilocalization cusp observed in the magnetoresistance (MR) of topological insulators at low temperatures and low magnetic fields, we find that the high-field MR in Bi2Te2Se is linear in field. At fields up to B = 14 T, the slope of this linear-like MR is nearly independent of temperature over the range T = 7 to 150 K. We find that the linear MR arises from the competition between a logarithmic phase coherence component and a quadratic component. The quantum phase coherence dominates up to high temperatures, where the coherence length remains longer than the mean free path of electrons.

Electrical Resistivity of Thin Single‐Crystal Gold Films

Abstract: Resistivities of evaporated or sputtered polycrystalline and epitaxially grown single‐crystal gold films of thickness 100–1000 A have been measured in situ during deposition. Single‐crystal gold films have been grown epitaxially on cleaved mica by sputtering and, as indicated by electron diffraction studies, are atomically smooth over large areas. The resistivities of such films are very close to the bulk value for all thicknesses greater than a limiting thickness at which the film becomes continuous. Since the limiting thickness is appreciably lower than the mean free path for conduction electrons, this result is considered to be a consequence of the existence of specular (elastic) reflection of electrons from the film surface. Resistivities of polycrystalline films of thicknesses comparable to the electron mean free path are higher than the bulk value; and, for films grown on cold substrates, their dependence on thickness is in qualitative agreement with the theory of diffuse (inelastic) scattering of conduction electrons from the surface. For polycrystalline films deposited on heated substrates, the measured resistivity appears to be dominated chiefly by structural changes occurring during growth.

Anisotropic optical properties of arrays of gold nanorods embedded in alumina

Abstract: A series of thin films comprising gold nanorods embedded in an alumina matrix have been fabricated with lengths ranging from 75 to $330\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. Their optical properties, expressed in terms of extinction $\ensuremath{-}\mathrm{ln}(T)$, where $T$ is optical transmittance, have been measured as a function of wavelength, rod length, angle of incidence, and incident polarization state. The results are compared to a Maxwell-Garnett based theory modified to take into account the strongly anisotropic nature of the medium. Transverse and longitudinal plasmon resonances are observed. The interaction between the nanorods leads to the splitting of the longitudinal resonance with the longer-wavelength resonance being forbidden for direct optical observations. The shorter-wavelength resonance related to the symmetric coupling between longitudinal plasma excitations in the nanorods depends on rod length, polarization state, and angle of incidence of the probing light. The impact of electron confinement on the optical properties of the gold rods is also seen and may be incorporated into the Maxwell-Garnett theory by restricting the mean free path of the conduction electrons to produce excellent agreement between observations and the complete theory. Annealing experiments that modify the physical structure of the gold confirm this conclusion.

The secondary electron emission yield for 24 solid elements excited by primary electrons in the range 250–5000 ev: a theory/experiment comparison

Abstract: The secondary electron (SE) yield, delta, was measured from 24 different elements at low primary beam energy (250-5,000 eV). Surface contamination affects the intensity of delta but not its variation with primary electron energy. The experiments suggest that the mean free path of SEs varies across the d bands of transition metals in agreement with theory. Monte Carlo simulations suggest that surface plasmons may need to be included for improved agreement with experiment.