Phonon lifetime

The approach of Yoshikawa et al. accounts for size-related changes in the phonon lifetime, leading to larger downshift and higher peak asymmetry compared to Ager et al. While the differences are considerably small for larger crystals, they become significant for crystal sizes below 10 nm and are therefore important... 

A more precise measurement of local sample temperature is made possible by the anharmonicity of the crystal vibrational potential energy. Phonon-phonon interactions that reduce individual phonon lifetimes, phonon softening, and thermal expansion give rise to increasing peak width and a change in peak frequency... 

Pure diamond contains only sp carbon (a bonds), which in the Raman spectra results in a single diamond zone center optical phonon peak, occurring at 1332 cm"- -. The line width is a qualitative measure of the crystalline quality of the film. The more defects in the probed area, the shorter the phonon lifetime and... 

Figure 8 shows visible-Raman spectra for moderately boron-doped ( — 10 cm ) microcrystalline and nanocrystalline diamond thin films. The spectrum for the microcrystalline film consists of the one-phonon diamond line centered at 1333 cm The line width (FWHM) is ca. 10 cm and, to a first approximation, is inversely related to the phonon lifetime [123,130]. The line position is negligibly shifted from that for a reference... 

Raman resonance frequency. The two measuring methods complement each other, in that the measurements in the frequency domain work hest in the range of short phonon lifetimes (< 5 ps) and vica versa. 

The main focus of this section of the lecture is on the lifetimes of optical phonons. It is for these phonons that a new experimental effort has produced new definitive and interesting results. I will approach the theoretical basis of phonon lifetimes in terms of very simple introductory ideas of phonons in general, plus a short review of what is known about their lifetimes. 

The starting point for most theoretical approaches to calculations of phonon lifetimes is the Hamiltonian of the harmonic... 

It is important to note at this point that the LA phonon lifetime against spontaneous decay varies as oT, i.e, high frequency LA phonons are predicted to decay much more rapidly than low frequency phonons. In simple systems near T 0, the spontaneous three-phonon decay of LA phonons, described above, should dominate the observed temporal evolution of nonequilibrium phonon distributions (Orbach and Vredevoe, 1964). 

The problem is solved using an elegant phonon propagator and diagrammatic technique. The general solution for the reciprocal of the phonon lifetime at the absolute zero of temperature is... 

For a harmonic crystal the phonon lifetime is infinite and there is no scattering of thermal phonons.To understand the mechanism on how the guest-host interactions lead to the anomalous temperature dependence of the thermal conductivity, the lifetimes were calculated for phonon-phonon scatterings as a result of the anharmonic terms in the xenon-water potential of xenon hydrate in the small and large cage. The inverse relaxation time (lifetime), of a lattice vibration with frequency C0j q) (/ is the branch index and q is the direction of the momentum transfer) is related to the transition rate, W, of the lattice wave scattered from state qj q f by a defect according to, ... 

The inverse of this, Xp = 1/Fg, is often referred to as the phonon lifetime. As a result, the spectrum of the Brillouin doublet is broadened by an amount... 

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