Phonon scattering Subject

Lerner [189] found that oxidized PAN fibers subjected to heat treatment temperatures of 715-945 K are semiconductors. The room temperature conductivity is dominated by the contributions of impurity states, but these are not related to defects in the polymer. There is a decrease in conductivity on ageing in air caused by a decrease in the electron-phonon scattering time. The conductivity increases at temperatures above 473 K, as the samples aged in air outgas. 

In harmonic crystals, the vibrations are phonons, i.e. plane waves involving the motion of all atoms in the sample. Phonons are described by a frequency illuminated volume seen by the detector, and fields irradiated by aU polarizable units interfere. As a consequence, one phonon scattering processes (first-order Raman scattering) are subjected to the selection rules ... 

In order to compute the lifetime of a phonon of energy E, one averages the Golden Rule scattering rate (7ig A /pCj )tanh(p /2) with respect to n(e, A), subject to the resonance condition E = y/EA + A [8, 11, 93]. This yields two contributions to the decay rate ... 

It is clear even from a very qualitative consideration, that an exciton with a wavevector k will be scattered by phonons, and an increase of temperature will decrease its mean free path. If an exciton is localized and changes its local position by hopping from one molecule to another, the thermal motions will intensify the exciton diffusion (for more details about this subject see Ch. 14). Studies of the mobility of excitons are very important for biophysics. 

The simplest model of charge transport in delocalized bands is the Drude model, which assumes the carriers are free to move under the inhuence of an applied electric held, but subject to collisional damping forces. Note that the scattering centers are not the nuclei of the background material, but rather phonons (lattice vibrahons) or impurities. A statistical equahon for estimahng the mean drift velocity of the carriers in the direction of the electric held may be written as... 

W. Richter, Resonant Raman Scattering in Semiconductors Electric Susceptibility. Light Scattering. Experimental Method.s. One-Phonon Deformation Potential Scattering. Infrared Active LO Phonons. Multiphonon Scattering. Conclusions. List of Symbols. References. Subject Index. 

Basic principles. In Raman spectroscopy, a laser beam (monochromatic light) is directed perpendicularly at the sample. The major part of the light is subject to the common optical laws (absorption, reflection and transmission). A very small part (less than 10 of the incident beam) is reflected via an inelastic scattering of the photons by the lattice phonons. This is the first order Raman scattering. This is the only Raman scattering effect observed for diamond at the excitation energies used. The... 

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