PHONONS IN AMORPHOUS MATERIALS

Abstract
A brief review is given of phonons in amorphous materials as seen in Raman scattering, infrared absorption and inelastic neutron scattering. It is shown that phonons (i.e. quantised harmonic vibrations) are well defined in network structures and a description is given of the standard theoretical technique which is to build a finite model and then use one of a number of numerical techniques to obtain the eigenvalue spectrum of the dynamical matrix. Particular emphasis is given to newer theoretical techniques that do not require the building of a model. The results are illustrated with reference to experiments in elemental semiconductors like Si and Ge and two component glasses like SiO₂, GeS₂, etc.