Theoretical Investigations of Surface Effects in Solids, Anharmonic Properties of Crystals and Surfaces, and Properties of Semiconductors

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A research program in theoretical condensed matter physics which will increase our knowledge and understanding of surface physics, the anharmonic properties of crystals and surfaces, and the properties of semiconductors is planned. The study of surface physics will include theoretical determinations of the dispersion curves for surface phonons on low index surfaces of metals, the amplification of surface polaritons, the propagation of surface polaritons in superlattices layered parallel or perpendicular to the free surface of the sample, and the properties of localized interface and impurity states in quasicrystals. Computer simulation studies of the anharmonic properties of crystals and surfaces will provide results for thermodynamic properties and excitation lifetimes that are correct to all orders in the anharmonicity. Phonon transport phenomena in dielectric crystals, such as phonon viscosity, thermal conductivity, and ultrasonic attenuation, will be studied on the basis of numerical solutions of the linearized Peierls Boltzmann equation for realistic crystal models. The linewidths of surface phonons due to lattice anharmonicity will also be investigated. A theoretical effort will be made on the excitations and statistical mechanics of bounded nonlinear media. Theoretical investigations into the properties of semiconductors will focus on the lifetimes of excited impurity states and the effects of electron-phonon interaction on impurity states in silicon inversion layers. Localized electronic states in compensated semiconductors will also be studied.