This award will support Professors Richard Wallis and Alexei Maradudin of the University of California at Irvine in a research collaboration with Professor Virginio Bortolani of the University of Modena, Italy. The investigators intend to focus on surface phonons, whose dispersion curves have been measured for a wide variety of metals, insulators, and semiconductors by the inelastic helium atom scattering technique. They intend to carry out a concerted theoretical and computational effort to provide values for the surface phonon linewidths as functions of temperature for copper, silver, and gold surfaces. The required anharmonic parameters will be determined from the known third order elastic constants. The researchers also intend to carry out calculations of surface phonon dispersion curves and eigenvectors for surfaces of noble metals and face-centered-cubic transition metals. Much progress has been made in recent years in the experimental determination of surface phonon dispersion curves of a broad fange of crystal surfaces, using inelastic electron scattering and inelastic helium atom scattering. The latter technique has been applied with great success to a wide range of materials and keeps providing new insights into the study of surface dynamics. The proposed collaboration will enable the U.S. investigators to benefit from the expertise of the Italian investigators in calculating accurate phonon frequencies and eigenvectors for noble metal surfaces. The U.S.side will contribute in turn its expertise in calculating the linewidths of surface phonons, which stems from their comprehensive program studying anharmonic effects at crystal surfaces.
