Surface phonons of thin GaSe and InSe films epitaxially grown on the Si(111)(1x1)-H surface

Surface-phonon-dispersion curves of the (001) surfaces of the GaSe and InSe films epitaxially grown on the hydrogen-terminated Si(111)(1 x 1) surface have been investigated by high-resolution inelastic helium-atom scattering. The phonon-dispersion curves of the GaSe(001) thin epitaxial films are ver y similar to those of the single crystals investigated previously. For comp arison with the experiments, density-functional theory based on the plane-w ave pseudopotential method has been used to determine the phonon-dispersion curves of bulk GaSe and InSe in a consistent formalism. No difference is f ound between the surface and bulk phonons of these two layered compounds, a s expected due to weak interlayer interaction forces. The high quality of t he time-of-flight spectra presented here together with the ab initio calcul ations provide insight into the phonon dynamics of GaSe(001), and a charact erization of the phonon modes of InSe(001).