Surface phonons of thin GaSe and InSe films epitaxially grown on theSi(111)(1×1)−Hsurface

Abstract

Surface-phonon-dispersion curves of the (001) surfaces of the GaSe and InSe films epitaxially grown on the hydrogen-terminated $\mathrm{Si}(111)(1\ifmmode\times\else\texttimes\fi{}1)$ surface have been investigated by high-resolution inelastic helium-atom scattering. The phonon-dispersion curves of the GaSe(001) thin epitaxial films are very similar to those of the single crystals investigated previously. For comparison with the experiments, density-functional theory based on the plane-wave pseudopotential method has been used to determine the phonon-dispersion curves of bulk GaSe and InSe in a consistent formalism. No difference is found between the surface and bulk phonons of these two layered compounds, as expected due to weak interlayer interaction forces. The high quality of the time-of-flight spectra presented here together with the ab initio calculations provide insight into the phonon dynamics of GaSe(001), and a characterization of the phonon modes of InSe(001).