VIBRATIONAL-MODES OF EPITAXIAL MONOLAYER ADSORBATES ON SEMICONDUCTOR SURFACES STUDIED BY RAMAN-SCATTERING

Raman scattering was used to study zone-center vibrational modes of hi ghly ordered, epitaxial monolayers on semiconductor surfaces. By utili zing resonance conditions of the incident laser light to electronic su rface states the Raman cross section could be sufficiently enhanced to record the inelastically scattered light from the monolayer vibration s using a standard Raman setup. For three systems, namely As on Si(111 ), Sb on InP(110), and Sb on GaAs(110), vibrational modes were detecte d. The polarization selection rules were tested to determine the symme try type of the vibration, whereas the resonance enhancement could be related to critical points in the joint density of states (gaps) in th e two-dimensional electronic band structure at the surface.