Energy-loss-spectroscopy studies on the adsorption of hydrogen on cleaved Si(111)-(2×1) surfaces

Localized vibrations of hydrogen adsorbed on Si(111)-(2×{}1) cleaved surfaces have been investigated by energy-loss spectroscopy (ELS). A new vibrational mode of ω=100 meV has been found after exposure to molecular hydrogen. Its intensity is dependent on the surface step density indicating that this mode is related to adsorption sites near or on step atoms. Models for this type of adsorption are proposed. Off-specular measurements and spectra taken after coadsorption of deuterium show evidence for the simultaneous existence of SiH, SiH₂, and SiH₃ configurations indicating an erosive action of hydrogen even at an early stage of adsorption.