Anharmonic adlayer vibrations on the Si(111): H surface

Using infrared absorption spectroscopy, the frequency and linewidth of the H-stretching vibration on the Si(111):H-(1x1) surface has been measured ove r a temperature range of 14-350 K. An ab initio calculation of the temperat ure dependence of the anharmonic frequency shift and the intrinsic linewidt h of this mode has been carried out, which fully accounts for the quantum n ature of the atomic vibrations by using interacting phonon theory. The theo retical results show that at temperatures greater than 200 K,both line shif t and linewidth of the stretching mode are primarily due to strong anharmon ic coupling to the bending modes, which suffer decay into substrate modes v ia cubic anharmonicity. At low temperatures, direct coupling to various pho non modes of the substrate dominates the temperature dependence of the line shift. In addition, predictions are made for the frequency shift due to ze ro-point motion of the atoms. A strong sensitivity of the frequency on the shape of the Si-H potential has been found that makes quantitative predicti ons of the influence of zero-point motion very difficult. As a byproduct, t he temperature dependence of the interatomic distances near the surface has been obtained and a decrease of the H-SI distance with increasing temperat ure is predicted. [S0163-1829(99)02016-0].