Hydrogen adsorption and desorption on Si(100) and Si(111) surfaces investigated by in situ surface infrared spectroscopy

The hydrogen adsorption and desorption on Si(100)(2 x 1) and Si(111)(7 x 7) were investigated by using in situ surface infrared spectroscopy in the mu ltiple internal reflection geometry. At initial stages of room-temperature adsorption of atomic hydrogen, dangling bonds of surface silicon atoms are terminated by hydrogen with the surface reconstruction structure retained, producing the so-called 'double-occupied dimer' (HSi-SiH) on Si(100)(2 x 1) and the monohydride Si (Si-H) perpendicular to the surface on Si(111)(7 x 7). On Si(111)(7 x 7), hydrogen adsorption onto the adatom and the rest ato m have been distinguished, which have two different Si-H vibration frequenc ies. For high hydrogen exposure, atomic hydrogen breaks the surface Si-Si b onds (dimer bonds and backbonds) to produce higher hydride species: dihydri de (SiH2) and trihydride (SiH3). Upon annealing of the hydrogen-exposed sur face at moderate temperatures, trihydride species are thoroughly etched awa y with monohydride and dihydride remaining. We find that the conversion fro m the monohydride to the dihydride phase occurs during thermal annealing of the hydrogen-saturated Si(100)surface. Thermal annealing of the hydrogen-e xposed Si(111) surface produces hydrogen-terminated (1 x 1) domains. (C) 19 99 Published by Elsevier Science B.V. All rights reserved.