Hydrogen chemisorption on Si(111)

Valence-electron energy spectra of two different structural models for hydrogen adsorption on Si(111) surfaces are calculated employing self-consistent pseudopotentials. The two structural models correspond to attaching hydrogen atoms to one (monohydride) or three (trihydride) silicon dangling bonds per substrate surface atom. The spectral results for the monohydride phase are in excellent agreement with earlier calculations and with experimental data obtained on hydrogenated surfaces starting with clean annealed 7 x 7 surfaces. It has recently been proposed by Pandey et al. that the drastic spectral changes occuring for hydrogen adsorbed on 1 x 1 quenched surfaces may be accounted for by the trihydride model. While the present calculations basically confirm this result, some discrepancies remain between the experimental and theoretical spectra. Possible explanations for the discrepancies are given