ELECTRONIC AND ATOMIC-STRUCTURE OF GE SI(111)-7X7 IN THE INITIAL-STAGES OF GE CHEMISORPTION/

We present a theoretical study of the initial stages of Ge chemisorpti on on Si(111)-7 x 7 in the DAS model. Three Ge adsorption mechanisms a re studied: substitution, addition and substitution followed by additi on of a Si atom (permutation). The threefold hollow (H-3) and threefol d filled (T-4) sites are considered as possible adsorption sites. We c ompute the adsorption energies and the densities of states in the fram ework of the crystalline extension of the extended Huckel theory. Subs titution seems to be unlikely when compared to addition and permutatio n. An interpretation of the surface states A, A(1) and A(2) observed i n photoemission is proposed.