OPTICAL SPECTROSCOPY STUDY OF HYDROGENATION OF THE SI(111)-7X7 SURFACE

Deposition of foreign atoms on silicon surfaces gives rise to a variet y of phenomena, which are the subject of very active research, Fundame ntally and technologically important, the chemisorption of hydrogen at Si(111)-7 x 7 surface is Still under debate due to its complex struct ure, the existence of different adsorption sites and the etching in th e process of adsorption. We present both experimental and theoretical optical spectroscopy results on the atomic hydrogen adsorption at the Si(lll)-7 x 7 surface, The real-time optical, namely differential refl ectivity, measurements were performed by means of an in-situ spectrome ter with 60 degrees angle of incidence. Structural changes upon H adso rption have been monitored by LEED. Microscopical calculation of the o ptical properties of the full scale Si(lll)-7 x 7 DAS structure was do ne within a sp(3)s tight-binding approach. In order to model the stru ctural changes due to H adsorption, we calculated the relative differe nce in reflectivity Delta R/R between the dean Si(lll)-7 x 7 and hydro genated Si(lll)-1 x 1:H surfaces. The surface optical response has bee n decomposed into the various components, due to surface-to-surface, s urface-to-bulk, bulk-to-surface and bulk-to-bulk states transitions, T he microscopic origin of the different contributions is discussed in d etail, The comparison with the theoretical results allowed us to clari fy the origin of the main optical peaks observed experimentally at the hydrogenated Si(111)-7 x 7 surface.