Nature of the hydride species on the hydrogenated silicon (111)-(7 .times. 7) surface

We present a scanning tunneling microscopy and spectroscopy study of the nature of the hydride species present on the hydrogenated Si(111)-(7×7) surface. The hydrogenation proceeds in two stages: first reaction occurs at the surface dangling bond sites while at higher coverages H serves to relax the strained bonds formed by the surface reconstruction. This relaxation process produces large exposed regions of the rest layer, isolated adatom trihydride species, and adatom islands which together account for the SiH x species on the surface