Surface structural transition of Si(111)2 × 1 induced by sodium

We have investigated sodium deposition on the cleaved Si(111)2 × 1 surface employing k-resolved direct and inverse photoemission, low-energy electron diffraction (LEED) and work-function measurements. We find that Na lifts the 2 × 1 reconstruction yielding a 1 × 1 LEED pattern. This is in contrast to K which leaves the 2 × 1 surface intact, and Cs which transforms it into a √3 × √3 R30° overlayer structure. The Na-induced empty and occupied surface states reveal the surface to be semiconducting as in the Cs case, but in contrast to K which forms a metallic interface system. Hence, the alkali metals do not behave similarly or iso-electronically in their bonding to the cleaved Si(111) surface, which points to the importance of their differing atomic radii and/or polarizabilities. © 1992.