Comprehensive study of the metal/semiconductor character of adatom-induced Ag/Si(111) reconstructions

A root21 x root21 reconstruction can be formed by either Ag or Au adsorption on the Ag/Si(111) root3 x root3 surface. The electronic structures determined by angle-resolved photoemission from these two root21 x root21 surfaces show clear similarities. The presence of the extra Ag or Au adatoms results in a metallic surface with two surface state bands near the Fermi level. Only one of these bands crosses the Fermi level instead of two as reported in the literature. A tiny amount of Ag deposited onto the root21 x root21-Ag surface below 100 K transforms it into a 6x6 periodicity. The additional Ag leads to an interesting transition from the metallic root21 x root21 surface to a semiconducting 6x6 surface with a gap of about 0.2 eV with respect to the Fermi level.