POTASSIUM ADSORPTION ON THE POLAR NBC(111) SURFACE - ANGLE-RESOLVED PHOTOEMISSION-STUDY

Angle-resolved photoemission spectroscopy with synchrotron radiation h as been used to study the adsorption mechanism of K on a NbC(111) surf ace. The coverage-dependent measurements of the valence-band region sh ow that the K 4s state is hybridized with the surface stares at around the Fermi level on the NbC(111) surface to form bonding and antibondi ng states. In the initial stage of adsorption, only the bonding state, mainly composed of Nb 4d states, is occupied, which results in a pola rized overlayer. The antibonding state, mainly composed of K 4s states , becomes occupied after depolarization to form a metallic overlayer. The overall results are compatible with the adsorption model proposed by our previous core-level photoemission study; the K 4s state interac ts with the surface states on the NbC(111) surface, and the adsorption proceeds via a polarization-depolarization transition. (C) 1997 Elsev ier Science B.V.