Modification of a Shockley-Type Surface State on Pt(111) upon Deposition of Gold Thin Layers

We present a first-principles fully-relativistic study of surface and interface states in the n one monolayer (ML) Au/Pt(111) heterostructures. The modification of an unoccupied s - p -type surface state existing on a Pt(111) surface at the surface Brillouin zone center upon deposition of a few atomic Au layers is investigated. In particular, we find that the transformation process of such a surface state upon variation of the Au adlayer thickness crucially depends on the nature of the relevant quantum state in the adsorbate. When the Au adlayer consists of one or two monolayers and this relevant state has energy above the Pt(111) surface state position, the latter shifts downward upon approaching the Au adlayer. As a result, in the 1 ML Au/Pt(111) and 2 ML Au/Pt(111) heterostructures at the equilibrium adlayer position, the Pt-derived surface state experiences strong hybridization with the bulk electronic states and becomes a strong occupied resonance. In contrast, when the number n of atomic layers in the Au films increases to three or more, the Pt(111) surface state shifts upward upon reduction of the distance between the Pt(111) surface and the Au adlayer. At equilibrium, the Pt-derived surface state transforms into an unoccupied quantum-well state of the Au adlayer. This change is explained by the fact that the relevant electronic state in free-standing Au films with n ≥ 3 has lower energy in comparison to the Pt(111) surface state.