Faceting of W(111) induced by Pd and Pt adlayers — a photoemission study

Abstract

High resolution photoelectron spectroscopy using synchrotron radiation is used to probe indirectly the substrate electronic response of faceting of W(111) induced by adsorbed Pd and Pt monolayers. The W 4 f 7 2 core level is measured in this study. For clean W(111), there are three components observed in W 4 f 7 2 photoemission due to surface, subsurface and bulk atoms, respectively; the core level shift between surface and bulk atoms is 430 meV. Upon adsorption of Pd or Pt at 300 K, only a bulk-like W 4 f 7 2 peak is observed. The interface peak associated with W atoms at the PdW or PtW interface of the W(111) face coincides with the W bulk peak. Upon annealing of the metal-covered W(111) above ∼750 K, the entire surface undergoes a transition from planar to faceted; the W 4 f 7 2 core level associated with Pd- and Pt-covered W(211) facets broadens and its centroid shifts to the lower binding energy side of the W bulk peak. The centroid shift and peak broadening are attributed to W atoms at the PdW or PtW(211) interface of the facets. The relation between the interfacial energy and the binding energy difference of the interface W 4 f 7 2 peak and the surface W 4 f 7 2 peak is discussed.