FACETING OF W(111) INDUCED BY PD AND PT ADLAYERS - A PHOTOEMISSION-STUDY

High resolution photoelectron spectroscopy using synchrotron radiation is used to probe indirectly the substrate electronic response of face ting of W(111) induced by adsorbed Pd and Pt monolayers. The W 4f(7/2) core level is measured in this study. For clean W(111), there are thr ee components observed in W 4f(7/2) photoemission due to surface, subs urface and bulk atoms, respectively; the core level shift between surf ace and bulk atoms is 430 meV. Upon adsorption of Pd or PI at 300 K, o nly a bulk-like W 4f(7/2) peak is observed. The interface peak associa ted with W atoms at the Pd-W or Pt-W interface of the W(111) face coin cides with the W bulk peak. Upon annealing of the metal-covered W(111) above similar to 750 K, the entire surface undergoes a transition fro m planar to faceted; the W 4f(7/2) core level associated with Pd- and Pr-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 b roadening 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 bi nding energy difference of the interface W 4f(7/2) peak and the surfac e W 4f(7/2) peak is discussed.