Ultrathin metals films on W(221): Structure, electronic properties and reactivity

Nanoscale pyramidal facets with (211) faces are formed when W(111) surface is covered by monolayer film of certain metals (including Pt, Pd and Au) an d annealed to T greater than or equal to 750 K. In the present work, we foc us on the structure, electronic properties and reactivity of planar W(211) covered by ultrathin films of platinum and palladium. The measurements incl ude soft X-ray photoelectron spectroscopy using synchrotron radiation, Auge r electron spectroscopy, low energy electron diffraction (LEED) and thermal desorption spectroscopy. The metal film growth and evolution during anneal ing has been investigated for coverages ranging from 0 to 8 monolayers. The films grow initially in a layer-by-layer mode at 300 K. LEED, Auger, and S urface Core Level Shift (SCLS) measurements reveal that for coverages of on e monolayer, the films are stable up to temperatures at which desorption oc curs. In contrast, at higher coverages, SCLS data indicate that surface all oys are formed upon annealing films of Pt and Pd; surface alloy formation i s not seen for Au overlayers. These findings are discussed in terms of stru ctural and electronic properties of these bimetallic systems. Relevance to catalytic properties for acetylene cyclization over Pd/W(211) is also discu ssed.