Structural and electronic properties of Sn overlayers and Pd/Sn surface alloys on Pd(111)

The first two layers of Sn deposited on Pd(lll) at 300 K grow in layer-by-layer fashion after which crystallite formation commences. The electronic properties of these overlayers are dependent on the size of the 3D sn islands. The occurrence of Sn --> Pd Valence charge-transfer is inferred, due allowance being made for initial and final state effects in the photoemission data. Evidence is presented for a significant Pd surface core-level shift enhancement by Sn of approximate to 0.7 eV. Depending on the initial Sn loading, heating generates stable monolayer (Pd,Sn) or multilayer (Pd,Sn) surface alloys exhibiting root 3 and (2 x 2) periodicities, respectively. The very different CO adsorption capacity of these two phases indicates that on Pd/Sn alloy surfaces, only pure Pd threefold hollow-sites are capable of strongly chemisorbing CO. (C) 1997 Elsevier Science B.V.