Electronic structure of the La-Pt(111) surface alloy

The electronic and structural properties of the La-Pt(111) surface alloy ha ve been studied by angle-resolved photoemission, core-level spectroscopy an d photoelectron diffraction. For low lanthanum coverages [<0.5 monolayers ( ML)] annealing of as-deposited films at 900 K produces no structural change in the surface: as witnessed by low-energy electron diffraction (LEED) and core-level spectroscopy. The k(parallel to) dispersion for such surfaces i s very similar to the Pt(111) surface band structure. Annealing of surfaces with higher lanthanum coverages (>1 ML) produces a surface alloy which dis plays a (2 x 2) LEED pattern. The k(parallel to) band structure for this al loy is changed dramatically compared with that of Pt(111). Photoelectron di ffraction shows that lanthanum is situated in sites with six-fold rotationa l symmetry in the surface alloy. For the platinum sites our data an inconcl usive, but in accordance with a structural model proposed for the Ce-Pt(111 ) surface alloy based on the layered Pt5Ce compound. We also present eviden ce for a surface-related state on Pt(111) that has not previously been disc ussed. (C) 2000 Published by Elsevier Science B.V. All rights reserved.