ADSORPTION PROPERTIES OF A MIXED SURFACE STUDIED BY HIGH-RESOLUTION CORE-LEVEL PHOTOEMISSION - CO 0.5 ML PD RH(111)/

The coverage-dependent adsorption properties of a laterally heterogene ous bimetallic surface have been investigated by high resolution core level photoemission and low energy electron diffraction. The specific system under study was CO adsorbed on a Rh(111) surface onto which 2D Pd islands (coverage 0.5 ML) were formed by vapor deposition. The CO a dsorption properties of the heterogeneous surface were compared with C O adsorption on a Rh(lll) surface covered with a full Pd monolayer and with previous results for the CO/Rh(111) system. For low exposures CO is only found on the Rh(111) patches which can be explained by diffus ion of CO from the Pd islands onto Rh parts in the adsorption process. At higher exposures CO diffusion from Rh to Pd is indicated. The orig in of the diffusion processes can be found in the different coverage-d ependent CO adsorption energies on the two surface parts. (C) 1998 Els evier Science B.V. All rights reserved.