Surface modification by metal deposition

The adsorption of metal films is a promising way to modify the physical and chemical properties of substrate surfaces. In the present work several aspects such as growth structure, electronic properties, surface alloy formation and adsorption behavior of such films is discussed on the basis of LEED, ARUPS, PAX, Delta Phi, and TDS results for the deposition of Cu on different Pt surfaces. In a first part results on the growth of multilayer films of Cu on Pt(111) obtained by dynamical work function measurements are presented. Intermediate coadsorption of oxygen on a previously deposited Cu film of 2 ML leads to oscillatory work function changes during further Cu deposition. This behavior is discussed in terms of a growth model which considers the influence of surface morphology via the Smoluchowski effect. On the reconstructed Pt(100) surface the deposition of Cu at 300 K leads to a lifting of the reconstruction in the Cu-covered areas, while the Cu-free part of the surface stays reconstructed. This is in agreement with results of Au/Pt(100) and Ag/Pt(100), but in the case of Cu/Pt(100) strain minimization cannot be the only reason for this restructuring so that additional electronic effects must be taken into account. For multilayer Cu deposited on Pt(100) the segregation of Pt leads to alloying and chemical ordering in the temperature range between 500 and 1000 K. Several phase transitions between disordered and ordered surface alloys can be found. Both, a Cu3Pt(100) and a ''Cu5Pt3(100)'' surface alloy are Cu terminated as detected by PAX, while after annealing to 1000 K the surface again consists only of Pt atoms in the reconstructed arrangement. As an example for modified chemical properties of metal films with respect to the bulk material adsorption experiments of molecular hydrogen on Cu/Pt(100) at 100 and 300 K are presented. In contrast to bulk Cu they show the capability to dissociate H-2 for coverages of up to 10 ML Cu.