Investigations of bimetallic systems with regard to their surface composition, morphology and adsorption properties for reactive gases like e.g. CO are of great importance for the development of new catalysts with higher efficiency and durability. In the present study the preparation and compositional, electronic, and structural characterization of thin gold films deposited on a Pt(111) single crystal have been studied by means of Ultraviolet Photoelectron Spectroscopy (UPS) and Low Energy Electron Diffraction (LEED) as a function of film thickness, ranging from submonolayer amounts up to multilayers, and temperature. The detected absence of extra spots in the LEED measurements after gold deposition indicates an initial pseudomorphic growth of the gold films. Experiments with UPS and related methods like PAX (Photoemission of Adsorbed Xenon) show a strong temperature dependence of the surface morphology. Deposition of gold at a sample temperature of 150 K results in quite rough gold films. Annealing the freshly prepared film for a short period of time above room temperature causes a significant smoothening verified by a strong increase of the work function and a completely different structure of the 5p1\2 and 5p3\2 xenon peaks. At an annealing temperature of 900 K gold starts to diffuse into the platinum bulk resulting in the formation of a surface alloy. At 1100 K the full incorporation of gold is completed within a few minutes. The electronic properties of the resulting Au-Pt surface alloys seem to be nearly independent from the deposited amount of gold in the investigated range of 1 – 10 monolayers. The disappearance of gold atoms from the surface regions has been verified by Scanning Tunnelling Microscopy (STM). After annealing the surface up to 1050 K for 5 minutes the formation of gold islands surrounded by areas of bare platinum on the former completely gold covered surface can be observed.
After characterization of the Au-Pt alloy films adsorption experiments with various probe molecules have been done. These studies have led to the interesting result that the alloyed Au-Pt surface possesses a noticeable lower affinity towards CO, but comparable adsorption properties concerning butadiene in comparison to the clean Pt(111) surface. |