Surface segregation and chemisorption of CO and oxygen on Pt25Ni75(111) studied by XPS and HREELS

After sputtering and annealing to different temperatures TA the chemically disordered (111) surface of a Pt25Ni75 crystal exhibits a composition that depends strongly on TA. This has been already observed earlier by ion scattering and scanning tunneling microscopy [M. Schmid et al., Nucl. Instrum. Methods B 82 (1993) 259]. To complement this work, we have used angle-resolved X-ray photoelectron spectroscopy (XPS) to investigate the segregation behaviour a few layers below the surface. We have also used high-resolution electron energy loss spectroscopy (HREELS) to study adsorbate vibrations on differently prepared surfaces of Pt25Ni75(111) after exposure to O2 and CO at room temperature.