Comparative study of annealing effects for Cu/Pt(1 1 1) films with and without oxygen

The effect of annealing on Cu/Pt(111) films with and without oxygen has been studied by low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), and ultraviolet photoelectron spectroscopy (UPS). While the first Cu layer on bare Pt(111) grows pseudomorphically the second layer grows epitaxial and rotationally commensurate to the Pt(111) substrate. Only after a 1.2 ML Cu/Pt(111) film was annealed at temperatures above 600 K, the (1 × 1) structure was observed indicating alloy formation. After exposing the 1.2 ML Cu/Pt(111) system to 12 L O₂ at 320 K, no new LEED features were observed. Annealing of this system at temperatures between 600 and 700 K causes a 2 × 2 structure to emerge. AES and UPS measurements suggest the co-existence of a copper oxide at a Cu-Pt alloy. At higher temperatures, the copper adatoms diffuse into the Pt(111) substrate to form an alloy while the oxygen desorbs.