GROWTH AND STRUCTURE OF THIN PT FILMS ON CU(111) STUDIED BY LOW-ENERGY LI-SCATTERING( ION)

The growth and structure of thin Pt films on Cu(111) have been studied by low energy Li+ ion scattering. The results are compared to those o btained from a Cu3Pt(111) single crystal alloy. Deposition of Pt on Cu (111) at coverages up to a few monolayers at room temperature less tha n or equal to 50 degrees C) and then annealing to 300 degrees C result in the formation of a metastable surface alloy. This surface alloy ha s been examined to consist of at least three layers of Cu3Pt by analyz ing the incident angle dependence associated with shadowing effects. T he experimental results also show that the surface composition depends strongly on annealing temperature. The formation of a relatively stab le surface alloy in local equilibrium over the few topmost layers is d iscussed on the basis of the segregation and ordering behaviour. No su rface chemical ordering of the surface alloy has been evidenced in thi s study.