Thickness effect on alloying of ultrathin Co films on Pt(111): a real timeand in situ UHV study with synchrotron x-ray diffraction

We study the alloying of ultrathin Co deposits (3 and 10 monolayer) on a Pt (111) substrate. The surface film evolution is followed in real time during annealing by X ray diffraction, which provides the depth profile with atom ic resolution. We fully characterize the formation of Pt-Co surface alloys before dissolution; the kinetics is shown to depend on the Co thickness. Fo r the 10 monolayer film, the dominant hcp phase exhibits a strong resistanc e to interdiffusion while for the 3 monolayer deposit the surface him is pr ogressively enriched in Pt. Finally, whatever the annealing treatment and t he film thickness, the stabilized alloy is close to Pt60Co40 bulk-like, aft er heating around 450 degrees C. (C) 1998 Elsevier Science B.V. All rights reserved.