PHOTOELECTRON DIFFRACTION STUDY OF ULTRATHIN-FILM GROWTH OF NI ON PT(111)

X-ray photoelectron diffraction (PD) based on a forward scattering app roach (FS-PD) has been used to study the growth mode of the first few Ni monolayers deposited on the Pt(lll) surface, with a particular atte ntion to the initial stages of epitaxy, i.e. the formation of the firs t atomic layer. Strong evidences for a layer-by-layer (or Frank-Van de r Merwe) growth mode are reported, substantiated also by theoretical s imulations carried out with the single scattering cluster-spherical wa ve (SSC-SW) framework. The first Ni monolayer grows strained in-plane to match the substrate pseudomorphically even if there is a 10% mismat ch between the lattice parameters of Ni and Pt. The multilayer (up at least to six monolayers) maintains the horizontal strain and consequen tly shows a vertical spacing contraction (tetragonal distorsion). It r etains the overall threefold symmetry and azimuthal orientation of the substrate, indicative of a single-domain epitaxial fee stacking. Ther e is also some evidence (even if it is not conclusive) for the fact th at the Ni atoms of the first monolayer occupy hcp sites of the substra te surface.