Electronic structure and interface formation during nickel deposition on polycrystalline aluminum

The deposition of nickel on polycrystalline aluminum substrates has been st udied at room temperature by X-ray photoelectron spectroscopy (XPS), angle- resolved X-ray photoelectron spectroscopy (ARXPS), and valence band X-ray p hotoelectron spectroscopy (VBXPS). The growth of the nickel on the aluminum surface has been found to occur in two stages: Formation of NiAlx (x appro ximate to 0.45) islands 10 ML thick up to a coverage theta (NiAlx) = 0.7, f ollowed by the formation of metallic nickel islands with constant thickness of 8 ML that grow over the intermetallic islands previously formed. The si multaneous lateral growth of both kinds of islands is also observed during the second stage. During the first stage, the VBXPS spectra suggest a net c harge transfer from nickel to aluminum with the sequential formation of NiA l3, Ni2Al3, NiAl, and Ni3Al phases.