GROWTH OF ULTRATHIN PD FILMS ON AL(001) SURFACES

High-energy ion backscattering spectroscopy (HEIS) and X-ray photoelec tron spectroscopy (XPS) were used to determine the growth mode and the interface structure of ultrathin Pd films deposited on Al(001) surfac es at room temperature. Measured Al and Pd surface peak areas for MeV He+ ions incident normal to the surface show that Pd atoms intermix wi th and displace Al substrate atoms. The mixing continues for Pd covera ges from 0-5 monolayers, at which point a Pd metal film begins to grow on the alloy surface. XPS measurements of the Pd 3d photopeaks show a chemical shift that is consistent with the formation of an AlPd-like compound during the mixing phase, and Pd metal thereafter. HEIS result s further reveal that the alloyed overlayer as well as the Pd metal fi lm have some degree of axial alignment with respect to the Al substrat e. The XPS intensity measurements are consistent with this two-stage g rowth model.