THERMAL-STABILITY OF ULTRATHIN CR FILMS ON PT(111)

The thermal stability of ultrathin chromium films on Pt(111) has been studied using low-energy He+ ion scattering spectroscopy, X-ray photoe lectron spectroscopy, low-energy electron diffraction, and scanning tu nneling microscopy. At room temperature, Cr grows on Pt(111) with a mo dified Stranski-Krastanov growth mode (almost complete wetting of the first two layers with subsequent three-dimensional island growth). Upo n annealing, chromium diffuses into the Pt lattice. This causes a smoo thening of the surface features. A flat Pt(111) surface, devoid of Cr, is regained after prolonged annealing above 770 K. Ar lower temperatu res, metastable Cr-Pt surface alloys are formed. The apparent composit ion and stability of these surface alloys are dependent upon the amoun t of Cr deposited initially. Both the Cr adlayer and Pt surface atoms were found to be perturbed at the interface. Experimental and theoreti cal results indicate that a redistribution of charge between Pt and Cr occurs upon alloy formation with the greatest perturbation experience d by the Pt atoms.