GROWTH AND PROPERTIES OF THIN AG FILMS ON PT(100) SURFACES

Adsorption of Ag on Pt(100) surfaces including the multilayer regime h as been studied using the low energy electron diffraction, X-ray photo electron spectroscopy, ultraviolet electron spectroscopy, and thermal desorption spectroscopy methods. Deposition of Ag sub-monolayers on Pt (100) below 300 K leads to the formation of three-dimensional crystall ites, which decompose into a pseudomorphic layer upon annealing above approximate to 350 K. Deposition of Ag multilayers proceeds along the same growth mode. Adsorbed Ag lifts the hex reconstruction of the Pt(1 00) surface. Up to an Ag coverage of approximate to 0.8, Ag desorbs ac cording to a zero-order desorption rate law, E(des) = 322 kJ mol(-1). This desorption order is interpreted by the presence of a mixed Pt/Ag layer on top of the square Pt(100) substrate into which all excess Pt atoms from the hex surface are expelled upon lifting of the reconstruc tion. Therefore, Ag desorption reflects the decomposition of a monolay er-confined Ag-Pt alloy. Between Ag coverages of Theta approximate to 0.7 and Theta = 1, first-order desorption is observed, while above The ta = 1 zero-order desorption is again observed (E(des) = 288 kJ mol(-1 )). A 760 K annealed Ag monolayer suffices to suppress CO adsorption. XP spectra reveal a binding energy shift of the Ag 3d(5/2) level from 367.5 eV (monolayer) to 368.1 eV (thick multilayer). In UP spectra an Ag/Pt(100) interface state at 1.5 eV below the Fermi level is observed , which is interpreted to stem from Pt 5d electrons. Low-temperature d eposited Ag sub-monolayers exhibit in IP spectra a broad 4d band struc ture, which collapses upon annealing into two extremely narrow AE 4d e mission peaks, Delta E approximate to 0.2 eV, at 4.6 eV and 4.8 eV. Th ey are interpreted as emission from chain-like structures of Ag atoms in the mixed Pt/Ag layer structures which are formed in the annealing process.