Photoemission spectroscopy of platinum overlayers on silicon dioxide films

Soft x-ray photoelectron spectroscopy (SXPS) has been used to study ultrath in Pt films on silicon dioxide as model supported-catalyst materials. Using monochromatic synchrotron radiation. Pt 4f rind Si 2p core level photoelec tron peaks were measured as a function of platinum coverage in the range 0- 10 hit. The bulk silicon and silicon dioxide film Si 2p peaks each show a b inding energy decrease within the first ML of dosing. However, the effect i s stronger for the silicon dioxide Si 2p peak, indicating an increased scre ening of the 2p electrons by the metal overlayer. We also observe a monoton ic increase of the work function of the ultrathin film Pt/SiO2 system with coverage from 4.52 initially to 5.58 eV at similar to 10 ML. The Pt 4f(7/2) core level binding energy decreased from similar to 72.2 to similar to 70. 9 eV between 0 and similar to 10 ML coverage. This binding energy shift at low dose (less than or equal to 1 ML), the coverage dependence of the Pt li ne shape and intensity, and the large saturation coverage for the work func tion are each consistent with two-dimensional cluster-island growth. The me tallic nature of the Pt overlayer with dose is quantitatively verified by n onlinear, least-squares numerical fitting of the Pt;tf SXPS peak line shape s with Gaussian-broadened Doniach-Sunjic functions. (C) 2000 American Vacuu m Society. [S0734-211X(00)05704-8].