AVS 46th International Symposium
    Surface Science Division Wednesday Sessions
       Session SS3+EM-WeM

Paper SS3+EM-WeM7
Photoemission Spectroscopy of Platinum Overlayers on Silicon Dioxide Films

Wednesday, October 27, 1999, 10:20 am, Room 604

Session: Surface Electronic Structure
Presenter: J.W. Keister, Army Research Office
Authors: J.W. Keister, Army Research Office
J.E. Rowe, Army Research Office
J.J. Kolodziej, Rutgers University
T.E. Madey, Rutgers University
Correspondent: Click to Email
Soft x-ray photoelectron spectroscopy has been used to study ultrathin Pt films on silicon dioxide as model supported-catalyst materials. Using monochromatic synchrotron radiation (NSLS U4A - Brookhaven), platinum and silicon core-level photoelectron peaks were measured as a function of platinum coverage in the range, 0 - 10 monolayers (ML). The bulk Si and SiO@sub 2@ film Si(2p) peaks both show a binding energy drop within the first ~ 0.5 ML of dosing. However, the effect is stronger for the SiO@sub 2@ film Si(2p) peak, indicating an increased screening of the 2p electrons by the metal overlayer. We also observe a monotonic increase of the Pt film workfunction with coverage from 4.52 eV initially to 5.59 eV at ~ 10 ML. The Pt(4f) and valence band spectra display changes with Pt dose which are also consistent with increased screening, from non-metallic below ~ 0.5 ML to metallic as coverage increases. The Pt core level decreases its binding energy from ~ 72.2 eV to ~ 70.9 eV between 0 and 10 ML coverage. The coverage dependence of the Pt lineshape and intensity, and the large saturation coverage for the workfunction change indicate cluster growth (Volmer-Weber growth). The increasingly metallic nature of the Pt overlayer with dose is quantified by numerical lineshape fitting with Gaussian-broadened Doniach-Sunjic functions, as appropriate for varying amounts of metallic screening. Further quantitative results and interpretation in terms of nucleation and growth of Pt clusters will be discussed.