AVS 47th International Symposium
    Surface Science Wednesday Sessions
       Session SS3-WeA

Paper SS3-WeA6
Low Energy Dynamics for S/Cu

Wednesday, October 4, 2000, 3:40 pm, Room 210

Session: Surface and Interface Structure I
Presenter: C.J. Hirschmugl, University of Wisconsin, Milwaukee
Authors: C.J. Hirschmugl, University of Wisconsin, Milwaukee
M.V. Pykhtin, University of Georgia
S.P. Lewis, University of Georgia
Correspondent: Click to Email
Dissociated H@sub 2@S on Cu(100) at 300K has been studied by a combination of AES, LEED, and Far-IRAS in the 200-2200 cm@super -1@ frequency range using synchrotron radiation. Density functional theory (DFT) calculations for a p(2x2) ordered overlayer of S on Cu have also been completed. In the Far-IRAS experiments, diffusive scattering of substrate electrons from the adsorbates gives rise to a broadband infrared absorption. This behavior was induced by sulfur coverages up to and including the p(2x2) overlayer (0.25 monolayers (ML)). DR/R at high frequency (2200 cm@super -1@) changes monotonically with increasing coverage up to 0.125 of a monolayer, and then remains constant. For the low-coverage linear regime, we calculate a scattering cross section @sigma@ of sulfur for the substrate free electrons and the e-hole pair damping rate @eta@ for the S hindered translation. We apply expressions arising from a "friction" model proposed by Persson to determine these parameters from the broadband infrared absorption data. In addition, we determine both @sigma@ and @eta@ for the ordered overlayer from previously published inverse photoemission results and DFT calculations, using a complementary theory proposed by Persson. The scattering cross section for the disordered overlayer (below 0.125 ML coverage of S) is determined to be approximately 20 Å @super 2@ from the infrared results. The scattering cross section for the ordered overlayer is dramatically smaller, approximately 3 Å @super 2@ as determined from both the photoemission results and DFT calculations. The non-linear behavior in the background change for S adsorption is attributed to a changing cross section, or a disorder to order effect.