Geometrical Structure, Phase Diagrams, and Core-Level Binding Energiesof Metal Surfaces: Calculations, Simulations, and Experiments

University dissertation from Div. of Synchrotron Radiation Research, Lund University, Box 118, SE-221 00 Lund, Sweden

Abstract: This thesis concerns clean and adsorbate covered metal surfaces and surface alloys. These systems have been studied using theoretical and experimental methods. In the first part of the thesis, the different techniques that have been utilized in this work are presented, and the included publications are summarized. The second part of the thesis consists of seven original publications. In the first two papers, the structure of two aluminum-alkali surface alloys are determined using low energy electron diffraction, high resolution core level photoemission spectroscopy and density functional theory calculations. The first is a three-layer Al3Li surface alloy which is found to have a Al3Ti-type structure. In the second paper, the structure and formation of an Al(100)-(?5x?5)R27°-Na surface alloy is investigated. In the third paper, the phase diagram of Al(100)-Na surface alloys is studied as a function of stoichiometry and temperature. An order-disorder phase transition is characterized using LEED and HRCLS and this, as well as the phase diagram, is reproduced in first principles Monte Carlo simulations with input parameters from DFT calculations. Paper IV is an experimental and theoretical study of the surface core level shifts (SCLS) of two low-index aluminum surfaces, Al(100) and Al(111). The experimental and theoretical results are in excellent agreement. These measurements provide the first experimental determination of the SCLS od Al(111), For Al(100), the core level shift of the second layer is also resolved. Furthermore, the Al 2p photemission peak is found to consist of a no-phonon line and satellite structures at higher binding energies corresponding to phonon losses. In Paper V, the SCLS of two stepped rhodium surfaces are studied using HRCLS. The components from terraces and step edges of a vicinal surface are resolved for the first time. We also demonstrate how this may be used to show that initial oxygen adsorption occurs on the steps and not on the terraces of the vicinal surfaces. The last two papers are experimental and theoretical studies of CO adsorption on Rh(111). In the experimental study, the fine structure components due to vibrational excitation of the C-O stretch mode are clearly resolved in the C1s emission peaks and are found to be site specific. Furthermore, a new C1s HRCLS component is resolved at intermediate coverages. It is suggested that the new component is due to CO adsorbed in bridge sites on the surface. This is supported by the calculated core level shifts in paper VII.

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