AVS 47th International Symposium
    Surface Science Tuesday Sessions
       Session SS1-TuM

Paper SS1-TuM7
Multiplet Splitting and Crystal Field Strengths at Iron Oxide Surfaces

Tuesday, October 3, 2000, 10:20 am, Room 208

Session: Reactions on Oxides and Environmental Chemistry
Presenter: T. Droubay, Pacific Northwest National Laboratory
Authors: T. Droubay, Pacific Northwest National Laboratory
S.A. Chambers, Pacific Northwest National Laboratory
B.P. Tonner, University of Central Florida
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The metal core-level spectra of 3d-transition metal oxides exhibit complex lineshapes due to multiplet splitting in the final state. The crystal field splitting largely determines the degree of multiplet structure. We have measured surface and bulk-sensitive Fe 2p core-level spectra at high energy resolution for several MBE-grown iron oxide epitaxial films. Line shape differences are observed between surface and bulk sensitive photoemission spectra, indirectly revealing differences in crystal field strength. In order to determine the surface crystal field strength, we have utilized XAS L-edge spectra of bulk iron oxides, and have calculated these spectra from first principles using an atomic multiplet theory. Agreement of ultra-high resolution experimental absorption spectra and theoretical models is excellent. We then used the theoretical multiplet model to simulate the bulk-sensitive XPS core-level spectra by broadening to account for the increased lifetime and adjusting peak heights to optimize agreement between theory and experiment. This step produced an accurate value for the bulk crystal field strength. The metal ion site symmetry was then reduced in the calculation and agreement re-optimized between theory and surface sensitive XPS spectra to obtain the equivalent surface crystal field strength. Determination of the crystal field strength at the surface may provide an insight into oxide surface reactivity.