Circular dichroism in core photoelectron emission from (1x1) oxygen on W(110): experiment and multiple-scattering theory

We have measured the circular dichroism in angular distributions (CDAD) of W 4f emission from a stable one-monolayer structure of oxygen on W(110) that is locally (1X1) in character. Photoelectrons were excited at kinetic energies of approximately 250 eV from the two chemically-shifted peaks present in these spectra (for bulk W and 'oxide' W bound to three O atoms) using right and left circularly polarized radiation (RCP and LCP, respectively), as well as linearly polarized radiation (LP) to provide a reference data set. Measurements were made over a large fraction of the solid angle above the surface, using a new beamline and experimental station at the Advanced Light Source. In switching between RCP and LCP, the data are found to show large CDAD effects of up to +/-50%, as well as both peak 'rotation' effects las first discussed by Daimon et al. in measurements on Si(100)), and more complex changes that are not so simply described. Multiple scattering diffraction calculations are found to very well reproduce all of the effects seen experimentally, and to represent a more accurate way of dealing with such effects than a prior peak rotation model. The LP data is also found to closely resemble the sum of the RCP and LCP intensities, and this is quantitatively explained. Such CDAD effects are thus expected to be generally seen in all work in solid materials, and important to allow for in studies of magnetic materials, with multiple scattering theory expected to yield a quantitative description of hem. (C) 2000 Elsevier Science B.V. All rights reserved.