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

Invited Paper SS3-WeA1
Adsorbate Structure Determination on Surfaces using Normal-Incidence X-ray Standing Waves

Wednesday, October 4, 2000, 2:00 pm, Room 210

Session: Surface and Interface Structure I
Presenter: D.P. Woodruff, University of Warwick, UK
Correspondent: Click to Email

X-ray standing waves (XSW) provide a particular simple way of obtaining quantitative information on adsorption geometries on well-characterised surfaces, and working a normal incidence (NIXSW) to the Bragg scatterer planes offers some specific advantages. In particular, under these conditions the experiment is extremely tolerant of crystal mosaicity and can be applied routinely to metal crystals. Normal incidence also implies lower photon energies, typically around 3 keV, making photoemission detection of the photoabsorption straight-forward. Photoemission detection offers two important advantages, namely easier access to low atomic-number species, and the possibility of obtaining chemical-state specific structural information through the use of 'chemical shift' in the photoelectron binding energies. On the other hand, photoemission detection requires the use of a modified interpretational scheme to take account of non-dipole effects in the angular dependence of the photoemission. These various aspects of the technique will be illustrated with recent results including: the direct measurement of non-dipole angular parameters; the use of chemical-shift NIXSW to determine the local geometries of coadsorbed molecular fragments (e.g. PF@sub 3@ species produced by X-ray fragmentation on Ni(111) and CH@sub 3@SH, CH@sub 3@S- and S on Cu(111) following surface reaction), and determinations of the temperature-dependent local structure of CO adsorbed on Ni(111).