X-ray photoelectron diffraction from adsorbate core levels in the energy range 500–10000 ev and with polarized radiation: a theoretical study

X-ray photoelectron diffraction (XPD) from adsorbate core levels shows considerable promise as a surface-structural probe, especially since a simple single-scattering theory appears capable of describing such photoelectron diffraction. In the past, several types of XPD structural investigations have been made using conventional Al Kα radiation, including determinations of bond orientations for diatomic molecular adsorption and of vertical bond distances for atomic adsorption. In this work, a theoretical investigation has been made within the single-scattering cluster model to determine the possible advantages and disadvantages of using different photon energies over a broad range from 500 to 10000 eV and/or a polarized radiation source in such structure determinations. Two test cases, of intramolecular scattering in C 1s polar scans above vertically adsorbed CO and of interatomic scattering in O 1s azimuthal scans for c (2 × 2) O on Cu(100), are considered in detail. In general, precision in determining bond orientations can be unproved by using higher energies and/or polarized radiation, although it may be more difficult to obtain the data owing to lower percent effects and lower total intensities. In azimuthal scans, going to higher energy yields narrower features, but requires much lower takeoff angles and concomitantly lower intensities. Other aspects of using variable energy and polarization in XPD are also considered.