Direct structure analysis of W(110)-(1x1)-O by full solid-angle x-ray photoelectron diffraction with chemical-state resolution

The atomic structure of the W(110)-(1 x 1)-O surface with an additional (1 x 12) periodicity has been determined using full solid-angle X-ray photoelectron diffraction (XPD) patterns with chemical-state resolution. The W 4f binding energy of atoms directly bonded to oxygen is 0.73 eV higher than that of "bulk" W atoms. The full solid-angle XPD data for this shifted peak show strong forward focusing peaks, making it possible to estimate the adsorbate position directly. The oxygen is found to be in a triply-coordinated site, with a height of about 1.1 Angstrom above the first-layer W atoms, and a lateral distance between the oxygen atom and the top of the triangle of W atoms of l=1.5 Angstrom, which is shifted from the centered position of l=1.67 Angstrom. This position of the oxygen atoms was then used as a starting point for a more refined structure analysis by fitting theoretically calculated patterns to the observed XPD data. This gives a more precise position of z=0.84 Angstrom and l=1.52 Angstrom, in good agreement with the XPD estimate. (C) 1998 Elsevier Science B.V. All rights reserved.