Determination of adsorbate geometries from final state scattering in X-ray photoemission: Carbon monoxide and oxygen on (001) Ni

• Published in: Materials science and engineering 1980, Vol.42, p.111-119
• Main Authors: Petersson, L.-G, Kono, S, Hall, N.F.T, Goldberg, S, Lloyd, J.T, Fadley, C.S, Pendry, J.B
• Format: Article
• Language: English
• ISSN: 0025-5416
• DOI: 10.1016/0025-5416(80)90018-X

Azimuthal anisotropies in deep core level X-ray photoemission from atoms adsorbed on single-crystal surfaces have recently been observed and been found to be well described by a single-scattering model, thereby providing a new method for determining surface atomic geometries. We here apply this technique to a molecular chemisorption system, specifically c(2 × 2) CO on (001) Ni. When the C 1s intensity is measured as a function of the polar angle, a peak in intensity with magnitude I max /I back = 1.5 and a full width at half maximum intensity of 25° is found to be centered on the surface normal. The average orientation of CO is thus determined to be within 12° of normal. Also oxygen atoms chemisorbed on (001) Ni were studied as a function of exposure to O 2. The azimuthal variation of the O 1s intensity is strongly dependent on the oxygen coverage. For voverages greater than 0.5 monolayer the best agreement between theory and experiment is obtained if the oxygen atoms are assumed to lie approximately coplanar with the surface nickel atoms. For lower coverages (⪅0.3) an adsorbate vertical position of about 0.8 Å above the first nickel layer gives the best fit. These results are in qualitative agreement with prior experimental studies of this system using other methods and thus suggest a potentially wide applicability of similar measurements for surface structure determinations.