X-RAY PHOTOELECTRON DIFFRACTION STUDY OF THE RECONSTRUCTED NI(110)-1X2-H SURFACE

Hydrogen-induced reconstruction of Ni(110) was studied by X-ray photoelectron diffraction (XPD) in the polar angle (theta) scanning mode. The angle-resolved emission of Ni2p and Ni3p photoelectrons along the [001] and [110BAR] azimuths for the 1 x 1 and the reconstructed 1 x 2-H surface of Ni(110) was measured at 120 K. The XPD patterns showed intensity differences, DELTAI(rec)(theta) = I(theta, 1 x 2) - I(theta, 1 x 1), which are characteristic of the reconstruction process. These differences, amounting to about 8% of the minimum intensity in a single distribution, exhibit positive and negative excursions for the [001] azimuth. The maxima in DELTAI(rec) are frequently observed at the same angles where minima exist in I(theta), and minima in DELTAI(rec) correlate with maxima in I(theta). These changes are attributed to altered forward scattering and diffraction directions, elastic diffuse and inelastic scattering (attenuation), all due to the shifting of near-surface atoms. The differences DELTAI(rec) for the [110BAR] azimuth are negative over the whole range of polar angles indicative of elastic diffuse scattering and inelastic damping of the bulk forward scattering peaks. Single scattering cluster calculations for the 1 x 1- and 1 x 2-H-Ni(110) surface are compared with the experimental results; the intensity differences are approximatety consistent with a row-pairing reconstruction.