A scanned-energy mode photoelectron diffraction study of the structure of Ni(111)(2x2)-O

A scanned-energy mode photoelectron diffraction study has been conducted of the Ni(111)(2 x 2)-O chemisorption phase using O Is modulation spectra recorded in a range of different emission directions. The O atom is found to occupy the ''fcc'' hollow site, directly above third layer Ni atoms. The exact O-Ni outermost layer spacing and the possible magnitude of outermost substrate layer ''rumpling'' and lateral distortions have been investigated through comparisons with the results of multiple scattering theory calculations. The Values obtained are compared with those given by several recent LEED studies, and the relative sensitivity of the two methods to some of these parameters is discussed. In particular, the problem of parameter-coupling in structure determination is investigated. The combination of the present results and those of the most recent LEED studies indicate that there is no significant lateral distortion of the outermost Ni layer.