Comparative study of angle-resolved valence-band photoemission from half-monolayer structures of C, N, and O on Ni(100)

Angle-resolved synchrotron-radiation photoemission has been used to map the adsorbate-induced surface valence bands of the simple chemisorbed Ni(100)c(2×2)-O structure and the reconstructed Ni(100)(2×2)-N structure; the results are compared with a similar previous study of the reconstructed Ni(100)(2×2)-C structure. The oxygen adsorption system shows three 2p-derived bands broadly in agreement with early calculations by Liebsch, although the splitting of the $p_z$ and $p_x$,$p_y$ bands at the Γ¯ point is revealed convincingly only in data taken in the second surface Brillouin zone and folded back to the zone center; at normal emission on the Ni(100) substrate, emission due to a Ni satellite peak confuses the interpretation. The two adsorbate-induced reconstructed surfaces show some systematic differences, both in the presence of additional structure close to the Fermi level and in the apparent absence of a 2p-derived band which can be assigned to $p_z$ character. Symmetry of the glide plane restricts the observed adsorbate band dispersion to be close to that of the unreconstructed Ni(100)-O structure, c(2×2).