Electronic structure studies of Ni(100) surface reconstructions resulting from carbon, nitrogen, or oxygen atom adsorption

Solid-state Fenske-Hall band structure calculations have been used to study the different surface structures which result from adsorption of a half monolayer of Q N, or 0 atoms on the Ni(I 0 0) surface. C or N atoms sit nearly coplanar with the surface Ni atoms and induce the "clock" reconstruction of the surface. In contrast, adsorbed 0 atoms sit slightly above the Ni(I 0 0) surface plane and have little effect on the overall surface structure. The local environments of the Q N, and 0 atoms on these surfaces are similar to their environments in a series of late transition metal carbonyl clusters, suggesting that some of the same electronic factors may play a role in favoring the different structures. Results of the calculations indicate that when adsorbates occupy coplanar sites on Ni(I 0 0), much of the Ni-Ni bonding within the surface layer and between the surface- and second-layers is disrupted. On the G and N-covered surfaces the disruption is more than compensated for by the formation of strong adsorbate-Ni bonds and by new Ni-Ni surface bonds resulting from the clock reconstruction. When 0 is forced into a coplanar site, however, both the higher electron count and increased electronegativity of the 0 atoms lead to severe disruption of the surface bonding and weak Ni-O bonds. When 0 atoms sit above the surface, they form more polar Ni 0 bonds, contribute less electron density to the Ni surface bands, and cause less disruption to Ni-Ni surface bonds. These results suggest that, similar to the organometallic clusters, the site preferences of Q N, and 0 atoms are directly related to their electron count, and in turn to the relative occupation of both Ni-Ni and X-Ni (X = Q N, 0) antibonding bands. (C) 2002 Elsevier Science B.V. All rights reserved.