Berlin 2012 – scientific programme
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O: Fachverband Oberflächenphysik
O 14: Adsorption on semiconductors, oxides and insulators II
O 14.4: Talk
Monday, March 26, 2012, 16:45–17:00, MA 041
Adsorbate-induced reconstructions of the polar NiO(111) surface — •Christina Ebensperger and Bernd Meyer — Interdisziplinäres Zentrum für Molekulare Materialien und Computer-Chemie-Centrum, Universität Erlangen-Nürnberg
Bulk-truncated structures of polar surfaces are intrinsically unstable and especially susceptible to reconstructions and reactions with adsorbates. Indeed, our DFT+U calculations show that the adsorption of small molecules (H2, O2, H2O, CO, CO2) on NiO(111) alters the surface structure considerably. Phase diagrams of the energetically most stable surface reconstructions depending on temperature and pressure conditions exhibit a wide variety of configurations with different degree of surface hydroxylation and carbonate formation. An adsorbate free (2×2)-O-octopolar structure, a fully hydroxylated (1×1)-OH surface and tridentate carbonate complexes including O surface atoms are energetically most favorable. Interestingly, in many cases the transformation between different stable phases does not only involve adsorption or desorption of molecules and the rearrangement of Ni and O surface atoms, but also requires mass transport/diffusion of NiO units. NEB calculations for reaction barriers of subprocesses of transformations between surface structures explain the observed high thermal stability of surface carbonates and hydroxyl groups.
[1] C. Ebensperger, B. Meyer, phys. stat. sol. (b) 248 (2011) 2229