Through an interplay between density functional projected augmented wave calculations and Tersoff-Hamann (TH) simulations we model the adsorption and STM imaging of a commensurate Lepidocrocite TiO2 ultra-thin film on Ni(110). The fully optimised overlayer is found to be stable in agreement with recent experimental data.[1] A direct geometrical coincidence between the Ni[1-10] row and Lepidocrocite Oxygen bottommost layer is calculated to be strongly favourite over other possible adsorption configurations by 0.25 eV/TiO2 unit. The optimised metal-oxide adsorption distances for the most stable geometry are found to be in the range 1.6-1.9 Å and the maximum out of plane buckling is 0.37 Å for the topmost Oxygen layer. Careful analysis of the electronic structure for the optimised system reveals a close coincidence between the Fermi energy of the global system and the onset of the Lepidocrocite conduction band. Our TH results at 0.86 V assign experimental STM protrusions for this phase to Lepidocrocite topmost Oxygen atoms in line with the recently proposed for a Lepidocrocite bi-layer imaged on Pt(110)-(1x2).[2] Tungsten tip-induced atomic displacements for several tip-surface distances are calculated and found to deeply affect STM corrugation. In fact, it is shown that the experimental STM apparent heights (0.5-0.9 Å) can be accounted for only explicitly considering the different elastic properties of topmost Ti and O atoms.
References
[1] A.C. Papageorgiou. G. Cabailh, Q. Chen, A. Resta, E. Lundgren, J.N. Andersen, G. Thornton, sumbitted
[2] T. Orzali, M. Casarin, G. Granozzi, M. Sambi, A. Vittadini, Phys. Rev. Lett. 2006, 97, 156101. |