Regensburg 2019 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 8: Metal Substrates I: Adsorption and Reactivity
O 8.2: Vortrag
Montag, 1. April 2019, 10:45–11:00, H25
Ground state structure for 0.5 ML oxygen on Rh(100) — Tilman Kißlinger1, Margareta Wagner2, Michael Schmid2, Ulrike Diebold2, •M. Alexander Schneider1, and Lutz Hammer1 — 1Ls. f. Festkörperphysik, Univ. Erlangen — 2Inst. f. Angewandte Physik, TU Wien
The structure of 0.5 ML oxygen on Rh(100) was so far reported by experiment [1] and theory [2] to be a (2×2)-2O supercell where O sits on threefold hollow sites of the clockwise-anticlockwise reconstructed Rh(100). Newly taken LEED-IV data at first sight confirm this model with a quite low Pendry R-factor of R = 0.12. However, like in [1] the model fails to explain extinctions of diffraction spots in the LEED pattern and it also disagrees with DFT calculations that predict a 12 pm buckling between surface Rh atoms. Allowing for positional disorder of oxygen within the (2×2)-2O cell improves the fit of our LEED-IV data taken at 100 K and restores the symmetry elements. By STM at room temperature a (2×2) periodicity is found while at 77 K and 4 K the system is well-ordered with c(4×4)-4O surface cell. Applying DFT to a model with alternate occupation of threefold hollow sites by oxygen atoms reproduces the experimental STM image and shows that the c(4×4)-4O is energetically more favourable than the (2×2)-2O by 4 meV per oxygen atom. Furthermore, the new model describes the LEED-IV data with R = 0.08 even better, i.e. the structural elements of the c(4×4)-4O are locally present also at 100 K. [1] A. Baraldi et al., PRL 82, 4874 (1999) [2] D. Alfè et al., Surf. Sci. 410, 151 (1998)