Regensburg 2016 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 43: Oxides and Insulators: Adsorption I
O 43.1: Vortrag
Dienstag, 8. März 2016, 14:00–14:15, H6
Dissociated but not separated: Adsorption of water at the SrO surface of ruthenates — Florian Mittendorfer1, Daniel Halwidl1, Bernhard Stöger1, Wernfried Mayr-Schmölzer1, Jiri Pavelec1, David Fobes2, Jin Peng2, Zhiqiang Mao2, Gareth Parkinson1, Michael Schmid1, •Josef Redinger1, and Ulrike Diebold1 — 1Inst. of Applied Physics, TU Wien, Vienna, Austria — 2Dept. of Physics, Tulane University, New Orleans, USA.
Despite their great promise in applications ranging from solid oxide fuel
cells to catalysts, molecular level knowledge about the surface chemistry of perovskite oxides is surprisingly poor. To gain more insight, we follow the formation of the first monolayer of H2O at the (001) surfaces of
Srn+1RunO3n+1 (n=1,2) using low-temperature STM,
XPS, and DFT. These layered perovskites cleave between neighbouring SrO planes, yielding almost ideal, rocksalt-like surfaces. An adsorbed monomer dissociates and forms a pair of hydroxide ions. The OH stemming from the original molecule stays trapped at Sr-Sr bridge positions, circling the surface OH with a measured activation energy of 187 ± 10 meV confirming almost perfectly the calculated DFT value of 171 meV [1]. At higher coverage, dimers of dissociated H2O assemble into one-dimensional chains and form a percolating network where H2O adsorbs molecularly in the gaps. Our work clearly shows that caution is needed when applying surface chemistry concepts derived for binary rocksalt oxides to perovskites.
D. Halwidl et. al., Nature Materials, doi: 10.1038/nmat4512, 2015.