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H. Over, A.P. Seitsonen, E. Lundgren, M. Schmid, P. Varga:
"Experimental and simulated STM images of stoichiometric and partially reduced RuO₂(110) surfaces including adsorbates";
Surface Science, 515 (2002), 143 - 156.

We present experimental and DFT-simulated STM images of ultrathin RuO₂(110) films on Ru(0001),
including adsorbates such as oxygen and CO. We are able to identify the under-coordinated O atoms on the
RuO₂(110) surface with STM, i.e. the bridging O atoms and the on-top O atoms. The partial reduction of the
RuO₂(110) surface by CO exposure at room temperature leads to a surface where part of the bridging O
atoms have been removed and some of the vacancies are occupied by bridging CO. When dosing 10 L of CO
at room temperature, all the RuO₂(110) surface becomes mildly reduced in that all bridging O atoms are
replaced by bridging CO molecules. Annealing the surface to 600 K produces holes on the terraces of such
a mildly reduced RuO₂(110) surface. These pits are not generated by the recombination of lattice O with
CO, but rather these pits are assigned to a complex temperature-induced rearrangement of surface atoms
in the topmost RuO₂ double layer of RuO₂(110). With this process the bridging O atoms are again populated
and surplus Ru atoms agglomerate in small islands at the rims of the holes.

http://www.iap.tuwien.ac.at/www/SURFACE/abstracts/A2002E11.HTML