Experimental investigations have shown that bridging oxygen (O br ) atoms on the highly non-stoichiometric TiO 2 (110) surface cluster together into nearest-neighbor pairs. Theoretically, this behavior has been observed in simulations of an O br vacancy interaction model for TiO 2 (110) in the high-vacancy-concentration limit. However, an interaction model that focuses on oxygen vacancies is ill-equipped to explain the behavior of interacting oxygen adatoms on a nearly fully reduced (i.e., O br

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... -depleted) surface. Therefore, to better understand this behavior, we have constructed an adatom-adatom lattice-gas model for oxygen on the fully reduced TiO 2 (110) surface and performed an extensive set of Monte Carlo simulations on this model. 1875-3892 c