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P. Scheiber, A. Riss, M. Schmid, P. Varga, U. Diebold:
"Observation and Destruction of an Elusive Adsorbate with STM: O₂/TiO₂ (110)";
Physical Review Letters, 105 (2010), 2161011 - 2161014.

When a slightly defective rutile TiO2ð110Þ surface is exposed to O2 at elevated temperatures, the
molecule dissociates at defects, filling O vacancies (VO) and creating O adatoms (Oad) on Ti5c rows. The
adsorption of molecular O2 at low temperatures has remained controversial. Low-temperature scanning
tunneling microscopy of O2, dosed on TiO2ð110Þ at a sample temperature of # 100 K and imaged at 17 K,
shows a molecular precursor at VO as a faint change in contrast. The adsorbed O2 easily dissociates during
the STM measurements, and the formation of Oad ´s at both sides of the original VO is observed.