Observation and Destruction of an Elusive Adsorbate with STM: O2/TiO2(110)

When a slightly defective rutile TiO2(110) surface is exposed to O-2 at elevated temperatures, the molecule dissociates at defects, filling O vacancies (V-O) and creating O adatoms ( O-ad) on Ti-5c rows. The adsorption of molecular O-2 at low temperatures has remained controversial. Low-temperature scanning tunneling microscopy of O-2, dosed on TiO2(110) at a sample temperature of approximate to 100 K and imaged at 17 K, shows a molecular precursor at V-O as a faint change in contrast. The adsorbed O-2 easily dissociates during the STM measurements, and the formation of O-ad 's at both sides of the original V-O is observed.