Measurement of the surface-growth kinetics of reduced TiO2„110... during reoxidation using time-resolved scanning tunneling microscopy

We have employed variable-temperature scanning tunneling microscopy ~STM! to follow the kinetics of reoxidation of a nonstoichiometric TiO2 ~110! single-crystal surface. The surface is seen to grow during reoxidation between 573 and 1000 K and at pressures from 5310 to 2310 mbar O2 . The reaction proceeds by combination of gas-phase O2 with mobile interstitial Ti 31 from the bulk. The surface is observed to grow new layers of TiO2 in a cyclic process, resulting in the formation of alternate layers of (131) and cross-linked (132). The growth rate was calculated by measuring the area of new material grown on consecutive STM images of the same area. The rate shows a linear dependence upon oxygen pressure, with an Arrhenius plot indicating an activation barrier of ;2564 kJ mol ~0.2560.04 eV/O2 molecule! for the surface reaction.