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

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Smith, R. D. ; Bennett, R. A. ; Bowker, Michael (2002)

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 5×10-8 to 2×10-6 mbar O2. The reaction proceeds by combination of gas-phase O2 with mobile interstitial Ti3+ 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 (1×1) and cross-linked (1×2). 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 ∼25±4 kJ mol-1 (0.25±0.04 eV/O2 molecule) for the surface reaction.
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