Measurement of the surface-growth kinetics of reducedTiO2(110)during reoxidation using time-resolved scanning tunneling microscopy

Abstract

We have employed variable-temperature scanning tunneling microscopy ͑STM͒ to follow the kinetics of reoxidation of a nonstoichiometric TiO 2 ͑110͒ single-crystal surface. The surface is seen to grow during reoxidation between 573 and 1000 K and at pressures from 5ϫ10 Ϫ8 to 2ϫ10 Ϫ6 mbar O 2 . The reaction proceeds by combination of gas-phase O 2 with mobile interstitial Ti 3ϩ from the bulk. The surface is observed to grow new layers of TiO 2 in a cyclic process, resulting in the formation of alternate layers of (1ϫ1) and cross-linked (1ϫ2). 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 ϳ25Ϯ4 kJ mol Ϫ1 ͑0.25Ϯ0

Surface and interstitial Ti diffusion at the rutile TiO2(110) surface

“…Whilst our finding that Ti interstitials are more energetically favourable than adatoms agrees with experimental results for adatoms diffusing down into the bulk upon annealing, 14 trapping them in the bulk by such a large amount as 2.5 eV does not accord with the re-growth of reduced rutile at elevated temperature, even if oxygen ad-species promote the growth. 9,10,15 We conclude that the empirical QEq potential of Hallil et al 28 overestimates the adsorption energy of the interstitials with respect to the adatom energy.…”

Surface and interstitial transition barriers in rutile (110) surface growth

“…11,12 The observations showed that the rutile ͑110͒ surface grows by combination of gas-phase oxygen with mobile interstitial Ti 3+ ions from the bulk. The diffusion and reaction of titanium interstitials with adsorbed oxygen have been examined theoretically, 13 and it was found that the energy barriers for Ti interstitial diffusion and reaction were 0.75 and 1.2 eV, respectively.…”

Adsorption, Diffusion and Desorption of Chlorine on and from Rutile TiO2{110}: A Theoretical Investigation

“…This titanium-covered surface is then oxidised by molecular oxygen and further TiCl 4 can adsorb and decompose. Bowker and co-workers investigated the kinetics of the reoxidation of reduced TiO 2 {110} [9], however, the full cycle of the growth is not yet fully understood. A scheme of the presumed surface growth from layer n to layer n+1 is given in Figure 1.…”