TiO2 thin film prepared by atomic layer deposition was subjected to annealing in hydrogen at temperatures 350-500 degrees C. Hydrogenation induced the formation of disordered states and oxygen vacancies that resulted in increased surface roughness. Furthermore, it was discovered that oxygen vacancies were mostly formed on the surface, and their concentration and distribution uniformity increased with increasing temperature. The most uniform distribution of oxygen vacancies with the highest surface density was obtained after annealing at 500 degrees C, which is consistent with the lowest electron-hole recombination rate and highest photoactivity of the modified TiO2. (C) 2015 Elsevier Inc. All rights reserved.