Photochemical Reactivity of Titania Films on BaTiO₃Substrates: Origin of Spatial Selectivity

Titania films, 15−100 nm thick, have been grown on BaTiO 3 substrates and used to photochemically reduce Ag + to Ag 0 and oxidize Pb 2+ to Pb 4+ under ultraviolet illumination. Atomic force microscopy was used to show that the reactions are spatially selective and that the pattern of products on the film surface reproduces the pattern of products on the bare substrate. The influence of the substrate on the pattern of reactants is diminished as the film thickness increases and is quenched when the film is donor-doped with Nb. The results indicate that for thin (15 nm) films, dipolar fields from the ferroelectric domains cause carriers generated in the substrate to travel through the film to react on the surface.