Structure Sensitivity of Photochemical Oxidation and Reduction Reactions on SrTiO3 Surfaces

The photochemical reduction of Ag and oxidation of Pb from aqueous solution by SrTiO3 leave insoluble reaction products (silver and PbO2, respectively) on the surface. Microscopic analysis has been used to relate the rates of these two reactions to the structure and orientation of SrTiO3 surfaces. The nonpolar (100) surface is the most reactive for silver reduction and the composition of the termination layer does not influence this reaction. On the polar (111) surface, the reduction and oxidation reactions occur on terraces with different terminations and opposite charges; this leads to a nonuniform distribution of reaction products. The polar (110) surface is the least reactive, and the majority of the reaction products are observed at steps along <100> directions where the more reactive {100} surfaces are exposed. The distribution of oxidation products found on (110) terraces is also influenced by the composition and charge of the surface termination. The results show that the photochemical reactivity of SrTiO3 is anisotropic and that, on polar surfaces, dipolar fields arising from charged surface domains influence the transport of photogenerated charge carriers and promote spatially selective oxidation and reduction reactions.