LETTERS Spatial Separation of Photochemical Oxidation and Reduction Reactions on the Surface of Ferroelectric BaTiO3

When BaTiO3 is illuminated by ultraviolet light in aqueous solutions containing dissolved Pb2+ or Ag+ cations, photochemical reaction products are deposited on the surface in patterns that correspond to the underlying ferroelectric domain structure. On the basis of an analysis of the domain polarization, oxidized Pb and reduced Ag accumulate on the surfaces of domains with opposite polarization. When the domain dipole has its negative end directed toward the surface, Pb is oxidized, and when the dipole is reversed, Ag is reduced. On the basis of these observations, we propose that the static dipolar fields in the different domains separate photogenerated charge carries. In those domains where photogenerated holes are driven to the solid-liquid interface, oxidation is preferred. In oppositely oriented domains, where the field drives photogenerated electrons to the surface, the reduction reaction is preferred. Thus, the separation of charge carriers in the ferroelectric domains creates patterns of oxidized and reduced products on the surface of BaTiO3 that correspond to the domain structure.