Titania films, 15-100 nm thick, have been grown on BaTiO 3 substrates and used to photochemically reduce Ag þ to Ag 0 and oxidize Pb 2þ to Pb 4þ 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 donordoped 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.
Titania films were grown on BaTiO 3 (BTO) substrates by pulsed laser deposition to create (001) Anatase ||(100) BTO , (100) Rutile ||(111) BTO , and (110) Rutile ||(110) BTO heterostructures. The photochemical reactivity was evaluated by observing the amount of silver reduced by each film under identical conditions. The thickest films (100 nm) had reactivities that varied with the phase of titania and the crystal orientation. Thin films (15 nm), on the other hand, had reactivities that were approximately the same. Furthermore, reaction products were spatially distributed in patterns consistent with the underlying domain structure of the substrate. For the case of (110) Rutile ||(110) BTO , the thin films are more reactive than the thick films, showing that the dipolar fields in the ferroelectric substrate enhance the reactivity of (110) rutile.
Titania films have been grown on polycrystalline BaTiO3 (BTO) substrates at 700°C by pulsed laser deposition. Electron backscatter diffraction (EBSD) was used to determine grain orientations in the substrate before growth, and the phase and orientation of the supported films after growth. All BaTiO3 grains within 26° of (001) were covered by anatase films with an orientation relationship of (001)Anatase||(001)BTO and [100]Anatase||[100]BTO. Rutile with a variety of orientations grew on BaTiO3 grains with orientations closer to (110) and (111). EBSD mapping provides an efficient means for determining phase and orientation relationships of films over all orientation parameters.
Ba1-xSr
x
TiO3 solid solutions with x = 0−1 were used to photochemically reduce aqueous Ag+ to Ag0. The reduction of Ag on BaTiO3 is spatially selective and correlated to the locations of positive ferroelectric domains. On SrTiO3, silver reduction is spatially uniform. As strontium is added to BaTiO3, there is a continuous change from spatially localized to uniform reactivity that is complete at x > 0.27. The relative heights of the silver deposits, as measured by atomic force microscopy, were used to quantify the relative reactivities. A local maximum in the reactivity is observed at x = 0.26, which is near the cubic-tetragonal phase boundary. The change from spatially selective to spatially uniform reactivity is associated with decreased polarization as the strontium concentration increases. The local maximum in reactivity near the phase boundary is associated with an anomalously high dielectric constant at this composition that enlarges the space-charge region. The results are consistent with the idea that the width of the space-charge region is an important factor in determining the photochemical reactivity.
Optical absorption and reflectance spectroscopy have been used to monitor the photochemical reactivity of Ba1−xSrxTiO3 solid solutions with aqueous solutions containing methylene blue. Atomic force microscopy indicates that methylene blue is reduced on the surfaces of domains that have a positive surface polarization. The results indicated that SrTiO3 and BaTiO3 have similar reactivities. As the second component is added to either of the pure materials, the reactivity decreases. However, there is a sharp maximum in reactivity at the tetragonal‐to‐cubic phase boundary. This is attributed to the anomalously high dielectric constant at this composition that increases the width of the space charge region and charge carrier separation in the near surface region.
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