Fig. 1

a Schematic of photoanode fabrication: simultaneous process of patterning a TiO₂ film and transferring the ZnO NRs while imprinting. SEM images: b the mold with periodically aligned vertical ZnO NRs on the GaN substrate. The inset is a photo image of the whole ZnO NR mold (a quarter size of 2-in. GaN wafer). c The transferred tilted ZnO NR array on the TiO₂ film. The inset shows a dye-adsorbed ZNL/TiO₂ photoanode in an area of 4 cm². d A defect area, where ZnO NRs were not transferred on the TiO₂ film, showing hole trenches. e The holey TiO₂ film, which was achieved by complete wet etching of the embedded ZnO NRs with an acidic solution. All scale bars, 2 μm