Fabrication and correlation between photoluminescence and photoelectrochemical properties of vertically aligned ZnO coated TiO2 nanotube arrays

We report on a study on the correlation between the photoluminescence and the photoelectrochemical properties of ZnO–TiO2 heterogeneous nanostructure composed of anatase TiO2 nanotubes and wurtzite ZnO coatings. Vertically aligned ZnO coated TiO2 nanotube (ZnO/TiO2 NT) arrays have been fabricated by atomic layer deposition of ZnO coatings on electrochemical anodization formed TiO2 nanotubes. The obtained ZnO/TiO2 NT arrays show higher photoresponse to shorter wavelength light than to longer wavelength light. A reduction in photoluminescence and an enhancement in photoelectrochemical activity are observed for annealed ZnO/TiO2 NT arrays. ZnO/TiO2 NTs with thinner ZnO coatings rather than thicker ZnO coatings have better photoelectrochemical properties. Compared with bare TiO2 NT arrays, an increase in photocurrent of about 50 percent is obtained for the arrays of 450°C annealed of ZnO/TiO2 NTs with 10-cycle deposition of ZnO coatings under visible illumination with cutoff of 420nm.