Controlled Thermal Annealing Tunes the Photoelectrochemical Properties of Nanochanneled Tin-Oxide Structures

We study the effect of thermal annealing conditions (up to 400 degrees C) and atmospheres (air, Arand O-2) on a newly developed nanochannel tin-oxide structure. The nanochanneled structures were prepared by self-organized anodization of metallic tin. Thermal annealing conditions have a strong impact on the crystallinity and content of Sn2+ defects present in the structure, and thus have a strong influence on the photoresponse characteristics of the films. Photocurrent measurements show that films annealed at 200 degrees C in Ar atmosphere exhibit a band gap as low as 2.4 eV and a photoresponse in the visible range. This effect is ascribed to a large content of Sn2+ defects in the structure and the improved crystallinity of the films annealed at this temperature. On the contrary, the Sn2+ content is decreased when annealing at 400 degrees C under aerobic conditions, which correlates with a shift in the film band gap to 3.2 eV, closer to the reported value for pure SnO2 (3.6 eV).