Photocatalytic study for indium tantalum oxide thin film in visible light

Indium tantalum oxide thin film was deposited by sputtering using three different designs: 5–7 and 10–14 nm alternative layers of Ta₂O₅ and In₂O₃ and co-sputtering of In₂O₃ and Ta₂O₅. Then, as-deposited films were rapidly annealed at different temperatures to assess the thermal effects on microstructures and photocatalytic functions. Results from XRD and energy-dispersive x-ray spectrometer indicate that crystalline InTaO₄ emerges in 5–7 and 10–14 nm stacks of films but absent in the co-sputtered films. Since crystalline InTaO₄ is capable of photocatalysis under both ultraviolet and visible light, the authors particularly tested the annealed films in water to degrade methylene blue under visible light. The photo-induced degradation on methylene blue by 5–7 and 10–14 nm stacks can reach 45% after 6-h continuous exposure. Using UV-Visible-Near Infrared spectroscopy, the authors can estimate the optical bandgaps in these annealed films and from these estimations, a mechanism for the photocatalysis is discussed. This mechanism is similar to the other electron-hole separation and transfer across the heterogeneous junctions in semiconductors.