Che-Wei Chang

In this study, ZnO–WO₃ composite nanorods were synthesized through a combination of hydrothermal growth and sputtering method. The structural analysis results revealed that the as-synthesized composite nanorods had a homogeneous coverage of WO₃ crystallite layer. Moreover, the ZnO–WO₃ composite nanorods were in a good crystallinity. Further post-annealed the composite nanorods in a hydrogen-containing atmosphere at 400 °C induced the local phase transformation between the ZnO and WO₃. The ZnO–WO₃ composite nanorods after annealing engendered the coexistence of ZnWO₄ and WO₃ phase in the shell layer which increased the potential barrier number at the interfacial contact region with ZnO. This further enhanced the ethanol gas-sensing response of the pristine ZnO–WO₃ composite nanorods. The experimental results herein demonstrated a proper thermal annealing procedure of the binary composite nanorods is a promising approach to modulate the gas-sensing behavior the binary oxide composite nanorods.

Direct current (DC) magnetron sputtering deposited WO₃ films with different crystalline qualities were synthesized by postannealing at various temperatures. The in-situ DC sputtering deposited WO₃ thin film at 375 °C exhibited an amorphous structure. The as-grown WO₃ films were crystallized after annealing at temperatures of 400–600 °C in ambient air. Structural analyses revealed that the crystalline WO₃ films have an orthorhombic structure. Moreover, the crystallite size of the WO₃ film exhibited an explosive coarsening behavior at an annealing temperature above 600 °C. The density of oxygen vacancy of the WO₃ films was substantially lowered through a high temperature annealing procedure. The optical bandgap values of the WO₃ films are highly associated with the degree of crystalline quality. The annealing-induced variation of microstructures, crystallinity, and bandgap of the amorphous WO₃ thin films explained the various photoactivated properties of the films in this study.