Crystal phase content-dependent functionality of dual phase SnO2–WO3 nanocomposite films via cosputtering crystal growth

Abstract

In this study, crystalline SnO₂–WO₃ nanocomposite thin films were grown through radio-frequency cosputtering of metallic Sn and ceramic WO₃ targets. The W content in the SnO₂ matrix was varied from 5.4 at% to 12.3 at% by changing the WO₃ sputtering power during thin-film growth. Structural analyses showed that increased WO₃ phase content in the nanocomposite films reduced the degree of crystallization of the SnO₂ matrix. Moreover, the size of the composite films' surface crystallites increased with WO₃ phase content, and the large surface crystallites were composed of numerous nanograins. Addition of WO₃ crystals to the SnO₂ matrix to form a composite film improved its light harvesting ability. The SnO₂–WO₃ nanocomposite films exhibited improved photodegradation ability for Rhodamine B dyes compared with their individual constituents (i.e., SnO₂ and WO₃ thin films), which is attributable to the suitable type II band alignment between the SnO₂ and WO₃. Moreover, an optimal WO₃ phase content (W content: 5.4 at%) in the SnO₂ matrix substantially enhanced the ethanol gas-sensing response of the SnO₂ thin film. This suggested that the heterojunctions at the SnO₂/WO₃ interface regions in the nanocomposite film considerably affected its ethanol gas-sensing behavior.