Dealloying Derived Synthesis of W Nanopetal Films and Their Transformation into WO3

Cross-linked W nanopetals were synthesized by dealloying the sputtered W−Al alloy film in HNO 3 aqueous solution for 24 h under open circuit conditions. Scanning electron microscopy, X-ray diffraction, and transmission electron microscopy characterizations demonstrate that the W nanopetals are less than 100 nm in thickness and have a cubic crystal structure. The W nanopetals were transformed into monoclinic phase WO 3 nanopetals by a controlled thermal oxidation process at 500 °C in air. A gas sensor made using the WO 3 nanopetals showed promising NO 2 sensing performance. The present work indicates a new approach to fabricate high surface area oxide materials for applications such as gas sensors, catalysis, and photochemical devices.