Nanostructured tungsten and tungsten trioxide films prepared by glancing angle deposition

Nanostructured tungsten (W) and tungsten trioxide (WO3) films were prepared by glancing angle deposition using pulsed direct current magnetron sputtering at room temperature with continuous substrate rotation. The chemical compositions of the nanostructured films were characterized by X-ray photoelectron spectroscopy, and the film structures and morphologies were investigated using X-ray diffraction and high resolution scanning electron microscopy. Both as-deposited and air annealed tungsten trioxide films exhibit nanostructured morphologies with an extremely high surface area, which may potentially increase the sensitivity of chemiresistive WO3 gas sensors. Metallic W nanorods formed by sputtering in a pure Ar plasma at room temperature crystallized into a predominantly simple cubic β-phase with <100> texture although evidence was found for other random grain orientations near the film/substrate interface. Subsequent annealing at 500 °C in air transformed the nanorods into polycrystalline triclinic/monoclinic WO3 structure and the nanorod morphology was retained. Substoichiometric WO3 films grown in an Ar/O2 plasma at room temperature had an amorphous structure and also exhibited nanorod morphology. Post-deposition annealing at 500 °C in air induced crystallization to a polycrystalline triclinic/monoclinic WO3 phase and also caused a morphological change from nanorods into a nanoporous network.