HRTEM Microstructural Characterization of β-WO(3) Thin Films Deposited by Reactive RF Magnetron Sputtering

Though tungsten trioxide (WO(3)) in bulk, nanosphere, and thin film samples has been extensively studied, few studies have been dedicated to the crystallographic structure of WO(3) thin films. In this work, the evolution from amorphous WO(3) thin films to crystalline WO(3) thin films is discussed. WO(3) thin films were fabricated on silicon substrates (Si/SiO(2)) by RF reactive magnetron sputtering. Once a thin film was deposited, two successive annealing treatments were made: an initial annealing at 400 °C for 6 h was followed by a second annealing at 350 °C for 1 h. Film characterization was carried out by X-ray diffraction (XRD), high-resolution electron transmission microscopy (HRTEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM) techniques. The β-WO(3) final phase grew in form of columnar crystals and its growth plane was determined by HRTEM.