Liquid phase deposition synthesis of hexagonal molybdenum trioxide thin films

Hexagonal molybdenum trioxide thin films with good crystallinity and high purity have been fabricated by the liquid phase deposition (LPD) technique using molybdic acid (H2MoO4) dissolved in 2.82% hydrofluoric acid (HF) and H3BO3 as precursors. The crystal was found to belong to a hexagonal hydrate system MoO3.nH2O (n~0.56). The unit cell lattice parameters are a=10.651 Å, c=3.725 Å and V=365.997 Å3. Scanning electron microscope (SEM) images of the as-deposited samples showed well-shaped hexagonal rods nuclei that grew and where the amount increased with increase in reaction time. X-ray photon electron spectroscopy (XPS) spectra showed a Gaussian shape of the doublet of Mo 3d core level, indicating the presence of Mo6+ oxidation state in the deposited films. The deposited films exhibited an electrochromic behavior by lithium intercalation and deintercalation, which resulted in coloration and bleaching of the film. Upon dehydration at about 450 °C, the hexagonal MoO3.nH2O was transformed into the thermodynamically stable orthorhombic phase.