Aerosol assisted chemical vapour deposition of MoO3 and MoO2 thin films on glass from molybdenum polyoxometallate precursors; thermophoresis and gas phase nanoparticle formation

Abstract

Aerosol assisted chemical vapour deposition (AACVD) of molybdenum polyoxometallates dissolved in acetonitrile or water yielded adhesive thin films of molybdenum oxides on glass. At substrate temperatures of 300-350 uC single phase MoO 3 was obtained, from 350-500 uC mixed phases of MoO 3 -MoO 2 were formed and at 500-550 uC single phase MoO 2 was observed. The morphology of the as-deposited molybdenum oxide films was found to be dependent upon a number of factors including the nature of the precursor used, the deposition temperature and position of the film within the reactor. Needles, spheres, agglomerates and platelets formed depending on the conditions. The films with a needle-like microstructure displayed enhanced hydrophobicity to water droplets (125u contact angle). X-Ray diffraction showed that the MoO 3 films had typical cell constants of a = 3.96, b = 13.85, c = 3.69 A ˚and the MoO 2 films had typical cell constants of a = 5.62, b = 4.84, c = 5.56 A ˚, b = 119.32u. The MoO 2 films were readily converted to MoO 3 by annealing in air for 30 minutes at 600 uC. The MoO 3 films functioned as gas sensors showing a linear change in electrical resistance upon exposure to trace amounts of ethanol vapour in air.

Polyoxometalate Complexes as Precursors to Vanadium‐Doped Molybdenum or Tungsten Oxide Thin Films by Means of Aerosol‐Assisted Chemical Vapour Deposition

“…Sample XPS spectra for the Mo 3d and W 4f transitions of POM 1 and 3 is shown in Figure . The Mo‐based POMs 1 and 2 showed Mo 3d 5/2 peaks at 232.9 and 232.7 eV, respectively, which correspond to Mo in the 6+ oxidation state . Peaks at lower binding energies that correspond to reduced states in the Mo 3d XPS spectra were also observed.…”

“…Thin films of Mo oxides have been previously made using dual‐source precursors, such as molybdenum hexacarbonyl, [Mo(CO) 6 ] and oxygen, and from single‐source precursors such as molybdenum pentacarbonyl 1‐methylbutylisonitrile . Molybdenum(VI) oxide exists in two basic crystal structures with different molecular vibrational and optical properties: α‐MoO 3 with orthorhombic symmetry and metastable monoclinic β‐MoO 3 ; MoO 2 also has a monoclinic structure . Molybdenum trioxide (MoO 3 ), the technologically more significant form of the oxide, exists in the orthorhombic phase and has a double‐layered structure .…”

“…[1] An umber of different structural types of POM clusters exist [1, 2b] but the Keggins tructure was the first to be discovered. [1] Keggin-type POMs can be represented by the formula [XM 12 O 40 ] nÀ in which Xi st he central heteroatom (e.g.,P ,S io rB )w ith four oxygen atoms bonded tetrahedrally to it, andM(usually Mo, Wo rV )i st he addendao rp eripheral atom (the metal atoms that make up the framework).T he cen-tral atom is surrounded by 12 octahedronsm ade of MO 6 and all the oxygen atomsa re shared except for the 12 terminal oxygen atoms, which are attached to only one atom.…”

Preparation of MoO3Thin Films by Spray Pyrolysis and its Gas Sensing Performance

“…The observed peaks from XRD spectrum is well matches with the standard data [25]. The average crystallite size was calculated from major peaks using Scherer formula [26] which was found to be 124 nm, indicating their nanocrystalline nature.…”

Gas sensing properties of thermally evaporated lamellar MoO3

“…A number of techniques was reported for the deposition of MoO 3 including pulse laser deposition [12], thermal evaporation [20], sputtering [21], sol-gel [1,22], spray pyrolysis [23], chemical vapour deposition [24,25], and electro-deposition [26]. The deposition of MoO 3 using evaporative techniques is advantageous as it can produce highly crystalline and stratified structures.…”