Abstract
MoO3 films were deposited on Corning glass and silicon substrates held at room temperature (303 K) by RF magnetron sputtering of metallic molybdenum target at a fixed oxygen partial pressure of 4x10 -4 mbar and sputter pressure of 4x10 -2 mbar. The as deposited films were annealed in air at different temperatures in the range 473 – 673 K. X-ray diffraction studies suggest that the as-deposited and the films annealed at 473 K were amorphous in nature, while those annealed at 573 and 673 K were polycrystalline with mixed phases of α- orthorhombic and β- monoclinic MoO3. Scanning electron microscope images of the films annealed at 573 and 673 K exhibited nanoflower like and nanodisk like structures due to improvement in the crystallinity. Fourier transform infrared studies showed the characteristic vibrations of MoO3 with shift in the vibrational modes of Mo = O and Mo – O – Mo with increase of annealing temperature. The optical absorption edge of the films shifted towards lower wavelengths side with increase of annealing temperature. Optical band gap of as-deposited films was 2.98 eV with refractive index 2.01, while those annealed at 673 K showed the optical band gap of 3.15 eV and refractive index of 2.08. The MoO3 films annealed at 673 K were of nanocrystalline with crystallite size of 39 nm with optical band gap of 3.15 eV and refractive index of 2.08 were favorable for electron blocking and hole-selective layers in bulk-heterojuction solar cells.
Highlights
Molybdenum oxide (MoO3) is a material finds potential applications due to its abundance and attractive properties such as catalyst, gas sensing and electrochromism [1,2,3,4]
The films annealed in O2 the band gap increased from 3.93 to 3.97 eV with increase of annealing temperatures from 473 to 773 K. It revealed that the crystallographic structure and optical band gap of the MoO3 films critically depend on the annealing temperatures and ambient of annealing
Uthanna et al [19] reported on the DC magnetron sputtered MoO3 films formed at room temperature were of amorphous while those deposited at 473 K were orthorhombic phase
Summary
Molybdenum oxide (MoO3) is a material finds potential applications due to its abundance and attractive properties such as catalyst, gas sensing and electrochromism [1,2,3,4]. Uthanna et al [19] reported on the DC magnetron sputtered MoO3 films formed at room temperature were of amorphous while those deposited at 473 K were orthorhombic phase. An attempt is made in the deposition of MoO3 films at room temperature by RF magnetron sputtering and studied the effect of post-deposition annealing in air on the structural and morphological and optical properties. MoO3 thin films were deposited onto glass and silicon substrates held at room temperature (303 K) by sputtering of pure metallic molybdenum target in oxygen and argon gas mixture using reactive RF magnetron sputtering technique. The as-deposited and the MoO3 films annealed at different temperatures were characterized by studying their chemical composition, crystallographic structure and surface morphology, chemical binding configuration and optical properties. The optical transmittance of the films formed on glass substrates was recorded using UV-Vis-NIR double beam spectrophotometer (Perkin - Elmer Spectrophotometer Lamda 950) in the wavelength range 300 - 1500 nm
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