Influence of Annealing on the Optical Properties and Chemical and Phase Compositions of Tungsten-Oxide Films (original) (raw)
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ISRN Optics, 2012
Tungsten oxide (WO3) thin films were deposited on to unheated Corning glass and silicon substrates by RF magnetron sputtering of metallic tungsten target at various oxygen partial pressures in the range 4×10-2–1×10-1 Pa. The influence of oxygen partial pressure on the structure and surface morphology and the optical and photoluminescence properties of the films were investigated. X-ray diffraction studies revealed that the deposited films were amorphous in nature. Fourier transform infrared transmission spectra confirmed that the presence of stretching vibration of W-O-W and deformation of W-O bonds related to the WO3. The optical transmittance of the films at wavelengths >500 nm increased from 62% to 85% with the increase of oxygen partial pressure. The optical band gap of the films increased from 3.00 to 3.14 eV and the refractive index of the films decreased from 2.26 to 2.08 with the increase of oxygen partial pressure from 4×10−2 to 1×10−1 Pa, respectively. The photoluminesc...
Structures and electrochromic properties of tungsten oxide films prepared by magnetron sputtering
Applied Surface Science, 2005
Tungsten oxide (WO 3) films were deposited by DC magnetron sputtering of tungsten target in O 2 /Ar atmosphere. The structures of the films following the various O 2 flow rate in a fixed Ar gas supply were investigated by X-ray diffraction patterns, Raman spectra and transmission electron microscopy. The electrochromic properties were characterized by a cyclic voltammetry and UV-vis absorption spectra. The results show that nanocrystalline WO 3 film with crystallite size about 10-20 nm, deposited at 16 sccm O 2 , has larger charge capacity and coloration efficiency than the other amorphous films. Post-annealing the film at 200 8C would create 30-50 nm nanocrystalline film, whose electrochromic properties are promoted further due to even larger internal volume, essential to conduct ions and electrons for electrochromic intercalation. However, the electrochromic property deteriorates apparently in the film with 60-100 nm nanocrystallites annealed at 300 8C, which may be caused by another electrochromism occurring always in the well-crystallized WO 3 films.
Annealing effect on the formation of nanocrystals in thermally evaporated tungsten oxide thin films
Materials Science and Engineering B-advanced Functional Solid-state Materials, 2004
The effect of thermal annealing on tungsten oxide (WO 3 ) thin films deposited by vacuum evaporation was investigated. The properties of films were studied in terms of annealing temperature and annealing time. It was found that the crystallinity and physical properties of WO 3 films were changed by annealing temperature as low as 100 • C. The X-ray diffraction (XRD) and Raman spectroscopy indicated that the as-deposited films were composed of nanometer size grains. While the crystal structure remained monoclinic, the size of crystals changed from nanometers to hundreds of nanometers by annealing in 100-600 • C range. It was also found that the films annealed at 500 • C for 5 h had low surface roughness, good adhesion and high optical transmittance whereas films annealed at 600 • C were delaminated. Surface topography was also investigated with atomic force microscopy (AFM). The optical gaps calculated from the transmission spectra were in good agreement with those reported for crystalline WO 3 films.
Iranian Journal of Physics Research, 2016
Tungsten trioxide (WO3) thin films were coated onto fluorine tin oxide coated glass substrates, using electrodeposition technique via aqueous solution of peroxotungstic acid. WO3 films were evaluated as a function of annealing temperature (60°C, 100°C, 250°C and 400°C). The films were analyzed by field emission Scanning Electron Microscopy (SEM), UV-visible spectrometer and cyclic voltammogram. The films had high transmission in optical visible region. Using optical transmittance and cyclic voltammogram measurements, the electrochromic properties of WO3 films were investigated in a non-aqueous lithium perchlorate in propylene carbonate electrolyte. Increasing the annealing temperature will decrease electrochromic and optical properties of WO3 films, since it leads to increasing the size of grains. Therefore, having been annealed at 60°C, WO3 film exhibited a noticeable electrochromic performance with a high transmission modulation and Coloration Efficiency Efficiency (CE) of 64.1 cm 2 C −1 at wavelength equal to 638 nm.
Thin Solid Films, 2008
We report the effect of inert gas (argon and helium) along with different concentrations of oxygen on the structural and optical properties of the rf magnetron sputtered nanocrystalline tungsten oxide thin films. The crystal structure and surface morphology were studied by X-ray diffraction (XRD) and atomic force microscope (AFM), respectively. We find that the atomic mass of the sputtering gas significantly affects the primary crystallite size as well as the surface morphology and texture. We were able to relate the higher oxidation of the tungsten atoms with low partial pressure of oxygen when films are deposited in helium instead of argon. It was also observed that the bandgap of the WO 3 films increases with increase in the partial pressure of oxygen.
Spectroscopic analysis of tungsten oxide thin films
Journal of Materials Research, 2010
We present a detailed study of the morphology and composition of tungsten oxide (WO 3 ) thin films, grown by radio frequency magnetron reactive sputtering at substrate temperatures varied from room temperature (RT) to 500 C, using infrared (IR) absorption, Raman spectroscopy, and x-ray photoelectron spectroscopy (XPS). This work includes valuable new far-IR results about structural changes in microcrystalline WO 3 . Both IR absorption and Raman techniques reveal an amorphous sample grown at RT and initial crystallization into monoclinic structures for samples grown at temperatures between 100 and 300 C. The Raman spectra of the samples grown at high temperatures indicate, apart from the monoclinic structure, a strain effect, with a distribution revealed by confocal Raman mapping. XPS indicates that the film surface maintains the stoichiometry WO x , with a value of x slightly greater than 3 at RT due to oxygen contamination, which decreases with increasing temperature.
Characterization of tungsten oxide films of different crystallinity prepared by RF sputtering
Physica B: Condensed Matter, 2003
Thin films of tungsten oxide have been prepared onto heated and un-heated substrates to get different degrees of crystallinity. The structure study has been characterized by X-ray diffraction, scanning electron microscope and scanning force microscope. Films deposited onto un-heated substrates proved to be amorphous, while those prepared onto heated substrates, 473pT s p573 K showed orthorhombic structure. Monoclinic order was formed at T s > 573 K. Due to the high degree of preferred orientation, Voigt analysis of a single reflection has been used to determine the microstructure parameters. The investigations lead to a two-phase-model characterized by nanocrystallites B12 nm dispersed in an amorphous matrix even for films deposited onto unheated substrates. The substrate temperature increases the number of crystallites rather than the size even for films sputtered onto unheated substrate. The microstrain was found to increase markedly with the sputtering power. The dark resistivity measurements at room temperature showed values of 1.58 Â 10 7 O cm for amorphous tungsten oxide with one order of magnitudes lower for crystalline films. It shows linear dependence with oxygen concentration during sputtering. Conductivity versus temperature measurements revealed thermal activation energy of 0.77 and 0.84 eV for amorphous and crystalline tungsten oxide, respectively.
Structural and Optical Properties of CVD Thin Tungsten Oxide Films
physica status solidi (a), 1999
Thin amorphous and polycrystalline tungsten oxide films were prepared by chemical vapour deposition at atmospheric pressure from a metalorganic precursor ± ± tungsten hexacarbonyl. The dependence of the structural and optical properties of tungsten oxide films on the technological conditions has been investigated by XRD, Raman spectroscopy and spectroscopic ellipsometry.