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The Effect of Metal Oxides on Gasochromic Properties of WO3 Thin Films Formed by Pulsed Laser Deposition

Nematollahi, Mohammad Reza | 2010

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 40472 (04)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Mahdavi, Mohammad
  7. Abstract:
  8. Physical and chemical properties of tungsten oxide thin films change reversibly while exposure to hydrogen gas. This property is called gasochromic. To enhance optical properties of such films, nanostructured, amorphous and porous thin films of (WO3)1-x(MeO)x (MeO= TiO2, MoO3, NiO; x=0.09, 0.17, 0.23, 0.29, 0.33) were fabricated by Pulsed Laser Deposition. Molar percentage of Me/W (Me= Ti, Mo and Ni) was changed in films with respect to targets; for Ti and Ni always a reduction, but for Mo an enhancement for low percentages was observed. The reason is the existence of thermal ablation mechanism during deposition, in the other word is different vapor pressure effect. An increment in x for films mixed by TiO2 caused an increasing the band gap from 3 eV to 3.6 eV. However, for MoO3 by x=0.09 the band gap was increased to 3.6 eV; while for more increment in x, it was reduced to 3.1eV. Moreover, as it is expected, the enhancement of x results in higher band gap for NiO. Investigation of gasochromic response of thin films came to the result that adding metal oxides to tungsten oxide, decreases coloration velocity and contrast. Reversibility was preserved by adding TiO2, while by adding MoO3 and NiO the coloration was irreversible. The WO3 thin films mixed by MoO3 provided darker color for normal eye and they were completely opaque in exposure to hydrogen gas. Furthermore, by changing the parameters of deposition, one can fabricate films with better coloration contrast, velocity and quality.
  9. Keywords:
  10. Gasochromic ; Pulsed Laser Deposition (PLD) ; Tungsten Oxide ; Titanium Oxide ; Nickle Oxide ; Molybdenum Oxide ; Mixed Oxide

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