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Yosefi, Mahdie | 2010

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 40332 (04)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Moshfegh, Alireza
  7. Abstract:
  8. ZnO is a wide and direct band gap (3.37 eV) semiconducting material with a large exciton binding energy (60 meV). It has been extensively studied in the last few years owing to its potential applications in various fields such as surface acoustic wave devices (SAW), transparent electrode, solar cell windows, photovoltaic devices, gas sensors and photoelectrochemical cells. Recently, much attention has been paid to rare-earth (RE) doped ZnO for possible applications in visible emitting phosphors in displays, high power lasers, and other optoelectronic devices. In this thesis, initially ZnO thin films were deposited on glass and ITO substrates using sol-gel dip-coating method. Optical and surface properties of the deposited films in various sol concentration and different annealing temperature changed from 300ºC to 500ºC had been investigated. UV-Visible spectrophotometer, atomic force microscopy (AFM), X-ray diffraction and X-ray photoelectron spectroscopy had been used. Among different sol concentrations, the film for 0.1 M showed the highest transmittance and the best morphology, so this sol concentration had been used for later research. According to our data analysis, the band gap energy and the transmittance of the films decreased by increasing annealing temperature, but the average grain size the films and their surface roughness increased by rising the annealing temperature. Moreover, ZnO thin films containing different amounts of cerium were deposited on glass and ITO substrates using sol-gel dip-coating method, and their photoelectrochemical properties had been studied in details. Based on optical properties, the band gap energy for the pure ZnO and 2, 5, 10, 15, 20 and 30 at.% Ce:ZnO nanocomposite thin films were determined at 3.349, 3.349, 3.357, 3.376, 3.405, 3.421 and 3.643, respectively. According to XPS analysis, thin films contain CeO2. Since the band gap of this oxide (3.6-3.8 eV) is higher than ZnO, so the band gap of Ce:ZnO should be greater than pure ZnO. the highest value of photocurrent was achieved for the ZnO thin films containing 10% Ce. It is important to know that too much doped Ce4+ could become the recombination center of electron–hole pairs. Thus, there is an optimum doping content.

  9. Keywords:
  10. Sol-Gel Method ; Nanocomposite ; Cerium-Doped Zinc Oxide ; Photoelectrochemical Cell

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