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Preparation and Stabilizing Graphene Sheets for Gas Sensing Application

Mirmotallebi, Mona | 2012

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 43892 (04)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Iraji zad, Azam
  7. Abstract:
  8. Graphene is one of the most attractive subjects for scientists in the last decade. Its unique properties has been probed by many research groups and innumerable projects have been developed to investigate applications of graphene in electronics, mechanics, biophysics etc. Due to high surface to volume ratio and magnificent electron mobility in graphene, it is a suitable candidate for gas sensing. This has been proved by several theoretical and experimental researches for various gases such as CO, NH3 and NO2 etc. In present thesis, graphene has been prepared chemically and transferred to silicone substrates that are previously coated with a 300 nanometer silicone dioxide layer, by dip coating method and using two-phase solution. Then the samples were characterized by Raman Spectroscopy, X-ray Diffraction, Atomic Force Microscopy, Optical Microscopy and Scanning Electron Microscopy. Homogeneity and thickness of the films were studied by variation in parameters of both methods of coating. We applied variable gate voltage, and sample resistance was measured using two gold comb shape electrodes to determine type of films’ charge carriers. Since Fermi energy level depends on gate voltage, we adjust it to specify Dirac point energy, in which samples show highest resistivity. Introducing humidity ranging from 30% to 70%, we observed a change in sample current ratio about 270%. When Fermi level is set above (below) Dirac point we observed positive( negative) variation in current (ΔI/I), means type of charge carriers affect the current direction. At last, graphene sensing mechanism is discussed through experiments on samples with different carrier types and it is shown that the effect of humidity on samples’ conductivity is completely dependent on their carriers’ type
  9. Keywords:
  10. Graphine ; Fermi Level ; Dip Coating ; Two-Phase Solution ; Gas Sensing

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