| Summary: | 碩士 === 國立成功大學 === 材料科學及工程學系 === 104 === The aim of this research is to study the effect the degree of reduction of reduced graphene oxide in the methanol sensing performance.
Graphene oxide synthesized by Hummers method as the starting material was deposited on the silicon substrate with 300 nm thermal oxide layers on top by spin-coating process producing graphene oxide thin film. The graphene oxide film was thermally reduced at various reduction temperatures i.e. 2000C, 3500C, 5000C and 8500C for two hours in the vacuum condition (~10-3 Torr). The graphene oxide film before and after thermal reduction at various temperatures was then characterized by Scanning Electron Microscope (SEM), X-Ray Photoelectron Spectroscopy (XPS), Raman Spectroscopy, X-Ray Diffraction Spectroscopy and Electrical Measurement.
Oxygen containing functional group was partially removed after thermal reduction along with the restoration of sp2-carbon bond rendered the recovery of its conductivity. However, the structural defects such as vacancies, porous and cracking of carbon-carbon bond was introduced after severe thermal reduction at 8500C for two hours. The poor quality porous-like graphite material was formed after severe thermal reduction at 8500C for two hours. Moreover, graphene oxide reacted back with the residual oxygen gas on the furnace tube upon annealing at very high temperature. Yet, the carbon fraction reacting with the residual oxygen gas is much less than the recovered sp2-carbon fraction upon reduction at 8500C for two hours.
The simple two electrode device of graphene oxide and reduced graphene oxide were carried out by nickel/gold metal deposition on top of graphene oxide and reduced graphene oxide film. Moreover, the silicon back-gated transistor device with 90 nm silicon dioxide as the dielectric layer was also performed to assure the semiconducting behavior of reduced graphene oxide at 2000C.
Those simple two electrode devices were further applied to detect methanol gas at various concentrations. Graphene oxide reduced at 2000C was found to be the highest sensitivity, the fastest response and best recovery. We also detect the acetone gas using the graphene oxide reduced at 2000C for 2 hours.
In this report, a contribution of the new parameter called released gas fraction and higher sensitivity is presumably found if it is compared with previous report reported by Lipatov and co-workers. We also proposed the mechanism of the selectivity of reduced graphene oxide detecting methanol and acetone gases also the mechanism of the degree of reduction affecting the sensitivity.
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