Synthesis and characterization of graphene: a raman study of the effect of electromagnetic and proton irradiations on graphene
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Date
2009
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Abstract
Graphene, a single atomic layer of hexagonally arranged sp2–hybridized carbon atoms, with a thickness of only 0.34 nm, exhibits unique properties. The current interest in graphene can be attributed to three main reasons. Firstly, various forms of graphite, nanotubes, buckyballs and others can all be viewed as derivatives of graphene. Secondly, the scalability of graphene devices to nano-dimensions makes it a promising candidate for applications in nano-devices. Thirdly, its electron transport properties are described by the Dirac equation which allows access to quantum electrodynamics in a simple condensed matter experiment. The methods for obtaining individual graphene sheets have progressed, from ripping it with adhesive tape, or gently pushing small graphite crystals along a hard surface to produce high quality graphene by cleaving of graphite, to oxidation of graphite using the modified Hummers method developed by M. Hirata et al. (Carbon 42(2004)). In this research the graphene was synthesized using the modified Hummers method which resulted in a suspension of graphene oxide flakes in distilled water. The graphene oxide (GO) was then chemically reduced to produce graphene or reduced graphene oxide (rGO). The physical properties of the resulting graphene films were characterized and the effects of irradiation by an excimer pulsed laser (UV radiations), visible light (green) and proton irradiation were investigated. During the irradiations the dose of the radiation was varied in order to track the changes in the properties of the materials as a function of the flux. The different spots were then characterized using Raman spectroscopy to measure the created disorder. The Raman spectra of the samples irradiated by light displayed the D and G mode. The Raman spectra characteristics for the UV irradiated sample were similar to that of the proton irradiated sample. In both cases there was a splitting of the G mode. It was then concluded that the splitting of the G band similar to that found in semiconducting Single Walled Nanotubes is an indication that the samples are semiconducting. However the G line shape is highly sensitive to whether the SWNT is metallic or semiconducting and in the UV irradiated sample there was a transition from semiconducting to more metallic as the irradiation was increased.
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Thesis presented in fulfilment of the requirements for the degree of Master of Science in the Department of Physics & Engineering at the University of Zululand, South Africa, 2009.
Keywords
Graphene