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Synthesis of Graphene and Graphene-Based Composite Membrane, Yuanjun Fan
Vibration membrane equipped for earphone requires high performance in both mechanical properties and electronic properties. With extraordinary properties on both, graphene and graphene-based composite materials appear as a promising candidate for this application. Chemical vapor deposition (CVD) is believed to be the most convenient way to synthesize a large area (on scale of square centimeters) as well as a homogeneous thickness for the membrane. The thesis focuses on applying control variable experiment method to analyze different effects on mechanical property of the two CVD setting parameters: cooling rate, and hydrocarbon precursor. For isolating the specimens efficiently, a modified electrochemical method is presented to replace the traditional chemical method. Also, a feasible home-made device is presented to measure the ultimate tensile stress (UTS) of the nano-scale thickness membrane. The result of the experiments show that changing cooling rate from 10 to 20 , as well as hydrocarbon precursor from methane to ethanol induces a positive influence on the graphene membrane’s UTS. The enhanced effect obtained by changing the cooling rate is twice the result obtained by changing the hydrocarbon precursor.
For the synthesis of graphene-based composite membrane, graphene oxide (GO) and polymer material polyethylenimine (PEI) is used. Spin coating is chosen as the membrane fabrication method as it has the advantage of controlling membrane’s thickness below micrometer by stacking layer after layer. Different fabrication factors, including spin coating speed, solution concentration, laminated layer, and hydroiodic acid (HI) reduction treatment are involved to investigate the different effect on the UTS of as-synthesized GO composite membrane. The result reveals that the UTS has a strong correlation ship with the composite thickness. But the maximal measured UTS (54Mpa) of all specimen is for a medium thickness of 450nm. This is due to the HI reduction treatment, which can reduce almost 60% of average thickness per layer and increase 51% of UTS at the same time, compared to specimens without the HI treatment.
Advisors: Qin Zhou and Eveline Baesu