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CHEMICAL VAPOUR DEPOSITION OF GRAPHENE ON COPPER-NICKEL ALLOY
[Thesis]. Manchester, UK: The University of Manchester; 2018.
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Abstract
Among all the methods of produce graphene, chemical vapour deposition (CVD) is the most promising route, due to the high quality of the graphene film produced and the large scalability. The mechanism of graphene growth by CVD on a metal substrate is believed to be controlled by its solubility for carbon with precipitation dominant at high carbon solubility and surface diffusion at low solubility. This thesis is exploring the impact of C solubility in the catalytic substrates, on the CVD growth of graphene. Cu-Ni alloys show complete solid solubility across their composition range and can be used to explore the influence of C solubility on graphene growth. Graphene is grown on Cu-Ni alloys of composition Cu, Cu70-Ni30, Cu55-Ni45, Cu33-Ni67 and Ni in a hot-wall CVD reactor. Firstly, the growth was achieved on pure metals (Cu and Ni) using CH4 as a C source and the produced film was characterised by Raman spectroscopy and scanning electron microscopy (SEM). The C profile within the substrate bulk was measured by glow discharge optical emission stereoscopy (GDOES). The latter showed the difference in bulk C content between Cu and Ni, which reflects the influence on the graphitic film on the surface. The CVD growth of graphene on Cu-Ni alloy showed a transition from bilayer graphene (BLG) to few layer graphene (FLG) surface coverage when the Ni content increased, which is accompanied by an increase in the diffusion of C in the bulk and incubation time. The cooling rate showed a significant effect on the graphene surface coverage; however, the influence varied with Ni content. The fluid flow simulation indicated that the gas velocity beneath the substrate is very low which results in a lower mass transfer to the bottom substrate surface. Gas-phase kinetics simulation reveals the impact of gas residence time on the concentration of active species; moreover, the concentration increases down the stream of the flowing gas. Finally, the surface reactions of the CH4/H2 mixture model showed a good agreement with the experimental observations under low growth pressure; however, it failed at high growth pressure.