The Role of Microwave Plasma Temperature During Graphene Nanosheets Deposition on Dielectric Substrate: Modelling and Experiment

Abstract

The relation between plasma temperature and properties of graphene nanosheet layer deposited on Si/SiO2 substrate by decomposition of ethanol in microwave plasma torch discharge at atmospheric pressure was investigated in dependence on delivered microwave power and gas flow rates. Plasma modelling was carried out using COMSOL Multiphysics software with delivered microwave power, gas flow rates and experimental reactor geometry as input parameters. Results of the heat flow and fluid dynamics modelling were compared with substrate temperature measured by thermocouple integrated in quartz tube substrate holder. The graphene nanosheets layer was characterized by SEM, Raman spectroscopy and 4-point probe method. The layers were severals tens of μm thick and their sheet resistance varied from 2 to 40 kΩ/sq. The properties of individual graphene nanosheets, 2D/G and D/G Raman band ratio, as well as the sheet resistance of their conductive network were correlated with the increase of plasma temperature with increasing microwave power. The substrate temperature increased linearly with delivered microwave power and the layer sheet resistance was decreasing with increasing microwave power and saturated at 2 kΩ/sq and D/G ratio of 0.6.

Structure of microwave plasma-torch discharge during graphene synthesis from ethanol

“…This is rather similar to a material deposited on the walls of the reactor. As we showed in our previous study [71], the gas recirculates in the reactor vessel and the carried nanomaterial is deposited all over the reactor walls instead of being simply carried away through the gas exhaust. This effect leads to homogenisation of the nanopowder produced, as evidenced by the fact that the material collected from the different parts of the reactor walls has essentially the same properties.…”