Role of inert gas in the Cvd-graphene synthesis over polycrystalline nickel foils

The role of the inert gas during CVD-graphene growth over polycrystalline nickel foils is reported. Nitrogen, hydrogen and methane were used as inert, reduction and carbonaceous gases, respectively. Graphene samples were characterized by using Optical Microscopy, Raman Spectroscopy and SEM equipped with EDX. Four different colors were distinguished over the optical microscope images. These colors were analyzed by Raman Spectroscopy and correlated to each type of graphene deposited over the foil (monolayer, bilayer, few-layers and multilayer). An Excel-VBA application was developed, which was used for computing the percentage of each type of graphene, resulting in an estimation of the graphene quality value. It was verified that the incorporation of the inert gas in the reaction step during CVD-graphene synthesis greatly influenced the quality of the obtained graphene. Different temperatures and percentages of nitrogen were studied in order to define the optimal reaction conditions. A factorial design study was performed to find the best experimental conditions leading to the highest quality graphene value, which resulted to be the following ones: 947 °C and 13 vol % of nitrogen in the feed stream, 1 min of reaction time, a relation between CH4 and H2 of 0.07 v/v, and a total flow of gases of 80 Nml/min.