Thickness control of graphene deposited over polycrystalline nickel

Abstract

The optimization of the graphene growth over polycrystalline nickel foils using an atmospheric pressure Chemical Vapor Deposition set-up is reported. CH₄ and H₂ were used as precursor gases. Optical microscopy and Raman spectroscopy were used for graphene characterization. A thickness value related to the number of graphene layers in the synthesized samples was quantified using an Excel-VBA application, which assigned a thickness value between 0 and 1000 and allowed one to know the percentage of each type of graphene (monolayer, bilayer, multilayer) deposited over the Ni foil. The influence of reaction temperature, CH₄/H₂ flow rate ratio and reaction time was studied in detail. Optical microscopy showed that the samples were not homogeneous, being covered with multilayer, few-layer, bilayer and monolayer graphene. Synthesis variables were optimized according to the thickness value. There was observed a maximum thickness value (781) for 980 °C, a CH₄/H₂ flow rate ratio of 0.07 v/v and a reaction time of 60 seconds. At these conditions, about 77% of the Ni foil was covered with monolayer graphene.