Improving the growth of monolayer CVD-graphene over polycrystalline iron sheets

Abstract

A high quality graphene film, mostly composed of monolayer graphene, was successfully grown on polycrystalline iron foil by the CVD process using methane as the carbonaceous source. The effect of the reaction temperature, the CH₄/H₂ flow rate ratio and the total flow of gases (CH₄/H₂) on the formation of graphene during the reaction step at different reaction times was investigated. Optical microscopy and Raman spectroscopy were used as characterization techniques. A homemade Excel-VBA application was designed in order to determine the percentage of the different types of graphene (monolayer, bilayer, few-layer and multilayer) deposited on the metal foil, thus a quantitative quality value was computed. A graphene film deposited under the optimal experimental conditions showed a high percentage of monolayer graphene (62.4% in the sample), a high I_2D/I_G ratio (∼2.9), a low I_D/I_G ratio (∼0.026) and a narrow FWHM of the 2D peak (∼22 cm⁻¹). The optimal synthesis conditions were found to be: 1025 °C, CH₄/H₂ = 0.25 v/v, total flow (CH₄ + H₂) = 80 N ml min⁻¹ and reaction time = 7 min.