Gamma irradiation effect studies on monolayer CVD grown graphene on metallic substrates

Graphene is a two-dimensional material and has demonstrated an exceptional electronic and photonic properties for unlimited applications including its use in extreme environments of the space. There are several known techniques of formation of graphene onto different types of substrates such as the substrate transfer process and direct deposition. In this work, we deposited monolayer graphene over copper and nickel substrates in NanoCVD-8G Graphene reactor using argon plasma, and methane as a carbon source and studied effects of gamma irradiation using Cobalt-60 source. Radiation effects on crystalline structure of graphene is examined using Raman Spectroscopy and X-ray Photo Electron Spectroscopy (XPS). In our experiment, we used irradiation dose from 1 kGy to 2.65 kGy for different samples of graphene over copper and nickel substrates. For the graphene grown on the nickel substrates, we exposed the irradiation dose of 1.0 kGy and 2.5 kGy on two samples, respectively. For the graphene grown on the copper substrates, we exposed 1.25 kGy, 1.75 kGy, and 2.65 kGy irradiation dose on three samples, respectively. We observed D-peak in graphene deposited over nickel and copper substrates caused by disordered structure of graphene after Co-60 exposure. After the Raman spectroscopy and XPS studies, same amount of irradiation was used for second set of irradiation dose experiment. XPS data on Co-60 exposed samples showed four peaks positioned at 284.8eV, 285.3eV, 286.0 eV and 288.5 eV for C-C, C-OH, C-O-C and COOH bonds, respectively. Analysis of the results shows weakening of C-C bonds and formation of C-OH, C-O-C and COOH bonds implying reduced electrical conductivity of graphene.