Characterization of electron-irradiated graphene drums containing air at atmospheric pressure

We expose graphene drums containing air at atmospheric pressure to electron irradiation at an energy and dosage of 20 keV and 1.58 x 10¹⁷e^-/cm², respectively, using a JEOL JSM-7001F field emission scanning electron microscope. The graphene drums consist of monolayer (ML) graphene exfoliated over 4.6 µm diameter holes etched into a SiO₂ substrate. We observe, after irradiation, a Raman D peak to Raman G peak ratio, I_D/I_G that is as high as 6.3 for suspended ML drums and 0.9 for ML supported on the SiO₂ substrate. We attribute the significant I_D/I_G difference between both samples to the air in the drums. The air contains high amounts of water molecules that we propose dissociate due to the incident electrons and produce adsorbed species on the graphene. We present Raman spectroscopy data, including I_D/I_D’ ratios, where I_D’ is the intensity of the D’ peak, and annealing studies. We conclude that the defects are likely sp³-type defects instead of vacancies. Our method of irradiating graphene at atmospheric pressure could be a potential way of modifying graphene at high coverages for applications such as hydrogen storage.