Mitigating E-beam-induced Hydrocarbon Deposition on Graphene for Atomic-Scale Scanning Transmission Electron Microscopy Studies

CVD grown graphene used in (scanning) transmission electron microscopy ((S)TEM) studies must undergo a careful transfer of the one-atom-thick membrane from the growth surface (typically a Cu foil) to the TEM grid. During this transfer process, the graphene invariably becomes contaminated with foreign material. This contamination proves to be very problematic in the (S)TEM because often >95% of the graphene is obscured and imaging of the pristine areas results in e-beam-induced hydrocarbon deposition which further acts to obscure the desired imaging area. In this article, we examine two cleaning techniques for CVD grown graphene that mitigate both aspects of the contamination problem: visible contamination covering the graphene, and invisible contamination that deposits onto the graphene under e-beam irradiation. The visible contamination may be removed quickly by a rapid thermal annealing to 1200 C in situ and the invisible e-beam-deposited contamination may be removed through an Ar/O2 annealing procedure prior to imaging in the (S)TEM.