An experimental sample cleaning protocol has been developed at Oak Ridge National Lab to render graphene sufficiently clean for prolonged imaging by (S)TEM. The two-part protocol involves a gross clean by baking in argon/oxygen at 500oC, followed by in situ flashing to 1200oC. In order to remain clean, the sample must be kept at 800oC throughout the observation period.
Reference: O Dyck, et al., “Mitigating E-beam-induced Hydrocarbon Deposition on Graphene for Atomic-Scale Scanning Transmission Electron Microscopy Studies”, arXiv:1709.00470.