Cleaning of graphene surfaces by low-pressure air plasma

The polymer residues still present on a chemical vapour-deposited graphene surface after its wet transfer by the poly(methyl methacrylate) method to the arbitrary substrates, tend to cause problems such as electrical degradation and unwanted intentional doping. In this study, by using an effective cleaning method for the graphene surface by air-assisted plasma, the graphene surface was cleaned significantly without damaging the graphene network, which resulted in the reduction (approx. 71.11%) of polymer residues on its surface. The analysis reveals that this approach reduced the D-band (impurities, polymer residues) formation while maintaining the π-bonding of the graphene, which affects conductivity. By characterizations of the optical microscope, Raman spectroscopy and atomic force microscopy, we obtained a significantly cleaner graphene surface (roughness of 4.1 nm) compared to pristine graphene (roughness of 1.2 nm) on a SiO₂ substrate. In addition, X-ray photoelectron spectroscopy data revealed that the C1s peak of the air-assisted graphene film was higher than the one of a pristine graphene film, indicating that a cleaner graphene surface was obtained.