Direct Observation of Poly(Methyl Methacrylate) Removal from a Graphene Surface

Poly(methyl methacrylate) (PMMA) is commonly used as a temporary support layer for chemical vapor deposition (CVD) graphene transfer; it is then removed by a chemical or thermal treatment. Regardless of the method used for PMMA removal, polymer residues are left on the graphene surface, which alter its intrinsic properties. A method based on isotope labeling of PMMA and time-of-flight secondary ion mass spectrometry (ToF-SIMS) has now been developed to identify, locate, and quantify these residues. It is shown that vacuum annealing does not completely remove the PMMA residues but, instead, transforms them into amorphous carbon. In contrast, air annealing under optimized conditions generates a PMMA-free surface with limited damage to the graphene structure. This cleaned graphene surface demonstrates low friction which is comparable with that of pristine graphene film.