Ways to eliminate PMMA residues on graphene —— superclean graphene

Graphene as a promising 2D material has been widely studied due to its unique properties. Transferring CVD graphene to other substrates from its original metal foil is important for its practical application. However, the removal of PMMA that is commonly used as the supporting mediator during the transferring process is troublesome, because PMMA molecules disturb the essential properties of graphene and conventional acetone treatment fails to completely remove PMMA from graphene surface. Thermal annealing treatments are earliest to be put into cleaning PMMA residues, while plasma and ion beam treatment generally have a higher cleaning efficiency. Light treatment is relatively mild compared to other techniques, and relies on the interaction between specific material and contaminants. Mechanical treatments can simply reach significant cleaning effect and enjoy a bright future. In this review, we summarize the current methods to reduce PMMA residues in detail, and their mechanisms behind are discussed systematically.