Controlled Synthesis of Surface-clean Monolayer Graphene

Controlled synthesis surface-clean monolayer graphene was achieved. Monolayer Graphene was achieved by mechanical exfoliation (ME) and chemical vapor deposition (CVD), and then transferred to SiO2 (300nm)/Si substrates. There were tape residues left on the surface of the ME graphene, and poly (methyl methacrylate) (PMMA)/photoresist residues left on the surface of the CVD graphene after the transferring and lithography process. Annealing method was used to clean all these kinds of residues. Annealing processes were performed at different temperatures in both vacuum and N-2/H-2. It is conclude that N-2/H-2 is crucial for the removing of residues, and 400 degrees C is favorable for removing the residues. Atomic force microscope (AFM) images and Raman spectra were taken to confirm the effect of the annealing.