Investigation of the influence on graphene by using electron-beam and photo-lithography

The changes in Raman spectra of graphene flakes after lithography processing are systematically investigated. It is found that substantial changes in the intensity of several Raman peaks are observed after lithography processes involving electron-sensitive and photon-sensitive resists. This finding is related to the generation of disorder and introduction of impurities in the graphene flakes. It is observed that the disorder induced after spin coating PMMA resist on the graphene flakes cannot be removed by acetone but can be eliminated by means of an annealing process. The use of the AZ6624 photo-sensitive resist produces Raman changes typical for amorphization. When using this resist, the disorder-induced changes in the Raman spectra persist even after the same annealing process, implying that the contamination caused by the used photo-sensitive resist is more difficult to eliminate. The present results emphasize the important role played by the lithography process, often taken for granted, in the physical properties of graphene.