Swift heavy ions induced irradiation effects in monolayer graphene and highly oriented pyrolytic graphite

Monolayer graphene and highly oriented pyrolytic graphite (HOPG) were irradiated by swift heavy ions (Bi-209 and Sn-112) with the fluence between 10(11) and 10(14) ions/cm(2). Both pristine and irradiated samples were investigated by Raman spectroscopy. It was found that D and D' peaks appear after irradiation, which indicated the ion irradiation introduced damage both in the graphene and graphite lattice. Due to the special single atomic layer structure of graphene, the irradiation fluence threshold Phi(th) of the D band of graphene is significantly lower (<1 x 10(11) ions/cm(2)) than that (2.5 x 10(12) ions/cm(2)) of HOPG. The larger defect density in graphene than in HOPG indicates that the monolayer graphene is much easier to be damaged than bulk graphite by swift heavy ions. Moreover, different defect types in graphene and HOPG were detected by the different values of I-D/I-D'. For the irradiation with the same electronic energy loss, the velocity effect was found in HOPG. However, in this experiment, the velocity effect was not observed in graphene samples irradiated by swift heavy ions. (C) 2014 Elsevier B.V. All rights reserved.