Mega-electron-volt proton irradiation on supported and suspended graphene: A Raman spectroscopic layer dependent study

Graphene samples with 1, 2, and 4 layers and 1 + 1 folded bi-layers and graphite have been irradiated with 2 MeV protons at fluences ranging from 1 x 1015 to 6 x 1018 ions/cm2. The samples were characterized using visible and UV Raman spectroscopy and Raman microscopy. The ion-induced defects were found to decrease with increasing number of layers. Graphene samples suspended over etched holes in SiO2 have been fabricated and used to investigate the influence of the substrate SiO2 for defect creation in graphene. While Raman vibrational modes at 1460 cm-1 and 1555 cm-1 have been observed in the visible Raman spectra of substantially damaged graphene samples, these modes were absent in the irradiated-suspended monolayer graphene.