Electron Irradiation of Chemical Vapor Deposition Grown Graphene in Ultra High Vacuum and X-Ray Photoelectron Characterization*

We present results for the electron irradiation of chemical vapor deposition grown graphene to a dosage of 1 x 10¹⁷ electrons/cm² with a beam energy of 1.5 keV under ultra-high vacuum (UHV) conditions with a base pressure of 3.0 x 10^-10 tor. The sample was exposed to air before irradiation. We conducted Raman spectroscopy and find that the ratio of the intensity of the Raman D peak to the G peak is about 2.6 on the irradiated sample. This is an indicator of high defect density. We also conducted x-ray photoelectron spectroscopy (XPS) and find a broadened C 1s peak as well as a shifted O 1s peak in the spectra after irradiation as compared to the pristine sample. This is an indicator that defects are adsorbates on the surface of the graphene. Deconvolution of the C 1s peak into graphene (C-C/C=C), hydroxyl (C-OH), epoxide (C-O-C), and carboxyl (-COOH) components provides insight into the nature of the defects.