Low-Energy X-ray and Ozone-Exposure Induced Defect Formation in Graphene Materials and Devices

We have evaluated the responses of graphene materials and devices to 10-keV X-ray irradiation and ozone exposure. Large positive shifts are observed in the current-voltage characteristics of graphene-on-SiO2 transistors irradiated under negative gate bias. Moreover, significant radiation-induced increases are found in the resistance of suspended graphene layers; the charge neutral point (CNP) of the graphene layer also shifts positively with increasing total dose. Raman spectroscopy shows that similar defects are generated in graphene-on-SiO2 sheets by 10-keV X-ray irradiation and ozone exposure. First principles calculations of the relevant binding energies, and reaction and diffusion barriers for oxygen on graphene, strongly suggest that oxygen adsorption and reactions, along with the resulting p-type doping, can lead to the observed degradation of irradiated or ozone-exposed graphene materials and devices.