Electron Irradiation Induced Changes of the Electrical Transport Properties of Graphene
Woo, Sung Oh
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This research investigates the effect of electron irradiation on transport properties in graphene Field Effect Transistor (FET) devices. Upon irradiation, graphene is doped with electrons and adsorbs molecules by transfer of accumulated electrons in graphene to environmental molecules, resulting in the deterioration of transport properties. Molecules adsorbed after electron irradiation in ambient condition were observed by Atomic Force Microscopy (AFM). In-situ transport properties were measured in a vacuum after electron irradiation. In addition, hysteresis in the transport properties appeared as a result of electron irradiation. The origin of the hysteresis was investigated by exposing the electron beam irradiated graphene to ambient condition. As environmental molecules are adsorbed on graphene, the hysteresis disappears. In addition, annealing in a vacuum also removes the hysteresis. We conclude that the hysteresis is the result of polar adsorbates on graphene induced by electron irradiation. In addition, the effect of electron irradiation on a PMMA (Poly Methyl Methacrylate)/Graphene bilayer was studied. We observed a deterioration of the electrical transport properties of a graphene FET. Prior to electron irradiation, we observed that the PMMA layer on graphene did not degrade the carrier transport of graphene but improved its electrical properties instead. As a result of the electron irradiation on the bilayer, defects could be observed by Raman spectroscopy. We suggest that the degradation of the transport behavior originates from the binding of atoms or molecules generated by the PMMA backbone secession process.