Charge Transport in UV-Oxidized Graphene and Its Dependence on the Extent of Oxidation

Abstract

Graphene oxides with different degrees of oxidation are prepared by controlling UV irradiation on graphene, and the charge transport and the evolution of the transport gap are investigated according to the extent of oxidation. With increasing oxygenous defect density nD, a transition from ballistic to diffusive conduction occurs at nD≃1012 cm−2 and the transport gap grows in proportion to nD. Considering the potential fluctuation related to the e−h puddle, the bandgap of graphene oxide is deduced to be Eg≃30nD(1012cm−2) meV. The temperature dependence of conductivity showed metal–insulator transitions at nD≃0.3×1012 cm−2, consistent with Ioffe–Regel criterion. For graphene oxides at nD≥4.9×1012 cm−2, analysis indicated charge transport occurred via 2D variable range hopping conduction between localized sp2 domain. Our work elucidates the transport mechanism at different extents of oxidation and supports the possibility of adjusting the bandgap with oxygen content.