Controlled oxidative functionalization of monolayer graphene by water-vapor plasma etching

We report studies on the controlled step-by-step oxidative functionalization of monolayer graphene by chemically reactive water-vapor plasma dry etching. The use of a porous mask on top of the graphene sheets as a filter is essential to reduce the density of free radicals and weaken the sputtering effect. Micro-Raman spectroscopy, X-ray photoelectron spectroscopy and atomic force microscopy showed that the oxidation occurred in a mild and controllable way, and that a wide variety of oxygen-containing functional groups can be evenly and incrementally incorporated onto the carbon lattice. By monitoring the electrical property changes in the graphene at different levels of oxidation, we observed a transformation of the electrical conduction process from continuum percolation to variable range hopping and/or electric-field-driven tunneling, due to the progressive increase of sp3-based basal plane distortion that disrupts the transport of carriers delocalized in the sp2 carbon network.