Engineering work function of graphene oxide from p to n type using a low power atmospheric pressure plasma jet

In this work, we demonstrate doping graphene oxide (GO) films using a low power atmospheric pressure plasma jet (APPJ) with tunable work function. The surface potential of the plasma functionalized GO films was adjusted to 120  10 mV by varying plasma parameters. X-ray spectroscopy used to probe these changes in electronic structure of systematically functionalized GO films by plasma. Detailed investigation using X-ray photoelectron spectroscopy and near edge X-ray absorption fine structure spectroscopy revealed the reactive nitrogen species in the plasma induce finite changes in the surface chemistry of the GO films, introducing additional density of states near the top of the valence band edge. Nitrogen introduced by the atmospheric pressure plasma is predominantly in a graphitic configuration with a varying concentration of pyridinic nitrogen. Additionally, evidence of gradual de-epoxidation of these GO films with increasing plasma exposure was also found. We attribute this variation in work function values to the configuration of nitrogen in the graphitic structure as revealed by X-ray spectroscopy. With pyridinic nitrogen the electronic states of GO became electron deficient, inducing a p-type doping and increase in graphitic nitrogen increased the electron density of GO leading to an n-type doping effect. Nitrogen doping was also found to decrease the resistivity 138 MΩsq-1 to 4 MΩsq-1.These findings are extremely useful in fabricating heterojunction devices like sensors and optoelectronic devices where band structure alignment are key to device performance when GO is used as a charge transport layer and can be extended to other known 2D systems as well