Nonlinear Electrical and Linear Optical Properties of Layered Graphene Oxide

We measured a significant, two orders of magnitude decrease in the resistance of layered (5 - 100 nm) reduced graphene oxide. The resistance drops as the number of layers increases, lending a notion to the influence of out-of-plane transport being modulated by modifications to the changes in electronic structure, as additional layers are added. These changes are observed for line and area resistance, as well, indicating that geometry doesn’t play major role. In parallel with this result, we report spectroscopic study (Raman, FTIR) on the same samples, where the ratio of spectral D (1350 cm^-1) and G (1580 cm^-1) features shows unusual dependence on the thickness (the number of layers of graphene oxide), in that it mimics the dependence of the resistance on thickness. Detailed spectroscopic study of various bonds (some sp2 related, some not) shows a number of features that are potentially relevant for explanation of observed resistance behavior. The role of carbon vacancies is also studied, showing that the bonding of molecules external to graphene oxide becomes modified in the presence of vacancies. AFM and electron micoscopy studies complement these findings and show how layered graphene oxide large area, nanoscale thickness scale structures evolve with controlled defects.