Structural Evolution of Reduced Graphene Oxide of Varying Carbon sp 2 Fractions Investigated via Coulomb Blockade Transport

We investigate the structural evolution of reduced graphene oxide (RGO) sheets with carbon sp 2 fractions varying from 55 to 80% using low-temperature Coulomb blockade (CB) transport. At 4.2 K, all RGO sheets exhibit a complete suppression of current (CB) below a threshold voltage V t, the value of which decreased from 3.34 to 0.25 V with increasing carbon sp 2 fraction. From the temperature-dependent V t, we calculate an effective charging energy and individual graphene domain size of 160 meV and 1.34 nm at 55% carbon sp 2 fractions, respectively. These values are 20 meV and 4.18 nm at 80% carbon sp 2 fractions, respectively. This implies that with increasing reduction, newly formed sp 2 domains increase the effective size of the graphene domain. For an applied voltage V > V t, the current I follows a scaling law I ∼ [( V – V t )/ V t ] α where the scaling parameter α increases from 2.11 to 3.40 with increasing sp 2 fraction, suggesting that increasing sp 2 fraction creates more topological defects on the RGO. Our report provides a much desired insight into the structural evolution of RGO sheets.