The nano-scale resistive memory effect of graphene oxide
An attractive+ to graphene for a range of applications is graphene oxide (GO). GO is an insulator because of the hydroxyl, carboxyl, carbonyl and epoxide functional groups presenting on the basal surface or edge and becomes a semiconductor or semimetal as it is reduced back toward graphene. Here we demonstrate that graphene oxide can be reversibly reduced and oxidized in nanometer-scale by applying bias voltages by the nano-tip of conductive atomic force microscopy system. The low resistance state (LRS) when reduced and a high resistance state (HRS) when oxidized can be achieved under the opposite applied bias direction. The LRS (around 10 KΩ and HRS (around 40 M Ω) were stable for more than 103 s, and no obvious degradation was observed during the tests. Threshold voltages for reduction and oxidation, which can be considered as the set and reset voltages is around -6.5 V and +7 V, respectively. It is shown that the hydrogen (H+) ions and hydroxyl ions (OH-) dissociated from the water meniscus formed between the tip and GO in ambient condition at room temperature plays an essential role in the resistive memory switching. It is also found that the negative bias is responsible for the reduction, which is related the transition from HRS to LRS, and the positive bias is responsible for the oxidation, which is related the transition from LRS to HRS, respectively. Raman spectroscopy and X-ray photoelectron spectroscopy is performed to confirm this resistive memory switching behaviors.