Identifying and Clearing Individual Oxygen Impurities on Graphene Through the Use of NO2 As a Radical Scavenger

We present a novel method to detect and eliminate oxygen adatoms on a graphene basal plane, which can be observed as individual single-electron transfer (SET) events through graphene Hall measurements. The central idea, supported by first-principles calculations, is to use NO2 as a radical scavenger, effectively targeting and removing oxygen impurities on graphene. The reaction between NO2 and the oxygen adatom produces a negatively charged NO3− species and creates a hole carrier in graphene. Subsequently, NO3− reacts with NO2 to form N2O5, accompanied by an electron back-donation to graphene. The thermal decomposition of N2O5 produces neutral NO3, which can accept an electron from graphene and return to the NO3− state. Under conditions of low oxygen impurity levels and NO2 partial pressures, these SET reactions induce intermittent, step-like changes in the graphene's Hall resistivity ρxy at room temperature. Notably, the simulated ρxy patterns during NO2 adsorption closely resemble previously observed patterns [Schedin et al., Nat. Mater. 6 (2007) 652–655], suggesting a connection to the proposed SET reactions for unintentionally introduced oxygen impurities. Furthermore, we find that NO2 also reacts with hydroxyl and peroxide groups on the graphene basal plane, removing them by forming HNO3 and N2O5, respectively. Our findings offer a promising approach to remove oxygen-containing functional groups from graphene, paving the way for obtaining high-quality graphene from reduced graphene oxide.