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 rho(xy) at room temperature. Notably, the simulated rho(xy) 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. Further-more, 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.