Chemical reactions and thermal stability of oxygen impurities on graphene

Oxygen as an impurity is known to degrade conductivity in graphene, but annealing at moderate temperature reverses the effect. Here we report first-principles calculations of oxygen binding and reactions on graphene that elucidate the underlying physics. We find that two O atoms can form an O dimer that can desorb from graphene with an overall activation barrier of 1.3 eV. Oxygen can also be removed in a more complicated reaction in which C atoms in graphene are consumed. We find that structural defects such as Stone-Wales defect and grain boundaries show enhanced binding to O atoms due to the local strain, facilitating the O reaction. If H atoms coexist, an O atom can bind to an H atom forming an OH group, which can also be removed by thermal annealing due to the weak binding, resulting in defect-free graphene.