Two-Step Mechanism for Low-Temperature Oxidation of Vacancies in Graphene

We study the oxidation of vacancies in graphene by ab initio atomistic thermodynamics to identify the dominant reaction mechanisms. Our calculations show that the low-temperature oxidation occurs via a two-step process: Vacancies are initially saturated by stable O groups, such as ether (C-O-C) and carbonyl (C-0.22em-0.22em=-0.22em-0.22emO). The etching is activated by a second step of additional O₂ adsorption at the ether groups, forming larger O groups, such as lactone (C-O-C-0.22em-0.22em=-0.22em-0.22emO) and anhydride ($O-0.22em-0.22em=-0.22em-0.22emC{{{-}}}O{{{-}}}C-0.22em-0.22em=-0.22em-0.22emO$), that may desorb as ${CO}₂$ just above room temperature. Our studies show that the partial pressure of oxygen is an important external parameter that affects the mechanisms of oxidation and that allows us to control the extent of etching.