Cu oxidation kinetics through graphene and its effect on the electrical properties of graphene

The oxidation kinetics of Cu through graphene were evaluated from the surface coverage of Cu oxide (F _ox) by varying the oxidation time (t _ox = 10-360 min) and temperature (T _ox = 180-240 °C) under an air environment. F _ox, as a function of time, well followed the Johnson-Mehl-Avrami-Kolmogorov equation; thus, the activation energy of Cu oxidation was estimated as 1.5 eV. Transmission electron microscopy studies revealed that Cu₂O formed on the top of the graphene at grain boundaries (G-GBs), indicating that Cu₂O growth was governed by the out-diffusion of Cu through G-GBs. Further, the effect of Cu oxidation on graphene quality was investigated by measuring the electrical properties of graphene after transferring. The variation of the sheet resistance (R _s) as a function of t _ox at all T _ox was converted into one curve as a function of F _ox. R _s of 250 Ω sq^-1 was constant, similar to that of as-grown graphene up to F _ox = 15%, and then increased with F _ox. The Hall measurement revealed that the carrier concentration remained constant in the entire range of F _ox, and R _s was solely related to the decrease in the Hall mobility. The variation in Hall mobility was examined according to the graphene percolation probability model, simulating electrical conduction on G-GBs during Cu₂O evolution. This model well explains the constant Hall mobility within F _ox = 15% and drastic F _ox degradation of 15-50% by the concept that the electrical conduction of graphene is disconnected by Cu₂O formation along with the G-GBs. Therefore, we systematically developed the oxidation kinetics of Cu through graphene and simultaneously examined the changes in the electrical properties of graphene.