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

Abstract

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.