| 초록 |
The observation of color change by Cu oxidation after CVD graphene growth is a simple and very useful method for observing graphene morphology. However, there are some studies on the oxidation process of Cu through graphene, but systematic studies are insufficient. In particular, there is no study on the quality change of graphene during the Cu oxidation process. In this study, the oxidation kinetics of Cu through graphene were systematically evaluated from the surface coverage of Cu oxide (Fox) by varying the oxidation time (tox = 10–360 min) and temperature (Tox = 180°C–240°C) under air environment. Fox, 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. Cross-sectional 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 (Rs) as a function of tox at all Tox was converted into one curve as a function of Fox. Rs of 250 Ω/sq. was constant, similar to that of as-grown graphene up to Fox = 15%, and then increased with Fox. The Hall measurement revealed that the carrier concentration remained constant in the entire range of Fox, and Rs 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 Fox = 15% and drastic Fox 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. |
