Promotion of the structural repair of graphene oxide thin films by thermal annealing in water-ethanol vapor

•Thermal annealing in water vapor promotes the structural repair of graphene oxide.•Structural repair results in the excellent electrical transport properties.•Carrier mobility of the reduced graphene oxide films exceeds 100 cm2/Vs.•Water vapor selectively etches amorphous carbon structures. In order to apply graphene oxide (GO) materials as graphene in the electronic devices, it is an essential issue to restore the six-membered ring structure composed of sp2 carbon. Thermal annealing in ethanol vapor promotes the removal of oxygen-containing groups and the structural repair of the vacancy, efficiently. Unfortunately, the metastable carbon bonds such as phase boundaries and sp3-defects still remain in the reduced GO (rGO). In this study, thermal annealing in water-assisted ethanol vapor is used for the reduction process of GO thin films. The structural analysis using Raman spectra indicates that the crystallinity of the rGO thin films strongly depend on the concentration of water. In particular, when the concentration of ethanol and water vapor is the same value, the crystallinity is significantly improved compared to the reduction process using only ethanol. This result indicates that the metastable structures such as phase boundaries and sp3-defects are preferentially etched over stable six-membered ring structure in carbon bonds. As a result, the excellent carrier mobility exceeding 100 cm2/Vs at room temperature (140 cm2/Vs at 77 K) is observed.