With its exceptional charge mobility, graphene holds great promise for applications in next-generation electronics. In an effort to tailor its properties and interfacial characteristics, the chemical functionalization of graphene is being actively pursued. The oxidation of graphene via the Hummers method is most widely used in current studies, although the chemical inhomogeneity and irreversibility of the resulting graphene oxide compromises its use in high-performance devices. Here, we present an alternative approach for oxidizing epitaxial graphene using atomic oxygen in ultrahigh vacuum. Atomic-resolution characterization with scanning tunnelling microscopy is quantitatively compared to density functional theory, showing that ultrahigh-vacuum oxidization results in uniform epoxy functionalization. Furthermore, this oxidation is shown to be fully reversible at temperatures as low as 260 °C using scanning tunnelling microscopy and spectroscopic techniques. In this manner, ultrahigh-vacuum oxidation overcomes the limitations of Hummers-method graphene oxide, thus creating new opportunities for the study and application of chemically functionalized graphene.
Bibliographical noteFunding Information:
This work was supported by the National Science Foundation (award nos EEC-0647560, DMR-0906025 and DMR-1121262), the Office of Naval Research (award nos N00014-09-1-0180 and N00014-11-1-0463) and the US Department of Energy (award no. DE-SC0001785). K.H.B. acknowledges support from NSERC (Canada), M.C.H. acknowledges a W. M. Keck Foundation Science and Engineering Grant, and M.Z.H. acknowledges partial support by the Program to Disseminate Tenure-Track System of the Ministry of Education, Culture, Sports, Science and Technology of Japan (MEXT) granted to Gunma University. The authors thank J. Lyding for the use of his STM control software. S.Y., K.M., T.K. and J.Y. thank K. Mase at KEK-PF for maintenance of BL13A. Computational resources were provided by the National Science Foundation Network for Computational Nanotechnology.