Monolayer Selective Methylation of Epitaxial Graphene on SiC(0001) through Two-Step Chlorination–Alkylation Reactions

One of the real challenges in realization of many of graphene’s anticipated applications is the development of a common chemical route for modifying graphene with varieties of functionalities. Here, we successfully demonstrate the organic modification of epitaxial graphene (EG) grown on the Si-face of SiC substrate through two-step chlorination–alkylation reactions. Pristine and chemically modified graphene are characterized by scanning tunneling microscope and spectroscopy, X-ray photoelectron spectroscopy, and Raman measurements. The first-step photochlorination is found to occur very selectively on the monolayer graphene region leaving the bi- and trilayer graphene regions clean. Consequently, the CH₃-functionalized graphene is observed only in the monolayer graphene regions after the chlorinated EG was treated with CH₃MgBr in air-free condition. Both Cl and CH₃ are observed to be chemically bonded to the basal plane of the graphene. The CH₃-functionalized graphene is thermally more stable than that of the chlorinated graphene. The present two-step chlorination–methylation procedure is expected to open a new route for organic modification of graphene with different functional groups using a variety of Grignard reagents.