Halogenation of epitaxial graphene grown on the Si-face of the SiC(0001) substrate and its further reaction with Grignard reagent

Abstract

The halogenation of graphene has drawn considerable attention both from a technological and chemical point of view because fluorine- and chlorine-modified graphene can be directly used as an electronic material or as an intermediate for further modification and synthesis of composite materials. Herein, we report the reaction of fluorine, chlorine, bromine and iodine with epitaxial graphene (EG) grown on the Si-face of the SiC(0001) substrate and then the further reaction of the halogen-modified EG with Grignard reagents. Irrespective of the layer thickness, EG grown on SiC is fully fluorinated when exposed to XeF₂ and reaches saturation coverage in ∼16 h under XeF₂ vapor at room temperature. Unlike fluorination, we recently reported (J. Phys. Chem. C, 2014, 118, 1014) that chlorination is very selective onto the monolayer graphene and that the chemisorbed Cl can be readily replaced by alkyl groups when treated with an alkyl Grignard reagent. In the present study, we found that not only the alkyl group, but also the chlorinated EG on SiC can be functionalized with fluoro-substituted aryl groups by reaction with an appropriate Grignard reagent. On the other hand, the fluorinated EG on SiC seems robust toward Grignard reagents. A very small concentration of bromine can be detected on EG on SiC following the reaction with Br₂ under UV light. Iodine does not react with EG on SiC at room temperature.