Graphene Episulfide : Covalent Sulfur Addition to Graphene Surfaces

Abstract Graphene surfaces require chemical functionalization before it can be processed into graphene-based materials or used in device applications. Covalent addition reactions on graphene have been developed to build robust interfaces, but the chemistry at play builds on strategies involving either harsh oxidation or free radical attack, which generally offers poor control over reactivity and yields low coverage of grafts at the surface. Covalent addition of sulfur atoms onto the surface of graphene is here presented as an alternative strategy. Graphene episulfide is synthesized via a gas phase reaction in moderate conditions of temperature by a catalyst and solvent free protocol. Using Raman and photoemission spectroscopies, we demonstrate the presence of covalent bonds between sulfur atoms and graphene. By comparing the experimental results with ab-initio calculations of the vibrational and electronic states of models of graphene episulfide, a new interface mainly composed of sulfur bridges is proposed. The conditions to reach stoeichiometric ratios with sulfur approaching the theoretical limit is presented.