Electrochemically Driven Covalent Functionalization of Graphene from Fluorinated Aryl Iodonium Salts

Chemical functionalization is required to adapt graphene's properties to many applications. However, most covalent functionalization schemes are spontaneous or defect driven and are not suitable for applications requiring directed assembly of molecules on graphene substrates. In this study, we demonstrate the electrochemically driven covalent bonding of trifluoromethylphenylene (CF3Ph) onto epitaxial graphene. Submonolayer and full monolayer chemisorption was demonstrated by varying the duration of the electrochemical driving potential. A 10x increase in the CF3Ph density was obtained by varying the duration of the graphene electrochemical potential by 4x. A maximum closed-pack density of 1 X 10(14) molecules.cm(-2) was observed. Chemical, electronic, and defect states of CF3Ph graphene were studied by photoemission spectroscopy, spatially resolved Raman spectroscopy, and water contact angle measurement. Covalent attachment rehybridized some of the delocalized graphene sp(2) orbitals to localized sp(3) states. Increased water contact angles and work functions were observed for increasing CF3Ph functionalization densities, which is consistent with increasing concentration and orientation of fluorine on the graphene surfaces. Control over the relative spontaneity (reaction rate) of covalent graphene functionalization is an important first step to the practical realization of directed molecular assembly on graphene.