(756a) Understanding and Controlling the Substrate Effect On Graphene Electron Transfer Chemistry Via Reactivity Imprint Lithography

Graphene has exceptional electronic, optical, mechanical, and thermal properties that make it promising for electronic, optoelectronic, and sensing applications. The chemical functionalization of graphene has been pursued to control its electronic properties and interactions with other materials. Covalent modification of graphene by organic diazonium salts has been used to achieve these goals, but because graphene is only a single atomic layer, it is strongly influenced by the underlying substrate. In this paper, we show a stark difference in the rate of electron transfer reactions with organic diazonium salts for monolayer graphene supported on a variety of substrates. Reactions proceed rapidly for graphene supported on SiO₂ and Al₂O₃ (sapphire), but negligibly on alkyl-terminated and hexagonal boron nitride (hBN) surfaces, as shown by Raman spectroscopy. We develop a model of reactivity based on substrate-induced electron-hole puddles in graphene, as the local Fermi level fluctuations directly influence the electron transfer rate between the graphene and diazonium molecule. We also develop a new patterning technique called reactivity imprint lithography (RIL) for spatially patterning chemical groups on graphene by patterning the underlying substrate, and apply it to the covalent tethering of proteins on graphene.