Role of Metal Centers in Tuning the Electronic Properties of Graphene-Based Conductive Interfaces

A major bottleneck in the fabrication of efficient bio-organic nanoelectronic devices resides in the strong charge recombination that is present at the different interfaces forming the complex system. An efficient way to overcome this bottleneck is to add a self-assembled monolayer (SAM) of molecules between the biological material and the electrode that promotes an efficient direct electron transfer whilst minimising wasteful processes of charge recombination. In this work, the presence of a pyrene-nitrilotriacetic acid layer carrying different metal centers as SAM physisorbed on graphene is fully described by mean of electrochemical analysis, field emission scanning electron microscopy, photoelectrochemical characterisation and theoretical calculations. Our multidisciplinary study reveals that the metal center holds the key role for the efficient electron transfer at the interface. While Ni2+ is responsible for an electron transfer from SAM to graphene, Co2+ and Cu2+ force an opposite transfer, from graphene to SAM. Moreover, since Cu2+ inhibits the electron transfer due to a strong charge recombination, Co2+ seems the transition metal of choice for the efficient electron transfer.