Functionalized Bilayer Graphene Devices: Achieving Selectivity and Sensitivity

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Graphene is an atomically-thin surface of carbon atoms with remarkable electrical transport properties that are sensitive to the nearby distribution of molecular species; this makes graphene an exciting material in the conception of sensor devices. Functionalization of the surface is however necessary to impart any selectivity to these devices, which means dressing the graphene surface with chemical groups able to capture selectively the target analyte. While various gas, ion and biomolecular sensors have been demonstrated using functionalized graphene devices, the vast majority rely on non-covalent adsorption to immobilize the functional groups onto the surface, which raises issues of stability and reproducibility. Covalent chemistry could improve immobilization by binding directly the functional groups into the carbon lattice, but this creates defects that are detrimental to the electrical conduction of the graphene. There is thus a fundamental opposition between the needs for selectivity and sensitivity in the conception of graphene sensors. To unlock this conundrum, we propose an original architecture based on functionalized bilayer graphene. In this design, covalent functional sites can be tethered to the top layer, even at high densities, while the bottom layer preserves its electrical conduction. In addition, the twist angle between the orientation of the two layers becomes a new degree of freedom in the design, unexplored in the context of sensors. In this project, our team will investigate two key challenges in the application of functionalized graphene bilayers as sensors: (1) how to control the distribution of functional sites at the surface of the top layer, and (2) how to model the sensitivity of the bottom layer to the capture of an analyte by these functional sites. To address these, our team brings together a very large range of experimental and numerical techniques, including ab initio calculations, molecular dynamics simulations, scanning probes and hyperspectral imaging, photoelectron and impedance spectroscopy as well as electrical transport measurements, that will be strategically correlated to generate a unique multidimensional understanding of the functionalized bilayer structure and the impact of the twist angle.