Photoswitchable Monolayer and Bilayer Graphene Devices Enabled by In Situ Covalent Functionalization

A chemical approach is demonstrated for covalent functionalization of graphene devices with photochromic azobenzene moieties using diazonium chemistry. The approach utilizing in situ generated aryl diazonium cations enables multilayer deposition of photochromic species on graphene surfaces. It is demonstrated that the thickness of the resulting optically responsive films can be tuned from about 1 to over 20 nm by varying the functionalization time. Cis and trans forms of azobenzene can be achieved by illumination with UV and visible light, respectively, which enables reversible optically tunable change in the doping level of graphene. Interestingly, the bilayer graphene devices, while showing robust photoswitching, do not exhibit any considerable degradation of conductivity and charge carrier mobilities upon chemical functionalization, which is not the case for monolayer graphene devices. This work paves a way for multilayer functionalization of graphene devices with photochromic species and highlights bilayer graphene as a promising platform for high mobility devices with covalent functionalization.