Surface modification of graphene with thionine: Formation of p-n junctions

Abstract The association of graphene with organic molecules gives rise to several possibilities for application of these composite systems that range from biosensing to selective doping and construction of p-n junctions. In the specific case of p-n junctions, organic molecules such as aminopropyltriethoxysilane and polyethylenimine are currently employed to create these bipolar structures in graphene. Following this concept, in this work, we make use of electrical characterization and Raman spectroscopy to show that the association of thionine with graphene leads to the formation of p-n junctions. While Raman and electrical transport investigations show that thionine n-dopes graphene, the formation of p-n junctions is evidenced by the appearance of a second charge neutrality point in the transfer curves of graphene transistors. More importantly, we show that these results are observed for a large number of graphene devices, which demonstrates that the use of thionine provides a robust and reproducible method for the construction of p-n junctions in graphene devices.