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First-principles study of multi-control graphene doping using light-switching molecules

The high carrier mobility in graphene promises its utility in electronics applications. Azobenzene is a widely studied organic molecule for switchable optoelectronic devices that can be synthesized with a wide variety of ligands and deposited on graphene. Using first-principles calculations, we investigate graphene doping by physisorbed azobenzene molecules with various electron-donating and -accepting ligands. We confirm previous experimental results that demonstrate greater p-doping of graphene for the trans compared to cis configuration when using a SO$_3$ electron-accepting ligand, however we find that NO$_2$ ligands maximize the p-doping difference between isomers. We also examine how these doping effects change when the graphene monolayer is supported on a silica substrate. We then extend these findings by examining the doping effects of an applied electrical bias and mechanical strain to the graphene, which lead to changes in doping for both the trans and cis isomers. These results demonstrate a new type of multi-control device combining light, electric field, and strain to change carrier concentration in graphene.