Tuning the Band Gap of MoS2 Single Layer with Aryl Diazonium Salts

Abstract

We report on the surface functionalization of molybdenum disulfide flakes (MoS₂) with 4-nitrobenzenediazonium (4-NBD) tetrafluoroborate salt to alter their electronic band gap and subsequent excitonic properties. The 2D materials composed of a few layers were grown by chemical vapor deposition over SiO₂/Si. Raman and photoluminescence analyses of the MoS₂ functionalized surface were conducted using confocal measurements to evaluate the spontaneous formation of polyaryl clusters and azo bonds at the surface of MoS₂ and their stability under laser exposure. Gap mode tip-enhanced Raman and photoluminescence measurements on MoS₂ flakes transferred onto the Au surface were conducted in the vicinity of the polyaryl clusters, enabling the mapping of the excitons and revealing the formation of charged excitons. These results are indicative of a charge transfer process from the MoS₂ flake to the diazonium salts, which in turn act as a p-type dopant for MoS₂. Contact potential difference measurements were conducted to quantify the electronic work function of the modified MoS₂ surface.