Photoluminescence quenching in mixed-dimensional heterostructures from non-covalent functionalization of monolayer WSe₂via aryl diazonium chemistry

Monolayer WSe₂ is an important member of the 2D layered materials family due to its valley physics and excitonic properties with potential applications in quantum optoelectronics. Chemical functionalization of monolayer WSe₂ has been performed with nitrobenzenediazonium (4-NBD), resulting in surface functionalization with nitrophenyl oligomers that induces hole doping of the monolayer. Here, we discuss the optical properties of 4-NBD-treated WSe₂ at the limit of full coverage of the nitrophenyl oligomers. In ambient conditions, we observe strong photoluminescence (PL) quenching and redshifting. Moreover, the PL at low temperature shows a nearly complete quenching of the exciton fine structures beyond the neutral exciton. This quenching effect is reversible upon oligomer removal and can be attributed to processes beyond hole doping. X-ray photoelectron spectroscopy reveals that the functionalization is non-covalent, and further elucidates the mixed-dimensional heterojunction formation that contributes to PL quenching in a manner consistent with first-principles calculations. Overall, these results demonstrate that diazonium functionalization is an effective pathway for modifying the optical properties of monolayer WSe₂.