Bidirectional Electronic Tuning of Single-Layer MoS₂ with Conjugated Organochalcogens

We report a bidirectional tuning of the electronic properties of single-layer molybdenum disulfide (MoS 2 ) by n-doping with the electron donating tetrathiafulvalene (TTF) and p-doping with the electron accepting bithiazolidinylidene (BT). Using Kelvin probe force microscopy (KPFM), we spatially monitored changes in the work function of monolayer MoS 2 on silicon oxide (SiO 2 ) and sapphire (Al 2 O 3 ). KPFM, in conjunction with spectroscopic characterization, showed MoS 2 work function shifts as significant as 1.24 eV for TTF doping, and 0.43 eV for BT doping, when Al 2 O 3 was employed as the underlying substrate. Less dramatic changes were observed for MoS 2 on SiO 2 /Si, revealing a significant impact of substrate selection on the electronic properties of this 2D material. High-level computations helped guide experiments on chemical modulation of the electronic properties of this transition-metal dichalcogenide.