Bidirectional Electronic Tuning of Single-Layer MoS2 with Conjugated Organochalcogens

We report a bidirectional tuning of the electronic properties of single-layer molybdenum disulfide (MoS2) 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 MoS2 on silicon oxide (SiO2) and sapphire (Al2O3). KPFM, in conjunction with spectroscopic characterization, showed MoS2 work function shifts as significant as 1.24 eV for TTF doping, and 0.43 eV for BT doping, when Al2O3 was employed as the underlying substrate. Less dramatic changes were observed for MoS2 on SiO2/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.