Convection‐Flow‐Assisted Preparation of a Strong Electron Dopant, Benzyl Viologen, for Surface‐Charge Transfer Doping of Molybdenum Disulfide

作者：Keigo Matsuyama; Akito Fukui; Kohei Miura; Hisashi Ichimiya; Yuki Aoki; Yuki Yamada; Prof. Atsushi Ashida; Prof. Takeshi Yoshimura; Prof. Norifumi Fujimura; Prof. Daisuke Kiriya

来源：ChemistryOpen, 2019, 8(7): 908-914.

DOI：10.1002/open.201900169

• Transition metal dichalcogenides
• Benzyl viologen
• Redox reactions
• Molecular doping
• Convection flow

Abstract Transition metal dichalcogenides (TMDCs) have received attention as atomically thin post‐silicon semiconducting materials. Tuning the carrier concentrations of the TMDCs is important, but their thin structure requires a non‐destructive modulation method. Recently, a surface‐charge transfer doping method was developed based on contacting molecules on TMDCs, and the method succeeded in achieving a large modulation of the electronic structures. The successful dopant is a neutral benzyl viologen (BV0); however, the problem remains of how to effectively prepare the BV0 molecules. A reduction process with NaBH4 in water has been proposed as a preparation method, but the NaBH4 simultaneously reacts vigorously with the water. Here, a simple method is developed, in which the reaction vial is placed on a hotplate and a fragment of air‐stable metal is used instead of NaBH4 to prepare the BV0 dopant molecules. The prepared BV0 molecules show a strong doping ability in terms of achieving a degenerate situation of a TMDC, MoS2. A key finding in this preparation method is that a convection flow in the vial effectively transports the produced BV0 to a collection solvent. This method is simple and safe and facilitates the tuning of the optoelectronic properties of nanomaterials by the easily‐handled dopant molecules.