Direct Observation of Charge Transfer between NO<sub><i>x</i></sub> and Monolayer MoS<sub>2</sub> by Operando Scanning Photoelectron Microscopy
Ingvild Julie Thue Jensen, Ayaz Ali, Patrick Zeller, Matteo Amati, Matthias Schrade, Per Erik Vullum, Marta Benthem Muñiz, Prashant Bisht, Takashi Taniguchi, Kenji Watanabe, B. R. Mehta, Luca Gregoratti, Branson D. Belle
Abstract
Atomically thin transition-metal dichalcogenides (MoS<sub>2</sub>, WSe<sub>2</sub>, etc.) have long been touted as promising materials for gas detection because of their tunable band gaps; however, the sensing mechanism, based on a charge-transfer process, has not been fully explored. Here, we directly observe the effect of this charge transfer on the doping levels in MoS<sub>2</sub> upon exposure to NO<sub>x</sub> by performing scanning photoelectron microscopy (SPEM) on a monolayer MoS<sub>2</sub> transistor under bias conditions in a gas environment. By a comparison of the operando SPEM maps of the transistor with and without exposure to NO<sub>x</sub> gas, a downward shift in the Fermi level position could be detected, consistent with NO<sub>x</sub> gas making the MoS<sub>2</sub> channel less n-type.