Systematic Study of Oxygen Vacancy Tunable Transport Properties of Few‐Layer MoO 3− x Enabled by Vapor‐Based Synthesis

Bulk and nanoscale molybdenum trioxide (MoO 3 ) has shown impressive technologically relevant properties, but deeper investigation into 2D MoO 3 has been prevented by the lack of reliable vapor‐based synthesis and doping techniques. Herein, the successful synthesis of high‐quality, few‐layer MoO 3 down to bilayer thickness via physical vapor deposition is reported. The electronic structure of MoO 3 can be strongly modified by introducing oxygen substoichiometry (MoO 3− x ), which introduces gap states and increases conductivity. A dose‐controlled electron irradiation technique to introduce oxygen vacancies into the few‐layer MoO 3 structure is presented, thereby adding n‐type doping. By combining in situ transport with core‐loss and monochromated low‐loss scanning transmission electron microscopy–electron energy‐loss spectroscopy studies, a detailed structure–property relationship is developed between Mo‐oxidation state and resistance. Transport properties are reported for MoO 3− x down to three layers thick, the most 2D‐like MoO 3− x transport hitherto reported. Combining these results with density functional theory calculations, a radiolysis‐based mechanism for the irradiation‐induced oxygen vacancy introduction is developed, including insights into favorable configurations of oxygen defects. These systematic studies represent an important step forward in bringing few‐layer MoO 3 and MoO 3− x into the 2D family, as well as highlight the promise of MoO 3− x as a functional, tunable electronic material.