Local Structure of Sulfur Vacancies on the Basal Plane of Monolayer MoS<sub>2</sub>.

Garcia-Esparza, Angel T; Park, Sangwook; Abroshan, Hadi; Paredes Mellone, Oscar A; Vinson, John; Abraham, Baxter; Kim, Taeho R; Nordlund, Dennis et al. · ACS Nano · 2022

basic_science · Level V

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Abstract

The nature of the S-vacancy is central to controlling the electronic properties of monolayer MoS<sub>2</sub>. Understanding the geometric and electronic structures of the S-vacancy on the basal plane of monolayer MoS<sub>2</sub> remains elusive. Here, <i>operando</i> S K-edge X-ray absorption spectroscopy shows the formation of clustered S-vacancies on the basal plane of monolayer MoS<sub>2</sub> under reaction conditions (H<sub>2</sub> atmosphere, 100-600 °C). First-principles calculations predict spectral fingerprints consistent with the experimental results. The Mo K-edge extended X-ray absorption fine structure shows the local structure as coordinatively unsaturated Mo with 4.1 ± 0.4 S atoms as nearest neighbors (above 400 °C in an H<sub>2</sub> atmosphere). Conversely, the 6-fold Mo-Mo coordination in the crystal remains unchanged. Electrochemistry confirms similar active sites for hydrogen evolution. The identity of the S-vacancy defect on the basal plane of monolayer MoS<sub>2</sub> is herein elucidated for applications in optoelectronics and catalysis.