Local Structure of Sulfur Vacancies on the Basal Plane of Monolayer MoS2

Angel T. Garcia-Esparza, Sangwook Park, Hadi Abroshan, Oscar A. Paredes Mellone, John Vinson, Baxter Abraham, Taeho R. Kim, Dennis Nordlund, Alessandro Gallo, Roberto Alonso-Mori, Xiaolin Zheng, Dimosthenis Sokaras
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ACS Nano

The nature of the S-vacancy is central to controlling the electronic properties of monolayer MoS2. Understanding the geometric and electronic structures of the S-vacancy on the basal plane of monolayer MoS2 remains elusive. Here, operando S K-edge X-ray absorption spectroscopy shows the formation of clustered S-vacancies on the basal plane of monolayer MoS2 under reaction conditions (H2 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 H2 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 MoS2 is herein elucidated for applications in optoelectronics and catalysis.

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