Probing Multiphased Transition in Bulk MoS<sub>2</sub> by Direct Electron Injection.

Dhakal, Krishna P; Ghimire, Ganesh; Chung, Kyungwha; Duong, Dinh Loc; Kim, Sung Wng; Kim, Jeongyong · ACS Nano · 2019

basic_science · Level V

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Abstract

Structural phase transitions in layered two-dimensional (2D) materials are of significant interest owing to their ability to exist in multiple metastable states with distinctive properties. However, phase transition in bulk MoS<sub>2</sub> by nondestructive electron infusion has not yet been realized. In this study, we report the 2H to 1T' phase transition and in-between intermediates in bulk MoS<sub>2</sub> using MoS<sub>2</sub>/[Ca<sub>2</sub>N]<sup>+</sup>·e<sup>-</sup> heterostructures, in which kinetic free electrons were directly injected into MoS<sub>2</sub>. We observed various phases in MoS<sub>2</sub> ranging from heavily doped 2H to a distorted lattice state and then on to a complete 1T' state. Snapshots of the multiphase transition were captured by extraordinary Raman shift and bandgap reduction and were further elucidated by theoretical calculations. We also observed a weakening in interlayer coupling in the vicinity of the metallic regime, which led to an unusually strong photoluminescence emission, suggesting light-efficient bulk MoS<sub>2</sub>. Our results thus suggest the optoelectronic applications that can fully utilize the multiphase transition of bulk 2D materials.