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  Haverkamp, R.; Sorgenfrei, N.L.A.N.; Giangrisostomi, E.; Neppl, S.; Kühn, D.; Föhlisch, A.: Directional charge delocalization dynamics in semiconducting 2H-MoS₂ and metallic 1T-Li_xMo₂. Scientific Reports 11 (2021), p. 6893/1-7

10.1038/s41598-021-86364-2
Open Accesn Version

Abstract:
The layered dichalcogenide MoS2 is relevant for electrochemical Li adsorption/intercalation, in the course of which the material undergoes a concomitant structural phase transition from semiconducting 2H-MoS2 to metallic 1T-LixMoS2. With the core hole clock approach at the S L1 X-ray absorption edge we quantify the ultrafast directional charge transfer of excited S3p electrons in-plane (∥) and out-of-plane (⊥) for 2H-MoS2 as τ2H,∥=0.38±0.08 fs and τ2H,⊥=0.33±0.06 fs and for 1T-LixMoS2 as τ1T,∥=0.32±0.12 fs and τ1T,⊥=0.09±0.07 fs. The isotropic charge delocalization of S3p electrons in the semiconducting 2H phase within the S-Mo-S sheets is assigned to the specific symmetry of the Mo-S bonding arrangement. Formation of 1T-LixMoS2 by lithiation accelerates the in-plane charge transfer by a factor of ∼1.2 due to electron injection to the Mo-S covalent bonds and concomitant structural repositioning of S atoms within the S-Mo-S sheets. For excitation into out-of-plane orbitals, an accelerated charge transfer by a factor of ∼3.7 upon lithiation occurs due to S-Li coupling.