Abstract
An investigation of the unoccupied electronic structure of the transition-metal dichalcogenide tin disulphide has been conducted using core-hole clock spectroscopy. Polarization-dependent x-ray absorption in the tender x-ray regime at the S K edge and maps of the resonant Auger spectra in the S KLL Auger kinetic energy range have been recorded. Supported with ab initio calculations of the unoccupied electronic structure, these allow us to relate resonances in the absorption cross section to excitations along various directions in the Brillouin zone. We observe anisotropy in the x-ray absorption cross section in polarization directions in plane and out of plane of the crystal. There is also anisotropy in the charge transfer dynamics as inferred from the coherent and noncoherent parts of the resonant Auger spectra. This approach can be generally used to interpret dynamics in unoccupied states, e.g., in layered structure or heterogenous interfaces.
Highlights
Transition-metal dichalcogenides (TMDs) are among the candidates for two-dimensional (2D) materials beyond graphene and have shown promise in applications, e.g., for next-generation electronics [1] and in rechargeable batteries [2]
In conclusion we have shown that charge transfer in SnS2 is anisotropic comparing in-plane and out-of-plane excitation directions through excitations with different x-ray polarization direction
Using 2D maps of the resonant Auger electron spectra in the S KLL Auger regime and orbital projected electronic structure calculations of the unoccupied states, we can in detail interpret the x-ray absorption cross section and how it depends on polarization direction and orbital character
Summary
Transition-metal dichalcogenides (TMDs) are among the candidates for two-dimensional (2D) materials beyond graphene and have shown promise in applications, e.g., for next-generation electronics [1] and in rechargeable batteries [2]. TMDs are a family of layered materials weakly bonded through van der Waals forces with the chemical formula MX2 where M is a transition-metal ion and X is a chalcogenide ion. CHCS uses the finite lifetime of a core-excited state as an internal clock to measure the dynamical processes. Using this technique with excitation energies in the tender x-ray range allows the probe to be both chemically specific and it can probe processes down to percent of the core-hole lifetime (tens of attoseconds) [9]
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