Vibrational and electronic excitations in TMD monolayers and heterostructures probed by resonance Raman spectroscopy

Viner, Jacob (2022) Vibrational and electronic excitations in TMD monolayers and heterostructures probed by resonance Raman spectroscopy. University of Southampton, Doctoral Thesis, 142pp.

Record type: Thesis (Doctoral)

Abstract

This thesis presents the results of a resonance Raman study of TMD monolayers and heterostructures. These measurements allow the 2s Rydberg excitons to be characterised in heterostructures for the first time. This data is used in conjunction with a model of the Coulomb potential in heterostructures to allow the effects of exciton binding energy and the single particle band gap to be measured in the monolayers and heterostructures. This showed shifts in single particle band gap of -25 ±5 meV and -31 ±5 meV for WSe₂ and MoSe₂ respectively and with corresponding changes in exciton binding energy of -8 ±0.5 meV and -19 ±1 meV on formation of a heterostructure. Hyperbolic phonon polariton (HPP) states are also probed in hBN encapsulating TMD layers via resonance Raman spectroscopy. Excitons in the TMD layers excite HPPs in the hBN. The high resolution Raman measurements of the lineshape of the HPP modes were compared with a model of the dispersion relation. This revealed large momenta were being accessed, >50 000 cm^-1 which requires a breaking of momentum conservation in the HPP Raman scattering process.

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