Abstract
We study the semiconducting rhenium dichalcogenides ReX2, where X is sulfur (S)
or selenium (Se), a class of transition metal dichalcogenides (TMDs) with a distorted
lattice structure. These materials have a single symmetry operation: inversion symmetry,
which leads to a lack of spin-orbit splitting. We use density functional theory (DFT) to
study the electronic dispersion of bulk ReSe2 and ReS2, which have complicated band
structures with many close-lying band gaps. We show the importance of studying the full
Brillouin zone rather than only the high symmetry points when trying to determine the
nature of the band gap in these materials. Thereafter, we calculate the band structure of
monolayer ReSe2 and identify which orbitals contribute to the low energy behaviour at
the valence band edge. We compare our DFT calculations to experimental angle-resolved
photoemission spectroscopy (ARPES) measurements. Furthermore, we compare DFT
data to ARPES data which uses different polarisations, exploiting the symmetry of
the underlying atomic orbitals. We find that the out-of-plane orbitals do not contribute
significantly to the top of the valence band, unlike in many other TMDs. These materials
are thus shown to display quasi-one-dimensional behaviour, with anisotropy along the
Re chains. We then calculate band structures of Janus ReSSe, where the chalcogen layers
on either side of Re are composed of S on one side and Se on the other. The distorted
structures of rhenium TMDs motivates the study of Janus-like rhenium dichalcogenides
with varying numbers of substituted chalcogens in pure ReSe2 or ReS2. We calculate
formation energies and predict the substitutions most likely to take place, before showing
the effect of these substitutions on the valence and conduction bands. The broken
inversion symmetry in these Janus and Janus-like materials leads to significant spinorbit
splitting, which could have uses in spintronics applications. Hence, we have studied
the band structures of rhenium dichalcogenides and shown that these materials have
complicated band structures and strong anisotropy which lead to interesting effects not
seen in other TMDs, making them promising candidates for applications in optoelectronic
devices.
Date of Award | 16 Jun 2021 |
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Original language | English |
Awarding Institution |
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Supervisor | Marcin Mucha-Kruczynski (Supervisor) & Daniel Wolverson (Supervisor) |
Keywords
- TMD
- DFT
- ARPES
- Rhenium