14 de Setembro de 2026 às 09:19
Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.In this study, we analyze transition metal dichalcogenides (TMDs) with the
general com- position MX2 (M = W, Mo; X = S). We present a comparative
analysis of the temperature- dependent optical properties of monolayer (1L) and
twisted bilayer MoS2 (TBM) nanosys- tems using Raman and
photoluminescence (PL) spectroscopies. We investigate the beha- vior of
phonon modes, as well as exciton and trion energies, over a temperature range
from 93 K to 573 K. Our findings reveal a pronounced increase in the
anharmonicity of the A1 ′ and moir ́e-induced FA1 ′ phonon modes in the TBM
sample. This enhanced anhar- monicity is attributed to an increase in normal
and umklapp phonon scattering processes, enabled by the emergence of
phonon branches due to the nanoscale moir ́e effects induced by interlayer
rotation. Furthermore, PL measurements demonstrate improved thermal
stability of the negatively charged A− and neutral A0 excitons in TBM,
reinforcing its potential for nanoscale optoelectronic applications. Regarding
triangular tungsten disul- fide (WS2 triangle) and monolayer WS2 film, we
conducted analyses under both ambient and vacuum conditions, focusing on
the differences between the interior regions and the triangular edges.
Furthermore, we examined the behavior of phonon modes, as well as exciton
and trion energies, for the triangle and for suspended or supported WS2 film at
low temperatures (20 to 298 K). An extraordinary increase in the PL intensity of
the suspended WS2 triangle is observed compared to the supported one, due
to edge effects inherent to the sample. The decrease in Raman and PL
intensities when comparing the film to the WS2 triangle occurs because the film
is polycrystalline and the PL undergoes suppression at the grain boundaries.
Changes in the Raman shift, as well as the shift and reduction in PL intensity
under vacuum conditions, are consequences of strain and the alternation
between neutral and charged exciton recombination inherent to the WS2 mo-
nolayer. These results provide valuable insights into the temperature-dependent
optical behavior of MoS2 moir ́e superlattices, advancing the understanding of
phonon and exciton interactions in twisted 2D nanosystems; suspended and/or
supported 2D nanosystems for applications in optoelectronics, thermal
management and guiding the design of functional nanomaterials.
