Pulsed laser deposition (PLD) can
be considered a powerful method
for the growth of two-dimensional (2D) transition-metal dichalcogenides
(TMDs) into van der Waals heterostructures. However, despite significant
progress, the defects in 2D TMDs grown by PLD remain largely unknown
and yet to be explored. Here, we combine atomic resolution images
and first-principles calculations to reveal the atomic structure of
defects, grains, and grain boundaries in mono- and bilayer MoS2 grown by PLD. We find that sulfur vacancies and MoS antisites are the predominant point defects in 2D MoS2. We predict that the aforementioned point defects are thermodynamically
favorable under a Mo-rich/S-poor environment. The MoS2 monolayers
are polycrystalline and feature nanometer size grains connected by
a high density of grain boundaries. In particular, the coalescence
of nanometer grains results in the formation of 180° mirror twin
boundaries consisting of distinct 4- and 8-membered rings. We show
that PLD synthesis of bilayer MoS2 results in various structural
symmetries, including AA′ and AB, but also turbostratic with
characteristic moiré patterns. Moreover, we report on the experimental
demonstration of an electron beam-driven transition between the AB
and AA′ stacking orientations in bilayer MoS2. These
results provide a detailed insight into the atomic structure of monolayer
MoS2 and the role of the grain boundaries on the growth
of bilayer MoS2, which has importance for future applications
in optoelectronics.
Chemical vapor deposition (CVD) has been established as a versatile route for the large-scale synthesis of transition metal dichalcogenides, such as tungsten disulfide (WS2).
The two-dimensional material hexagonal boron nitride (hBN) hosts luminescent centres with emission energies of ∼ 2 eV which exhibit pronounced phonon sidebands. We investigate the microscopic origin of these luminescent...
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