3 research outputs found
Hyperdislocations in van der Waals Layered Materials
Dislocations
are one-dimensional line defects in three-dimensional crystals or
periodic structures. It is common that the dislocation networks made
of interactive dislocations be generated during plastic deformation.
In van der Waals layered materials, the highly anisotropic nature
facilitates the formation of such dislocation networks, which is critical
for the friction or exfoliation behavior for these materials. By transmission
electron microscopy analysis, we found the topological defects in
such dislocation networks can be perfectly rationalized in the framework
of traditional dislocation theory, which we applied the name “hyperdislocations”.
Due to the strong pinning effect of hyperdislocations, the state of
exfoliation can be easily triggered by 1° twisting between two
layers, which also explains the origin of disregistry and frictionlessness
for all of the superlubricants that are widely used for friction reduction
and wear protection
Impact of Polar Edge Terminations of the Transition Metal Dichalcogenide Monolayers during Vapor Growth
The
polar edges of two-dimensional monolayer transition metal dichalcogenides
(TMD) and their alloys are examined by combined theoretical (density
functional theory) and experimental approaches. For these polar edges,
the growth reaction energies between different edge terminations are
considered instead of the surface free energies. Due to different
energy evolutions during growth on the zigzag edges between MoS<sub>2</sub> and WS<sub>2</sub>, the S-ZZ edges in the WS<sub>2</sub> monolayer
flakes more easily decompose into sawtooth-like edges in M-ZZ type
as compared to the MoS<sub>2</sub> monolayer; thus, the hexagonal
morphology can be seen more often in WS<sub>2</sub>. Moreover, the
observed anisotropic short-range order in the MoS<sub>2</sub>/WS<sub>2</sub> alloys is originated from the freezed edge configurations
during growth, explainable by the growth kinetics and thermodynamics
of the Mo-ZZ-edges. The determination of the growing edge terminations
is of great importance for the controllable synthesis of the emergent
two-dimensional TMD materials
Observing Grain Boundaries in CVD-Grown Monolayer Transition Metal Dichalcogenides
Two-dimensional monolayer transition metal dichalcogenides (TMdCs), driven by graphene science, revisit optical and electronic properties, which are markedly different from bulk characteristics. These properties are easily modified due to accessibility of all the atoms viable to ambient gases, and therefore, there is no guarantee that impurities and defects such as vacancies, grain boundaries, and wrinkles behave as those of ideal bulk. On the other hand, this could be advantageous in engineering such defects. Here, we report a method of observing grain boundary distribution of monolayer TMdCs by a selective oxidation. This was implemented by exposing directly the TMdC layer grown on sapphire without transfer to ultraviolet light irradiation under moisture-rich conditions. The generated oxygen and hydroxyl radicals selectively functionalized defective grain boundaries in TMdCs to provoke morphological changes at the boundary, where the grain boundary distribution was observed by atomic force microscopy and scanning electron microscopy. This paves the way toward the investigation of transport properties engineered by defects and grain boundaries