Role of Chemical Potential in Flake Shape and Edge Properties of Monolayer MoS₂

Abstract

The precise control of edge geometry and crystal shape of monolayer MoS 2 is particular of importance for their applications in nanoelectronics and photo-electro catalysts. Here we reveal a crucial role of chemical potential in the determination of equilibrium shape (ES) and edge structure of monolayer MoS 2 by using density-functional theory calculations. Applying Wulff construction rule, our results demonstrate the shape evolution of monolayer MoS 2 flake from the dodecagonal shape, then to the hexagonal shape, to the triangular shape with the variation of chemical potential from the Mo-rich to the S-rich condition, and the edge structure of ES changes correspondingly from mixed zigzag/armchair edges to pure zigzag edges. This finding can be applied to explain extensive experimental observations about the morphology of MoS 2 domains. Meanwhile, the edge magnetism and electronic structures of monolayer MoS 2 domains are found to be dependent on their edge structure, which provides specific guidance for the magnetic modulation of monolayer MoS 2 and designing more effective MoS 2 -based catalysts.

Stacking-controllable interlayer coupling and symmetric configuration of multilayered MoS2

“…However, when the Mo:S atomic ratio is between growths I and II (here; 0.48), the MoS 2 crystal will transform into a truncated triangle. 28,31 Additional evidence supporting the above information is given by energy-dispersive spectroscopy analysis (Supplementary Table). Based on the APCVD system, multi-stacked MoS 2 crystals can be formed not only in the shape of triangles but also in the shapes of truncated triangles and hexagons, as shown in Supplementary Figures 2b and c. We further describe the transformation of the MoS 2 crystals from a monolayer to complete bilayer in Supplementary Figure S2d.…”

“…Therefore, the lateral layer size decreases with an increasing height, and monolayer-by-monolayer-stacked MoS 2 crystals are finally formed. [29][30][31][32][33][34] Stacking-oriented phonon frequencies in the Raman spectra We critically examined the high-energy phonons in the Raman spectra of multi-stacked MoS 2 crystals and exploited the stacking-induced structural changes and interlayer vdW interactions. As illustrated in Figure 2a, a MoS 2 crystal consists of two well-defined, strong Raman bands attributed to lattice vibrations in two specific directions, which are denoted as in-plane (E 2g 1 ) and out-of-plane (A 1g ) vibrations.…”

Edge structures and properties of triangular antidots in single-layer MoS2

“…We observe a triangular shape with ZZ S edges. 29,38 According to the Raman spectrum of the as-prepared sample in Fig. 5(b), the Raman shifts of the E 2g and A 1g modes are 386.3 and 407.2 cm À1 .…”

“…Figure 1(h) illustrates the antidot construction in a triangular Mo edge cluster, which is commonly created in S-rich conditions. 29,38 The three edges of the grey triangle correspond to Mo edges of the MoS 2 triangular samples typically observed in experiments. The orientation of the blue/red triangle is identical/ opposite to the gray triangle, illustrating the AC/ZZ Mo edge antidot.…”

“…25 Controlling the properties of single-layer MoS 2 is important to meet the requirements of key applications. It has been demonstrated that an electric field, 26 strain, 27 defects, 28 and the edge structure 29 are effective means for introducing electronic and optical modulations. Specifically, the edge structure has been found to be crucial for optimizing the performance of epitaxial MoS 2 nanosheets.…”