Morphological Evolution of Monolayer MoS₂ Single-Crystalline Flakes

Abstract

Understanding and controlling the growth morphology of two-dimensional crystals of transition metal dichalcogenides (TMDs) is essential in developing high-quality crystalline material for spintronics, valleytronics, electronics, and optics. Here we report our studies on the evolution of crystallite morphology of MoS2 observed in chemical vapor deposition. It is shown that as time goes on, the growth morphology of MoS2 flakes undergoes a transition from a triangle to a star shape, then back to a triangle, and finally to a bulgy irregular morphology. By tuning the temperature of the element sources, the atomic ratio of S and Mo on the growing interface can be adjusted. The variation of the S/Mo ratio affects the edge diffusion length and nucleation behavior on the edge of crystallite, leading to different growth morphologies. Our observations provide clues on how to engineer the morphology and control the quality of TMD crystalline sheets.

Controllable Synthesis of Large-Scale Monolayer MoS2 Dendritic Flakes with Serrated Edges and Their Multimodal Microscopy and AFM Characterizations

“…reported the morphological evolution of CVD-grown 2D MoS 2 crystals from a triangular to a dendritic shape via tailoring substrate construction, and the annealed MoS 2 dendrites with rough edges of up to ∼500 μm exhibit good and highly durable HER performance . Such dendritic MoS 2 flakes are systemically studied by CVD method by tuning the amount of MoO 3 , varying the deposition location, manipulating the S supply, and varying the growth time, with different temperatures of S powder, Mo/S flux ratios, and introduction times of S, to estimate the HER performance of these MoS 2 flakes. Yang et al reported the creation of CVD-grown 2D MoS 2 flakes with varied concentrations of S vacancies by utilizing a helium ion beam, and they indicated that the concentration increase of S vacancies can induce variations in the local strain and electrical conductivity, which are essential to increasing the activity of catalysts .…”

Study on the Morphological Mechanism of MoS2 Growth by NaCl‐Assisted Chemical Vapor Deposition

“…Because of the direct band gap of sample 1, it exhibits very high luminescence peaks at 624 nm and 672.3 nm. On the other hand, sample 2 exhibits a much lower luminescence peak at 675.8 nm due to the presence of defects mainly referring to grain boundaries [13] . Finally, a significant decrease in PL luminescence intensity of sample 3 can be attributed to the shift in the crystalline nature of the MoS 2 film from a single‐layer direct bandgap to a multilayer indirect bandgap.…”

Structure modulation of two-dimensional transition metal chalcogenides: recent advances in methodology, mechanism and applications

“…In addition, controlling the reaction time can help to achieve relatively complete structural evolution for either thermodynamic or kinetic modulation. 143 The improvement in mechanism for structure modulation through reaction condition transformations will benefit from entire evolutionary pathways instead of several steps.…”