Wafer-Scale Uniform Synthesis of 2D Transition Metal Dichalcogenides Single Crystals via Chemical Vapor Deposition

Abstract

Metrics & MoreArticle Recommendations CONSPECTUS: Two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDCs), most with a formula of MX 2 (M = Mo, W; X = S, Se, etc.), have emerged as ultrathin channel materials in next-generation electronics, due to their atomic thickness, tunable bandgap, and relatively high carrier mobility, etc. To propel their practical applications in integrated circuits, large-scale preparation of large-domain MX 2 single crystals and singlecrystal films is significantly important. Among all the synthetic methods, chemical vapor deposition (CVD) has shown great promise for the controllable syntheses of large-area uniform 2D materials with electronic-grade quality and reasonable cost. So far, intensive efforts have been devoted to the controllable growth of MX 2 single crystals with large sizes, controlled thicknesses, fast growth rates, and unidirectional orientations. However, due to the complexity of the precursor species (mostly like solid powders) and their gradient feeding distributions along the gas flow direction, it is still a huge challenge to synthesize large-area MX 2 samples with centimeter-scale uniformity, which inevitably hinders their practical applications in industry. More significantly, due to the noncentrosymmetric structures of MX 2 , antiparallel domains and twin grain boundaries usually evolved on most substrates (e.g., mica, C-sapphire). These defective grain boundaries usually exhibit metallic characteristics and serve as conducting channels, seriously impairing the electrical and optical properties of related devices. This review thereby focuses on the recent progresses on the CVD syntheses of large-scale uniform, large-domain MX 2 flakes and single-crystal films, primarily on the single-crystal insulating substrates, amorphous insulating substrates and single-crystal metal substrates. Some promising growth strategies toward improving the thickness uniformity, domain size and crystal quality of MX 2 are highlighted, through modulating the key parameters in the CVD processes, such as precursor type, substrate category/crystallinity or growth promoter. The key mechanisms that directing the uniform orientations of individual domains and their merging toward single-crystal films are also highlighted. Besides, the applications of the 2D MX 2 in high-performance electronic devices are also discussed. Finally, the current challenges for the wafer-scale syntheses of MX 2 single crystals and their applications are prospected. The potential opportunities in this field are also proposed in terms of the wafer-scale production and thickness control of 2D MX 2 , epitaxial growth of wafer-scale MX 2 single-crystals, damage-free, and easy-processing transfer of wafer-scale MX 2 , as well as the highperformance electronics/optoelectronics based on wafer-scale MX 2 . We believe this review can provide a basic guidance for the controllable growth of wafer-scale MX 2 single crystals, and inspire more researchers to design innovative synthesis routes to promote their...

Substrate engineering for wafer-scale two-dimensional material growth: strategies, mechanisms, and perspectives

“…Taking the growth of TMDCs as an example, the CVD process consists of two steps, the mass transport and the surface kinetics reaction, 1,11,39,41 as shown in Fig. 2a.…”

“…In this regard, chemical vapor deposition (CVD) provides a scalable and controllable pathway for synthesizing high-quality wafer-scale single-crystal 2D materials. 11,39…”

“…Some meaningful reviews 33,35,39,46,47 on the growth of wafer-scale 2D materials have been reported. They are concerned with material structures, growth methods, the dynamic process, and growth mechanisms.…”

Molecular Engineering Strategies toward Molybdenum Diselenide Design for Energy Storage and Conversion

“…The advantages of using appropriate intermediate catalyst should also be considered. [44] In the study of Zhang et al, the adsorption of Na atoms, which originated from the molten soda-lime glass contributed considerably to the decrease in energy barrier for the nucleation of MoSe 2 , thus effectively boosting the fast and large-scale growth of monolayer MoSe 2 . [39] Similarly, Yang et al precoated NaCl, which served as the source of Na atoms, on a quartz substrate to promote the growth rate of MoS 2 .…”

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“…1 In particular, 2D transition metal dichalcogenides (TMDCs) are ultrathin and superflexible and can be a potential choice for growth in future deformable electronics, novel optical devices and sensors, if the issues of large scale fabrication and cracking are tackled efficiently. [2][3][4] In this regard, the mechanical behavior of atomically thin 2D materials has been actively investigated to ensure mechanical reliability. For example, the in-plane stiffness of single layer MoS 2 is reported to be ∼180 ± 60 N m −1 with a Young's modulus of 270 ± 100 GPa.…”