Dual Catalytic and Self‐Assembled Growth of Two‐Dimensional Transition Metal Dichalcogenides Through Simultaneous Predeposition Process

Abstract

The recent introduction of alkali metal halide catalysts for chemical vapor deposition (CVD) of transition metal dichalcogenides (TMDs) has enabled remarkable two‐dimensional (2D) growth. However, the process development and growth mechanism require further exploration to enhance the effects of salts and understand the principles. Herein, simultaneous predeposition of a metal source (MoO3) and salt (NaCl) by thermal evaporation is adopted. As a result, remarkable growth behaviors such as promoted 2D growth, easy patterning, and potential diversity of target materials can be achieved. Step‐by‐step spectroscopy combined with morphological analyses reveals a reaction path for MoS2 growth in which NaCl reacts separately with S and MoO3 to form Na2SO4 and Na2Mo2O7 intermediates, respectively. These intermediates provide a favorable environment for 2D growth, including an enhanced source supply and liquid medium. Consequently, large grains of monolayer MoS2 are formed by self‐assembly, indicating the merging of small equilateral triangular grains on the liquid intermediates. This study is expected to serve as an ideal reference for understanding the principles of salt catalysis and evolution of CVD in the preparation of 2D TMDs.

Metatungstate Chemical Vapor Deposition of WSe2: Substrate Effects, Shapes, and Morphologies

“…Reaction (2) is also possibly mediated by SC, leading to the formation of intermediate Na-based byproduct compounds [62]. The exact nature of the entire set of chemical, crystallization, and growth processes of the liquid precursor-intermediated CVD approach is not yet fully understood [44,63]. We presume that it is similar to the model proposed recently for Na 2 WO 4 [33] (Mo [64,65], Nb [66]) complexes within the framework of the vapor-liquid-solid mechanism for TMDC, where the eutectic precursor phase/substrate interface [66] and thermodynamic nucleation evolution [67,68] play key roles.…”

Edge-Rich 3D Structuring of Metal Chalcogenide/Graphene with Vertical Nanosheets for Efficient Photocatalytic Hydrogen Production

“…Hydrogen has been extensively studied as an ideal clean energy source to replace conventional fossil fuels. Photocatalytic and photoelectrochemical (PEC) hydrogen generation by water splitting using sunlight is a promising strategy to produce hydrogen fuel by harvesting solar energy for energy storage use. − Transition metal compounds or Transition metal chalcogenides (TMDs), which are two-dimensional (2D) layered structures, have revitalized an upsurge in research interest because of exceptional electronic, photoelectric, and energy harvesting performance. − Among these TMDs, molybdenum disulfide (MoS 2 ) and tungsten disulfide (WS 2 ) have recently attracted considerable attention as a suitable material for cocatalysis or photocatalytic hydrogen generation due to their relatively high mobility (a few hundred cm 2 V –1 s –1 ), superior catalytic properties, and an adequate bandgap that is compatible with sunlight. − …”

First principles calculations of the electronic configuration and photocatalytic performance of GaSe(Ga2SSe)/MoS2(MoSSe) heterojunctions

“…8 The bandgap values of TMDs varied strongly with the number of layers and increased when the number of layers was reduced from multilayer to single-layer. 9 Similar to graphene, 2D MoS 2 has only a single layer or several layers of the bulk material, and the monolayer MoS 2 structure was successfully accessed by Novoselov in 2005 employing a mechanical exfoliation technique, 10 which provides a brilliant application prospect in the domain of field-effect devices, optoelectronic devices, photocatalysis and sensors owing to the large specific surface area of 2D MoS 2 . Nevertheless, for TMDs and 2D GaSe photocatalyst schemes, photogenerated electrons and holes could not be segregated efficiently, and there are shortcomings in meeting appropriate band edge positions and bandgap widths simultaneously.…”