Chemical Vapor Transport Reactions for Synthesizing Layered Materials and Their 2D Counterparts

Abstract

semimetals (Si and Ge) to transition metal dichalcogenides (TMDs), which can be tuned from semiconductors to superconductors, have been intensively investigated. [8] Despite the recent advances in 2D materials, it is still challenging to obtain 2D materials with desired layers and size in facile and controllable manners.Indeed, continuous research has been carried out on the synthesis of 2D materials. [9] Generally, two synthetic strategies, known as top-down and bottom-up, are applied to obtain 2D materials. In the common top-down strategy, 2D materials are exfoliated from their bulk counterparts. Differently, using the bottom-up strategy, 2D materials with a few thin layers, even an atomically thin layer, can be directly synthesized from small building blocks such as molecules and atoms. [10] In these synthetic strategies for 2D materials, chemical vapor transport (CVT) reaction, an old yet powerful technology, plays an important role because CVT reactions can be used for both topdown and bottom-up syntheses of 2D materials. [11] CVT reactions represent a category of reactions with one common feature: a condensed phase, typically a solid, sublimes in the presence of a gaseous reactant (the mineralizer), and then deposits elsewhere usually in the form of crystals. [12] Notably, CVT is different from chemical vapor deposition (CVD), another chemical vapor-based approach for synthesizing 2D materials. Specifically, the main difference between CVT and CVD lies in the source materials for synthesizing products, where solid reactants are typically used in CVT and gaseous precursors are usually applied in CVD. The difference induces consequent differences in reactor design, operational control, and product features, thus bringing strengths and drawbacks for each approach. Since the discovery of CVT reaction by Bunsen in 1851, comprehensive understanding of CVT reactions in both experimental exploration and theoretical modeling has been established. [13] Furthermore, thousands of CVT reactions have been applied till now, producing a great variety of pure and crystalline solids, including metals, metalloids, intermetallic phases, metal oxides, halides, chalcogen halides, chalcogenides, and pnictides. [13,14] The knowledge about CVT reactions, together with the large number of applicable reactions, can offer opportunities for the controllable synthesis of 2D materials and the exploration of new 2D materials. Unfortunately, for the preparation of 2D materials, in stark contrast to the wide application of CVD, 2D materials, namely thin layers of layered materials, are attracting much attention because of their unique electronic, optical, thermal, and catalytic properties for wide applications. To advance both the fundamental studies and further practical applications, the scalable and controlled synthesis of large-sized 2D materials is desired, while there still lacks ideal approaches. Alternatively, the chemical vapor transport reaction is an old but powerful technique, and is recently adopted for synthesizing 2D material...

Recent Advances in 2D Metal Monochalcogenides

“…The top-down approach relies on the exfoliation of thin 2D crystals from their parent layered bulk crystals and the most important are based on mechanical (ME), liquid phase (LPE), and electrochemical exfoliation (EE). [4,5,[91][92][93] While, the most important bottom-up approaches include wet chemical synthesis (WCS), pulsed laser and chemical vapor deposition (PLD and CVD). Those methods are based on chemical reactions of certain precursors at given experimental conditions.…”

Recent Advances in 2D Layered Phosphorous Compounds

“…In the case of CVT process, the precursors and transport agents are combined into the hot end of an evacuated and sealed quartz tube, and the precursors will be transported into the cold end for chemical reaction and then form bulk crystals at a certain temperature gradient (Figure 2b). [ 4 ] Through this method, bulk crystals of FePS 3 , [ 28 ] FePSe 3 , [ 66 ] NiPS 3 , [ 74 ] MnPS 3 , [ 75 ] CrPS 4 , [ 70 ] CuInP 2 S 6 [ 76 ] and b‐AsP [ 58 ] (Figure 2d–f) are successfully synthesized, which can be further used for the exfoliation of 2D flakes.…”

“…2D van der Waals layered materials have ignited the enthusiasm of researchers due to the unique structure and fascinating layer‐dependent features distinct from their bulk counterparts. [ 1–7 ] Numerous researches about 2D layered materials mainly focused on graphene, [ 8 ] hexagonal boron nitride (hBN), [ 9 ] Mxene, [ 10,11 ] black phosphorous (BP), [ 12,13 ] and transition metal dichalcogenides (TMDs). [ 14–16 ] Recently, 2D LPCs have gradually attracted extensive attention as a new member of 2D materials.…”

2D Re‐Based Transition Metal Chalcogenides: Progress, Challenges, and Opportunities

“…Chemical vapor transport (CVT) growth is a classic and mature technique for the synthesis of bulk crystal materials. [77] At present, the fundamental property investigation and functional device fabrication of the most 2D materials are highly relied on the 2D nanosheets mechanically exfoliated from the bulk crystals synthesized via CVT method, [78][79] and ReX 2 is no exception. In general, the CVT method is equipped with a sealed ampoule tube containing the precursor and transport agent, and then the growth is performed in low pressure and high temperature for about several to ten days.…”

“…In general, the CVT method is equipped with a sealed ampoule tube containing the precursor and transport agent, and then the growth is performed in low pressure and high temperature for about several to ten days. [ 77 ] Bhattacharya and coworkers developed a modified Bridgman method without transport agent to synthesize high‐quality ReS 2 and ReSe 2 bulk single crystals ( Figure –) by using the pure Re powder and S/Se powder. [ 80 ] Just recently, Jiao and coworkers developed an approach for directly synthesizing thin ReX 2 flakes by CVT through carefully tuning the growth kinetics together with a specially designed quartz ampoule with a neck to separate the powders from the growth substrate.…”