Phase Engineering of Two‐Dimensional Transition Metal Dichalcogenides

Abstract

Since the successful isolation of single‐layer graphene with an atomic thickness, various van der Waals (vdW) materials have been intensively studied owing to their unique properties. Among the families of vdW materials, transition metal dichalcogenides (TMDs) have served as representatives because of their diverse band structures and intriguing quantum states, unlike those observed in their bulk counterparts. Particularly, unconventional polymorphic phases of TMDs increase the degrees of freedom in device fabrication and property modulation. As variations in structural phases significantly change the electrical, physical, and chemical properties of materials, phase engineering is essential for the new paradigm of TMD‐based devices. In this review, diverse strategies that can induce and control structural phases in TMDs are explored. After introducing the polymorphic phase changes and the resulting electronic band structures, the various empirical approaches used for manipulating phases in vdW materials, including phase‐selective synthesis and post‐synthesis treatments, are summarized. The group‐VI TMDs are considered as reference, and the analysis is extended to other TMDs across various groups in the periodic table. In addition to providing a comprehensive survey of the recent progress in TMD applications, the challenges for TMD applications and potential opportunities in emerging fields are discussed.

Exploring Anisotropic Carrier Transport in WSe2–WTe2 Superlattices: A Computational Study

“…It is found that the hexagonal phase is the most thermodynamically stable phase for WSe 2 . On the other hand, the orthorhombic phase is the most stable phase of WTe 2 , rather than the hexagonal one . Due to this difference, an intermediate state emerges at x = 0.5, where both the hexagonal (2H) and orthorhombic (Td) phases coexist in the material .…”

“…42 On the other hand, the orthorhombic phase is the most stable phase of WTe 2 , rather than the hexagonal one. 43 Due to this difference, an intermediate state emerges at x = 0.5, where both the hexagonal (2H) and orthorhombic (Td) phases coexist in the material. 26 In this study, we propose a layered material consisting of a superlattice formed by the combination of WSe 2 and WTe 2 .…”

“…Our calculations agree well with previous DFT calculations. 38,43 The substitution of Te atoms with Se atoms in 2H-WSe 2 to form the 2H phase of WSe 2 − WTe 2 results in a reduction in the band gap to 0.79 eV. This decrease in the band gap can be attributed to the larger atomic radius of Te compared to Se, leading to an increased interatomic distance between W and Te atoms.…”

Engineered Two-Dimensional Transition Metal Dichalcogenides for Energy Conversion and Storage

“…4−6 Phase-engineering in many ways is a deeply convoluted engineering tool for TMDs, as it is synergistically correlated and induced by many other engineering strategies or vice versa, such as intercalation/exfoliation, defects, thermochemical treatments, strain engineering, and structural distortions. 49,360 With exfoliation and intercalation by alkali ions, organic ligands have led to 2H-to-1T phase transformations in TMDs. Detailed studies on exfoliations of TMDs (MoS 2 , MoSe 2 , WS 2 , and WSe 2 ) using aromatic intercalants such as phenyllithium, sodium naphthalenide, and sodium anthracenide elucidated the intercalation effects on electrochemical HER performance, with PhLi-intercalated MoS 2 showing the best performance due to its high edge density and exposure of metal-ion sites.…”

A Mini Review: Phase Regulation for Molybdenum Dichalcogenide Nanomaterials

“…Different phase structures lead to huge disparity in the properties of the TMDC nanomaterials [ 21 , 22 , 23 , 24 , 25 ]. For example, molybdenum disulfide (MoS 2 ) exhibits all three phase structures.…”