3R-MoS₂ in Review: History, Status, and Outlook

Abstract

Transition metal dichalcogenides (TMDs) of molybdenum and tungsten are layered van der Waals materials that exhibit a rich array of polytypes. The different possible arrangements of the constituents of the “two-dimensional” MX2 sheets (where M = group 4–10 elements, X = chalcogen) give rise to a host of interesting and tunable phenomena. Molybdenite, or molybdenum disulfide (MoS2) in its most abundant and thermodynamically stable form, 2H-MoS2, is perhaps the most widely used TMD, though the potential applications of its metastable polytypes have been recognized only recently. From among the polytypes, the 3R-MoS2 (rhombohedral) phase has attracted the most interest because of its thermodynamic stability, ABC stacking (as opposed to the AA′ of the more common 2H-MoS2), and lack of inversion symmetry. These properties make it an excellent candidate for photonics, optoelectronics, and catalysis. Because the literature on this material is rapidly expanding, this review seeks to summarize the history, known and predicted characteristics, syntheses, and applications, as well as common misconceptions of, and surrounding, 3R-MoS2. Although the review is chemically focused, it includes suggested reading to cover a broader scope.

Scroll-like and platy molybdenite-3R from the Ufaley metamorphic block, South Urals: EBSD, XRD, SEM, EPMA and ICP-MS study

“…Many publications are devoted to the influence of impurities, in particular, rhenium, on the appearance of the 3 R polytype of molybdenite (Khurshudyan et al , 1969; Newberry, 1979a, 1979b; McCandless et al , 1993; Strachan et al , 2021). As a rule, molybdenite-3 R are enriched in rhenium, but сonsideration of the available analyses shows that high-rhenium natural molybdenites (up to 4.7 wt.%, Voudoris et al , 2009) can crystallise in the 2 H polytype (Newberry, 1979b; Voudouris et al 2009, Ciobanu et al , 2013).…”

“…Tube, bulbous and fullerene-like nanostructures are known for many synthetic 2D-materials such as elemental carbon and Mo, Re and W disulfides, etc. They draw attention due to their outstanding structure-dependent properties such as immense specific surface, outstanding electrical and catalytic properties and the possibility of their application as lubricants (Ramakrishna et al , 2010; Spear et al , 2015; Strachan et al , 2021 and references therein). Molybdenite has a layered structure formed by two-dimensional (2D) continuous layers consisting of trigonal prisms of MoS 2 with a molybdenum atom in the centre and six sulfur atoms at the top and bottom.…”

Recent progress on hierarchical MoS2 nanostructures for electrochemical energy storage

“…[22][23][24][25] In previous reports, the applications of TMDs included solid lubricants, 26 electrocatalysts, 27 photocatalysts, 28 gas sensors, 29 optoelectronics, 30,31 and rechargeable batteries. [32][33][34] As one important type of TMDs, MoS 2 has demonstrated a high mobility of 200 cm 2 V −1 s −1 and direct bandgap of 1.9 eV in the nanoscale. 35 In the review of the crystallographic configuration, MoS 2 demonstrated different phases, including the most thermodynamically stable hexagonal (2H), metastable trigonal (1T), and second most stable rhombohedral (3R) phases.…”

Free-Standing Multilayer Molybdenum Disulfide Memristor for Brain-Inspired Neuromorphic Applications

“…The 2H phase has a trigonal prismatic configuration, whereas 1T MoS 2 is an octahedral structure . There is also a 3R phase that has the same trigonal prismatic configuration as 2H but a different stacking order of S–Mo–S chevrons . The different crystalline phase structure leads to different and unique electrical properties.…”

“…31 There is also a 3R phase that has the same trigonal prismatic configuration as 2H but a different stacking order of S−Mo−S chevrons. 32 The different crystalline phase structure leads to different and unique electrical properties. 2H-MoS 2 , as the most thermodynamically stable phase, behaves as a n-type semiconductor with an indirect band gap of 1.2 eV (bulk) to a direct band gap of 1.8 eV (monolayer) and a charge carrier mobility of 0.1−10 cm 2 V −1 s −1 for a single layer.…”