High Phase Purity of Large‐Sized 1T′‐MoS₂ Monolayers with 2D Superconductivity

Abstract

The development of transition metal dichalcogenides has greatly accelerated research in the 2D realm, especially for layered MoS2. Crucially, the metallic MoS2 monolayer is an ideal platform in which novel topological electronic states can emerge and also exhibits excellent energy conversion and storage properties. However, as its intrinsic metallic phase, little is known about the nature of 2D 1T′‐MoS2, probably because of limited phase uniformity (<80%) and lateral size (usually <1 µm) in produced materials. Herein, solution processing to realize high phase‐purity 1T′‐MoS2 monolayers with large lateral size is demonstrated. Direct chemical exfoliation of millimeter‐sized 1T′ crystal is introduced to successfully produce a high‐yield of 1T′‐MoS2 monolayers with over 97% phase purity and unprecedentedly large size up to tens of micrometers. Furthermore, the large‐sized and high‐quality 1T′‐MoS2 nanosheets exhibit clear intrinsic superconductivity among all thicknesses down to monolayer, accompanied by a slow drop of transition temperature from 6.1 to 3.0 K. Prominently, unconventional superconducting behavior with upper critical field far beyond the Pauli limit is observed in the centrosymmetric 1T′‐MoS2 structure. The results open up an ideal approach to explore the properties of 2D metastable polymorphic materials.

Direct synthesis of metastable phases of 2D transition metal dichalcogenides

“…It is also reported that intercalation compounds containing other alkali metals, such as sodium and rubidium, can be used as precursors in the synthesis of 1T 00 0 MoS 2 single crystals. 56 Bulk crystals of the 1T 0 MoSe 2 with lateral size B100 mm have been demonstrated through a similar deintercalation (with I 2 solution) of a precursor obtained through a chemical reaction between alkali metal containing molybdenum precursors, such as potassium or sodium molybdate, and elemental selenium annealed in an inert atmosphere in an ampoule 69 or in an open system in a reducing H 2 /Ar atmosphere 68 (Fig. 5d).…”

“…66,67 Due to a large energy difference between the 2H and 1T 0 phases, the metastable group VI diselenides and disulphides are challenging to obtain in a pure form and the reports on their successful synthesis are limited. 21,[68][69][70][71] The crystal structure of the monoclinic 1T 0 phase of group VI diselenides and disulphides is still debated with the possible space groups being either P2 1 /m or C2/m; the latter has only been reported recently and is referred to as the 2M phase, where M stands for the monoclinic lattice system. 72 Unlike the semiconducting 2H counterparts, the corresponding 1T 0 and Td phases of group VI TMDs are semimetallic.…”

“…High-purity 1T 0 monolayers can then be isolated from the parent bulk crystals either mechanically 68 or via chemical exfoliation in solution. 69 In the case of chemical exfoliation, an additional lithium intercalation stage of bulk 1T 0 crystals is introduced followed by exfoliation in water. With such approach, the 1T 0 phase content in the final product reaches 97% 69 (Fig.…”

“…69 In the case of chemical exfoliation, an additional lithium intercalation stage of bulk 1T 0 crystals is introduced followed by exfoliation in water. With such approach, the 1T 0 phase content in the final product reaches 97% 69 (Fig. 4e and 5c).…”

Coordination assembly of 2D ordered organic metal chalcogenides with widely tunable electronic band gaps

“…I norganic two-dimensional (2D) materials, such as graphene, graphene oxide (GO), transition metal dichalcogenides (TMDs), hexagonal boron nitride (h-BN) and black phosphorus (BP), have received unprecedented attention in recent years due to their unusual chemical and physical properties [1][2][3][4][5][6][7][8] . Electronic band gaps are determinative in the electronic transportation and optical properties of these 2D materials [9][10][11] .…”