![]() Indeed, intercalation studies with organolithium treatment followed by exfoliation show evidence of persistency of 2H WSe 2 23. While for MoS 2 and WS 2 the 1T’ phase has been reported via these treatments, there is no current evidence that electron transfer can convert the 2H phase of WSe 2 into the 1T’. lithiation during exfoliation or organolithium treatment) 20 or doping beyond degenerate level 21 or applied mechanical strain 22. The 1T/1T’ phases are more commonly obtained via distortion of the 2H phase as a result of either electrical gating 19 or electron transfer during chemical treatment (i.e. The direct synthesis of the metastable 1T’ phase of high crystal quality and not stabilised by foreign species 17 is challenging and has only been recently reported for bulk MoS 2 and MoSe 2 crystals 18. This metastable 1T’ phase converts into the thermodynamically stable 2H phase once the charges are removed. Owing to the metastable nature of the 1T and 1T’phases of group VI sulphides and selenides (MoS 2, MoSe 2, WS 2 and WSe 2), direct synthesis of these materials generally leads to formation of the thermodynamically stable 2H phase 13, 14 with a few recent exceptions of wet-chemical synthesis of the WS 2 nanodisks 15 and WS 2 nanoribbons 16 with the distorted 1T structure, however, stabilised by the charged precursor residues intercalated between the layers. Moreover, 1T’ WSe 2 single layer is predicted to be a large gap quantum spin Hall (QSH) insulator suitable for application in spintronic devices 9 both operable at ambient temperature in contrast to the 1T’ WTe 2 10 and benefiting from chemical stability of the material compared to that of other currently known large gap QSH insulators such as stanene 11 and two-dimensional In-Sb compounds 12 existing in an inert atmosphere only. The 1T and 1T’ phases of group VI TMDs started to emerge only recently however, compared to the semiconducting 2H phase, they have exhibited an exceptional performance for electrocatalytic hydrogen evolution and energy storage applications owing to the dramatically reduced charge transfer resistance 7 due to their metallic nature 8. The versatility of properties of TMDs is enabled by the polymorphism of their monolayers, where metal coordination changes from trigonal prismatic (2H phase) to octahedral (1T phase) and distorted octahedral (1T’ phase). This synthesis design can potentially be extended to different materials providing direct access of metastable phases.Ītomically thin transition metal dichalcogenides (TMDs) have been attracting enormous attention in the past decades as promising materials for a variety of disparate applications ranging from flexible electronics 1 to electrocatalysis and photoelectrocatalysis 2, 3, electrochemical actuators 4 and energy storage devices 5 to the recently proposed topological electronic devices 6. The 1T’ WSe 2 nanosheets demonstrate a metallic nature exhibited by an enhanced electrocatalytic activity for hydrogen evolution reaction as compared to the 2H WSe 2 nanosheets and comparable to other 1T’ phases. The 1T’ phase is fully convertible into the semiconducting 2H phase upon thermal annealing at 400 ☌. 1T’ WSe 2 branched few-layered nanosheets are produced in high yield and in a reproducible and controlled manner. We design a kinetically-controlled regime of colloidal synthesis to enable the formation of the metastable phase. Here, we demonstrate the solution phase synthesis of the metastable distorted octahedrally coordinated structure (1T’ phase) of WSe 2 nanosheets. Access to metastable crystal phases is limited as their direct synthesis is challenging, restricting the spectrum of reachable materials. Crystal phase control in layered transition metal dichalcogenides is central for exploiting their different electronic properties. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |