Abstract
Crystal phase control in layered transition metal dichalcogenides is central for exploiting their different electronic properties. Access to metastable crystal phases is limited as their direct synthesis is challenging, restricting the spectrum of reachable materials. Here, we demonstrate the solution phase synthesis of the metastable distorted octahedrally coordinated structure (1T’ phase) of WSe2 nanosheets. We design a kinetically-controlled regime of colloidal synthesis to enable the formation of the metastable phase. 1T’ WSe2 branched few-layered nanosheets are produced in high yield and in a reproducible and controlled manner. The 1T’ phase is fully convertible into the semiconducting 2H phase upon thermal annealing at 400 °C. The 1T’ WSe2 nanosheets demonstrate a metallic nature exhibited by an enhanced electrocatalytic activity for hydrogen evolution reaction as compared to the 2H WSe2 nanosheets and comparable to other 1T’ phases. This synthesis design can potentially be extended to different materials providing direct access of metastable phases.
Highlights
Crystal phase control in layered transition metal dichalcogenides is central for exploiting their different electronic properties
Owing to the metastable nature of the 1T and 1T’phases of group VI sulphides and selenides (MoS2, MoSe2, WS2 and WSe2), 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 WS2 nanodisks[15] and WS2 nanoribbons[16] with the distorted 1T structure, stabilised by the charged precursor residues intercalated between the layers
Thin WSe2 nanosheets prepared via wet chemical approaches or vapour deposition techniques reported so far acquired the thermodynamically stable 2H phase[13,24,25] with the only exception of molecular beam epitaxy deposition, which led to the formation of nanometresized 1T’ WSe2 single layers[9]
Summary
Crystal phase control in layered transition metal dichalcogenides is central for exploiting their different electronic properties. Owing to the metastable nature of the 1T and 1T’phases of group VI sulphides and selenides (MoS2, MoSe2, WS2 and WSe2), 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 WS2 nanodisks[15] and WS2 nanoribbons[16] with the distorted 1T structure, stabilised by the charged precursor residues intercalated between the layers. This metastable 1T’ phase converts into the thermodynamically stable 2H phase once the charges are removed. We report a full study of the atomic structure
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