In this work it has been established that 3D nanoflowers of WS2 synthesized by chemical vapour deposition are composed of few layer WS2 along the edges of the petals. An experimental study to understand the evolution of these nanostructures shows the nucleation and growth along with 10 the compositional changes they undergo.The structural analogy of transition metal dichalcogenides 1 to graphite's layered structure, held together by van In this work, a fast, catalyst free and easily scalable chemical vapour deposition (CVD) technique for the controlled synthesis of well-defined tungsten disulphide (WS2) nanomaterials on (100) silicon-based substrates using tungsten(VI)chloride (WCl6-40 2 mmol at 99.9% purity) and sulphur (20 mmol at 80% purity) as precursors is presented in Fig S1. The predominant morphology (>90%) obtained by this process is WS2 nanoflower confirmed using electron microscopy as shown in Fig.1a and the chemistry verified using XRD and Raman in Fig S2. The morphology of the 45 WS2 nanostructures synthesised by the CVD technique can be tailored through the variation of just two key parameters: time 22 , as yet, a detailed analysis of their structure has not been undertaken. This 60 study looks to comprehend the structure of the nanoflower by disassembling it with the help of sonication. The nanoflowers disassembled into triangular petals (flakes) on sonication with one corner always broken, which suggests that these triangles are connected at only one of the edges to form the assembly of 3D 65 nanoflowers. We observed 10-100's of these triangular petals combining together to form spherical nanoflower structures as suggested by Li et al. 22 and evident from the SEM micrograph in Fig 1a. The nanoflowers are made up of molecular sheets stacked 70 together with a lattice spacing of 3.1 Å and lattice fringes of 0.62 nm, inferred for WS2. In Fig 2a, a cluster of the petals which constitute the nanoflowers is visualised from the edge view (beam perpendicular to c-axis), to reveal 6-8 molecular layers of WS2. These WS2 were stacked on top of each other to form the 75 petals. The distribution of the number of molecular layers to form the petal is not very uniform and varies from few layer (2-4) to increased number of layers up to 12/14. With the beam parallel to the c axis, the hexagonal packing can be clearly observed at the edges where the number of layers have reduced considerably to 80 1 µm
Nanoengineering of transition metal dichalcogenides (TMDs) (MX 2 : M= Mo, W, Nb; X= S, Se, Te) offers exciting new prospects for the production of two‐dimensional nanomaterials with tailored properties 1 . In particular, single layer TMD alloys, including Mo x W 1‐x S 2 and MoSe 2(1‐x) S 2x (x=0‐1), have been shown to have a compositionally modulated electronic structure 5,6,7,8 , providing a tunable band gap that could be advantageous for new nanoelectronic, optoelectronic or photonic applications. Powders of such nanostructured materials may also offer improved catalytic capabilities due to optimised edge structures 9 . However, to date, synthesis of these ternary alloys has been limited to exfoliation of flakes from single crystals that are produced by vapour transport using bulk Mo, W, and S 5,6 or MoS 2 7 , offering limited prospects for large‐scale manufacturing in the future. Here we investigate composition‐controlled Mo x W 1‐x S 2 nanoflakes synthesised by atmospheric‐pressure chemical vapour deposition (CVD) using novel Mo and W containing precursors 10 . Conventional TEM and EDX analysis, supported by complementary XPS, where used to investigate the shape and thickness of the flakes and demonstrates that the W dopant composition can be varied from as little as a few percent (x=0.98), to over 86% (x=0.14). Through atomic‐resolution annular dark field scanning transmission electron microscopy (STEM) using a Cs probe corrected JEOL ARM200F we directly observe the substitution of W atoms for Mo atoms within the MoS 2 lattice. This confirms the synthesis of alloyed dichalcogenides rather than heterostructures, with W randomly distributed throughout the nanoflakes 11 . This new method for growth of ternary 2D TMD alloys offers improved composition control for application as industrial catalysts, while opening a new avenue for bandgap engineering of monolayers in the future.
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