Nanoengineering of transition metal dichalcogenides (TMDs) (MX2: M= Mo, W, Nb; X= S, Se, Te) offers exciting new prospects for the production of two‑dimensional nanomaterials with tailored properties1. In particular, single layer TMD alloys, including MoxW1-xS2 and MoSe2(1-x)S2x (x=0-1), have been shown to have a compositionally modulated electronic structure5,6,7,8, 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 structures9. 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 S5,6 or MoS27, offering limited prospects for large-scale manufacturing in the future.
Here we investigate composition-controlled MoxW1-xS2 nanoflakes synthesised by atmospheric‑pressure chemical vapour deposition (CVD) using novel Mo and W containing precursors10. 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 MoS2 lattice. This confirms the synthesis of alloyed dichalcogenides rather than heterostructures, with W randomly distributed throughout the nanoflakes11. 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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To cite this abstract:Adrian Murdock, Juan G Lozano, Arunvinay Prabakaran, Frank Dillon, Nicole Grobert; Advanced STEM characterisation of composition controlled MoxW1 xS2 mixed transition metal dichalcogenide alloys grown by chemical vapour deposition. The 16th European Microscopy Congress, Lyon, France. https://emc-proceedings.com/abstract/advanced-stem-characterisation-of-composition-controlled-moxw1-xs2-mixed-transition-metal-dichalcogenide-alloys-grown-by-chemical-vapour-deposition/. Accessed: August 20, 2019
EMC Abstracts - https://emc-proceedings.com/abstract/advanced-stem-characterisation-of-composition-controlled-moxw1-xs2-mixed-transition-metal-dichalcogenide-alloys-grown-by-chemical-vapour-deposition/