Synthesis of Micron-Sized WS₂ Crystallites Using Atomic Layer Deposition and Sulfur Annealing

The synthesis of micron-sized WS 2 crystallites via atomic layer deposition (ALD) is reported for the first time using bis( t -butylimido)bis(trimethylsilylmethyl)tungsten and H 2 S as reactants, followed by post-deposition annealing. Self-limiting growth on silicon is demonstrated between 315 and 350 °C. As-deposited films are nanocrystalline, comprising a mix of WS 2 and WO 3 phases along with residual amounts of WO x N y and SiO x impurities. Post-deposition annealing in elemental sulfur at 600 °C induces the emergence of the 2LA(M), E 2g 1 (Γ), and A 1g (Γ) Raman vibration modes for WS 2 and increases crystallite size up to a few microns, the largest reported to date for ALD WS 2 . The growth substrate was found to impact WS 2 morphology. Films grown and annealed on silicon produced two distinct morphologies of WS 2 crystallites with (i) in-plane multilayered flake pyramids predominantly seen at 650 °C and (ii) out-of-plane “flowers” growing at 700 and 800 °C. Films grown and annealed on ZnS showed only out-of-plane “crumpled” flowers with a high density of WS 2 edge sites suitable for catalysis, while films grown and annealed on Al 2 O 3 showed predominately few-layered in-plane WS 2 flakes, suitable for electronic devices.