Controllable\nWater Vapor Assisted Chemical Vapor Transport\nSynthesis of WS₂–MoS₂ Heterostructure

Abstract

The vapor phase synthesis of two-dimensional transition-metal\ndichalcogenides\n(MX₂) and their heterostructures is often poorly reproducible\nand sensitive to uncontrolled environmental humidity. It was recently\nrealized that water vapor can play important roles in the growth of\nMX₂ by reacting with MX₂ at high temperature\nto form volatile metal oxyhydroxide (MO_<i>x</i>(OH)_<i>y</i>) and hydrogen chalcogenides (H₂X) that dramatically change the growth processes. Here we\nreport the controllable synthesis of WS₂, MoS₂, and their heterostructures using water-assisted chemical vapor\ntransport (CVT). The water vapor can be tunably delivered by thermal\ndehydration of calcium sulfate dihydrate (CaSO₄·2H₂O) solid precursor, which not only provides a much lower vapor\npressure baseline and a wider tunable range than liquid water but\nalso can be readily integrated into a chemical vapor deposition process.\nThis allows controlled growth of monolayer, multilayer, and spiral\nnanoplates of WS₂, as well as the lateral epitaxial growth\non the edge of MX₂, and more reproducible growth of large\narea WS₂–MoS₂ heterostructures. Raman\nand photoluminescence spectral mappings confirm the various types\nof WS₂–MoS₂ heterostructures. These results\nreveal insights into the growth mechanisms of MX₂ and provide\na general approach to the controllable growth of other metal chalcogenides.