Trickle Flow Aided Atomic Layer Deposition (ALD) Strategy for Ultrathin Molybdenum Disulfide (MoS₂) Synthesis

The synthesis of large-area and high-quality two-dimensional (2D) MoS₂ is undoubtedly a significant challenge till now. In this work, an effective strategy for achieving 2D MoS₂ with enlarged grain size by Ni-foam-based trickle flow atomic layer deposition (ALD) was suggested, by which MoS₂ grain sizes up to 420 nm (monolayer sample) and 400 nm (five-layer sample) were obtained under the covering of 1 mm-thick Ni foam with a 2 mm gap from the substrate at 460 °C. In terms of specific ALD experiments, the Ni foam with a certain thickness placed on top of the substrate made the original precursor flow into a trickle-fluidization source flow, which decreased the nucleation density effectively. Thus, MoS₂ with enlarged grain sizes were obtained based on the typical ALD mechanism of large-scale vertical growth under the action of steric hindrance after a planar parallel growth around the crystal nucleus. In addition, the Ni foam also achieved a stable temperature field by enhancing the heat transfer around the substrate and thus improved its crystallinity.