Vapor–Liquid–Solid-Mediated Layer-by-Layer Growth of Stepped-Wedge-Shaped WS2 Microribbons Using the Chemical Vapor Deposition Technique

The bottom-up approach of fabricating semiconductor microstructures is more cost-effective and time-efficient than the conventional top-down method of lithography. However, gaining control over the size, shape, position, and directionality of the structure is a big challenge. Controlled growth of microstructures of two-dimensional (2D) transition-metal dichalcogenides, which are emerging as promising materials for transparent and flexible electronics and valleytronics, has gained significant research interest recently. Here, we report a unique vapor–liquid–solid (VLS)-mediated growth, where the VLS process repeats itself multiple times along the same path that results in the formation of several tens of micrometer-long stepped-wedge-shaped WS2 microribbons of different widths and thicknesses. These ribbons are found to be vertically stacked WS2 monolayer stripes whose width decreases from the bottom to the top. It has been found that back-and-forth motion of the Na–W–O droplets that result from the mixture of precursor WO3 and promotor NaCl over a WS2 monolayer island along certain crystallographic directions multiple times results in the layer-by-layer growth of these ribbons. This study thus allowed us to determine a novel bottom-up route for constructing microstructures using 2D materials with shape, size, position, and orientation specificity.