Composition-Tunable Synthesis of Large-Scale Mo_{1- x}W_xS₂ Alloys with Enhanced Photoluminescence

Alloying two-dimensional transition metal dichalcogenides (2D TMDs) is a promising avenue for band gap engineering. In addition, developing a scalable synthesis process is essential for the practical application of these alloys with tunable band gaps in optoelectronic devices. Here, we report the synthesis of optically uniform and scalable single-layer Mo_1-xW_xS₂ alloys by a two-step chemical vapor deposition (CVD) method followed by a laser thinning process. The amount of W content (x) in the Mo_1-xW_xS₂ alloy is systemically controlled by the co-sputtering technique. The post-laser process allows layer-by-layer thinning of the Mo_1-xW_xS₂ alloys down to a single-layer; such a layer exhibits tunable properties with the optical band gap ranging from 1.871 to 1.971 eV with variation in the W content, x = 0 to 1. Moreover, the predominant exciton complexes, trions, are transitioned to neutral excitons with increasing W concentration; this is attributed to the decrease in excessive charge carriers with an increase in the W content of the alloy. Photoluminescence (PL) and Raman mapping analyses suggest that the laser-thinning of the Mo_1-xW_xS₂ alloys is a self-limiting process caused by heat dissipation to the substrate, resulting in spatially uniform single-layer Mo_1-xW_xS₂ alloy films. Our findings present a promising path for the fabrication of large-scale single-layer 2D TMD alloys and the design of versatile optoelectronic devices.