Synthesis of Large-Scale Single-Layer Mo1-X W x S2 Alloys with Highly Uniform and Tunable Photoluminescence

Abstract

Single-layer transition metal dichalcogenides (TMDs) exhibit high carrier mobility and photoluminescence; thus, the materials are well suitable for next-generation optoelectronic and nano-electronic devices application. It is essential to fabricate large-scale single-layer TMDs film with uniform and desirable spectral wavelengths. Here, we report the synthesis of optically uniform single-layer Mo1-x W x S2 alloys by a two-step CVD method followed by a laser thinning process and investigations on their excitonic behavior with compositional changes. The amount of W content (x) in the Mo1-x W x S2 alloy is systemically controlled by the co-sputtering technique, and the post-laser process allows layer-by-layer thinning of the as-synthesized few-layer Mo1-x W x S2 alloys down to a single-layer. Photoluminescence (PL) and Raman mapping analyses suggest that the laser-thinning of the Mo1-x W x S2 alloys is a self-limiting process caused via heat dissipation to the substrate, resulting in a spatially uniform single-layer Mo1-x W x S2 alloy films. As W content (x) increases, the single-layer alloys reveal controlled optical band gaps ranging from 1.871 to 1.971 eV. Furthermore, we found that the number of excessive charge carriers decreases as x increases, resulting in the change in the predominant component of the PL emission from trions for single-layer MoS2 to neutral excitons for single-layer WS2.