MoS2 Nanosheets with Narrowest Excitonic Line Widths Grown by Flow-Less Direct Heating of Bulk Powders: Implications for Sensing and Detection

Developing techniques for the high-quality synthesis of mono and few-layered two-dimensional (2D) materials with lowered complexity and cost continues to remain an important goal, both for accelerating fundamental research and for application development. We present the simplest conceivable technique to synthesize micrometer-scale single-crystal, less than 1 nm thick, triangular monolayers of MoS2, i.e., by direct heating of bulk MoS2 powder onto proximally placed substrates. Room-temperature excitonic line width values of our samples are narrower and more uniform than those of 2D-MoS2 obtained by most other techniques reported in literature, and comparable to those of ultraflat boronnitride (h-BN)-capped mechanically exfoliated samples, indicative of their high quality. Feature-rich Raman spectra absent in samples grown or obtained by most other techniques, also stand out as a testament of the high quality of our samples. A contact-growth mode facilitates direct growth of crystallographically wrinkled circular samples, which allows us to directly compare the optoelectronic properties of flat vs wrinkled growth from the same growth runs. Our method allows, for the first time, to quantitatively compare the impact of wrinkle on excitonic and Raman peak positions on identically synthesized 2D-MoS2. Wrinkles lead to average red shifts of similar to 30 meV in the A-exciton position and similar to 2 cm(-1) in the E-2g(1) Raman peak in these samples. Our findings open up several possibilities that expand 2D material research. By eliminating the need for carrier-gas flow, mechanical motion, or chemical reactions, our method can be either miniaturized for substantially low-cost, high-quality scientific research or potentially scaled-up for the mass-production of 2D crystals for commercial purposes. Moreover, we believe that this technique can also be extended to other transition metal dichalcogenides and other layered materials, providing scientists and engineers a low-cost platform for advancing research in sensing, detection, and fundamental discoveries.

Automated summary

The study presents a simple method for synthesizing high-quality MoS2 monolayers with narrower and more uniform excitonic line widths and feature-rich Raman spectra. The method opens up new possibilities in the field of 2D materials research and provides a low-cost platform for advancing research in sensing, detection, and fundamental discoveries for scientists and engineers.