Formation of Brightly Luminescent MoS₂ Nanoislands from Multilayer Flakes via Plasma Treatment and Laser Exposure

A robust and reliable method for enhancing the photoluminescence (PL) of multilayer MoS₂ is demonstrated using an oxygen plasma treatment process followed by laser exposure. Here, the plasma and laser treatments result in an indirect-to-direct band gap transition. The oxygen plasma creates a slight decoupling of the layers and converts some of the MoS₂ to MoO₃. Subsequent laser irradiation further oxidizes the MoS₂ to MoO₃, as confirmed via X-ray photoelectron spectroscopy, and results in localized regions of brightly luminescent MoS₂ monolayer triangular islands as seen in high-resolution transmission electron microscopy images. The PL lifetimes are found to decrease from 494 to 190 ps after plasma and laser treatment, reflecting the smaller size of the MoS₂ grains/regions. Atomic force microscopic imaging shows a 2 nm increase in thickness of the laser-irradiated regions, which provides further evidence of the MoS₂ being converted to MoO₃.