Surface Properties of Laser-Treated Molybdenum Disulfide Nanosheets for Optoelectronic Applications

Transition metal dichalcogenide two-dimensional materials have attracted significant attention due to their unique optical, mechanical, and electronic properties. For example, molybdenum disulfide (MoS₂) exhibits a tunable band gap that strongly depends on the numbers of layers, which makes it an attractive material for optoelectronic applications. In addition, recent reports have shown that laser thinning can be used to engineer an MoS₂ monolayer with specific shapes and dimensions. Here, we study laser-thinned MoS₂ in both ambient and vacuum conditions via confocal micro-Raman spectroscopy, imaging X-ray photoelectron spectroscopy (i-XPS), and atomic force microscopy (AFM). For low laser powers in ambient environments, there is insufficient energy to oxidize MoS₂, which leads to etching and redeposition of amorphous MoS₂ on the nanosheet as confirmed by AFM. At high powers in ambient, the laser energy and oxygen environment enable both MoS₂ nanoparticle formation and nanosheet oxidation as revealed in AFM and i-XPS. At comparable laser power densities in vacuum, MoS₂ oxidation is suppressed and the particle density is reduced as compared to ambient. The extent of nanoparticle formation and nanosheet oxidation in each of these regimes is found to be dependent on the number of layers and laser treatment time. Our results can shed some light on the underlying mechanism of which atomically thin MoS₂ nanosheets exhibit under high incident laser power for future optoelectronic applications.