Photoluminescence enhancement in multilayered MoSe2 nanostructures obtained by local anodic oxidation

Monolayers of transition metal dichalcogenides (TMDCs) exhibit attractive properties and are promising for fabricating photonic and optoelectronic devices, while bulk multilayered structures based on the same materials only recently has revealed many properties useful for nanophotonics. In this regard, the combination of monolayer and multilayer properties in one device (on a single flake) is an important and fruitful task that needs to be solved. In this work, we demonstrate the use of local anodic oxidation to improve the optical properties of multilayer MoSe2 flakes on a gold-covered substrate. Using this method, we fabricated nanostructures demonstrating extraordinarily enhanced photoluminescence (PL), with an intensity up to three orders of magnitude compared to that of the original structure. Low-frequency Raman spectroscopy showed that the nature of this PL enhancement is that the bindings between the layers inside the nanostructures are severely disrupted. This means that the nanostructures consist of quasi-monolayers, which is in good agreement with the intensity and the position of PL peak. Here, we also propose a mechanism of forming these quasi-monolayers. Therefore, this method allows using multilayer TMDC flakes on a conductive substrate to fabricate areas with quasi-monolayer optical properties, exhibiting an enhanced PL intensity.