(Invited) Molecular Chemistry to Achieve Large Photoluminescence Enhancement in Transition Metal Dichalcogenides

Abstract

I will focus on the following two topics along with the title; (1) the mechanism of the strong photoluminescence (PL) from monolayer (1L) transition metal dichalcogenides (TMDCs) by the superacid molecular treatment (Ref1), and (2) the unusual PL enhancement from bilayer (2L) TMDC (Ref.2).A direct band gap nature in semiconducting materials is a fascinating character for optical devices due to the strong absorption of photons and their luminescence properties. Monolayer TMDCs are known as direct band gap semiconductors, and a wide range of applications have been explored; however, some TMDCs, such as a representative MoS2, are known as a poor optical property. The PL quantum yield (QY) is less than several percent. Recently, superacid molecular treatment was demonstrated and achieved very strong PL; the mechanism is still in debate. In another case, bilayer (2L) TMDCs show an indirect band gap, and the PL intensity of them are usually very poor. Here, I will show our recent advancements on these topics about achieving strong PL from both 1L and 2L TMDCs. In detail, I will discuss (1) the mechanism of superacid treatment for monolayer MoS2 to achieve strong PL(Ref.1), and (2) strong PL enhancement in bilayer MoS2 by using superacid treatment with a combination of UV irradiation(Ref.2).Ref.1: Y. Yamada, et al. "Photoactivation of Strong Photoluminescence in Superacid-Treated Monolayer Molybdenum Disulfide", ACS Appl. Mater. Interfaces, 2020, 12, 36496–36504.Ref.2: Y. Yamada, et al. "Strong Photoluminescence Enhancement from Bilayer Molybdenum Disulfide via the Combination of UV-irradiation and Superacid Molecular Treatment", Applied Science 2021, in press.