Optimization Strategies for High Photoluminescence Quantum Yield of Monolayer Chemical Vapor Deposition Transition Metal Dichalcogenides.

Chemical vapor deposition (CVD) is a promising method to obtain monolayer transition metal dichalcogenides (TMDCs) with high quality and enough size to meet the requirements of practical photoelectric devices. However, the as-grown monolayers often exhibit a lower PL performance due to the stress between the as-grown TMDCs flakes and the substrate. Therefore, finding a facile method to effectively promote the photoluminescence quantum yield (PL QY) of CVD monolayer TMDCs with a clean surface is highly desirable for practical applications. In this work, based on the CVD monolayers MoS2 and MoSe2, the effect of various stress relaxation methods on the TMDCs PL enhancement is systemically studied. By comparing the different kinds of volatile solution treatment processes, as well as the traditional transfer process, it can be found that the volatile solution with a moderate volatilization rate such as ethanol or IPA is a preferred option to improve the PL performance of the CVD monolayer TMDCs, which also surpasses the traditional transfer method by avoiding wrinkles, defects, and contamination to the samples. PL QY of ethanol-treated CVD samples could increase by 6 times on average. Significantly, PL QY of CVD MoSe2 treated by ethanol can reach ∼16%, which is at the forefront of the previous reports of 2D MoSe2. Our study demonstrated an optimized method to enhance the PL QY of CVD monolayer TMDCs, which would facilitate TMDCs optoelectronics.

Enhanced optical sensitivity of molybdenum diselenide (MoSe2) coated side polished fiber for humidity sensing.

In this paper, a side-polished fiber (SPF) coated with molybdenum diselenide (MoSe2) is proposed, and its characteristic of relative humidity (RH) sensing is investigated. It is found in the experiment that an enhancement in RH sensitivity (0.321 dB/%RH) can be achieved in a very wide RH range of 32%RH to 73%RH for the proposed MoSe2 coated SPF (MoSe2CSPF). It is also shown that the MoSe2CSPF has a rapid response of 1s and recovery time of 4s, which makes the sensor capable of monitoring human breath. The experimental results suggest MoSe2 has a promising potential in photonics applications such as all-fiber optic humidity sensing networks.