Two-dimensional (2D) transition metal dichalcogenide (TMD) has emerged as an effective optoelectronics material due to its novel optical properties. Understanding the role of defects in exciton kinetics is crucial for achieving high-efficiency TMD devices. Here, we observe defects induced anomalous power dependence exciton dynamics and spatial distribution in hexagonal heterogeneous WS₂. With transient absorption microscopy study, we illustrate that these phenomena originate from the competition between radiative and defect-related non-radiative decays. To understand the physics behind this, a decay model is introduced with two defect-related channels, which demonstrates that more excitons decay through non-radiative channels in the dark region than the bright region. Our work reveals the mechanisms of anomalous exciton kinetics by defects and is instrumental for understanding and exploiting excitonic states in emerging 2D semiconductors.

Integrating surface enhanced Raman scattering (SERS) with microfluidics is the long-term goal for reduced volume, multiplex and automation fingerprint detection of biomolecules. High sensitivity, repeatability, stability, reusability and real-time detection are the performance goals of Raman detection in the aqueous solution environment. Here, we reported the study on cavity mode enhanced SERS detection of both surface-adsorbed molecules and non-surface-adsorbed molecules in the solution environment. The cavity modes had important influence on the SERS enhancement, especially for the non-surface adsorbed molecules. Uniform, repeatable, reusable and real-time Raman signal detection of the non-surface adsorbed Rhodamine 6G molecules was demonstrated. Our work is an important step for the practical on-chip microfluidic Raman detection applications.