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In 2D transition metal dichalcogenides (TMDs), trions have important applications in fundamental studies of multibody phenomena, novel optoelectronic devices, and valleytronic devices. However, the enhancement of trion emission, and in particular how the carrier dynamics is influenced when coupled with plasmonic cavity, is important for a deep understanding of trions and their further utilization. In this study, strong trion emission is achieved by coupling monolayer WS2 with a plasmonic nanocavity. Temperature‐dependent photoluminescence, dark‐field scattering measurement, and transient absorption spectroscopy are employed to investigate the trion and exciton behaviors in the hybrid structure. In plasmonic nanocavity, trion emission is enhanced by an order of magnitude, which is attributed to the conversion of excitons to trions via capturing photoionized carriers facilitated by Fano resonance. Further, the ultrafast dynamics of trions and excitons suggest that the plasmonic nanocavity enhances the hole cooling process and radiative recombination of excitons, as well as the formation and recovery process of trions. The results not only explain the enhancement of trion emission and carrier dynamics in the hybrid system but also provide one feasible method to obtain strong trion emission in TMDs, which makes the hybrid system a promising candidate for optoelectronic and valleytronic applications. [ABSTRACT FROM AUTHOR]

Cancer cell invasion is a major component of metastasis and is responsible for extensive cell diffusion into and major destruction of tissues. Cells exhibit complex invasion modes, including a variety of collective behaviors. This phenomenon results in the structural heterogeneity of the extracellular matrix (ECM) in tissues. Here, we systematically investigated the environmental heterogeneity facilitating tumor cell invasion via a combination of in vitro cell migration experiments and computer simulations. Specifically, we constructed an ECM microenvironment in a microfabricated biochip and successfully created a three-dimensional (3D) funnel-like matrigel interface inside. Scanning electron microscopy demonstrated that the interface was at the interior defects of the nano-scale molecular anisotropic orientation and the localized structural density variations in the matrigel. Our results, particularly the correlation of the collective migration pattern with the geometric features of the funnel-like interface, indicate that this heterogeneous in vitro ECM structure strongly guides and promotes aggressive cell invasion in the rigid matrigel space. A cellular automaton model was proposed based on our experimental observations, and the associated quantitative analysis indicated that cell invasion was initiated and controlled by several mechanisms, including microenvironment heterogeneity, long-range cell-cell homotype and gradient-driven directional cellular migration. Our work shows the feasibility of constructing a complex and heterogeneous in vitro 3D ECM microenvironment that mimics the in vivo environment. Moreover, our results indicate that ECM heterogeneity is essential in controlling collective cell invasive behaviors and therefore determining metastasis efficiency. [ABSTRACT FROM AUTHOR]

Single-crystal perovskites with excellent photophysical properties are considered to be ideal materials for optoelectronic devices, such as lasers, light-emitting diodes and photodetectors. However, the growth of large-scale perovskite single-crystal films (SCFs) with high optical gain by vapor-phase epitaxy remains challenging. Herein, we demonstrated a facile method to fabricate large-scale thin CsPbBr 3 SCFs (∼300 nm) on the c -plane sapphire substrate. High temperature is found to be the key parameter to control low reactant concentration and sufficient surface diffusion length for the growth of continuous CsPbBr 3 SCFs. Through the comprehensive study of the carrier dynamics, we clarify that the trapped-related exciton recombination has the main effect under low carrier density, while the recombination of excitons and free carriers coexist until free carriers plays the dominate role with increasing carrier density. Furthermore, an extremely low-threshold (∼8 μJ cm -2 ) amplified spontaneous emission was achieved at room temperature due to the high optical gain up to 1255 cm -1 at a pump power of 20 times threshold (∼20 P th ). A microdisk array was prepared using a focused ion beam etching method, and a single-mode laser was achieved on a 3 μm diameter disk with the threshold of 1.6 μJ cm -2 . Our experimental results not only present a versatile method to fabricate large-scale SCFs of CsPbBr 3 but also supply an arena to boost the optoelectronic applications of CsPbBr 3 with high performance.