In two dimensional (2D) transition metal dichalcogenides, defect-related processes can significantly affect carrier dynamics and transport properties. Using femtosecond degenerate pump-probe spectroscopy, exciton capture, and release by mid-gap defects have been observed in chemical vapor deposition (CVD) grown monolayer MoSe 2 . The observed defect state filling shows a clear saturation at high exciton densities, from which the defect density is estimated to be around 0.5 × 10 12 /cm 2 . The exciton capture time extracted from experimental data is around~1 ps, while the average fast and slow release times are 52 and 700 ps, respectively. The process of defect trapping excitons is found to exist uniquely in CVD grown samples, regardless of substrate and sample thickness. X-ray photoelectron spectroscopy measurements on CVD and exfoliated samples suggest that the oxygenassociated impurities could be responsible for the exciton trapping. Our results bring new insights to understand the role of defects in capturing and releasing excitons in 2D materials, and demonstrate an approach to estimate the defect density nondestructively, both of which will facilitate the design and application of optoelectronics devices based on CVD grown 2D transition metal dichalcogenides.

A novel ultrafast reflective grating-imaging technique has been developed to measure ambipolar carrier diffusion in GaAs/AlAs quantum wells and bulk GaAs. By integrating a transmission grating and an imaging system into the traditional pump−probe setup, this technique can acquire carrier diffusion properties conveniently and accurately. The fitted results of the diffusion coefficient and diffusion length in bulk GaAs agree well with the literature values obtained by other techniques. The diffusion coefficient and diffusion length of GaAs/AlAs quantum wells are found to increase with the well layer thickness, which suggests that interface roughness scattering dominates carrier diffusion in GaAs/AlAs quantum wells. With the advantages of simple operation, sensitive detection, rapid and nondestructive measurement, and extensive applicability, the ultrafast reflective grating-imaging technique has great potential in experimental study of carrier diffusion in various materials.

Students with emotional-behavioral disorders (EBDs) often learn in alternative classroom settings to provide more intensive instruction that meets their educational needs. Although research has demonstrated promise for several behavior intervention practices in general education settings, the generalizability of these practices to more restricted environments is unknown. Thus, this meta-analysis aimed to examine the class-wide behavior interventions tested in self-contained learning environments for students with EBDs. Studies investigating behavioral interventions in alternative elementary settings were systematically screened. Fifteen studies with 20 effect sizes met inclusion criteria and results from each study were synthesized. An estimated average effect was calculated ( g = 0.93, SE = 0.16), demonstrating that tested interventions are typically effective in self-contained learning environments to improve student behaviors. A thematic analysis and multi-level meta-regression were conducted to determine which elements are most beneficial to students in these unique learning environments. Results indicated that interventions that included relational supports, such as daily parent communication, differentially benefited students ( B = 1.26, SE = 0.15). Limitations include the small number of studies meeting inclusion criteria that have investigated behavior interventions in self-contained settings and the need for improved research quality. Implications suggest support for adapting standardized practice elements, such as group contingencies, to improve student behaviors in multiple learning environments.

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