Yao Zhu,Huan Yi,Qiaoyan Hao,Jidong Liu,Yuxuan Ke,Zhuo Wang,Dianyuan Fan,Wen jing Zhang
Monolayer WS 2 (1L-WS 2 ) possesses direct band gap, which is beneficial for light emitting applications. However, high quality sample obtained via mechanical exfoliation suffers from ultralow yield of large flakes while large 2D material monolayers synthesized by chemical vapour deposition (CVD) unintentionally induce many defects, resulting in low photoluminescence (PL) intensity. Herein, we firstly control the 1L-WS 2 scalable growth through H 2 introduction at the beginning of the CVD synthesis. Its domain size can be increased from 1 μm up to 20 μm with higher coverage, compared to that synthesized without H 2 introduction. Then, we propose scalable ways to anneal the obtained large 1L-WS 2 in Ar diluted hydrogen sulfide (H 2 S) atmosphere at 750 °C or to treat it with (3-mercaptopropyl) trimethoxysilane (MPS). Its PL intensity can be increased to 12 times by H 2 S or more interestingly to 30 times by MPS, respectively. Our systematic analyses show that the drastic PL improvements are mainly attributed to the reduction of structural defects by H 2 S and MPS, which is facilitated via the H– bond in them. The results help to explore routes to obtaining large-size single crystalline transition metal dichalcogenides monolayer (1L-TMDCs) and intense PL emission.
Post-fabrication defect passivation of organometal halide perovskites has become an efficient way to improve their photophysical properties, but the underlying mechanisms are still in debate. In this work, we used p-benzoquinone (p-BQ) to generate surface defects on methylammonium lead triiodide perovskite (MAPbI3), and found that a Usanovich acid–base (O2, acetone or acetonitrile) treatment can effectively passivate those defects and lead to photoluminescence (PL) enhancement. The passivation effect arose from partial neutralization of defect charges via electron transfer between passivation reagents and relevant defects. O2 accepted photo-generated electrons, formed negatively charged oxygen species and attached to the I vacancy site to reduce its PL quenching efficiency by neutralising the defects positive charge. Likewise, acetone accepted photo-generated holes, formed positively charged species and partially neutralised the defects negative charge. The reduced trapping ability of defects caused PL enhancement. In addition, the observed photo-catalysed oxidation of acetone by O2 on the crystal surface supported the single electron transfer mechanism, and showed the potential of MAPbI3 as a photo-catalyst.
In this work, we demonstrated tunable structured AlGaN-based nanoporous (NP) distributed Bragg reflectors (DBRs) with high-reflectivity through one-step vertical-lateral electrochemical etching (ECE). The aperture of nanopores in the doping layer and the size and density of V-pits on the surface of NP-DBRs can be tuned by controlling the etching bias. Furthermore, by further tuning the thickness of alternating layers, we achieved high reflectivity of NP-DBRs at multiple center wavelengths within the wavelength range from 280 to 800 nm. To explore its potential applications, MoS 2 with a photoluminescence (PL) emission in the red light region was grown for the first time on the NP-DBRs. Due to the light localized effect of surface V-pits and the high reflectivity of the bottom DBRs , the PL intensity of MoS 2 was significantly enhanced by a factor of 37.3 compared to the region without NP-DBRs. The PL enhancement of MoS 2 on porous AlGaN and different periodic NP-DBRs further validated the PL enhancement mechanism. The corresponding theoretical simulations also revealed that the PL enhancement should be attributed to the combined effect of enhanced light absorption and NP-DBRs induced emission interference. The fabricated AlGaN-based NP-DBRs provide a new approach for improving the quantum efficiency of two-dimensional layered materials, which holds significant importance for advancing the development of miniaturized and integrated 2D/3D heterogeneous structure systems in the field of optoelectronics.
危险品化学品经营许可证（带存储）