Highly Efficient SnIn4S8@ZnO Z-Scheme Heterojunction Photocatalyst for Methylene Blue Photodegradation.

Building heterojunctions is a promising strategy for the achievement of highly efficient photocatalysis. Herein, a novel SnIn4S8@ZnO Z-scheme heterostructure with a tight contact interface was successfully constructed using a convenient two-step hydrothermal approach. The phase composition, morphology, specific surface area, as well as photophysical characteristics of SnIn4S8@ZnO were investigated through a series of characterization methods, respectively. Methylene blue (MB) was chosen as the target contaminant for photocatalytic degradation. In addition, the degradation process was fitted with pseudo-first-order kinetics. The as-prepared SnIn4S8@ZnO heterojunctions displayed excellent photocatalytic activities toward MB degradation. The optimized sample (ZS800), in which the molar ratio of ZnO to SnIn4S8 was 800, displayed the highest photodegradation efficiency toward MB (91%) after 20 min. Furthermore, the apparent rate constant of MB photodegradation using ZS800 (0.121 min-1) was 2.2 times that using ZnO (0.054 min-1). The improvement in photocatalytic activity could be ascribed to the efficient spatial separation of photoinduced charge carriers through a Z-scheme heterojunction with an intimate contact interface. The results in this paper bring a novel insight into constructing excellent ZnO-based photocatalytic systems for wastewater purification.

Anomalous transmission and Anderson localization for alternating propagated and evanescent waves at the deep-subwavelength scale.

Deep-subwavelength features have a minimal impact on wave transport in all dielectric systems; thus the homogenization approach was commonly adopted. Recently, the breakdown of effective medium theory (EMT) for the incident wave near the total reflection (TR) angle was demonstrated in a deep-subwavelength dielectric multilayer. Additionally, anomalous transmission was reported at angles exceeding the TR angle when introducing disorder and was attributed to Anderson localization. Here we firstly demonstrated that the alleged anomalous transmission also occurs in the disorder-free case, illustrating that attributing anomalous transmission to Anderson localization deserves a more in-depth study. To clarify the underlying physics of this asserted anomalous transmission, Anderson localization and broken EMT, the incident angle dependent reflectivity and modes for ordered and disordered deep-subwavelength multilayers were investigated systematically. Actually, the EMT is still convincing and the anomalous transmission is reasonable after a simple correction. However, the anomalous transmission is more accessible and the permittivity correction is more imperative in the disordered system due to the Anderson localization. These findings can be expanded to other wave systems such as acoustic waves and matter waves, providing insight into EMT and deepening our understanding of the intriguing transport phenomena in deep subwavelength systems.

Sensing with Femtosecond Laser Filamentation.

Femtosecond laser filamentation is a unique nonlinear optical phenomenon when high-power ultrafast laser propagation in all transparent optical media. During filamentation in the atmosphere, the ultrastrong field of 1013-1014 W/cm2 with a large distance ranging from meter to kilometers can effectively ionize, break, and excite the molecules and fragments, resulting in characteristic fingerprint emissions, which provide a great opportunity for investigating strong-field molecules interaction in complicated environments, especially remote sensing. Additionally, the ultrastrong intensity inside the filament can damage almost all the detectors and ignite various intricate higher order nonlinear optical effects. These extreme physical conditions and complicated phenomena make the sensing and controlling of filamentation challenging. This paper mainly focuses on recent research advances in sensing with femtosecond laser filamentation, including fundamental physics, sensing and manipulating methods, typical filament-based sensing techniques and application scenarios, opportunities, and challenges toward the filament-based remote sensing under different complicated conditions.

Active control of terahertz waves based on p-Si hybrid PIT metasurface device under avalanche breakdown.

Active control of terahertz waves is a critical application for terahertz devices. Silicon is widely used in large-scale integrated circuit and optoelectronic devices, and also shows great potential in the terahertz field. In this paper, a p-Si hybrid metasurface device is proposed and its terahertz characteristics under avalanche breakdown effect is investigated. In the study, a plasmon-induced transparency (PIT) effect caused by the near-field coupling of the bright mode and the dark mode is observed in the transmission spectrum. Due to avalanche breakdown effect, the resonance of the PIT metamaterial disappears as the current increased. Carriers existed in the interface between the metasurface and substrate result to a dipole resonance suppression. When the current continues increasing, the maximal modulation depth can reach up to 99.9%, caused by the avalanche effect of p-Si. Experimental results demonstrate that the avalanche breakdown p-Si can achieve a performance modulation depth, bringing much more possibilities for terahertz devices.