No abstract

Metal–organic frameworks (MOFs) are considered potential materials in the gas sensor field because of their extremely porous, adjustable characteristics and high surface area. In this paper, based on a ZIF-8 precursor, ZnO-CuO hollow nanocage heterostructure materials were successfully fabricated by a multistep method, and the prepared ZnO-CuO sensor exhibited excellent respond to H2S. We found that when the mass ratio of CuO reaches 1 wt %, the response to 10 ppm hydrogen sulfide (H2S) was as high as 70, and the recovery time was 55 s at a low temperature of 115 °C. Such a ZnO-CuO sensor has a highly selective response to H2S gas. In addition, the lower detection limit can reach 200 ppb. Furthermore, the gas sensors also had high consistency and repeatability. Gas sensing mechanism studies have shown that the special nanocage structure with larger specific surface area helps to increase gas adsorption and diffusion on the surface of sensing materials, and the formation of p–n heterostructures by the introduction of CuO improves the sensitive and selective response to H2S. This work will improve the practical application of H2S gas sensors for their simple preparation method and research into the response mechanism.

With the rapid development of on-chip optics, integrated optical devices with better performance are desirable. Waveguide couplers are the typical integrated optical devices, allowing for the fast transmission and conversion of optical signals in a broad working band. However, traditional waveguide couplers are limited by the narrow operation band to couple the spatial light into the chip and the fixed unidirectional transmission of light flow. Furthermore, most of the couplers only realize unidirectional transmission under the illumination of the linear polarized light. In this work, a broadband polarization directional coupler based on a metallic catenary antenna integrated on a silicon-on-insulator (SOI) waveguide has been designed and demonstrated under the illumination of the circularly polarized light. By applying the genetic algorithm to optimize the multiple widths of the metallic catenary antenna, the numerical simulation results show that the extinction ratio of the coupler can be maintained larger than 18 dB in a wide operation band of 300 nm (from 1400 to 1700 nm). Moreover, the coupler can couple the spatial beam into the plane and transmit in the opposite direction by modulating the rotation direction of the incident light. The broadband polarization directional coupler might have great potential in integrated optoelectronic devices and on-chip optical devices.

Vortex lights with optical orbital angular momentum (OAM) have shown great promise in the areas of optical communication, optical manipulation and quantum optics. However, traditional methods for detecting the topological charge of vortex beams, such as interference and diffraction, are still challenging in miniaturization of the detection system and perfect matching of wave vectors. Here, a detection approach is proposed for measuring the topological charge of Laguerre-Gaussian (LG) vortex beam based on a catenary grating metasurface. According to the wave vector matching principle, the LG vortex beam can be coupled into surface plasmon polaritons (SPPs) waves propagating in different directions by using the well-designed catenary grating structure. The positive and negative of the topological charge can be distinguished by different arrangement of the catenary gratings. Besides, the propagation angle of the launched SPPs waves increases with the value of the topological charge. We believe that the proposed device would have a broader application prospect in high compact photonic integrated circuits.

Surface-enhanced Raman scattering (SERS) technique has become a powerful tool for detecting trace targets in the field of food-safety. However, it is a challenge to regulate the hot spots of the detection substrate and its interaction with target molecules for the enhancement of SERS activity. Herein, we reported the high performance SERS substrate based on Ag@ZIF-67 nanocomposite with sugar-coated haws like structure. It was found that the coverage of ZIF-67 particles on the surface of Ag nanowires can adjust the SERS ability of detection substrate. Compared with pure Ag nanowires, functionalized Ag nanowires exhibit outstanding SERS activity with good stability and uniformity. The detection limit of crystal violet (CV) and thiram can be as low as 10-10 M and 10-8 M, respectively. After 35 days, the SERS activity remains basically unchanged. Furthermore, it also has excellent SERS response to 5×10-5 M thiram residues on the surface of vegetables. Such high SERS activity can be attributed to the enrichment and screening molecular effect of porous ZIF-67 nanoparticles, and the surface plasmon resonance effect of Ag nanowires. This work provides a simple strategy for the on-site detection of pesticide residues in the actual applications.