Search

In this paper, we numerically demonstrate a dual-wavelength chiral metasurface with the chirality only existing at two resonant wavelengths, making use of the excitation of two quasi-bound states in the continuum (quasi-BICs). This chiral metasurface is constructed on the basis of photonic crystal slabs with square lattice of circular holes by introducing rectangular holes as perturbations. The two quasi-BICs supported by chiral metasurface are orthogonal to each other, thus the chirality at the two resonant wavelengths can be controlled independently by changing the geometry of the perturbations. Furthermore, a chirality-switchable metasurface is demonstrated taking advantage of the sensitivity of quasi-BICs to the variation of out-of-plane symmetry caused by changing refractive index of surroundings. The proposed chiral metasurface could find potential applications in nonlinear optics, sensing, imaging and near-to-eye displays.

As a promising flat optical element, metasurfaces possess the powerful ability to manipulate chromatic dispersion, resulting in achromatic imaging, ultracompact spectrometers, and wavelength-dependent multifunctional nano-devices. However, conventional chromatic metalenses are incapable of arbitrarily tailoring dispersion within different bandwidths. Here, with a supercell composed of two nanostructures, we can arbitrarily control the chromatic dispersion of the metalens by using the phase differential equation and genetic optimization. We design three metalenses to verify the simultaneous tailoring of different chromatic dispersions in dual bands, which exhibits stronger chromatic dispersion manipulation capability compared with a single-structure-cell-based metalens. Our approach paves a new way for dispersion engineering of metalenses with potential applications in spectral imaging and material analysis.

The bookstore is an integral part of campus public service, and it is an essential place for reading, learning and spending for teachers and students. Provided the current management and development problems faced by old campus bookstores, this article takes the old campus bookstore in the Huangjiahu campus of Wuhan University of Science and Technology as a research case while uses space syntax theory, Depthmap software, and axis models to analyzes and evaluate accessibility, and then optimize campus old location and layout of bookstores. Simultaneously, by using the analytic hierarchy process, the simulated bookstore sites of selection in the campus are tested at the target level, decision level and plan level. This article aims to propose optimization methods for the management and development of old campus bookstores from the perspective of spatial location selection through qualitative quantification and provide constructive references for similar research.

Supercapacitors are well-known as promising energy storage devices capable of bridging the gap between conventional electrolytic capacitors and batteries to deliver both high power and energy densities for applications in electric vehicles and a smart energy grid. However, many reported instances of high-capacitance pseudocapacitors employ strong Faradaic reactions that hinder fast charge–discharge cycles and long-term stability, limiting their commercial viability. In this study, we utilise an economical and solution-processable procedure to fabricate a Cs3Bi2I9-based symmetric supercapacitor employing both electric double layer capacitance and pseudocapacitance with an aqueous NaClO4 electrolyte to deliver an outstanding device areal capacitance of 2.4 F cm−2 and specific capacitance of 280 F g−1. The Cs3Bi2I9 device achieves an excellent 88% capacitance retention after 5000 charge–discharge cycles, proving its long-term cycle stability and promise as a practical supercapacitor. We characterise the time-dependent charge storage mechanisms through cyclic voltammetry and electrochemical impedance spectroscopy to find that electrostatic charge accumulation predominates at high potentials (0.3–0.6 V) whereas weak, Faradaic charge adsorption and pore penetration bolster charge storage at lower potentials (0.0–0.2 V).