Circular polarization-selective optical,photothermal,and optofluidic effects in chiral metasurfaces

Circular dichroism (CD) is extensively used in various material systems for applications including biological detection,enantioselective catalysis,and chiral separation.This paper introduces a chiral absorptive metasurface that exhibits a circular polarization-selective effect in dual bands-positive and negative CD peaks at short wavelengths and long wavelengths,respectively.Significantly,we uncover that this phenomenon extends beyond the far-field optical response,as it is also observed in the photothermal effect and the dynamics of thermally induced fluid motion.By carefully engineering the metasurface design,we achieve two distinct CD signals with high g factors (1) at the wavelengths of 877 nm and 1045 nm,respectively.The findings presented in this study advance our comprehension of CD and offer promising prospects for enhancing chiral light–matter interactions in the domains of nanophotonics and optofluidics.

Stabilization of mixed-halide lead perovskites under light by photothermal effects

Mixed-halide lead perovskites(MHLPs) are semiconductor materials with bandgaps that are tunable across the visible spectrum and have seen promising applications in photovoltaics and optoelectronics.However, their segregation into phases with enriched halide components, under resonant light illumination and/or electric field, have hindered their practical applications. Herein, we demonstrate the stabilization of the MHLP photoluminescence(PL) peak as a function of their excitation intensities.This effect is associated with the phase segregation of MHLPs and their subsequent remixing by photothermal heating. We conclude that the balance between these opposing processes dictates the equilibrium PL peak of the MHLPs. The findings in this work could serve as a potential approach to obtain MHLP with stable emission peaks under operating conditions.

Ultra-broadband nanowire metamaterial absorber

Broadband absorbers generally consist of plasmonic cavities coupled to metallic resonators separated by a dielectric film,and they are vertically stacking configurations.In this work,we propose an ultra-broadband nanowire metamaterial absorber composed of an array of vertically aligned dielectric nanowires with coaxial metallic rings.The absorber shows strong absorption from 0.2 to 7μm with an average absorption larger than 91%due to the excitation of gap surface plasmon polariton modes in Fabry–Perot-like resonators.Moreover,a refractory dielectric cladding can be added to improve the thermal stability of the absorber,showing a negligible impact on its absorption performance.The proposed absorber may find potential applications in solar energy harvesting,infrared imaging and spectroscopy,and optoelectronic devices.

Active spatial control of photothermal heating and thermo-actuated convective flow by engineering a plasmonic metasurface with heterodimer lattices

Thermo-plasmonics, using plasmonic structures as heat sources, has been widely used in biomedical and microfluidic applications. However, a metasurface with single-element unit cells, considered as the sole heat source in a unit cell, functions at a fixed wavelength and has limited control over the thermo-plasmonically induced hydrodynamic effects. Plasmonic metasurfaces with metal disk heterodimer lattices can be viewed to possess two heat sources within a unit cell and are therefore designed to photo-actively control thermal distributions and fluid dynamics at the nanoscale. The locations of heat sources can be switched, and the direction of the convective flow in the central region of the unit cell can be reversed by shifting the wavelength of the excitation source without any change in the excitation direction or physical actuation of the structural elements. The temperature and velocity of a fluid are spatiotemporally controlled by the wavelength selectivity and polarization sensitivity of the plasmonic metasurface. Additionally, we investigate the effects of geometric parameters on the surface lattice resonances and their impact on the temperature and fluid velocity of the optofluidic system. Our results demonstrate excellent optical control of these plasmonic metasurface heating and thermal convection performances to design flexible platforms for microfluidics.