MOF/Polymer-Integrated Multi-Hotspot Mid-Infrared Nanoantennas for Sensitive Detection of CO_(2) Gas

Metal-organic frameworks(MOFs)have been extensively used for gas sorption,storage and separation owing to ultrahigh porosity,exceptional thermal stability,and wide structural diversity.However,when it comes to ultra-low concentration gas detection,technical bottlenecks of MOFs appear due to the poor adsorption capacity at ppm-/ppblevel concentration and the limited sensitivity for signal transduction.Here,we present hybrid MOF-polymer physi-chemisorption mechanisms integrated with infrared(IR)nanoantennas for highly selective and ultrasensitive CO_(2) detection.To improve the adsorption capacity for trace amounts of gas molecules,MOFs are decorated with amino groups to introduce the chemisorption while maintaining the structural integrity for physisorption.Additionally,leveraging all major optimization methods,a multi-hotspot strategy is proposed to improve the sensitivity of nanoantennas by enhancing the near field and engineering the radiative and absorptive loss.As a benefit,we demonstrate the competitive advantages of our strategy against the state-of-the-art miniaturized IR CO_(2) sensors,including low detection limit,high sensitivity(0.18%/ppm),excellent reversibility(variation within 2%),and high selectivity(against C_(2)H_(5)OH,CH_(3)OH,N_(2)).This work provides valuable insights into the integration of advanced porous materials and nanophotonic devices,which can be further adopted in ultra-low concentration gas monitoring in industry and environmental applications.

An ADI Finite Volume Element Method for a Viscous Wave Equation with Variable Coefficients

Based on rectangular partition and bilinear interpolation,we construct an alternating-direction implicit(ADI)finite volume element method,which combined the merits of finite volume element method and alternating direction implicit method to solve a viscous wave equation with variable coefficients.This paper presents a general procedure to construct the alternating-direction implicit finite volume element method and gives computational schemes.Optimal error estimate in L2 norm is obtained for the schemes.Compared with the finite volume element method of the same convergence order,our method is more effective in terms of running time with the increasing of the computing scale.Numerical experiments are presented to show the efficiency of our method and numerical results are provided to support our theoretical analysis.

Expanding chiral metamaterials for retrieving fingerprints via vibrational circular dichroism

Circular dichroism(CD)spectroscopy has been widely demonstrated for detecting chiral molecules.However,the determination of chiral mixtures with various concentrations and enantiomeric ratios can be a challenging task.To solve this problem,we report an enhanced vibrational circular dichroism(VCD)sensing platform based on plasmonic chiral metamaterials,which presents a 6-magnitude signal enhancement with a selectivity of chiral molecules.Guided by coupled-mode theory,we leverage both in-plane and out-of-plane symmetry-breaking structures for chiral metamaterial design enabled by a two-step lithography process,which increases the near-field coupling strengths and varies the ratio between absorption and radiation loss,resulting in improved chiral light-matter interaction and enhanced molecular VCD signals.Besides,we demonstrate the thin-film sensing process of BSA andβ-lactoglobulin proteins,which contain secondary structures a-helix andβ-sheet and achieve a limit of detection down to zeptomole level.Furthermore,we also,for the first time,explore the potential of enhanced VCD spectroscopy by demonstrating a selective sensing process of chiral mixtures,where the mixing ratio can be successfully differentiated with our proposed chiral metamaterials.Our findings improve the sensing signal of molecules and expand the extractable information,paving the way toward label-free,compact,small-volume chiral molecule detection for stereochemical and clinical diagnosisapplications.

Preparation and visible photocatalytic dye degradation of Mn-TiO2/sepiolite photocatalysts

The performance of Mn-TiO2/sepiolite photocatalysts prepared by the solgel method and calcinated at different temperatures was studied in the photocatalytic degradation of direct fast emerald green dye under visible light irradiation,and a series of analytical techniques such as XRD,SEM,FTIR,TG-DSC,XPS,UV-vis-DRS and Raman spectroscopy were used to characterize the morphology,structure and optical properties of the photocatalysts.It is found that the anatase TiO2 was formed in all photocatalysts.Mn4+might incorporate into the lattice structure of TiO2 and partially replace Ti4+,thus causing the defects in the crystal structure and the broadening of the spectral response range of TiO2.At the same time,TiO2 particles were dispersed on the surface of the sepiolite,which immobilized TiO2 particles with sepiolite via the bond of Ti-O-Si.Mn-TiO2/sepiolite calcined at 400°C exhibits the highest photocatalytic activity and the degradation rate of direct fast emerald green is up to 98.13%.Meanwhile,it also shows good stability and universality.

Subwavelength on-chip light focusing with bigradient all-dielectric metamaterials for dense photonic integration

Photonic integrated circuits(PICs)provide a promising platform for miniaturized on-chip optical systems for communication,computation,and sensing applications.The dense integration of photonic components is one of the keys to exploit the advantages of PIC.Although light focusing is a fundamental and indispensable function in PICs,focusing light at the micro/nanometer-scale is challenging.Here,a bigradient on-chip metalens(BOML)is proposed to achieve ultrasmall focal lengths and spot sizes at the subwavelength scale for dense PICs.The design of BOML combines gradient geometry and gradient refractive index into one metalens by simultaneously engineering the length and width of subwavelength silicon slots.With a small device footprint of only 168μm,the BOML achieves efficient on-chip focusing with the recordbreaking figure-of-merits,which are the ratio of wavelength to focal length/spot size(0.268 and 2.83)and numerical aperture(1.78).Leveraging on the Fresnel design,the footprint of BOML is further reduced by 55.1%,and the numerical aperture is enhanced to 1.9.The demonstration of mode conversion and beam steering with efficiency over 80%and a tilting range of 7.2°holds the potential for highly dense on-chip photonic systems for optical communication,optical sensing,nonlinear optics,and neural networks for deep learning.

Loss-induced phase transition in mid-infrared plasmonic metamaterials for ultrasensitive vibrational spectroscopy

Metamaterials have proven their ability to possess extraordinary physical properties distinct from naturally available materials,leading to exciting sensing functionalities and applications.However,metamaterial-based sensing applications suffer from severe performance limitations due to noise interference and design constraints.Here,we propose a dual-phase strategy that leverages loss-induced different Fano-resonant phases to access both destructive and constructive signals of molecular vibration.When the two reverse signals are innovatively combined,the noise in the detection system is effectively suppressed,thereby breaking through the noise-related limitations.Additionally,by utilizing loss optimization of the plasmon-molecule coupling system,our dual-phase strategy enhances the efficiency of infrared energy transfer into the molecule without any additional fabrication complex,thereby overcoming the trade-off dilemma between performance and fabrication cost.Thanks to the pioneering breakthroughs in the limitations,our dual-phase strategy possesses an overwhelming competitive advantage in ultrasensitive vibrational spectroscopy over traditional metamaterial technology,including strong signal strength(×4),high sensitivity(×4.2),effective noise suppression(30%),low detection limit(13 ppm),and excellent selectivity among CO_(2),NH_(3),and CH_(4) mixtures.This work not only opens the door to various emerging ultrasensitive detection applications,including ultrasensitive in-breath diagnostics and high-information analysis of molecular information in dynamic reactions,but also gains new insights into the plasmon-molecule interactions in advanced metamaterials.