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.

Virtual metasurfaces:reshaping electromagnetic waves in distance

Metasurface has provided unprecedented freedoms in manipulating electromagnetic(EM) waves, exhibiting fascinating functions. Conventionally, these functions are implemented right on metasurfaces, where spatial modulations on EM wave amplitudes or phases are achieved by meta-atoms. This study proposes the concept of virtual metasurface(VM), which is formed by arrays of foci away from the entity metasurface. Unlike conventional metasurfaces, spatial modulations on the amplitudes or phases of EM waves occur in the air, with a focal length distance from the entity metasurface. As a proof of concept, we demonstrated a transmissive VM. The entity metasurface consists of transmissive focusing metasurface tiles(TFMTs) with the same focal length. Two TFMTs were designed with phase difference π to enable the most typical checkerboard configuration. The TFMTs were assembled to form the entity metasurface, whereas their foci formed the VM. Due to the π phase difference among adjacent foci, EM propagation along the normal direction was cancelled, leading to four tilted far-field beams. The concept of VM can be readily extended to higher frequencies from terahertz to optical regimes and may find wide applications in communication, camouflage, and other fields.

Full-colour nanoprint-hologram synchronous metasurface with arbitrary hue-saturationbrightness control

The colour gamut,a two-dimensional(2D)colour space primarily comprising hue and saturation(HS),lays the most important foundation for the colour display and printing industries.Recently,the metasurface has been considered a promising paradigm for nanoprinting and holographic imaging,demonstrating a subwavelength image resolution,a flat profile,high durability,and multi-functionalities.Much effort has been devoted to broaden the 2D HS plane,also known as the CIE map.However,the brightness(B),as the carrier of chiaroscuro information,has long been neglected in metasurface-based nanoprinting or holograms due to the challenge in realising arbitrary and simultaneous control of full-colour HSB tuning in a passive device.Here,we report a dielectric metasurface made of crystal silicon nanoblocks,which achieves not only tailorable coverage of the primary colours red,green and blue(RGB)but also intensity control of the individual colours.The colour gamut is hence extruded from the 2D CIE to a complete 3D HSB space.Moreover,thanks to the independent control of the RGB intensity and phase,we further show that a singlelayer silicon metasurface could simultaneously exhibit arbitrary HSB colour nanoprinting and a full-colour hologram image.Our findings open up possibilities for high-resolution and high-fidelity optical security devices as well as advanced cryptographic approaches.

Phase-field modeling of grain evolutions in additive manufacturing from nucleation,growth,to coarsening

A three-dimensional phase-field model is developed to simulate grain evolutions during powder-bed-fusion(PBF)additive manufacturing,while the physically-informed temperature profile is implemented from a thermal-fluid flow model.The phase-field model incorporates a nucleation model based on classical nucleation theory,as well as the initial grain structures of powder particles and substrate.The grain evolutions during the three-layer three-track PBF process are comprehensively reproduced,including grain nucleation and growth in molten pools,epitaxial growth from powder particles,substrate and previous tracks,grain re-melting and re-growth in overlapping zones,and grain coarsening in heat-affected zones.A validation experiment has been carried out,showing that the simulation results are consistent with the experimental results in the molten pool and grain morphologies.Furthermore,the grain refinement by adding nanoparticles is preliminarily reproduced and compared against the experimental result in literature.

Progress in wearable electronics/photonics—Moving toward the era of artificial intelligence and internet of things

The past few years have witnessed the significant impacts of wearable electronics/photonics on various aspects of our daily life,for example,healthcare monitoring and treatment,ambient monitoring,soft robotics,prosthetics,flexible display,communication,human-machine interactions,and so on.According to the development in recent years,the next-generation wearable electronics and photonics are advancing rapidly toward the era of artificial intelligence(AI)and internet of things(IoT),to achieve a higher level of comfort,convenience,connection,and intelligence.Herein,this review provides an opportune overview of the recent progress in wearable electronics,photonics,and systems,in terms of emerging materials,transducing mechanisms,structural configurations,applications,and their further integration with other technologies.First,development of general wearable electronics and photonics is summarized for the applications of physical sensing,chemical sensing,humanmachine interaction,display,communication,and so on.Then self-sustainable wearable electronics/photonics and systems are discussed based on system integration with energy harvesting and storage technologies.Next,technology fusion of wearable systems and AI is reviewed,showing the emergence and rapid development of intelligent/smart systems.In the last section of this review,perspectives about the future development trends of the next-generation wearable electronics/photonics are provided,that is,toward multifunctional,self-sustainable,and intelligent wearable systems in the AI/IoT era.

A flexible three-dimensional electrode mesh:An enabling technology for wireless brain-computer interface prostheses

The neural interface is a key component in wireless brain–computer prostheses.In this study,we demonstrate that a unique three-dimensional(3D)microneedle electrode on a flexible mesh substrate,which can be fabricated without complicated micromachining techniques,is conformal to the tissues with minimal invasiveness.Furthermore,we demonstrate that it can be applied to different functional layers in the nervous system without length limitation.The microneedle electrode is fabricated using drawing lithography technology from biocompatible materials.In this approach,the profile of a 3D microneedle electrode array is determined by the design of a two-dimensional(2D)pattern on the mask,which can be used to access different functional layers in different locations of the brain.Due to the sufficient stiffness of the electrode and the excellent flexibility of the mesh substrate,the electrode can penetrate into the tissue with its bottom layer fully conformal to the curved brain surface.Then,the exposed contact at the end of the microneedle electrode can successfully acquire neural signals from the brain.

Optically sizing single atmospheric particulates with a 10-nm resolution using a strong evanescent field

Although an accurate evaluation of the distribution of ultrafine particulate matter in air is of utmost significance to public health,the usually used PM2.5 index fails to provide size distribution information.Here we demonstrate a low-profile and cavity-free size spectrometer for probing fine and ultrafine particulate matter by using the enhanced particle-perturbed scattering in strong optical evanescent fields of a nanofiber array.The unprecedented size resolution reaches 10 nm for detecting single 100-nm-diameter nanoparticles by employing uniform nanofibers and controlling the polarizations of the probe light.This size spectrometry was tested and used to retrieve the size distribution of particulate matter in the air of Beijing,yielding mass concentrations of nanoparticles,as a secondary exercise,consistent with the officially released data.This nanofiber-array probe shows potential for the full monitoring of air pollution and for studying early-stage haze evolution and can be further extended to explore nanoparticle interactions.

A hybridized electromagnetic-triboelectric nanogenerator designed for scavenging biomechanical energy in human balance control

For human beings of different ages and physical abilities, the inherent balance control system is ubiquitous and active to prevent falling, especially in motion states. A hybridized electromagnetic-triboelectric nanogenerator (HETNG) is prepared to harvest biomechanical energy during human balance control processes and achieve significant monitoring functions. The HETNG is composed of a symmetrical pendulum structure and a cylinder magnet rolling inside. Four coils are divided into two groups which form into two electromagnetic generators (EMGs). Besides, two spatial electrodes attached to the inner wall constitute a freestanding mode triboelectric nanogenerator (TENG). With a rectification circuit, the HETNG presents a high output power with a peak value of 0.55 W at a load of 160 Ω. Along with human balance control processes during walking, the HETNG can harvest biomechanical energy at different positions on the trunk. Moreover, the HETNG applied in artificial limb has been preliminarily simulated with the positions on thigh and foot, for monitoring the actions of squat and stand up, and lifting the leg up and down. For the elder that walks slowly with a walking aid, the HETNG equipped on the walking aid can help to record the motions of forwarding and unexpected falling, which is useful for calling for help. This work shows the potential of biomechanical energy-driven HETNG for powering portable electronics and monitoring human motions, also shows significant concerns to people lacked action capability or disabled.

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.

班纳特倍增器纳米发电机与其离子迁移谱仪的机器学习辅助挥发性有机物探测

离子迁移分析谱是识别气相化合物的一种常用分析技术,可实现气体的快速响应与多种成分辨识与分析.然而,传统的离子迁移谱仪因高压的电离导致系统的体积过大、离子腔体的工作温度高、测量精度差,不适用于可挥发性有机物(VOCs)的浓度的检测.为解决这类问题,本文报道了一种纳米发电机的高压实现冷场与常压放电的离子迁移谱分析仪,主要是基于电荷积累机制的多开关调控纳米发电机,可实现几百甚至几千伏的直流偏压.试验测试显示该系统具有良好的离子迁移重复性与特征,可用于VOCs种类与其浓度的辨识.为了进一步提高测试效果,作者采用了深度学习算法提取特征,极大提高了VOCs的检测能力.该方法为物联网的环境检测提供了一种响应速度快、功耗低的便携式VOCs检测与成分分析的解决方案.

Spiniform phase-encoded metagratings entangling arbitrary rational-order orbital angular momentum

Quantum entanglements between integer-order and fractional-order orbital angular momentums(OAMs)have been previously discussed.However,the entangled nature of arbitrary rational-order OAM has long been considered a myth due to the absence of an effective strategy for generating arbitrary rational-order OAM beams.Therefore,we report a single metadevice comprising a bilaterally symmetric grating with an aperture,creating optical beams with dynamically controllable OAM values that are continuously varying over a rational range.Due to its encoded spiniform phase,this novel metagrating enables the production of an average OAM that can be increased without a theoretical limit by embracing distributed singularities,which differs significantly from the classic method of stacking phase singularities using fork gratings.This new method makes it possible to probe the unexplored niche of quantum entanglement between arbitrarily defined OAMs in light,which could lead to the complex manipulation of microparticles,high-dimensional quantum entanglement and optical communication.We show that quantum coincidence based on rational-order OAM-superposition states could give rise to low cross-talks between two different states that have no significant overlap in their spiral spectra.Additionally,future applications in quantum communication and optical micromanipulation may be found.