Ultrafast pyroelectric photodetection with on-chip spectral filters

Color Generation and Polarization-Sensitive Encryption by Laser Writing on Plasmonic Reflector Arrays

Plasmonic color printing presents a sustainable solution for vibrant and durable color reproduction by leveraging the light-manipulating properties of nanostructures. However, the fabrication of plasmonic nanostructures has posed challenges, hindering widespread adoption. In this paper, we introduce plasmonic reflector arrays (PRAs) composed of three layers─Ag nanoparticles (NPs), an Al2O3 spacer, and an Ag reflector─deposited via physical vapor deposition (PVD). By employing nanosecond and femtosecond laser writing techniques, we manipulate the surface morphology of silver nanoparticles on PRAs, resulting in a diverse range of structural colors that are both polarization-insensitive and polarization-sensitive. Furthermore, we demonstrate the versatility of nanosecond laser writing in creating intricate patterns on PRAs. Additionally, we propose a novel two-step method combining nanosecond and femtosecond laser processing to embed QR code patterns into PRAs, showcasing their potential for secure data encryption and transmission. This research underscores the promising applications of PRAs in advanced color printing and secure optical data encoding.

Split ring hole metamaterial-enhanced pyroelectric detector for efficient multi-narrowband terahertz detection

Derived from infrared pyroelectric detection, typical terahertz (THz) pyroelectric detectors have low sensitivity at low-frequency THz bands. Based on the high-efficiency absorption of the metamaterial perfect absorber (MPA), a novel split ring hole metamaterial-enhanced pyroelectric detector is proposed to achieve efficient multi-narrowband THz detection. Using high frequency simulation software (HFSS), the dimensional parameters including ring radius, ring width, connection beam width, array period, and thickness, are optimized to enhance efficient multi-narrowband absorption. The as-optimized metamaterial-enhanced detectors are fabricated via micro-nano manufacturing technology. The voltage responsiveness and noise equivalent power of the metamaterial-enhanced detector are tested by THz focused optical path and compared with those of the typical pyroelectric detector and the simulated MPA absorptivity. The results indicate that the metamaterial-enhanced detector has a multi-narrowband detection capability at 0.245 THz, 0.295 THz, and 0.38 THz, which is close to the simulated MPA absorptivity. Compared to the typical pyroelectric detector, the split ring hole metamaterial-enhanced detector can simultaneously achieve thermal absorption, thermal conduction, and pyroelectricity in the same MPA structure, providing faster response speed above 100 Hz chopper frequency and two times higher detection sensitivity at multi-narrowband THz frequencies. This research can be used for THz sensing, absorption filtering, biological macromolecule detection, and other applications.

New Nanophotonics Approaches for Enhancing the Efficiency and Stability of Perovskite Solar Cells

Over the past decade, the power conversion efficiency (PCE) of perovskite solar cells (PSCs) has experienced a remarkable ascent, soaring from 3.8% in 2009 to a remarkable record of 26.1% in 2023. Many recent approaches for improving PSC performance employ nanophotonic technologies, from light harvesting and thermal management to the manipulation of charge carrier dynamics. Plasmonic nanoparticles and arrayed dielectric nanostructures have been applied to tailor the light absorption, scattering, and conversion, as well as the heat dissipation within PSCs to improve their PCE and operational stability. In this review, it is begin with a concise introduction to define the realm of nanophotonics by focusing on the nanoscale interactions between light and surface plasmons or dielectric photonic structures. Prevailing strategies that utilize resonance-enhanced light-matter interactions for boosting the PCE and stability of PSCs from light trapping, carrier transportation, and thermal management perspectives are then elaborated, and the resultant practical applications, such as semitransparent photovoltaics, colored PSCs, and smart perovskite windows are discussed. Finally, the state-of-the-art nanophotonic paradigms in PSCs are reviewed, and the benefits of these approaches in improving the aesthetic effects and energy-saving character of PSC-integrated buildings are highlighted.

Compatible camouflage for dual-band guided-laser radar and infrared via a metamaterial perfect absorber

Laser-guided detector and infrared detection have attracted increasing attention in a wide range of research fields, including multispectral detection, radiative cooling, and thermal management. Previously reported absorbers presented shortcomings of lacking either tunability or compatibility. In this study, a metamaterial perfect absorber based on a Helmholtz resonator and fractal structure is proposed, which realizes tunable perfect absorptivity (α 1.06μ m >0.99,α 10.6μ m >0.99) of guided-laser radar dual operating bands (1.06 µm and 10.6 µm) and a low infrared average emissivity (ε¯3-5μ m =0.03,ε¯8-14μ m =0.31) in two atmospheric windows for compatible camouflage. The proposed perfect absorber provides a dynamically tunable absorptivity without structural changes and can be applied to optical communication, military stealth or protection, and electromagnetic detection.

Enhancing Light Out-coupling in Perovskite Light-Emitting Diodes through Plasmonic Nanostructures

Perovskite light-emitting diodes (PeLEDs) have emerged as promising candidates for lighting and display technologies owing to their high photoluminescence quantum efficiency and high carrier mobility. However, the performance of planar PeLEDs is limited by the out-coupling efficiency, predominantly governed by photonic losses at device interfaces. Most notably, the plasmonic loss at the metal electrode interfaces can account for up to 60% of the total loss. Here, we investigate the use of plasmonic nanostructures to improve the light out-coupling in PeLEDs. By integrating these nanostructures with PeLEDs, we have demonstrated an effectively reduced plasmonic loss and enhanced light out-coupling. As a result, the nanostructured PeLEDs exhibit an average 1.5-fold increase in external quantum efficiency and an ∼20-fold improvement in device lifetime. This finding offers a generic approach for enhancing light out-coupling, promising great potential to go beyond existing performance limitations.

Uncovering the Mechanisms of Triplet-Triplet Annihilation Upconversion Enhancement via Plasmonic Nanocavity Tuning

The nonlinear conversion of photons from lower to higher energy is important for a wide range of applications, from quantum communications and optoelectronics to solar energy conversion and medicine. Triplet-triplet annihilation upconversion (TTA UC), which utilizes an absorber/emitter molecular pair, is a promising tool for upconversion applications requiring low intensity light such as photovoltaics, photocatalysis, and bioimaging. Despite demonstrations of efficient TTA UC in solution, practical applications have proven difficult, as thin films retard the necessary energy transfer steps and result in low emission yields. In this work, TTA UC emission from a thin film is greatly enhanced through integration into plasmonic nanogap cavities consisting of a silver mirror, a nanometer-scale polymer spacer containing a TTA molecular pair, and colloidally synthesized silver nanocubes. Mechanistic studies performed by varying the nanocube side length (45-150 nm) to tune the nanogap cavity resonance paired with simulations reveal absorption rate enhancement to be the primary operative mechanism in overall TTA UC emission enhancement. This absorption enhancement decreases the TTA UC threshold intensity by an order of magnitude and allows TTA UC emission to be excited with light up to 120 nm redder than the usable wavelength range for the control samples. Further, combined nanogap cavities composed of two distinct nanocube sizes result in surfaces which simultaneously enhance the absorption rate and emission rate. These dual-size nanogap cavities result in 45-fold TTA UC emission enhancement. In total, these studies present TTA UC emission enhancement, illustrate how the usable portion of the spectrum can be expanded for a given sensitizer-emitter pair, and develop both mechanistic understanding and design rules for TTA UC emission enhancement by plasmonic nanostructures.

Ultrathin Pyroelectric Photodetector with Integrated Polarization-Sensing Metasurface

An abundance of metallic metasurfaces have been realized with miniscule, intricate features capable of tailored scattering, reflection, and absorption; however, high losses through heat limit their use in optoelectronics. Here, codesign of a detector and a polarization-sensing metasurface overcomes this challenge by utilizing the heat generation for integrated pyroelectric detection of the incoming light polarization. Using a nanogap metasurface with asymmetric metallic elements, polarization-sensitive photodetection exhibits high extinction ratios up to 19 for orthogonally polarized light and allows extraction of Stokes parameters with <12% deviation from theoretical values. This polarization-sensitive photodetector is ultrathin, consisting of active layers of only 290 nm, and exhibits fast response times of ∼2 ns. The structure is fully integrated, requiring no external cameras, detectors, or power sources, and points toward the creation of layered, multifunctional devices that utilize exotic metasurface properties for novel and compact sensing and imaging.

Ferroelectrically Modulated and Enhanced Photoresponse in a Self-Powered α-In2Se3/Si Heterojunction Photodetector

Photodetectors have been applied to pivotal optoelectronic components of modern optical communication, sensing, and imaging systems. As a room-temperature ferroelectric van der Waals semiconductor, 2D α-In₂Se₃ is a promising candidate for a next-generation optoelectronic material because of its thickness-dependent direct bandgap and excellent optoelectronic performance. Previous studies of photodetectors based on α-In₂Se₃ have been rarely focused on the modulated relationship between the α-In₂Se₃ intrinsic ferroelectricity and photoresponsivity. Herein, a simple integrated process and high-performance photodetector based on an α-In₂Se₃/Si vertical hybrid-dimensional heterojunction was constructed. Our photodetector in the ferroelectric polarization up state accomplishes a self-powered, highly sensitive photoresponse with an on/off ratio of 4.5 × 10⁵ and detectivity of 1.6 × 10¹³ Jones, and it also shows a fast response time with 43 μs. The depolarization field generated by the remanent polarization of ferroelectrics in α-In₂Se₃ provides a strategy for enhancement and modulation of photodetection. The negative correlation was discovered because the enhancement photoresponsivity factor of ferroelectric modulation competes with the photovoltaic behavior within the α-In₂Se₃/Si heterojunction. Our research highlights the great potential of the high-efficiency heterojunction photodetector for future object recognition and photoelectric imaging.

Broadband Photoresponses from Ultraviolet to Near-Infrared (II) Region through Light-induced Pyroelectric Effects in a Hybrid Perovskite

Broadband photodetection has shown a great promise for diverse applications, while the realization of plateau photoresponse from ultraviolet (UV) to near-infrared (NIR) spectral region is very challenging. Herein, we exploit photoexcited pyroelectric effect in a chiral hybrid perovskite, (N, N-dimethylcyclohexylammonium)PbBr₃ (1), serving as a new pathway to drive broadband photoactivities. It is a room-temperature pyroelectric with large polarization of ≈6.4 μC cm^-2 and high pyroelectric figure-of-merits (F_V =1.0×10^-2  cm²   μC^-1 and F_D =7.1×10^-5  Pa^-1/2 ). Strikingly, light-induced pyroelectric effect arising from spontaneous polarization is observed in 1, which cover UV (266 nm) to NIR-II (1950 nm) full spectral region. The broadband photoresponses actualized by pyroelectricity break the limit of optical band gap. As the first demonstration of photo-pyroelectricity covering UV-to-NIR spectral region in hybrid perovskites, this work paves a pathway to assemble high-performance smart devices.

Quantitative phase contrast imaging with a nonlocal angle-selective metasurface

Phase contrast microscopy has played a central role in the development of modern biology, geology, and nanotechnology. It can visualize the structure of translucent objects that remains hidden in regular optical microscopes. The optical layout of a phase contrast microscope is based on a 4 f image processing setup and has essentially remained unchanged since its invention by Zernike in the early 1930s. Here, we propose a conceptually new approach to phase contrast imaging that harnesses the non-local optical response of a guided-mode-resonator metasurface. We highlight its benefits and demonstrate the imaging of various phase objects, including biological cells, polymeric nanostructures, and transparent metasurfaces. Our results showcase that the addition of this non-local metasurface to a conventional microscope enables quantitative phase contrast imaging with a 0.02π phase accuracy. At a high level, this work adds to the growing body of research aimed at the use of metasurfaces for analog optical computing.

Contribution of Sub-Gap States to Broadband Infrared Response in Organic Bulk Heterojunctions

This work studied a series of infrared detectors comprised of organic bulk heterojunctions to explain the origin of their broadband spectral response from the visible to the infrared spanning 1 to 8 μm and the transition from photonic to bolometric operation. Through comparisons of the detector current and the sub-bandgap density of states, the mid- and long-wave infrared response was attributed to charge trap-and-release processes that impact thermal charge generation and the activation energy of charge mobility. We further demonstrate how the sub-bandgap characteristics, mobility activation energy, and effective bandgap are key design parameters for controlling the device temperature coefficient of resistance, which reached up to -7%/K, better than other thin-film materials such as amorphous silicon and vanadium oxide.

Percolated Plasmonic Superlattices of Nanospheres with 1 nm-Level Gap as High-Index Metamaterials

Nanophotonics relies on precise control of refractive index (RI) which can be designed with metamaterials. Plasmonic superstructures of nanoparticles (NPs) can suggest a versatile way of tuning RI. However, the plasmonic effects in the superstructures demand 1 nm-level exquisite control over the interparticle gap, which is challenging in a sub-wavelength NPs. Thus far, a large-area demonstration has been mostly discouraged. Here, heteroligand AuNPs are prepared, which are stable in oil but become Janus particles at the oil-water interface, called "adaptive Janus particles." NPs are bound at the interface and assembled into 2D arrays over square centimeters as toluene evaporates, which distinctively exhibits the RI tunability. In visible and NIR light, the 2D superstructures exhibit the highest-ever RI (≈7.8) with varying the size and interparticle gap of NPs, which is successfully explained by a plasmonic percolation model. Furthermore, fully solution-processable 2D plasmonic superstructures are proved to be advantageous in flexible photonic devices such as distributed Bragg reflectors.

Control of Nanoscale Heat Generation with Lithography-Free Metasurface Absorbers

Metasurfaces, artificially engineered surfaces comprised of subwavelength resonators, show promise for realizing a new generation of optical materials and devices. However, current metasurface architectures suffer from environmental degradation, a limited spectral range, and a lack of scalability. Here, we demonstrate a novel large-area embedded metasurface architecture that is environmentally robust and capable of a spectrally selective absorption of greater than 80% spanning from 330 to 2740 nm. These fully encapsulated metasurfaces leverage the capabilities of colloidal plasmonic nanoparticles with various crystallinities, materials, shapes, and sizes to access a larger spectral range and allow for control of nanoscale spatial losses and subsequent heat generation within the constituent elements of the metasurface. Through the selection of material, particle size, and shape, these metasurfaces can be designed across the ultraviolet (UV) to short-wave infrared (SWIR) region for various hot-electron, photodetection, photocatalysis, and photothermal processes.

Giant pyroelectricity in nanomembranes

Pyroelectricity describes the generation of electricity by temporal temperature change in polar materials^1-3. When free-standing pyroelectric materials approach the 2D crystalline limit, how pyroelectricity behaves remained largely unknown. Here, using three model pyroelectric materials whose bonding characters along the out-of-plane direction vary from van der Waals (In₂Se₃), quasi-van der Waals (CsBiNb₂O₇) to ionic/covalent (ZnO), we experimentally show the dimensionality effect on pyroelectricity and the relation between lattice dynamics and pyroelectricity. We find that, for all three materials, when the thickness of free-standing sheets becomes small, their pyroelectric coefficients increase rapidly. We show that the material with chemical bonds along the out-of-plane direction exhibits the greatest dimensionality effect. Experimental observations evidence the possible influence of changed phonon dynamics in crystals with reduced thickness on their pyroelectricity. Our findings should stimulate fundamental study on pyroelectricity in ultra-thin materials and inspire technological development for potential pyroelectric applications in thermal imaging and energy harvesting.

Tunable Infrared Detection, Radiative Cooling and Infrared-Laser Compatible Camouflage Based on a Multifunctional Nanostructure with Phase-Change Material

The nanostructure composed of nanomaterials and subwavelength units offers flexible design freedom and outstanding advantages over conventional devices. In this paper, a multifunctional nanostructure with phase-change material (PCM) is proposed to achieve tunable infrared detection, radiation cooling and infrared (IR)-laser compatible camouflage. The structure is very simple and is modified from the classic metal-dielectric-metal (MIM) multilayer film structure. We innovatively composed the top layer of metals with slits, and introduced a non-volatile PCM Ge₂Sb₂Te₅ (GST) for selective absorption/radiation regulation. According to the simulation results, wide-angle and polarization-insensitive dual-band infrared detection is realized in the four-layer structure. The transformation from infrared detection to infrared stealth is realized in the five-layer structure, and laser stealth is realized in the atmospheric window by electromagnetic absorption. Moreover, better radiation cooling is realized in the non-atmospheric window. The proposed device can achieve more than a 50% laser absorption rate at 10.6 μm while ensuring an average infrared emissivity below 20%. Compared with previous works, our proposed multifunctional nanostructures can realize multiple applications with a compact structure only by changing the temperature. Such ultra-thin, integratable and multifunctional nanostructures have great application prospects extending to various fields such as electromagnetic shielding, optical communication and sensing.

Predicting Laser-Induced Colors of Random Plasmonic Metasurfaces and Optimizing Image Multiplexing Using Deep Learning

Structural colors of plasmonic metasurfaces have been promised to a strong technological impact thanks to their high brightness, durability, and dichroic properties. However, fabricating metasurfaces whose spatial distribution must be customized at each implementation and over large areas is still a challenge. Since the demonstration of printed image multiplexing on quasi-random plasmonic metasurfaces, laser processing appears as a promising technology to reach the right level of accuracy and versatility. The main limit comes from the absence of physical models to predict the optical properties that can emerge from the laser processing of metasurfaces in which random metallic nanostructures are characterized by their statistical properties. Here, we demonstrate that deep neural networks trained from experimental data can predict the spectra and colors of laser-induced plasmonic metasurfaces in various observation modes. With thousands of experimental data, produced in a rapid and efficient way, the training accuracy is better than the perceptual just noticeable change. This accuracy enables the use of the predicted continuous color charts to find solutions for printing multiplexed images. Our deep learning approach is validated by an experimental demonstration of laser-induced two-image multiplexing. This approach greatly improves the performance of the laser-processing technology for both printing color images and finding optimized parameters for multiplexing. The article also provides a simple mining algorithm for implementing multiplexing with multiple observation modes and colors from any printing technology. This study can improve the optimization of laser processes for high-end applications in security, entertainment, or data storage.

Thin film block copolymer self-assembly for nanophotonics

The nanophotonic engineering of light-matter interactions has profoundly changed research behind the design and fabrication of optical materials and devices. Metasurfaces-arrays of subwavelength nanostructures that interact resonantly with electromagnetic radiation-have emerged as an integral nanophotonic platform for a new generation of ultrathin lenses, displays, polarizers and other devices. Their success hinges on advances in lithography and nanofabrication in recent decades. While existing nanolithography techniques are suitable for basic research and prototyping, issues of cost, throughput, scalability, and substrate compatibility may preclude their use for many metasurface applications. Patterning via spontaneous self-assembly of block copolymer thin films offers an enticing alternative for nanophotonic manufacturing that is rapid, inexpensive, and applicable to large areas and diverse substrates. This review discusses the advantages and disadvantages of block copolymer-based nanopatterning and highlights recent progress in their use for broadband antireflection, surface enhanced Raman spectroscopy, and other nanophotonic applications. Recent advances in diversification of self-assembled block copolymer nanopatterns and improved processes for enhanced scalability of self-assembled nanopatterning using block copolymers are also discussed, with a spotlight on directions for future research that would enable a wider array of nanophotonic applications.

Metamaterial microbolometers for multi-spectral infrared polarization imaging

Vanadium oxide (VO_x) microbolometers enable the construction of high-performance yet low-cost and uncooled imaging detectors in the mid-infrared spectrum. Typical micro-bolometers are broadband sensors with no polarization selectivity. Thus, imaging detectors based on microbolometers have to use separate spectral and polarization filters to select the target spectral bands and polarization states, and the resulting systems are complicated and bulky. Here we demonstrate that by using metamaterial absorbers (MAs), which are arrays of optical resonators with sub-wavelength dimensions and spacing, we simultaneously tailor the VO_x microbolometers' spectral and polarization responses, the need for separate spectral filters and polarizers can be mitigated. The MAs selectively absorb the TM polarization component of the incident light in a spectral band with tunable central wavelength and bandwidth while rejecting the TE polarization component. Two MAs with average TM absorption of 0.8322 in the 5.150 µm - 6.422 µm band and 0.7720 in the 5.867 µm - 7.467 µm band are fabricated, and the polarization extinction ratio (PER) are 42.24 and 42.65, respectively. The MAs are applied to VO_x micro-bolometers, and the measured detector responses agree well with the absorption spectra of the MAs. The achieved peak responsivities of two fabricated detectors are 1.0 V/W at 6.0 µm and 1.46 V/W at 6.8 µm, respectively. And the two detectors achieve a D* of 6.94×10⁵ cm·Hz^1/2W^-1 at 11Hz and 9.95×10⁵ cm·Hz^1/2W^-1 at 36Hz, respectively. Our work paved the way towards large format room temperature multi-spectral infrared polarization imaging detector.

Optical Bound States in the Continuum Enabled by Magnetic Resonances Coupled to a Mirror

Dielectric metasurfaces made of high refractive index and low optical loss materials have emerged as promising platforms to achieve high-quality factor modes enabling strong light-matter interaction. Bound states in the continuum have shown potential to demonstrate narrow spectral resonances but often require asymmetric geometry and typically feature strong polarization dependence, complicating fabrication and limiting practical applications. We introduce a novel approach for designing high-quality bound states in the continuum using magnetic dipole resonances coupled to a mirror. The resulting metasurface has simple geometric parameters requiring no broken symmetry. To demonstrate the unique features of our photonic platform we show a record-breaking third harmonic generation efficiency from the metasurface benefiting from the strongly enhanced electric field at high-quality resonances. Our approach mitigates the shortcomings of previous platforms with simple geometry enabling facile and large-area fabrication of metasurfaces paving the way for applications in optical sensing, detection, quantum photonics, and nonlinear devices.

High-Performing Self-Powered Photosensing and Reconfigurable Pyro-photoelectric Memory with Ferroelectric Hafnium Oxide

With highly diverse multifunctional properties, hafnium oxide (HfO₂ ) has attracted considerable attention not only because of its potential to address fundamental questions about material behaviors, but also its potential for applied perspectives like ferroelectric memory, transistors, and pyroelectric sensors. However, effective harvesting of the pyro-photoelectric effect of HfO₂ to develop high-performing self-biased photosensors and electric writable and optical readable memory has yet to be developed. Here, a proof-of-concept HfO₂ -based self-powered and ultrafast (response time ≈ 60 µs) infrared pyroelectric sensor with a responsivity of up to 68 µA W^-1 is developed. In particular, temporal infrared light illumination induced surface heating and, in turn, change in spontaneous polarization are attributed to robust pyro-photocurrent generation. Further, controllable suspension and reestablishment of the self-biased pyro-photocurrent response with a short electric pulse are demonstrated, which offers a conceptually new kind of photoreadable memory. Potentially, the novel approach opens a new avenue for designing on-demand pyro-phototronic response over a desired area and offers the opportunity to utilize it for various applications, including memory storage, neuromorphic vision sensors, classification, and emergency alert systems.

Mechanism, Material, Design, and Implementation Principle of Two-Dimensional Material Photodetectors

Two-dimensional (2D) materials may play an important role in future photodetectors due to their natural atom-thin body thickness, unique quantum confinement, and excellent electronic and photoelectric properties. Semimetallic graphene, semiconductor black phosphorus, and transition metal dichalcogenides possess flexible and adjustable bandgaps, which correspond to a wide interaction spectrum ranging from ultraviolet to terahertz. Nevertheless, their absorbance is relatively low, and it is difficult for a single material to cover a wide spectrum. Therefore, the combination of phototransistors based on 2D hybrid structures with other material platforms, such as quantum dots, organic materials, or plasma nanostructures, exhibit ultra-sensitive and broadband optical detection capabilities that cannot be ascribed to the individual constituents of the assembly. This article provides a comprehensive and systematic review of the recent research progress of 2D material photodetectors. First, the fundamental detection mechanism and key metrics of the 2D material photodetectors are introduced. Then, the latest developments in 2D material photodetectors are reviewed based on the strategies of photocurrent enhancement. Finally, a design and implementation principle for high-performance 2D material photodetectors is provided, together with the current challenges and future outlooks.

Plasmonic metamaterial absorbers with strong coupling effects for small pixel infrared detectors

Here we report a metal-insulator-metal (MIM) based infrared plasmonic metamaterial absorber consisting of deep subwavelength meander line nanoantennas. High absorption composed of two-hybrid modes from 11 μm to 14 μm is experimentally demonstrated with a pixel pitch of 1.47 μm corresponding to a compression ratio of 8.57. The physical mechanisms responsible for novelty spectral absorption, including the strong coupling between the plasmon resonances and the phonon vibrations, material loss from the dielectric spacer, localized surface plasmon resonance (LSPR), and Berreman mode excited by oblique incidence, have been systematically analyzed by finite-difference time-domain (FDTD) method, Fabry-Perot resonance model and two-coupled damped oscillator model. At oblique incidence, a spectral splitting related to the strong coupling between LSPR mode and Berreman mode is also observed. The distribution of local electromagnetic fields and ohmic loss are numerically investigated. Moreover, we evaluate the absorption performances with finite-sized arrays. We also show that the absorber can maintain its absorption with a 2 × 2 nanoantenna array. Such a miniaturized absorber can adapt to infrared focal plane arrays with a pixel size smaller than 5 μm, and thermal analysis is also performed. Our approach provides an effective way to minimize the antenna footprint without undermining the absorber performances, paving the way towards its integration with small pixels of infrared focal plane arrays for enhanced performances and expanded functionalities.

Artificial Intelligence of Things (AIoT) Enabled Virtual Shop Applications Using Self-Powered Sensor Enhanced Soft Robotic Manipulator

Rapid advancements of artificial intelligence of things (AIoT) technology pave the way for developing a digital-twin-based remote interactive system for advanced robotic-enabled industrial automation and virtual shopping. The embedded multifunctional perception system is urged for better interaction and user experience. To realize such a system, a smart soft robotic manipulator is presented that consists of a triboelectric nanogenerator tactile (T-TENG) and length (L-TENG) sensor, as well as a poly(vinylidene fluoride) (PVDF) pyroelectric temperature sensor. With the aid of machine learning (ML) for data processing, the fusion of the T-TENG and L-TENG sensors can realize the automatic recognition of the grasped objects with the accuracy of 97.143% for 28 different shapes of objects, while the temperature distribution can also be obtained through the pyroelectric sensor. By leveraging the IoT and artificial intelligence (AI) analytics, a digital-twin-based virtual shop is successfully implemented to provide the users with real-time feedback about the details of the product. In general, by offering a more immersive experience in human-machine interactions, the proposed remote interactive system shows the great potential of being the advanced human-machine interface for the applications of the unmanned working space.

Metamaterial perfect absorber simulations for intensifying the thermal gradient across a thermoelectric device

The thermal gradient across a thermoelectric device is the key to convert heat energy into electricity. Here, we propose a metamaterial perfect absorber (MPA) that increases the thermal gradient across a thermoelectric device by local heat generation through absorbing thermal radiation emitted from an infinite-size blackbody radiator. The MPA, when attached on top of a bismuth telluride thermoelectric device, generates local heat that propagates to the device, resulting in an additional thermal gradient. The amount of local heat generated at the MPA and the output power of the thermoelectric device loaded with the MPA are examined through numerical calculations.

Quasiperiodic metamaterials empowered non-metallic broadband optical absorbers

Realizing a polarization-insensitive broadband optical absorber plays a key role in the implementation of microstructure optoelectrical devices with on-demand functionalities. However, the challenge is that most of these devices involve the constituent metals, thus suffering from poor chemical and thermal stability and a complicated manufacturing process. In addition, the extreme contrast between the negative (metallic) and positive (dielectric) real parts of the constituent permittivities can cause additional problems in the design of structural devices. Based on these facts, this work proposes a design of planar broadband one-dimensional structure based on Fibonacci geometry. Experimental results show that the proposed planar structure exhibits high absorptivity behavior independent of polarization and angle in the wavelength range of 300-1000 nm. The absorptivity remains more than 80% when the incident angle is 60°. This proof-of-concept represents a new strategy for realizing non-metallic broadband optical absorbers with advantages of polarization-independence, low-cost, and wide-field-of-view and paves the way for light manipulation under harsh conditions.

Self-Powered Memristive Systems for Storage and Neuromorphic Computing

A neuromorphic computing chip that can imitate the human brain’s ability to process multiple types of data simultaneously could fundamentally innovate and improve the von-neumann computer architecture, which has been criticized. Memristive devices are among the best hardware units for building neuromorphic intelligence systems due to the fact that they operate at an inherent low voltage, use multi-bit storage, and are cost-effective to manufacture. However, as a passive device, the memristor cell needs external energy to operate, resulting in high power consumption and complicated circuit structure. Recently, an emerging self-powered memristive system, which mainly consists of a memristor and an electric nanogenerator, had the potential to perfectly solve the above problems. It has attracted great interest due to the advantages of its power-free operations. In this review, we give a systematic description of self-powered memristive systems from storage to neuromorphic computing. The review also proves a perspective on the application of artificial intelligence with the self-powered memristive system.

Interfering Plasmons in Coupled Nanoresonators to Boost Light Localization and SERS

Plasmonic self-assembled nanocavities are ideal platforms for extreme light localization as they deliver mode volumes of <50 nm³. Here we show that high-order plasmonic modes within additional micrometer-scale resonators surrounding each nanocavity can boost light localization to intensity enhancements >10⁵. Plasmon interference in these hybrid microresonator nanocavities produces surface-enhanced Raman scattering (SERS) signals many-fold larger than in the bare plasmonic constructs. These now allow remote access to molecules inside the ultrathin gaps, avoiding direct irradiation and thus preventing molecular damage. Combining subnanometer gaps with micrometer-scale resonators places a high computational demand on simulations, so a generalized boundary element method (BEM) solver is developed which requires 100-fold less computational resources to characterize these systems. Our results on extreme near-field enhancement open new potential for single-molecule photonic circuits, mid-infrared detectors, and remote spectroscopy.

Zero-bias mid-infrared graphene photodetectors with bulk photoresponse and calibration-free polarization detection

Bulk photovoltaic effect (BPVE), featuring polarization-dependent uniform photoresponse at zero external bias, holds potential for exceeding the Shockley-Queisser limit in the efficiency of existing opto-electronic devices. However, the implementation of BPVE has been limited to the naturally existing materials with broken inversion symmetry, such as ferroelectrics, which suffer low efficiencies. Here, we propose metasurface-mediated graphene photodetectors with cascaded polarization-sensitive photoresponse under uniform illumination, mimicking an artificial BPVE. With the assistance of non-centrosymmetric metallic nanoantennas, the hot photocarriers in graphene gain a momentum upon their excitation and form a shift current which is nonlocal and directional. Thereafter, we demonstrate zero-bias uncooled mid-infrared photodetectors with three orders higher responsivity than conventional BPVE and a noise equivalent power of 0.12 nW Hz^−1/2. Besides, we observe a vectorial photoresponse which allows us to detect the polarization angle of incident light with a single device. Our strategy opens up alternative possibilities for scalable, low-cost, multifunctional infrared photodetectors.

Here, graphene-based plasmonic metamaterials are used to generate an artificial bulk photovoltaic effect, enabling the realization of mid-infrared photodetectors with enhanced responsivity and calibration-free polarization detection at room temperature.

Electro-Optical Properties of Sputtered Calcium Lead Titanate Thin Films for Pyroelectric Detection

We report the deposition and characterization of calcium lead titanate (PCT) thin films for pyroelectric detectors. PCT films of thicknesses ranging from ~250 to 400 nm were deposited on both silicon and Si/SiN/Ti/Au substrates at 13 mTorr pressure by 200W radio frequency sputtering in an Ar + O2 environment. Substrates were kept at variable temperatures during the deposition. The PCT films were annealed at various temperatures in an O2 environment for 15 min. X-ray diffraction results confirm the polycrystalline nature of these films. Energy dispersive spectroscopy function of scanning electron microscope showed that the films are stoichiometric (Ca0.43Pb0.57) TiO3 (Ca/Ti = 0.5, Pb/Ti = 0.66). Temperature dependence of capacitance, pyroelectric current, and pyroelectric coefficient was investigated for different PCT films. Our results show that films deposited at 550 °C and 600 °C demonstrate better quality and larger values of the pyroelectric coefficient. On the other hand, the capacitance fabricated on the PCT films at 550 °C showed the highest value of pyroelectric current and pyroelectric coefficient which were 14 pA and at 30 °C was ~2 µC/m2K respectively at a higher temperature. In addition, we used density functional theory to determine the atomic and band structure, real and imaginary parts of dielectric constant and refractive index, and absorption and reflection constants with energy.

Nano-enabled sensing approaches for pathogenic bacterial detection

Infectious diseases caused by pathogenic bacteria, especially antibiotic-resistant bacteria, are one of the biggest threats to global health. To date, bacterial contamination is detected using conventional culturing techniques, which are highly dependent on expert users, limited by the processing time and on-site availability. Hence, real-time and continuous monitoring of pathogen levels is required to obtain valuable information that could assist health agencies in guiding prevention and containment of pathogen-related outbreaks. Nanotechnology-based smart sensors are opening new avenues for early and rapid detection of such pathogens at the patient's point-of-care. Nanomaterials can play an essential role in bacterial sensing owing to their unique optical, magnetic, and electrical properties. Carbon nanoparticles, metallic nanoparticles, metal oxide nanoparticles, and various types of nanocomposites are examples of smart nanomaterials that have drawn intense attention in the field of microbial detection. These approaches, together with the advent of modern technologies and coupled with machine learning and wireless communication, represent the future trend in the diagnosis of infectious diseases. This review provides an overview of the recent advancements in the successful harnessing of different nanoparticles for bacterial detection. In the beginning, we have introduced the fundamental concepts and mechanisms behind the design and strategies of the nanoparticles-based diagnostic platform. Representative research efforts are highlighted for in vitro and in vivo detection of bacteria. A comprehensive discussion is then presented to cover the most commonly adopted techniques for bacterial identification, including some seminal studies to detect bacteria at the single-cell level. Finally, we discuss the current challenges and a prospective outlook on the field, together with the recommended solutions.

Assembling Nano-Microarchitecture for Electromagnetic Absorbers and Smart Devices

Smart devices, nowadays, are inspiring the infinite vitality and possibilities of intelligent life, such as self-power electromagnetic (EM) nanogenerator and microsensor, smart window, thermally-driven EM absorber, interstellar energy deliverer, and so on. Herein, the latest and most impressive works of 3D nano-micro architectures and their smart EM devices are highly focused on. The most key information, including assembly strategy and mechanism, EM response, and approach-structure-function relationship, is extracted and well-organized with profundity and easy-to-understand approach. The merit and demerit are revealed by comparison. What's more, the brightest and most cutting-edge smart EM devices constructed by 3D nano-micro architectures are reported as highlights, and the device principles are deeply dissected. Finally, a profound and top comment on the fast-growing field as well as challenges are proposed, and the future directions are predicted intelligently.

Controlling Optically Driven Atomic Migration Using Crystal-Facet Control in Plasmonic Nanocavities

Plasmonic nanoconstructs are widely exploited to confine light for applications ranging from quantum emitters to medical imaging and biosensing. However, accessing extreme near-field confinement using the surfaces of metallic nanoparticles often induces permanent structural changes from light, even at low intensities. Here, we report a robust and simple technique to exploit crystal facets and their atomic boundaries to prevent the hopping of atoms along and between facet planes. Avoiding X-ray or electron microscopy techniques that perturb these atomic restructurings, we use elastic and inelastic light scattering to resolve the influence of crystal habit. A clear increase in stability is found for {100} facets with steep inter-facet angles, compared to multiple atomic steps and shallow facet curvature on spherical nanoparticles. Avoiding atomic hopping allows Raman scattering on molecules with low Raman cross-section while circumventing effects of charging and adatom binding, even over long measurement times. These nanoconstructs allow the optical probing of dynamic reconstruction in nanoscale surface science, photocatalysis, and molecular electronics.

Flexoelectronics of centrosymmetric semiconductors

Interface engineering by local polarization using piezoelectric^1-4, pyroelectric^5,6 and ferroelectric^7-9 effects has attracted considerable attention as a promising approach for tunable electronics/optoelectronics, human-machine interfacing and artificial intelligence. However, this approach has mainly been applied to non-centrosymmetric semiconductors, such as wurtzite-structured ZnO and GaN, limiting its practical applications. Here we demonstrate an electronic regulation mechanism, the flexoelectronics, which is applicable to any semiconductor type, expanding flexoelectricity^10-13 to conventional semiconductors such as Si, Ge and GaAs. The inner-crystal polarization potential generated by the flexoelectric field serving as a 'gate' can be used to modulate the metal-semiconductor interface Schottky barrier and further tune charge-carrier transport. We observe a giant flexoelectronic effect in bulk centrosymmetric semiconductors of Si, TiO₂ and Nb-SrTiO₃ with high strain sensitivity (>2,650), largely outperforming state-of-the-art Si-nanowire strain sensors and even piezoresistive, piezoelectric and ferroelectric nanodevices¹⁴. The effect can be used to mechanically switch the electronics in the nanoscale with fast response (<4 ms) and high resolution (~0.78 nm). This opens up the possibility of realizing strain-modulated electronics in centrosymmetric semiconductors, paving the way for local polarization field-controlled electronics and high-performance electromechanical applications.

Genetic optimization of plasmonic metamaterial absorber towards dual-band infrared imaging polarimetry

Mid-infrared imaging detectors are essential tools for many applications because they can visualize the objects in the dark via thermal radiation. However, these detectors have to pair with separate spectral and polarization filters to select the target spectral bands and polarization states, resulting in complicated and bulky imaging systems. One way to mitigate the need for separate spectral filters and polarizers is to use metamaterial absorbers, which are arrays of optical resonators with sub-wavelength dimensions and spacing, to tailor the responses of the detector pixels. Here we report an intelligent program based on the genetic algorithm that automates the design and optimization of a metal-insulator-metal based metamaterial absorber with multi-sized nanostrip antennas as the top layer. The program starts from a randomly generated pattern of the top antenna layer, and it iteratively approaches the optimized designs of two polarization selective MIM absorbers with wideband high absorption in the specified 3-5 (MWIR) band and 8-12 µm (LWIR) band. The measured absorption spectra of the two optimized designs agree well with the simulated results. The influences of the incident angle of light, the finite size of detector pixels, and the air gap between the neighboring pixels on the spectral absorption are numerically evaluated.

Tuning of polarized room-temperature thermal radiation based on nanogap plasmon resonance

When a one-dimensional (1D) metal array is coupled to a planar metal mirror with a dielectric gap, localized plasmon resonance is excited inside the gap at a specific polarization of light in free space. Herein, we report on the completely polarized, mid-infrared thermal radiation that is released from gap plasmon resonators with a nanometer-thick dielectric. We fabricated nanogap plasmon resonators with 1D Au or Ni array of various widths (w) using laser interference lithography. An atomic layer deposition process was used to introduce a 10 nm-thick alumina gap between a 1D metal array and a planar metal mirror. It was observed that only for the Au nanogap plasmon resonators, high-amplitude absorption peaks that were attributed to gap plasmon modes with different orders appeared at discrete wavelengths in a polarization-resolved spectrum. In addition, all the pronounced peaks were gradually redshifted with increasing w. At w = 1.2-1.6 µm, the fundamental gap plasmon mode was tuned to the main wavelengths (8-9 µm) of thermal radiation at room temperature (e.g., ∼300 K), which led to polarization-selective camouflage against standard infrared thermal imaging. The results of electromagnetic simulations quantitatively agreed with the measured absorbance spectra in both peak wavelength and amplitude. We believe that these experimental efforts towards achieving radiation/absorption spectra tailored at mid-infrared wavelengths will be further exploited in thermal-radiation harnessed energy devices, spectroscopic sensors, and radiative coolers.