Microsphere Arrays Research Articles

Flexible Asymmetrically Transparent Conductive Metamaterial Electrode Based on Photonic Nanojet Arrays

AbstractFlexible transparent electrodes, encompassing the combination of optical transparency and electrical conductivity, empower numerous optoelectronic applications. While the main efforts nowadays concentrate on developing wire meshes and conductive oxides, those technologies are still in a quest to find a balance between price, performance, and versatility. Here we propose a new platform, encompassing the advantages of nanophotonic design and roll‐to‐roll large‐scale lithography fabrication tools, granting an ultimate balance between optical, electrical, and mechanical properties. The design is based on an array of silica microspheres deposited on a patterned thin aluminum film attached to a flexible polymer matrix. Microspheres are designed to squeeze 80% light through nanoscale apertures with the aid of the photonic nanojet effect given the light impinges the structure from the top. The photonic structure blocks the transmission for the backpropagation direction thus granting the device with the high 5‐fold level of asymmetry. The patterned layer demonstrates a remarkable 2.8 Ω sq−1 sheet resistance comparable to that of a continuous metal layer. The high conductivity is shown to be maintained after a repeatable application of strain on the flexible electrode. Such remarkable optical, mechanical and electrical properties, makes the demonstrated device an essential component for applications, where such attributes are critically required.

Rapid fabrication of gold microsphere arrays with stable deep-pressing anisotropic conductivity for advanced packaging

Smooth metal microspheres with uniform sizes are ideal for constructing particle-arrayed anisotropic conductive films (ACF), but synthesis is hindered by challenges in controlling anisotropic metal growth. Here, we present a positioned transient-emulsion self-assembly and laser-irradiation strategy to fabricate pure gold microsphere arrays with smooth surfaces and uniform sizes. The fabrication involves assembling gold nanoparticles into uniform colloidosomes within a pre-designed microhole array, followed by rapid transformation into well-defined microspheres through laser heating. The gold nanoparticles melt and merge in a layer-by-layer manner due to the finite skin depth of the laser, leading to a localized photothermal effect. This strategy circumvents anisotropic growth, enables tunable control of microsphere size and positioning, and is compatible with conventional lithography. Importantly, these pure gold microspheres exhibit stable conductivity under deep compression, offering promising applications in soldering micro-sized chips onto integrated circuits.

Plasmonic structurally colored surfaces with metal film over microsphere lattices

Structural coloring through plasmonic nanostructures involves the manipulation of light interaction with nanostructured metallic surfaces to selectively reflect specific spectral ranges within the visible spectrum. Unlike conventional pigments that absorb light based on their chemical properties, plasmonic nanostructures achieve color through their physical configuration. This study investigates the potential of generating plasmonic structural colors by utilizing self-assembled colloidal microsphere lattices that are coated with thin metal films. Finite-Difference Time-Domain (FDTD) simulations are employed on realistic models to analyze the optical reflectance of dielectric microsphere lattices ranging in sizes from 300 to 700 nm, coated with varying thicknesses (20–200 nm) of different metals (Al, Ag, Au). The reflectance spectra are then translated into specific colors using a software algorithm, with the color representations plotted on CIE1931 diagrams. Furthermore, to validate the theoretical findings, two-dimensional polystyrene microsphere arrays coated with Au and Ag films are prepared, and their reflectance spectra and color images are examined. The resulting plasmonic colors can be adjusted by altering the sphere size, the type of metal used, and the thickness of the coating, demonstrating their potential for diverse color-based applications.

Template-Oriented-Assembly microsphere lithography for multi-type SiC microlens arrays

Silicon carbide (SiC) microlens arrays (MLAs) with a defined layout are used as an optical homogenizer in extremely high-temperature environments due to their excellent physicochemical properties. In this paper, a novel template-oriented-assembly microsphere lithography (TMSL) method is proposed to fabricate SiC MLA. Firstly, the metal micropyramid array (MPA) template was designed and fabricated by ultraprecision cutting and then converted to a polydimethylsiloxane (PDMS) surface. After that, the microspheres were assembled into a monolayer on the inverted MPA of PDMS. Subsequently, the microsphere array monolayer (MSM) was used as the stamper in the hot embossing process to create the photoresist MLA mask. Finally, the patterns on the photoresist mask were transferred to the SiC substrate by inductively coupled plasma (ICP) etching. The layout of lens units was determined by the MPA template and the positioning accuracy of MLA unit is mainly influenced by the form error in MPA mold manufacturing process. The transfer mechanism from the metal MPA template to SiC MLA was studied, and the transfer characteristics of theoretical analyses and experimental results were compared, confirming the feasibility and advantages of the TMSL method.

Triple-enhanced Raman scattering sensor based on superhydrophobic/-philic microsphere platform and heating evaporation assisted for high-sensitivity detection

The ability to detect molecules in small volumes of highly diluted solutions is crucial for applications such as food quality and safety, environmental monitoring, biomedical diagnostics, and so on. The primary concern lies in the sensitivity and efficiency of detection technology. In this work, an ultra-sensitive surface-enhanced Raman scattering (SERS) detection strategy is presented, which is based on superhydrophobic/-philic microsphere SERS (SSM-SERS) platform and heating evaporation assisted for high-sensitivity detection. Relying on the heating-assisted evaporation, the evaporation efficiency of the droplet is increased by 378.5 times, and the deposition area after evaporation is reduced by 10.4 times, leading to the extremely high detection efficiency and further enrichment of the target molecules. When the microspheres array approaches the superhydrophobic/-philic (SH/SHL) substrate, the optical-plasmonic hybrid structure is formed, enhancing light-matter interactions and resulting in an improvement of the Raman signal. The optimized SERS sensor is capable of detecting Rhodamine 6 G (R6G) at the femtomolar level (10−16 M), with a sample volume of only 5 μL and an enhancement factor of 3.29 × 109. Considering the misuse of fish drugs, malachite green (MG) and methylene blue (MB) were chosen to validate the performance of SERS sensor. These findings highlight the consistent high sensitivity of the SERS sensor, offering valuable insights for applications in food safety and related fields.

Super-resolution by converting evanescent waves in microsphere to propagating waves and light transmitted from its surface to nano-jet

The electro-magnetic (EM) waves transmitted through a thin object with fine structures is observed, by microsphere located above the thin object. The EM radiation transmitted through the object produces both evanescent waves, which include information on the fine structures of the object (smaller than a wavelength), and propagating waves which include the large image of the object (with dimensions larger than a wavelength). The super-resolutions are calculated by using Helmholtz equation. According to this equation, evanescent waves have an imaginary component of the wavevector in the z direction, leading the components of the wavevector, in the transversal directions, to becomes very large, so that the fine structures of the object can be observed. Due to the decay of the evanescent waves, only a small region near the contact point, between the thin object and the microsphere is effective for producing the super resolution effects. The image with super-resolution can be increased by a movement of the microsphere over the object, or by using arrays of microspheres. Both propagating and evanescent waves arrive at the inner surface of the microsphere. A coupling between the transmitted EM waves and resonances produced in the dielectric sphere, possibly obtained by Mie method, leads to product of the EM distribution function with the transfer function. While this transfer function might be calculated by Mie method it is possible also to use it as an experimental function. By Fourier transform of the above product we get convolution between the EM spatial modes and those of the transfer function arriving at the nano-jet, which leads the evanescent waves to become propagating waves, with effective very small wavelengths, and thus increase the resolution.

A Trilayer Structure with Surface Binary Microsphere Array for Radiative Cooling and Heating Regulation

A Trilayer Structure with Surface Binary Microsphere Array for Radiative Cooling and Heating Regulation

3D Surface-Enhanced Raman Scattering Substrate Based on an Array of Self-Assembled Au@SiO2 Microspheres

A quasi-periodic array of 3D gold-nanoparticle-capped SiO2 microspheres (Au@SiO2) was designed and prepared with a facile approach to enhance the Raman signal intensity of adsorbed biomolecules. Through adjusting the thickness and annealing of Au thin films initially deposited on arrays of self-assembled SiO2 microspheres, we were able to control the diameter of Au nanoparticles and their interparticle spacing to produce two types of plasmonic near-field hot spots, locating at the gaps of such densely arranged Au nanoparticles on individual SiO2 microspheres and in the gap regions of neighboring SiO2 microspheres, respectively. Such double near-field enhancement mechanism leads to a surface-enhanced Raman scattering (SERS) enhancement factor up to 3 × 106 for Rhodamine 6G molecules. The SERS signal intensity was highly uniform with a relative standard deviation of 4.5%. This 3D SERS substrate has significant potential for various applications in the field of SERS detection of analytes and wearable biosensing.

Silver coated PS microsphere array SERS microfluidic chip for pesticide detection

Carbendazim and acetamidine are pesticides that widely used to control pests and diseases in oilseed rape. In this paper, a rapid, accurate and reliable method was proposed for the detection of carbendazim and acetamidine with SERS microfluidic chip technology. Ag-ps(Polystyrene microspheres) microsphere SERS substrate was prepared by spin coating and magnetron sputtering deposition of Ag. The enhancement factor of prepared SERS substrate was 2.4 × 1010. The SERS detection working curves were well fitted and the linear parameters R2 were 0.987 and 0.994, respectively. The limit of detection was 0.01 mg/mL. The use of SERS microfluidic chip to detect carbendazim and acetamidine is expected to provide a way for the detection of pesticide residues in crops, which has broad application prospects in the field of food safety.

Microsphere lens array embedded microfluidic chip for SERS detection with simultaneous enhancement of sensitivity and stability

Surface enhanced Raman spectroscopy (SERS) utilizes the fingerprint features of molecular vibrations to identify and detect substances. However, in traditional single focus excitation scenarios, its signal collection efficiency of the objective is restricted. Furthermore, the uneven distribution of samples on the SERS substrate would result in poor signal stability, while the excitation power is limited to avoid sample damage. SERS detection system always requires precise adjustment of focal length and spot size, making it difficult for point-of-care testing applications. Here, we proposed a SERS microfluidic chip with barium titanate microspheres array (BTMA) embedded using vacuum self-assembled hot-pressing method for SERS detection with simultaneous enhancement of sensitivity and stability. Due to photonic nano-jets and directional antenna effects, high index microspheres are perfect micro-lens for effective light focusing and signal collecting. The BTMA can not only disperse excitation beam into an array of focal points covering the target uniformly with very low signal fluctuation, but enlarge the power threshold for higher signal intensity. We conducted a proof-of-principle experiment on chip for the detection of bacteria with immuno-magnetic tags and immuno-SERS tags. Together with magnetic and ultrasonic operations, the target bacteria in the flow were evenly congregated on the focal plane of BTMA. It demonstrated a limit of detection of 5 cells/mL, excellent signal reproducibility (error∼4.84%), and excellent position tolerance of 500 μm in X–Y plane (error∼5.375%). It can be seen that BTMA-SERS microfluidic chip can effectively solve the contradiction between sensitivity and stability in SERS detection.

Quick Response Auto‐Coding and Recognition of Mixed Vapors Via Microlaser Array Sensor

AbstractThe superior stimuli‐responsiveness, narrow linewidth, and high spectral multiplexing capacity of microlasers have led to their use as photonic tags for molecular labeling, encryption, and anticounterfeiting. However, the requirement of consistent lasing features for repeated measurements and the need for lasing features to change regularly with varying analytes pose a challenge to the efficient and convenient authentication of laser‐encoded photonic tags for practical applications. To address this challenge, an optical microsphere array is proposed that provides a set of real‐time typical lasing spectra collected from microspheres coated with specific recognition surface films of different sizes capable of recognizing one analyte or a mixture of analytes. These lasing spectra were transformed into 2D grayscale barcodes. Additionally, a gray value‐quick response code (GV‐QR code) is developed using deep learning methods, which enables the real‐time monitoring and identification of molecular concentration changes through GV‐QR autocoding, resulting in more precise, wide‐ranging, and reliable molecular detection.

Hedgehog-like NiMoSe microsphere arrays for efficient overall water splitting

We report a one-step hydrothermal method to synthesize hedgehog-like NiMoSe microsphere arrays on nickel foam (NiMoSe/NF), the morphology of which is determined by tuning the content of Ni2+ in the growth solution because Ni2+ can promote the growth of rod-like structure. Owning to the unique hedgehog-like microsphere structure composed of microrod arrays, NiMoSe/NF possesses a large catalytic active area for uploading more active sites, and is beneficial to electron transfer and gas precipitation during catalytic reactions. The synthesized NiMoSe/NF only requires an overpotential of 88 mV/190 mV to achieve a current density of 10 mA cm−2 with stability of 44 h/62 h for the hydrogen evolution reaction (HER)/oxygen evolution reaction (OER). When NiMoSe/NF is used as both the cathode and anode, the system can afford 10 mA cm−2 current density at low battery voltage of 1.50 V with a stability of 48 h. The work promotes the development of transition metal electrocatalysts for high-efficient splitting of water.

Ultra-low detection limit self-sensing nanocomposites with self-assembled conductive microsphere arrays for asphalt pavement health monitoring

Accurately monitoring micro-level strain within pavements poses a significant challenge in contemporary road engineering, limiting the effectiveness of early-stage pavement health diagnostics. Addressing this critical gap, this study introduces an innovative ultra-low detection limit sensor, specifically designed for intricate pavement health monitoring. It pivots on the unique structural design of a well-ordered 3D conductive network, where the self-assembly effect of microsphere arrays ingeniously mitigates the prevalent issue of nanofiller agglomeration within polymer matrices. The study highlights the significant role of carbon nanotubes (CNTs) length in shaping the structure of conductive networks, revealing that while longer CNTs lead to less uniform microsphere assemblies, they significantly enhance the bridging effect crucial for conductive pathways. To balance these traits, surface chemical modifications were strategically applied, effectively enhancing microsphere organization and dispersion, thereby elevating the conductive and sensing performance. The optimized sensor stands out for the ultra-low detection limit of 0.0005% (5 uε), significantly surpassing those of current strain sensors. Moreover, it exhibits remarkable sensitivity, evidenced by a gauge factor of 13.2, along with swift response and recovery times of 19 ms and 26 ms respectively, and impressive durability, enduring over 100,000 loading-unloading cycles. Field tests under diverse vehicular loads and speeds further validate the sensor's accuracy in capturing dynamic responses within pavement structures, a key factor in proactive pavement maintenance and management. Hence, this advancement shows promise in contributing to the development of safer and more resilient road networks, playing a beneficial role in the significant progress of intelligent transportation and sustainable infrastructure management.

High Sensitivity and Wide Linear Range Flexible Piezoresistive Pressure Sensor with Microspheres as Spacers for Pronunciation Recognition.

Flexible piezoresistive pressure sensors have received great popularity in flexible electronics due to their simple structure and promising applications in health monitoring and artificial intelligence. However, the contradiction between sensitivity and detection range limits the application of the sensors in the medium-pressure regime. Here, a flexible piezoresistive pressure sensor is fabricated by combining a hierarchical spinous microstructure sensitive layer and a periodic microsphere array spacer. The sensor achieves high sensitivity (39.1 kPa-1) and outstanding linearity (0.99, R2 coefficient) in a medium-pressure regime, as well as a wide range of detection (100 Pa-160.0 kPa), high detection precision (<0.63‰ full scale), and excellent durability (>5000 cycles). The mechanism of the microsphere array spacer in improving sensitivity and detection range was revealed through finite element analysis. Furthermore, the sensors have been utilized to detect muscle and joint movements, spatial pressure distributions, and throat movements during pronouncing words. By means of a full-connect artificial neural network for machine learning, the sensor's output of different pronounced words can be precisely distinguished and classified with an overall accuracy of 96.0%. Overall, the high-performance flexible pressure sensor based on a microsphere array spacer has great potential in health monitoring, human-machine interface, and artificial intelligence of medium-pressure regime.

Higher-order fractal transverse modes observed in microlasers

Two classes of higher-order, fractal spatial eigenmodes have been predicted computationally and observed experimentally in microlasers. The equatorial plane of a close-packed array of microspheres, lying on one mirror within a Fabry-Pérot resonator and immersed in the laser gain medium, acts as a refractive slit array in a plane transverse to the optical axis. Edge diffraction from the slit array generates the high spatial frequencies (&gt;104 cm−1) required for the formation of high-order laser fractal modes, and fractal transverse modes are generated, amplified, and evolve within the active medium. With a quasi-rectangular (4-microsphere) aperture, the fundamental mode and several higher-order eigenmodes (m = 2,4,5) are observed in experiments, whereas only the m = 1,2 modes are observed experimentally for the higher-loss resonators defined by triangular (3-microsphere) apertures. The fundamental and 2nd-order modes (m = 1,2) for the 4-sphere aperture are calculated to have qualitatively similar intensity profiles and nearly degenerate resonant frequencies that differ by less than &lt;0.1% of the free-spectral range (375 GHz) but exhibit even and odd parity, respectively. For all of the observed fractal modes, the fractal dimension (D) rises rapidly beyond the intracavity aperture array as a result of the high spatial frequencies introduced into the mode profile. Elsewhere, D varies gradually along the resonator axis and 2.2 &lt; D &lt; 2.5. Generating fractal laser modes in an equivalent optical waveguide is expected to allow the realization of new optical devices and imaging protocols based on the spatial frequencies and variable D values available.

Nano-Conveyor Belt on 2D Microsphere Arrays Levitated by Optical Quasi-Standing Wave

Nano-Conveyor Belt on 2D Microsphere Arrays Levitated by Optical Quasi-Standing Wave

Super-resolution imaging based on cascaded microsphere compound lenses.

In this paper, a cascaded microsphere compound lens (CMCL) is introduced, in which a 20-µm-diameter barium titanate glass (BTG) primary microsphere and a 250-nm-diameter or 200-nm-diameter polystyrene (PS) secondary microsphere array constitute CMCL1 and CMCL2, respectively. The field of view (FOV) depends on the size of the BTG microsphere, while the waist of the photon nanojet (PNJ) can be adjusted by the size of the PS microsphere. The narrower the waist of the PNJ, the higher the imaging resolution. In the experiment, a 200-nm-diameter hexagonally close-packed PS nanoparticle array is successfully observed by the CMCL with a high magnification of ∼11.6× and a FOV of ∼14µm, while the single BTG microsphere is incapable of observing the array. The point spread function is used to quantify the resolution of the CMCL. A well-designed CMCL can improve the imaging performances of a microsphere-assisted microscope.

CoSe2@ZnS microsphere arrays with remarkable electrochemical performance for hybrid asymmetric supercapacitor

This study presents a simple hydrothermal synthesis method for preparing CoSe2, ZnS, and their nanohybrid combinations (ZnS-70 % CoSe2 and ZnS-50 % CoSe2, referred to as ZC-1 and ZC-2) for the first time. These materials are intended for application in a supercapacitor (SC) and are synthesized through an ex-situ wet-chemical approach. The research thoroughly examines the electrochemical properties of as-prepared electrodes and how they relate to their structure and morphology to understand their charge storage mechanism better. The detailed characterization reveals that a one-step hydrothermal reaction obtains the cubic crystal structure of the ZnS with microsphere morphology, and the CoSe2 presents a snow crystals-like morphology with a highly smooth and transparent surface appearance. The systematic electrochemical examination declares the typical pseudocapacitive charge storage response owing to fast Faradaic redox reactions with good reversibility and rate capability. Notably, a high capacitance of CoSe2-ZnS nanohybrid (denoted as ZC-2) is realized by the synergistic effect between ZnS and CoSe2 supported by the impedance, cyclic voltammetry, and charge/discharge studies. High specific energy with a power of 46.71 Wh/kg (899.21 W/kg) and 9 Wh/kg (5400 W/kg) is realized by adding an optimal voltage and capacitance simultaneously by fabricating a hybrid asymmetric HASCs (ZC-2||AC HASC) in aqueous solution. This study believes that metal sulfide and selenide-based nanohybrids can be effective candidates for competing in the growing electrochemical energy storage demand.

High-throughput, highly sensitive and rapid SERS detection of Escherichia coli O157:H7 using aptamer-modified Au@macroporous silica magnetic photonic microsphere array.

The aim of this research was to develop a simple, rapid, sensitive, high-throughput detection method for foodborne Escherichia coli (E. coli) O157:H7 based on the aptamer-modified gold nanoparticles@macroporous magnetic silica photonic microsphere (Au@MMSPM). Such Au@MMSPM array system for E. coli O157:H7 not only integrated sample pretreatment with rapid detection, but also showed highly enhanced effect to develop a highly sensitive SERS assay. The established SERS assay platform gave a wide linear detection range (10-106 CFU/mL) and low limit of detection (2.20CFU/mL) for E. coli O157:H7. The whole analysis time including sample pretreatment and detection was 110min. This SERS-based assay platform provided a new high-throughput, highly sensitive and fast detection technology for monitoring E. coli O157:H7 in real samples from the fields of food industry, medicine and environment.

Collective-Motion-Enhanced Acceleration Sensing via an Optically Levitated Microsphere Array

Collective-Motion-Enhanced Acceleration Sensing via an Optically Levitated Microsphere Array