Microwire Arrays Research Articles

Electronic Surveillance and Security Applications of Magnetic Microwires

Applications in security and electronic surveillance require a combination of excellent magnetic softness with good mechanical and anticorrosive properties and low dimensionality. We overviewed the feasibility of using glass-coated microwires for electronic article surveillance and security applications, as well as different routes of tuning the magnetic properties of individual microwires or microwire arrays, making them quite attractive for electronic article surveillance and security applications. We provide the routes for tuning the hysteresis loops’ nonlinearity by the magnetostatic interaction between the microwires in the arrays of different types of amorphous microwires. The presence of neighboring microwire (either Fe- or Co-based) significantly affects the hysteresis loop of the whole microwires array. In a microwires array containing magnetically bistable microwires, we observed splitting of the initially rectangular hysteresis loop with a number of Barkhausen jumps correlated with the number of magnetically bistable microwires. Essentially, nonlinear and irregular hysteresis loops have been observed in mixed arrays containing Fe- and Co-rich microwires. The obtained nonlinearity in hysteresis loops allowed to increase the harmonics and tune their magnetic field dependencies. On the other hand, several routes allowing to tune the switching field by either postprocessing or modifying the magnetoelastic anisotropy have been reviewed. Nonlinear hysteresis loops have been also observed upon devitrification of amorphous microwires. Semihard magnetic microwires have been obtained by annealing of Fe–Pt–Si microwires. The observed unique combination of magnetic properties together with thin dimensions and excellent mechanical and anticorrosive properties provide excellent perspectives for the use of glass-coated microwires for security and electronic surveillance applications.

Increasing the yield and energy of high-intensity laser-produced positrons by adding microstructures

A microwire array target with added microstructures yields a near 100% increase in the laser-to-positron conversion efficiency and a 10 MeV increase in positron energy.

Enhancing positron production using front surface target structures

We report a target design which produced a substantial gain in relativistic electron-positron pair production using high-intensity lasers and targets with large-scale micro-structures on their surface. Comparing to an unstructured target, a selected Si microwire array target yielded a near 100% increase in the laser-to-positron conversion efficiency and produced a 10 MeV increase in the average emitted positron energy under nominally the same experimental conditions. We had established a multi-scale particle-in-cell simulation scheme to simulate both the laser absorption and the subsequent pair productions in a thick metal target. The experimental results are supported by the simulations demonstrating the performance increase is due to a higher conversion efficiency of laser energy into electrons with kinetic energies greater than 10 MeV due to enhanced direct laser acceleration of electrons enabled by the microwire array.

Decoding hindlimb kinematics from descending and ascending neural signals during cat locomotion

Objective. The main objective of this research is to record both sensory and motor information from the ascending and descending tracts within the spinal cord to decode the hindlimb kinematics during walking on a treadmill. Approach. Two different experimental paradigms (i.e. active and passive) were used in the current study. During active experiments, five cats were trained to walk bipedally while their hands were kept on the front frame of the treadmill for balance or to walk quadrupedally. During passive experiments, the limb was passively moved by the experimenter. Local field potential (LFP) activity was recorded using a microwire array implanted in the dorsal column (DC) and lateral column (LC) of the L3–L4 spinal segments. The amplitude and frequency components of the LFP formed the feature set, and the elastic net regularization was used to decode the hindlimb joint angles. Main results. The results show that there is no significant difference between the information content of the signals recorded from the DC and LC regions during walking on the treadmill, but the information content of the DC is significantly higher than that of the LC during passively applied movement of the hindlimb in the anesthetized cats. Moreover, the decoding performance obtained using the recorded signals from the DC is comparable with that from the LC during locomotion. However, the decoding performance obtained using the recording channels in the DC is significantly better than that obtained using the signals recorded from the LC. The long-term analysis shows that robust decoding performance can be achieved over 2–3 months without a significant decrease in performance. Significance. This work presents a promising approach to developing a natural and robust motor neuroprosthesis device using descending neural signals to execute the movement and ascending neural signals as the feedback information to control the movement.

Brilliant attosecond γ-ray emission and high-yield positron production from intense laser-irradiated nano-micro array

We investigate a novel scheme for brilliant attosecond γ-ray emission and high-yield positron production, which is accomplished with an ultra-intense laser pulse incident upon a Nano-Micro-array (NMA) with a substrate incorporated. This scheme is able to realize effectively electron acceleration and colliding geometry. Both the γ-ray flash and positron bunch are, then, generated with high conversion efficiency. At a laser intensity of 8 × 1023 W/cm2, ∼27% of the laser energy is transferred successfully into γ-rays and ∼0.7% of the laser energy into the positrons. As a consequence, ultra-short (∼440 as) and ultra-brilliant (∼1024 photons s−1 mm−2 mrad−2 per 0.1%BW at 15 MeV) γ-ray burst and high-yield (1.48 × 1011) and overdense (∼1022 cm−3) positron bunches are generated. We found a sub-linear scaling of laser-to-photon conversion efficiency (∝I00.75) and a superlinear scaling of laser-to-positron conversion efficiency (∝I02.5) with the laser intensity. Multi-dimensional particle-in-cell simulations show that particle (γ photon and positron) generation can be manipulated by the laser-focusing position and NMA's length and spacing. Optimal conditions for particle generation in NMAs are obtained, indicating that microwire arrays have the advantage over nanowire arrays in particle generation in the extreme laser fields. Furthermore, positron annihilation effects in the high-energy-density (HED) environment are discussed. The scheme using NMAs would provide effective avenues toward investigating attosecond nuclear science and HED physics with the coming 10 PW laser facilities.

High-performance UV–visible Photodetectors Based on CH3NH3PbI3-xClx/GaN Microwire Array Heterostructures

• Schematic drawing of the CH3NH3PbI3-xClx/GaN microwire array heterostructures photodetector. • Characterization of the CH3NH3PbI3-xClx/GaN microwire array photodetector. • Photoelectric performance compared to the hybrid three types of photodetectors from ultraviolet to visible light region. • I-V curves with or without perovskite layer measured in the dark and under 325 nm light irradiation. • The mechanism to improve the performance of heterostructure photodetector was discussed In recent years, the combination of perovskites with other materials to improve the photoelectric performance has received widespread attention. In this work, we demonstrate a hybrid heterostructure photodetector with the combination of GaN microwire array and perovskite. Compared to perovskite and GaN microwire array photodetectors, the hybrid CH 3 NH 3 PbI 3- x Cl x /GaN microwire array photodetector exhibits more excellent photoelectric performances in a wide detection range from ultraviolet to visible. Under 325 nm laser irradiation, the hybrid photodetector generates a large photocurrent (1.04 ×10 -5 A), a high on/off ratio (>10 4 ), a fast response time (raise time of 0.66 ms and decay time of 0.71 ms), and higher responsivity , detectivity. Meanwhile, when the perovskite is combined with the GaN microwire array, the device also has a higher photocurrent, on/off ratio, and faster photoresponse compared with the perovskite photodetector in the visible light region. This is interpreted as the effective separation photogenerated carriers at the hetero-interface, and the directional transfer of carriers within the one-dimensional GaN microwire array. This study sheds light on fabricating high-performance heterostructures photodetectors.

Primary Corrosion Processes for Polymer-Embedded Free-Standing or Substrate-Supported Silicon Microwire Arrays in Aqueous Alkaline Electrolytes

Solar fuel devices have shown promise as a sustainable source of chemical fuels. However, long-term stability of light absorbing materials remains a substantial barrier to practical devices. Herein, multiple corrosion pathways in 1 M KOH(aq) have been defined for TiO2-protected Si microwire arrays in a polymer membrane either attached to a substrate or free-standing. Top-down corrosion was observed in both morphologies through defects in the TiO2 coating. For the substrate-based samples, bottom-up corrosion was observed through the substrate and up the adjacent wires. In the free-standing samples, uniform bottom-up corrosion was observed through the membrane with all wire material corroded within 10 days of immersion in the dark in 1 M KOH(aq).

Optical and electrochemical effects of H2 and O2 bubbles at upward-facing Si photoelectrodes

Planar silicon and silicon microwire arrays oriented towards sunlight release layers of small gas bubbles that stir the electrolyte and do not impede photoelectrochemical water splitting.

Hybrid organolead halide perovskite microwire arrays/single CdSe nanobelt for a high-performance photodetector

The hybrid approach by combining organic–inorganic halide perovskite with semiconductor materials is considered as an effective route in improving photosensitivity and broader spectral response of the photodetector. Here, a photodetector based on hybrid organolead halide perovskite microwire arrays (CH3NH3PbI3 MAs)/single Cadmium Selenide nanobelt (CdSe NB) has been successfully fabricated and characterized for the first time by one-step methods combining thermal evaporation. The hybrid structure can promote the effective separation of the generated electron-hole pairs in photoluminescence and thus exhibits an amazing optoelectric performance. The photo-to-dark current ratio is as high as 2.152 × 103, the responsivity, external quantum efficiency and photodetectivity are 69.11A/W, 11000% and 8.6 × 1012 Jones, respectively. Besides, the rise and decay time of the device are 0.81 ms and 0.77 ms, respectively. The excellent optoelectronic properties compared to those of other CH3NH3PbI3/semiconductor hybrids indicate CH3NH3PbI3 MAs/single CdSe NB hybrids are promising building blocks for optoelectronic applications.

Capillary-Bridge Controlled Patterning of Stable Double-Perovskite Microwire Arrays for Non-toxic Photodetectors.

Single-crystalline lead halide perovskites with remarkable physical properties offer great potential in integrated optoelectronic applications but are restricted by their instability and toxicity. To address these problems, various strategies including lead-free halide double perovskites with high stabilities of heat, light, and moisture have been developed. However, it still requires an efficient method to pattern single-crystalline, double-perovskite micro-/nanostructures with strict alignment and ordered orientation for the integration of optoelectronic devices. Here, our solution-processing approach employs capillary bridges to control the dewetting dynamics and confine the crystallization in the assembly of non-toxic Cs2AgBiBr6 microwire arrays. We demonstrate the strict alignment, high crystallinity, eliminated grain boundary, and ordered orientation of these as-prepared single-crystalline, double-perovskite microwire arrays. Based on these high-quality microwire arrays, we fabricate high-performance photodetectors with a responsivity of 1,625 A W−1, on/off ratio of 104, and fast response speed of τdecay = 0.04 ms and τrise = 0.28 ms. The long-term crystallographic and spectroscopic stability of Cs2AgBiBr6 microwire arrays has also been demonstrated through the 1 month exposure to air conditioning. Our strategy provides a new perception to fabricate stable perovskite microarrays for the integration of non-toxic optoelectronic devices.

CHIME: CMOS-Hosted in vivo Microelectrodes for Massively Scalable Neuronal Recordings.

Mammalian brains consist of 10s of millions to 100s of billions of neurons operating at millisecond time scales, of which current recording techniques only capture a tiny fraction. Recording techniques capable of sampling neural activity at high spatiotemporal resolution have been difficult to scale. The most intensively studied mammalian neuronal networks, such as the neocortex, show a layered architecture, where the optimal recording technology samples densely over large areas. However, the need for application-specific designs as well as the mismatch between the three-dimensional architecture of the brain and largely two-dimensional microfabrication techniques profoundly limits both neurophysiological research and neural prosthetics. Here, we discuss a novel strategy for scalable neuronal recording by combining bundles of glass-ensheathed microwires with large-scale amplifier arrays derived from high-density CMOS in vitro MEA systems or high-speed infrared cameras. High signal-to-noise ratio (<25 μV RMS noise floor, SNR up to 25) is achieved due to the high conductivity of core metals in glass-ensheathed microwires allowing for ultrathin metal cores (down to <1 μm) and negligible stray capacitance. Multi-step electrochemical modification of the tip enables ultra-low access impedance with minimal geometric area, which is largely independent of the core diameter. We show that the microwire size can be reduced to virtually eliminate damage to the blood-brain-barrier upon insertion and we demonstrate that microwire arrays can stably record single-unit activity. Combining microwire bundles and CMOS arrays allows for a highly scalable neuronal recording approach, linking the progress in electrical neuronal recordings to the rapid progress in silicon microfabrication. The modular design of the system allows for custom arrangement of recording sites. Our approach of employing bundles of minimally invasive, highly insulated and functionalized microwires to extend a two-dimensional CMOS architecture into the 3rd dimension can be translated to other CMOS arrays, such as electrical stimulation devices.

Si Microwire-Array Photocathodes Decorated with Cu Allow CO2 Reduction with Minimal Parasitic Absorption of Sunlight

High loadings of Cu were integrated on the light-facing side of Si microwire arrays used under simulated sunlight for the photoelectrochemical reduction of CO2(aq) to hydrocarbons in 0.10 M KHCO3(a...

Perovskite Single‐Crystal Microwire‐Array Photodetectors with Performance Stability beyond 1 Year

Compared with thin-film morphology, 1D perovskite structures such as micro/nanowires with fewer grain boundaries and lower defect density are very suitable for high-performance photodetectors with higher stability. Although the stability of perovskite microwire-based photodetectors has been substantially enhanced in comparison with that of photodetectors based on thin-film morphology, practical applications require further improvements to the stability before implementation. In this study, a template-assisted method is developed to prepare methylammonium lead bromide (MAPbBr3 ) micro/nanowire structures, which are encapsulated in situ by a protective hydrophobic molecular layer. The combination of the protective layer, high crystalline quality, and highly ordered microstructures significantly improve the stability of the MAPbBr3 single-crystal microwire arrays. Consequently, these MAPbBr3 single-crystal microwire-array-based photodetectors exhibit significant long-term stability, maintaining 96% of the initial photocurrent after 1 year without further encapsulation. The lifetime of such photodetectors is hence approximately four times longer than that of the most stable previously reported perovskite micro/nanowire-based photodetector; this is thought to be the most stable perovskite photodetector reported thus far. Furthermore, this work should contribute further toward the realization of perovskite 1D structures with long-term stability.

Massively parallel microwire arrays integrated with CMOS chips for neural recording.

Multi-channel electrical recordings of neural activity in the brain is an increasingly powerful method revealing new aspects of neural communication, computation, and prosthetics. However, while planar silicon-based CMOS devices in conventional electronics scale rapidly, neural interface devices have not kept pace. Here, we present a new strategy to interface silicon-based chips with three-dimensional microwire arrays, providing the link between rapidly-developing electronics and high density neural interfaces. The system consists of a bundle of microwires mated to large-scale microelectrode arrays, such as camera chips. This system has excellent recording performance, demonstrated via single unit and local-field potential recordings in isolated retina and in the motor cortex or striatum of awake moving mice. The modular design enables a variety of microwire types and sizes to be integrated with different types of pixel arrays, connecting the rapid progress of commercial multiplexing, digitisation and data acquisition hardware together with a three-dimensional neural interface.

Electricity-powered artificial root nodule

Root nodules are agricultural-important symbiotic plant-microbe composites in which microorganisms receive energy from plants and reduce dinitrogen (N2) into fertilizers. Mimicking root nodules using artificial devices can enable renewable energy-driven fertilizer production. This task is challenging due to the necessity of a microscopic dioxygen (O2) concentration gradient, which reconciles anaerobic N2 fixation with O2-rich atmosphere. Here we report our designed electricity-powered biological|inorganic hybrid system that possesses the function of root nodules. We construct silicon-based microwire array electrodes and replicate the O2 gradient of root nodules in the array. The wire array compatibly accommodates N2-fixing symbiotic bacteria, which receive energy and reducing equivalents from inorganic catalysts on microwires, and fix N2 in the air into biomass and free ammonia. A N2 reduction rate up to 6.5 mg N2 per gram dry biomass per hour is observed in the device, about two orders of magnitude higher than the natural counterparts.

Wearable and Ultrasensitive Strain Sensor Based on High-Quality GaN pn Junction Microwire Arrays.

With the rapid growth in wearable electronics sensing devices, flexible sensing devices that monitor the human body have shown great promise in personalized healthcare. In the study, high-quality GaN pn junction microwire arrays with different aspect ratios and large-area uniformity are fabricated through an easy, repeatable fabrication process. The piezoelectric coefficient (d33 ) of GaN pn junction microwire arrays increases from 7.23 to 14.46 pm V-1 with the increasing of the aspect ratio, which is several times higher than that of GaN bulk material. Furthermore, flexible ultrasensitive strain sensor based on GaN microwires with the highest d33 is demonstrated to achieve the maximum open circuit voltage of 10.4 V, and presents excellent durability with stable output signals over 10 000 cycles with a response time of 50 ms. As a flexible and wearable sensor attached to the human skin, the GaN microwire pn junction arrays with such a high degree of uniformity can precisely monitor subtle human pulse and motions, which show great promise in future personalized healthcare.

Design and X-Band electromagnetic response of single negative metacomposite containing periodic curved Co-based ferromagnetic microwires

Metamaterials possess attractive electromagnetically left-handed properties yet their nature as an artificial structure rather than a material restricts their further applications. In this article we propose to use Co-based ferromagnetic microwires as periodical metamaterial units interweaved into a fabric to realize a “metacomposite” for steering wave propagation. By introducing ferromagnetic microwires in quartz fabric at three curvatures and periodic lengths, the electromagnetic response and microwave behaviors on both horizontally- and vertically-arranged directions were presented and investigated. Tensile behaviors of metacomposites with different ferromagnetic microwire morphologies were monitored by non-contact full field strain measurement system. At X band (8.2–12.4 GHz), metacomposites containing vertically-arranged ferromagnetic microwires show negative permittivity due to the dielectric resonance of microwire arrays. The dielectric response of metacomposites conformed to Lorentz-oscillator mode, behaving similarly to diluted plasma. When ferromagnetic microwires reached the lowest periodic curved length 2.5 mm with the highest curvature was obtained, the metacomposites presented the maximum microwave absorption of 34% and tensile stress of 273 MPa. The incorporation of ferromagnetic microwires exerts trivial influence on the mechanical properties yet homogenizes the strain and reduces the stress concentration on metacomposites. The metacomposite with a periodic curved length of 7.5 mm has less interweaving points and the highest surface float length, therefore achieving the maximum tensile strength of 458 MPa. The single negative metacomposites containing ferromagnetic microwires are featured with excellent structural properties and amenable microwave left-handed properties in controlling wave-propagating behavior, which is of practical engineering significance in structural health monitoring, sensing and stealth applications.

Force decoding using local field potentials in primary motor cortex: PLS or Kalman filter regression?

The development of brain-computer interface (BCI) systems is an important approach in brain studies. Control of communication devices and prostheses in real-world scenarios requires complex movement parameters. Decoding a variety of neural signals captured by micro-wire arrays is a potential applicant for extracting movement-related information. The present work was conducted to compare the functionality of partial least square (PLS) regression and Kalman filter to predict the force parameter from local field potential (LFP) signals of the primary motor cortex (M1). The signals were recorded using a 16-channel micro-wire array from the forelimb-related area of the M1 of three rats performing a behavioral task in which the force signal of the rat's forelimb paw was generated. Our results show that PLS regression and Kalman filters with the mean performance of 0.75 and 0.72 in terms of the correlation coefficient (CC) and 0.37 and 0.48 in terms of normalized mean square error (NMSE), respectively, are effective methods for decoding the force parameter from LFPs. Kalman filter underperforms PLS both in performance and speed. Although adding nonlinearity to the Kalman filter results in equally accurate CC performance as PLS, it has even more computational cost. Therefore, it is inferred that nonlinear methods do not necessarily have better functionality than linear ones and PLS, as a simple fast linear method could be an effectively applicable regression technique for BCIs.

Transparent, flexible MAPbI3 perovskite microwire arrays passivated with ultra-hydrophobic supramolecular self-assembly for stable and high-performance photodetectors.

The emergence of organic-inorganic hybrid perovskites (OHPs) has revolutionised the potential performance of optoelectronic devices; most perovskites are opaque and hence incompatible with transparent optoelectronics and sensitive to environmental degradation. Here, we have reported a single-step fabrication of ultra-long MAPbI3 perovskite microwire arrays over a large area using stencil lithography based on sequential vacuum sublimation. The environmental stability of MAPbI3 is empowered with a newly designed and synthesized transparent supramolecular self-assembly based on a mixture of two tripodal l-Phe-C11H23/C7F15 molecules, which showed a contact angle of 105° and served as ultra-hydrophobic passivation layers for more than 45 days in an ambient atmosphere. The MAPbI3 microwire arrays passivated with the supramolecular self-assembly demonstrated for the first time both excellent transparency of ∼89% at 550 nm and a remarkable photoresponse with a photo-switching ratio of ∼104, responsivity of 789 A W-1, detectivity of 1014 Jones, linear dynamic range of ∼122 dB, and rise time of 432 μs. Furthermore, the photodetector fabricated on a flexible PET substrate demonstrated robust mechanical flexibility even beyond 1200 bending cycles. Therefore, the scalable stencil lithography and supramolecular passivation approaches have the potential to deliver next-generation transparent, flexible, and stable optoelectronic devices.

Ferromagnetic Microwire Systems as a High-Gradient Magnetic Field Source for Magnetophoresis

The use of amorphous ferromagnetic microwires has potential for applications in biomedicine and biophysics. Microwire arrays create magnetic fields that are characterized by strong spatial gradients. A system of ferromagnetic microwires with magnetizations across the diameter may efficiently accumulate paramagnetic particles along the wire due to forced diffusion. For typical system parameters, the particles concentration at the wire surface increases more than twice for a characteristic time of 30 s. A pair of closely spaced microwires with diametric magnetizations (referred to as a dipole pair) yields a unique potential landscape with a two-dimensional minimum. The possibility of levitation of diamagnetic particles just above the dipole pair array was numerically demonstrated.