Microwire Arrays Research Articles

Template-assisted fabrication of PVK microwire arrays for high-performance flexible photodetectors

The development of flexible photodetectors is crucial for advancing wearable electronics and optoelectronic systems, but it faces significant challenges, such as maintaining high performance under mechanical strain and achieving cost-effective fabrication. Here, we fabricated a photodetector using poly(N-vinylcarbazole) (PVK) microwire arrays through a template-assisted method. The resulting devices exhibit high responsivity and exceptional mechanical flexibility, with the ability to maintain their photoelectric properties even when bent up to 150°. The photodetector exhibits high responsivity of 0.9 A W−1 and detectivity of 1.6 × 1010 Jones. This study demonstrates the potential of PVK microwire arrays for imaging applications, highlighting their suitability for integration into flexible and wearable devices.

Enhanced UV photodetection in SnO2 microwire arrays (MWAs) thin films by γ-ray irradiation

In this study, the gamma ray irradiation-induced photoelectric responses of SnO2 microwire arrays (MWAs) UV photodetectors were investigated and compared with the unirradiated state. The corresponding surface morphology, crystal structure, and XPS spectrum were analyzed. Results indicated that low doses (≤500krad) of gamma ray irradiation led to enhanced photocurrent and responsivity, whereas high doses resulted in significant degradation of the photoelectric response. At a radiation dose of 300krad, a photocurrent of 264 μA and a responsivity of 1.83 A/W were realized under 365 nm UV light illumination at a bias voltage of 5 V. These values represent an increase of 34.6 % and 44.1 %, respectively, compared with the unirradiated sample. Surprisingly, the fabricated SnO2 MWAs UV photodetectors demonstrated resilience to gamma ray irradiation doses up to 500krad, which is equivalent to the radiation dose accumulated by satellites in low-Earth orbit over 20 years. Our findings suggested that the fabricated SnO2 microwire arrays (MWAs) UV detector has the potential to be used for long-term space missions.

Crystalline Silicon Photocathode with Tapered Microwire Arrays Achieving a High Current Density of 41.7 mA cm⁻2

AbstractTo design a high‐efficiency crystalline silicon (c‐Si) photocathode, the photovoltage and photocurrent generated by the device must be maximized because these factors directly affect the hydrogen evolution reaction (HER). In this study, a c‐Si p–n junction is used to enhance the photovoltage of the c‐Si photocathode, and a tapered microwire array structure is introduced to increase the photocurrent. When tapered microwire arrays are employed on the front surface of the c‐Si photocathode, a current density of ≈41.7 mA cm−2 is achieved at 0 VRHE (reversible hydrogen electrode); this current density is the highest among all reported photocathodes including c‐Si, approaching the theoretical maximum value for c‐Si. Furthermore, a Ni foil/Pt catalyst is introduced on the opposite side of the incident light, simultaneously serving as an electrocatalyst to reduce side reactions in the HER and encapsulation layer to prevent c‐Si from contacting the electrolyte. Thus, a stable device is developed using c‐Si photoelectrochemical cells that have an efficiency exceeding 97% for >1000 h.

Electrode sharpness and insertion speed reduce tissue damage near high-density penetrating arrays

Objective. Over the past decade, neural electrodes have played a crucial role in bridging biological tissues with electronic and robotic devices. This study focuses on evaluating the optimal tip profile and insertion speed for effectively implanting Paradromics’ high-density fine microwire arrays (FμA) prototypes into the primary visual cortex (V1) of mice and rats, addressing the challenges associated with the ‘bed-of-nails’ effect and tissue dimpling. Approach. Tissue response was assessed by investigating the impact of electrodes on the blood-brain barrier (BBB) and cellular damage, with a specific emphasis on tailored insertion strategies to minimize tissue disruption during electrode implantation. Main results. Electro-sharpened arrays demonstrated a marked reduction in cellular damage within 50 μm of the electrode tip compared to blunt and angled arrays. Histological analysis revealed that slow insertion speeds led to greater BBB compromise than fast and pneumatic methods. Successful single-unit recordings validated the efficacy of the optimized electro-sharpened arrays in capturing neural activity. Significance. These findings underscore the critical role of tailored insertion strategies in minimizing tissue damage during electrode implantation, highlighting the suitability of electro-sharpened arrays for long-term implant applications. This research contributes to a deeper understanding of the complexities associated with high-channel-count microelectrode array implantation, emphasizing the importance of meticulous assessment and optimization of key parameters for effective integration and minimal tissue disruption. By elucidating the interplay between insertion parameters and tissue response, our study lays a strong foundation for the development of advanced implantable devices with a reduction in reactive gliosis and improved performance in neural recording applications.

Air-Stable Self-Driven UV Photodetectors on Controllable Lead-Free CsCu2I3 Microwire Arrays.

The rapid evolution of the Internet of Things has engendered increased requirements for low-cost, self-powered UV photodetectors. Herein, high-performance self-driven UV photodetectors are fabricated by designing asymmetric metal-semiconductor-metal structures on the high-quality large-area CsCu2I3 microwire arrays. The asymmetrical depletion region doubles the photocurrent and response speed compared to the symmetric structure device, leading to a high responsivity of 233 mA/W to 355 nm radiation. Notably, at 0 V bias, the asymmetric device produces an open-circuit voltage of 356 mV and drives to a short-circuit current of 372 pA; meanwhile, the switch ratio (Iph/Idark) reaches up to 103, indicating its excellent potential for detecting weak light. Furthermore, the device maintains stable responses throughout 10000 UV-light switch cycles, with negligible degradation even after 90-day storage in air. Our work establishes that CsCu2I3 is a good candidate for self-powered UV detection and thoroughly demonstrates its potential as a passive device.

Interface‐Confined Assembly of Layered Molecular Crystal Arrays Toward Wearable UV‐Radiation Monitor

AbstractOrganic semiconductors have significant potential for wearable optoelectronics due to their designable molecular structures, tunable photoelectronic properties, and flexibility. For their integration into optoelectronic devices, organic semiconductors need to be assembled into single‐crystalline arrays with both precise alignment of micro‐/nanostructures and long‐range order of molecules. In this study, an interface‐confined lithography technique is developed for fabricating organic single‐crystalline microwire arrays with layered molecular stacking and ordered crystallographic orientation toward wearable UV radiation monitor. This interface‐confined strategy introduces parallel gas–liquid–solid three‐phase contact line (TPCL) arrays to suppress the lateral growth of single crystals. Meanwhile, TPCLs with controlled dewetting direction promote longitudinal growth, thus universally yielding 1D arrays based on various organic semiconducting small molecules. These 1D single‐crystalline arrays exhibit high average mobility of 12.5 cm2 V−1 s−1 with uniform electronic properties of 9.3% variation, and good mechanical stability after 1000 bending times. Based on organic 1D arrays, wearable devices with robust photoresponsivity of 8.26 × 103 A W−1 and high mechanical flexibility achieve real‐time monitoring of UV radiation to prevent skin disease. This confined‐assembly strategy opens a new avenue to construct wearable optoelectronic devices for health monitoring.

High‐Performance Organic Phototransistors Based on Single‐Crystalline Microwire Arrays

AbstractHigh‐performance organic phototransistors (OPTs) have attracted considerable attention owing to their high photoresponse and low‐cost solution‐processing manufacturing. To meet the increasing demand for integrated optoelectronic circuits, organic single‐crystalline micro‐/nanowire arrays for OPTs construction are prominently anticipated. However, the manufacturing and patterning of organic single‐crystalline arrays have hit a bottleneck due to the uncontrollable dewetting dynamics. In this work, a capillary‐bridge lithography strategy is proposed to guide ordered nucleation and unidirectional dewetting of microfluid, thus enabling the large‐scale preparation of highly aligned organic single‐crystalline microwire arrays. Taking advantage of efficient carrier transport, a competitive average field‐effect hole mobility (μ) of 6.64 cm2 V−1 s−1 is obtained, and the high‐throughput one‐dimensional (1D) arrays based OPTs also exhibit excellent optoelectrical performance with photosensitivity (P) of 1.36 × 106, responsivity (R) of 3.18 × 104 A W−1, and specific detectivity (D*) of 9.22 × 1014 Jones. This work provides a guide for the designing and patterning of high‐throughput OPTs toward multifunctional integrated optoelectronics.

Microwire-based multifunctional microsensors for high-performance humidity and strain sensing

In this post-Moore era, on-chip components have transitioned into the “more Moore” and “more than Moore” technology routes. Serving as the foundational point and data source for all intelligent devices, sensors are undergoing development for multifunctionality, systematization, and integration. However, the current micro/nano multifunctional sensor fabrication technology is not sufficiently advanced to meet the requirements of practical applications. In this study, we prepared high-precision microwire arrays as multifunctional microsensors. This microsensor exhibited a highly sensitive response to humidity and bending strain. It has a sensitivity of up to 8520% and response time as low as 0.9/3.5 s (response/recovery) over a wide range of humidity variations from 23% to 97%. In the bending strain range of −0.4–0.4%, the microsensor exhibits a gauge factor of up to 267. This multifunctional microsensor has the potential for use in integrated intelligent devices.

Flexible, self-powered, and polarization-sensitive photodetector based on perovskite lateral heterojunction microwire arrays

The fabrication of different perovskite materials with superior properties into lateral heterostructures can greatly improve device performance and polarization sensitivity. However, the sensitivity of perovskites to solvents and environmental factors makes the fabrication of lateral heterojunctions difficult. Here, we realize high-quality perovskite microwire crystal heterojunction arrays using regioselective ion exchange. Photodetectors with responsivity and detectivity up to 748 A W−1 and 8.2×1012 Jones are fabricated. The photodetector exhibits responsivity as high as 13.5 A W−1 at 0 V bias. In addition, the device exhibits ultra-high polarization sensitivity with a dichroic ratio of 5.6, and 81% of its performance was maintained after 144 days of exposure to air.

Laser Microengineering in SnO2 microwire array films for high performance ultraviolet photodetectors

Tin oxide (SnO2) has emerged as promising applications in ultraviolet photodetectors (UV PDs) due to its prominent photoelectronic properties. However, the slow photoresponse of UV PDs based on SnO2 films limits the application. In this work, the absorbing intermediate layer-assisted femtosecond (fs) laser microprocessing technology is employed to engineer the SnO2 microwire arrays (MWAs) thin film. The obtained UV PDs based on SnO2 MWA films exhibit enhanced responsivity and ultrafast response in the UV region. Under light irradiation with a wavelength of 365 nm, the optimized responsivity and rising/decaying time reach 1.62 A/W and 0.89/2.3 ms with the bias voltage of 5 V. The results demonstrate that the SnO2 MWA film can serve as a high-performance photodetector in the UV region.

Conductive Polyaniline-Based Microwire Arrays for SO2 Gas Detection.

Polyaniline-based conductive polymers are promising electrochemical sensor materials due to their unique physical and chemical properties, such as good gas absorption, low dielectric loss, and chemical and thermal stabilities. The sensing performance is highly dependent on the structure and dimensions of the polyaniline-based conductive polymers. Although in situ oxidative polymerization combined with the self-assembly process has become one of the main processes for the preparation of flexible polyaniline-based gas sensors, how to prepare polyaniline materials into uniformly arranged microwire arrays is still an urgent problem. In this paper, an in-depth study was conducted on the preparation of polyaniline microwire arrays by combining a wettability interface dewetting process and a liquid-film-induced capillary bridges method. The factors influencing the preparation of polyaniline microwire arrays, including solution concentration, template width, evaporation temperature, and evaporation time, were investigated in detail. The wire formation rates were recorded from the results of SEM images. 100% microwires formation rate can be obtained by using a 1.0 mg mL-1 concentration of polyaniline solution and a 10 μm silicon template at an evaporation temperature of 80 °C for 18 h. The prepared microwire arrays can realize sulfur dioxide sensing at room temperature with a response speed of about 20 s and can detect sulfur dioxide gas as low as 1 ppm. Thus, the liquid-film-induced capillary bridge method shows a new possibility to prepare gas sensor devices for insoluble polymers.

Acquired alterations in nucleus accumbens responsiveness to a cocaine-paired discriminative stimulus preceding rats’ daily cocaine consumption

Resumption of drug taking is a primary focus for substance use disorder research and can be triggered by drug-associated environmental stimuli. The Nucleus Accumbens (NAc) is a key brain region which guides motivated behavior and is implicated in resumption. Yet, there remains a pressing need to characterize NAc neurons’ responsiveness to drug associated stimuli during withdrawal and abstinence. We recorded discriminative stimulus (DS) induced NAc activity via in vivo single-unit electrophysiology in rats that self-administered cocaine. Male and female rats implanted with a jugular catheter and a microwire array in NAc Core and Shell self-administered cocaine under control of a 30s auditory DS for 6 hours per session across 14 consecutive days. Rats acquired tone discrimination within 4 sessions. To exclude pharmacological effects of circulating cocaine from all neuronal analyses, we studied changes in DS-induced firing only for trials preceding the first infusion of cocaine in each of the 14 sessions, which were defined as “pre-drug trials.” NAc neuron responses were assessed prior to tone-evoked movement onset. Responsiveness to the DS tone was exhibited throughout all sessions by the NAc Core population, but only during Early sessions by the NAc Shell population. Both Core and Shell responded selectively to the DS, i.e., more strongly on drug taking trials, or Hits, than on Missed opportunities. These findings suggest that NAc Core and Shell play distinct roles in initiating cocaine seeking prior to daily cocaine consumption, and align with reports suggesting that as drug use becomes chronic, cue-evoked activity shifts from NAc Shell to NAc Core.

Enhanced laser-driven backward proton acceleration using micro-wire array targets

Micro-structured targets can be employed to enhance the coupling of laser energy to the high energy density plasma. Here we report on experimental measurement of enhanced proton beam energy from laser-driven micro-wire array (MWA) targets along the backward direction. An ultra-intense (∼2×1020W/cm2) laser pulse of ∼ 40 fs pulse duration interacts with the MWA structure and induces large population of energetic electrons. The enhanced sheath field efficiently accelerates protons both transversely and longitudinally. The spectrometers record proton cut-off energy of around 16 MeV and temperature 813keV along the backward direction, which is 20%−60% higher than that of a flat target under commensurate laser conditions. Comparison with particle-in-cell simulations suggests that the enhancement originates from the increased temperature and population of the hot electrons within the micro-wires. These measurements provide a direct probe of the high energy density plasma condition in laser-driven solid targets and a useful benchmark for further studies on laser-driven micro-structured targets.

Optogenetic stimulation of the superior colliculus suppresses genetic absence seizures.

While anti-seizure medications are effective for many patients, nearly one-third of individuals have seizures that are refractory to pharmacotherapy. Prior studies using evoked preclinical seizure models have shown that pharmacological activation or excitatory optogenetic stimulation of the deep and intermediate layers of the superior colliculus (DLSC) display multi-potent anti-seizure effects. Here we monitored and modulated DLSC activity to suppress spontaneous seizures in the WAG/Rij genetic model of absence epilepsy. Female and male WAG/Rij adult rats were employed as study subjects. For electrophysiology studies, we recorded single unit activity from microwire arrays placed within the DLSC. For optogenetic experiments, animals were injected with virus coding for channelrhodopsin-2 or a control vector, and we compared the efficacy of continuous neuromodulation to that of closed-loop neuromodulation paradigms. For each, we compared three stimulation frequencies on a within-subject basis (5, 20, 100 Hz). For closed-loop stimulation, we detected seizures in real time based on the EEG power within the characteristic frequency band of spike-and-wave discharges (SWDs). We quantified the number and duration of each SWD during each 2 h-observation period. Following completion of the experiment, virus expression and fibre-optic placement was confirmed. We found that single-unit activity within the DLSC decreased seconds prior to SWD onset and increased during and after seizures. Nearly 40% of neurons displayed suppression of firing in response to the start of SWDs. Continuous optogenetic stimulation of the DLSC (at each of the three frequencies) resulted in a significant reduction of SWDs in males and was without effect in females. In contrast, closed-loop neuromodulation was effective in both females and males at all three frequencies. These data demonstrate that activity within the DLSC is suppressed prior to SWD onset, increases at SWD onset, and that excitatory optogenetic stimulation of the DLSC exerts anti-seizure effects against absence seizures. The striking difference between open- and closed-loop neuromodulation approaches underscores the importance of the stimulation paradigm in determining therapeutic effects.

Selective Surface Engineering of Perovskite Microwire Arrays

AbstractThe surface of low‐dimensional perovskites play a crucial role in determining their intrinsic property. Understanding their characteristics and the influence of certain surfaces is valuable in designing functional surface‐engineered structures. Meanwhile, surface passivation can also be applied to stabilize and optimize the state‐of‐the‐art perovskite‐based optoelectronics. Herein, cesium lead bromide (CsPbBr3) microwire parallel arrays are designed and fabricated with specific (100)‐terminated crystal planes, which exhibit excellent photodetection performance with long‐term environment stability >3000 h. Notably, it is uncovered experimentally and theoretically that environmental oxygen can not only passivate the Br‐vacancy‐related trap states on the (100) surface, but also create charge carrier nanochannels to enhance the (opto)electronic properties. The coupling effects between oxygen species and the specific terminated crystal planes of perovskites highlight the importance of surface engineering for designing and optimizing perovskite‐based devices.

Improvement of electron mobility of mesoporous PCN-600 single crystal microwires aligned via the steric hindrance effect

One of mesoporous iron-based porphyrin metal-organic framework (MOF) materials, namely, PCN-600 exhibits one-dimensional channels, and features high stability in acid-base solutions and very high pore volume. It would be potentially applied in catalysis, lithium storage, solar cells, etc. However, when this material is prepared as a thin film, the thin film is usually un-oriented and its electron mobility is not strong enough. In this work, needle-like mesoporous PCN-600 single crystal microwires are first prepared via the solvothermal method with optimized synthesis procedure. Then, the acetone molecules adsorbed on the surface of adjacent PCN-600 microwires undergo the aldol condensation reaction under the catalysis of hydrochloric acid, and 4-hydroxy-4-methyl-pentanone-2 molecules are synthesized between adjacent PCN-600 microwires. Via the steric hindrance effect induced by 4-hydroxy-4-methylpentanone-2, the PCN-600 microwires are aligned to construct an array. Finally, the PCN-600 microwire array is transferred to an ITO substrate by a dipping method to form an oriented PCN-600 thin film. To demonstrate the feasibility of this oriented PCN-600 thin film applied in solar cells, its electron mobility is measured to be 117 ​cm2/Vs, which is twice that of poorly oriented film.

Enhanced polarized proton acceleration driven by femtosecond laser pulses irradiating a micro-structured solid–gas target

Herein, we propose a scheme based on collision-less shock acceleration (CSA) involving the use of composite targets comprising a micro-structured foil and a pre-polarized gas for obtaining high-energy polarized proton beams. Femtosecond laser pulses irradiate a microwire-array (MWA) target and efficiently heat the dense plasma, which moves toward the dilute plasma. Shocks are then introduced in the pre-polarized gas to accelerate upstream spin-polarized protons to relativistic velocities. Based on particle-in-cell simulations with added spin dynamics, protons with energies of 30–300 MeV are produced, and the polarization rate of protons in the high-energy region exceeds 90%. The simulations demonstrate an evident increase in the temperature and number of hot electrons owing to the presence of MWA structures, which increase both the longitudinal electric field strength associated with the shock and the energy of the reflected protons. During CSA, the bipolar magnetic field driven by hot-electron currents demonstrates a weak effect on the polarization level of the accelerated protons, resulting in a high polarization rate. The relationship between the energy of the polarized proton beam and the hot-electron temperature enables an optimization of the micro-structured target and other target components to enhance proton quality via the CSA process.

Bayesian prediction of psychophysical detection responses from spike activity in the rat sensorimotor cortex.

Decoding of sensorimotor information is essential for brain-computer interfaces (BCIs) as well as in normal functioning organisms. In this study, Bayesian models were developed for the prediction of binary decisions of 10 awake freely-moving male/female rats based on neural activity in a vibrotactile yes/no detection task. The vibrotactile stimuli were 40-Hz sinusoidal displacements (amplitude: 200 µm, duration: 0.5 s) applied on the glabrous skin. The task was to depress the right lever for stimulus detection and left lever for stimulus-off condition. Spike activity was recorded from 16-channel microwire arrays implanted in the hindlimb representation of primary somatosensory cortex (S1), overlapping also with the associated representation in the primary motor cortex (M1). Single-/multi-unit average spike rate (Rd) within the stimulus analysis window was used as the predictor of the stimulus state and the behavioral response at each trial based on a Bayesian network model. Due to high neural and psychophysical response variability for each rat and also across subjects, mean Rd was not correlated with hit and false alarm rates. Despite the fluctuations in the neural data, the Bayesian model for each rat generated moderately good accuracy (0.60-0.90) and good class prediction scores (recall, precision, F1) and was also tested with subsets of data (e.g. regular vs. fast spike groups). It was generally observed that the models were better for rats with lower psychophysical performance (lower sensitivity index A'). This suggests that Bayesian inference and similar machine learning techniques may be especially helpful during the training phase of BCIs or for rehabilitation with neuroprostheses.

High-Sensitivity Wireless Sensing Using Amorphous Magnetic Microwires

Glass-coated amorphous ferromagnetic microwires subjected to variations in mass loading and parallel wire arrays with 0.5–6-cm interwire spacing were found to deliver exceptional magnetomechanical and wireless giant magnetoimpedance (GMI) responses, in the kilohertz and microwave range, respectively. The microwires allow wireless quantification of microgram mass differences: the magnetomechanical resonance frequency measured in zero applied field demonstrates an approximately linear decrease of 3 Hz/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{g}$ </tex-math></inline-formula> , and a sensitivity response that is ten times greater than that reported for commercial METGLAS-type amorphous magnetic ribbons of comparable length. Microwave giant magnetoimpedance data collected from planar arrays of parallel microwires show either constructive or destructive interference when compared to data obtained from a single microwire. The exceptional responsiveness of the glass-coated amorphous ferromagnetic microwires to mass loading and to geometric arrangement, along with their small diameter and ease of fabrication, highlights their promise for a wide variety of sensor applications, including biosensing, civil infrastructure monitoring, and high-throughput remote detection schemes.

Magnetic confinement-enabled membrane reactor for enhanced removal of wide-spectrum contaminants in water: Proof of concept, synergistic decontamination mechanisms, and sustained treatment performance

Membrane chemical reactors (MCRs) have demonstrated a great potential for simultaneous removal of wide-spectrum pollutants in advanced water treatment. However, current catalyst (re)loading and catalytic reactivity limitations obstruct their practical applications. Herein, as a proof-of-concept, we report a hollow fiber membrane chemical reactor (HF-MCR) with high and sustainable catalytic reactivity, enabled by novel magnetic confinement engineering of the catalysts. Namely, the zerovalent iron (ZVI) nanocatalysts were spatially dispersed and confined to nearly parallel magnetic induction lines, forming forest-like microwire arrays in the membrane lumen. Such arrays exhibited ultrahigh hydrodynamic stability. The HF-MCR integrated sequential membrane separation and Fenton-like catalysis, thus being capable of high and synergistic wide-spectrum decontamination. The membrane separation process completely removed large nanoplastics (NPs) via size exclusion, and thus the subsequent Fenton-like catalysis process enhanced removal efficiency of otherwise permeated bisphenol A (BPA) and phosphate (P) by in situ generated reactive oxygen species (primarily 1O2) and iron (oxyhydr)oxides, respectively. Furthermore, highly dispersed ZVI arrays and their continuous surface depassivation driven by magnetic gradient and hydrodynamic forces conferred abundant accessible catalytic sites (i.e., Fe0 and FeII) to stimulate Fenton-like catalysis. The consequent enhancement of BPA and P removal kinetics was 3–765 and 49–492 folds those in conventional (flow-through or batch) systems, respectively. Periodic ZVI reloading ensured sustained decontamination performance of the HF-MCR. This is the first demonstration of the magnetic confinement engineering that enables efficient and unlimited catalyst (re)loading and sustainable catalytic reactivity in the MCR for water treatment, which is beyond the reach of current approaches.