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Nanostructured ultraviolet (UV) light sources represent a growing research field in view of their potential applications in wearable optoelectronics or medical treatment devices. In this work, we report the demonstration of the first flexible UV-A light emitting diode (LED) based on AlGaN/GaN core-shell microwires. The device is based on a composite microwire/poly(dimethylsiloxane) (PDMS) membrane with flexible transparent electrodes. The electrode transparency in the UV range is optimized: namely, we demonstrate that single-walled carbon nanotube electrodes provide a stable electrical contact to the membrane with high transparency (70% at 350 nm). The flexible UV-A membrane demonstrating electroluminescence around 345 nm is further applied to excite Zn-Ir-BipyPDMS luminophores: the UV-A LED is combined with the elastic luminophore-containing membrane to produce a visible amber emission from 520 to 650 nm. The obtained results pave the way for flexible inorganic light-emitting diodes to be employed in sensing, detection of fluorescent labels, or light therapy.

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The field of bioelectronics is developing exponentially. There is now a drive to interface electronics with biology for the development of new technologies to improve our understanding of electrical forces in biology. This builds on our recently published work in which we show wireless electrochemistry could be used to grow bioelectronic functional circuitry in 2D cell layers. To date our ability to merge electronics with in situ with biology is 3D limited. In this study, we aimed to further develop the wireless electrochemical approach for the self-assembly of microwires in situ with custom-designed and fabricated 3D cancer spheroids. Unlike traditional electrochemical methods that rely on direct electrical connections to induce currents, our technique utilises bipolar electrodes that operate independently of physical wired connections. These electrodes enable redox reactions through the application of an external electric field. Specifically, feeder electrodes connected to a power supply generate an electric field, while the bipolar electrodes, not physically connected to the feeder electrodes, facilitate the reduction of silver ions from the solution. This process occurs upon applying a voltage across the feeder electrodes, resulting in the formation of self-assembled microwires between the cancer spheroids.Thereby, creating interlinked bioelectronic circuitry with cancer spheroids. We demonstrate that a direct current was needed to stimulate the growth of conductive microwires in the presence of cell spheroids. Microwire growth was successful when using 50 V (0.5 kV/cm) of DC applied to a single spheroid of approximately 800 µm in diameter but could not be achieved with alternating currents. This represents the first proof of the concept of using wireless electrochemistry to grow conductive structures with 3D mammalian cell spheroids.

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Introduction: Many invasive and noninvasive neurotechnologies are being developed to help treat neurological pathologies and disorders. Making a brain implant safe, stable, and efficient in the long run is one of the requirements to conform with neuroethics and overcome limitations for numerous promising neural treatments. A main limitation is low biocompatibility, characterized by the damage implants create in brain tissue and their low adhesion to it. This damage is partly linked to friction over time due to the mechanical mismatch between the soft brain tissue and the more rigid wires. Methods: Here, we performed a short biocompatibility assessment of bio-inspired intra-cortical implants named "Neurosnooper" made of a microelectrode array consisting of a thin, flexible polymer-metal-polymer stack with microwires that mimic axons. Implants were assembled into poly-lactic-glycolic acid (PLGA) biodegradable needles for their intra-cortical implantation. Results and Discussion: The study of glial scars around implants, at 7 days and 2 months post-implantation, revealed a good adhesion between the brain tissue and implant wires and a low glial scar thickness. The lowest corresponds to electrode wires with a section size of 8 µm × 10 µm, compared to implants with the 8 µm × 50 µm electrode wire section size, and a straight shape appears to be better than a zigzag. Therefore, in addition to flexibility, size and shape parameters are important when designing electrode wires for the next generation of clinical intra-cortical implants.

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This article demonstrates scalable production of liquid metal (LM)-based microwires through the thermal drawing of extrudates. These extrudates were first co-extruded using a eutectic alloy of gallium and indium (EGaIn) as a core element and a thermoplastic elastomer, styrene-ethylene/butylene-styrene (SEBS), as a shell material. By varying the feed speed of the co-extruded materials and the drawing speed of the extrudate, it was possible to control the dimensions of the microwires, such as core diameter and shell thickness. How the extrusion temperature affects the dimensions of the microwire was also analyzed. The smallest microwire (core diameter: 52 ± 14 µm and shell thickness: 46 ± 10 µm) was produced from a drawing speed of 300.1 mm s-1 (the maximum attainable speed of the apparatus used), SEBS extrusion speed of 1.50 mm3 s-1, and LM injection rate of 5 × 105 µL s-1 at 190 °C extrusion temperature. The same extrusion condition without thermal drawing generated significantly large extrudates with a core diameter of 278 ± 26 µm and shell thickness of 430 ± 51 µm. The electrical properties of the microwires were also characterized under different degrees of stretching and wire kinking deformation which proved that these LM-based microwires change electrical resistance as they are deformed and fully self-heal once the load is removed. Finally, the sewability of these microwires was qualitatively tested by using a manual sewing machine to pattern microwires on a traditional cotton fabric.

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The recently proposed magnetoimpedance tomography method is based on the analysis of the frequency dependences of the impedance measured at different external magnetic fields. The method allows one to analyze the distribution of magnetic properties over the cross-section of the ferromagnetic conductor. Here, we describe the example of theoretical study of the magnetoimpedance effect in an amorphous microwire with inhomogeneous magnetic structure. In the framework of the proposed model, it is assumed that the microwire cross-section consists of several regions with different features of the effective anisotropy. The distribution of the electromagnetic fields and the microwire impedance are found by an analytical solution of Maxwell equations in the particular regions. The field and frequency dependences of the microwire impedance are analyzed taking into account the frequency dependence of the permeability values in the considered regions. Although the calculations are given for the case of amorphous microwires, the obtained results can be useful for the development of the magnetoimpedance tomography method adaptation for different types of ferromagnetic conductors.

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We have prepared NiMnGa glass-coated microwires with different geometrical aspect ratios, ρ = dmetal/Dtotal (dmetal-diameter of metallic nucleus, and Dtotal-total diameter). The structure and magnetic properties are investigated in a wide range of temperatures and magnetic fields. The XRD analysis illustrates stable microstructure in the range of ρ from 0.25 to 0.60. The estimations of average grain size and crystalline phase content evidence a remarkable variation as the ρ-ratio sweeps from 0.25 to 0.60. Thus, the microwires with the lowest aspect ratio, i.e., ρ = 0.25, show the smallest average grain size and the highest crystalline phase content. This change in the microstructural properties correlates with dramatic changes in the magnetic properties. Hence, the sample with the lowest ρ-ratio exhibits an extremely high value of the coercivity, Hc, compared to the value for the sample with the largest ρ-ratio (2989 Oe and 10 Oe, respectively, i.e., almost 300 times higher). In addition, a similar trend is observed for the spontaneous exchange bias phenomena, with an exchange bias field, Hex, of 120 Oe for the sample with ρ = 0.25 compared to a Hex = 12.5 Oe for the sample with ρ = 0.60. However, the thermomagnetic curves (field-cooled-FC and field-heating-FH) show similar magnetic behavior for all the samples. Meanwhile, FC and FH curves measured at low magnetic fields show negative values for ρ = 0.25, whereas positive values are found for the other samples. The obtained results illustrate the substantial effect of the internal stresses on microstructure and magnetic properties, which leads to magnetic hardening of samples with low aspect ratio.

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We provide comparative studies of the structural, morphological, microstructural, and magnetic properties of MnFePSi-glass-coated microwires (MnFePSi-GCMWs) and bulk MnFePSi at different temperatures and magnetic fields. The structure of MnFePSi GCMWs prepared by the Taylor-Ulitovsky method consists of the main Fe2P phase and secondary impurities phases of Mn5Si3 and Fe3Si, as confirmed by XRD analysis. Additionally, a notable reduction in the average grain size from 24 µm for the bulk sample to 36 nm for the glass-coated microwire sample is observed. The analysis of magnetic properties of MnFePSi-glass-coated microwires shows different magnetic behavior as compared to the bulk MnFePSi. High coercivity (450 Oe) and remanence (0.32) are observed for MnFePSi-GCMWs compared to low coercivity and remanent magnetization observed for bulk MnFePSi alloy. In addition, large irreversibility at low temperatures is observed in the thermal dependence of magnetization of microwires. Meanwhile, the bulk sample shows regular ferromagnetic behavior, where the field cooling and field heating magnetic curves show a monotonic increase by decreasing the temperature. The notable separation between field cooling and field heating curves of MnFePSi-GCMWs is seen for the applied field at 1 kOe. Also, the M/M5K vs. T for MNFePSi-GCMWs shows a notable sensitivity at a low magnetic field compared to a very noisy magnetic signal for bulk alloy. The common features for both MnFePSi samples are high Curie temperatures above 400 K. From the experimental results, we can deduce the substantial effect of drawing and quenching involved in the preparation of glass-coated MnFePSi microwires in modification of the microstructure and magnetic properties as compared to the same bulk alloy. The provided studies prove the suitability of the Taylor-Ulitovsky method for the preparation of MnFePSi-glass-coated microwires.

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Composite materials are frequently exposed to external factors during their operational service, resulting in internal structural damage which subsequently impacts their structural performance. This paper employs ferromagnetic materials for their sensitivity to magnetic field strength. By detecting variations in the magnetic field within the embedded ferromagnetic microwires of composite materials, the aim is to indirectly assess the health status of the composite materials. Firstly, a theoretical numerical model for magnetic field intensity at the crack site was established. Subsequently, a finite element model was employed to analyze the variations in the magnetic characteristics of ferromagnetic microwires at the crack site. Under different parameter conditions, the patterns of magnetic signals at the crack site were determined. The results indicate that with an increase in the angle between the external magnetic field and the crack, the fitted curve of the magnetic signal shows a linear increase. The distance between the peak and valley of the radial magnetic signal in the axial direction decreases, and the axial magnetic signal transitions from double-peak to single-peak. With the increase in crack depth, the fitted curve of the magnetic signal shows a linear increase, and the magnetic signal at the crack tip also exhibits a linear increase. An increase in crack width leads to a non-linear decrease in the fitted curve of the magnetic signal, and after reaching a certain width, the magnetic signal stabilizes. For two identical cracks at different distances, the magnetic signal exhibits a transition from a complete pattern to two complete patterns. With the increase in the external magnetic field, the magnetic signal shows a completely regular linear increase. By analyzing and calculating the variations in magnetic signals, the patterns of magnetic characteristics under the damaged state of ferromagnetic microwires were obtained. This serves as a basis for assessing whether they can continue in service and for evaluating the overall health status of composite materials.

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An approach was proposed to control the displacement of domain walls in magnetic microwires, which are employed in magnetic sensors. The velocity of the domain wall can be altered by the interaction of two magnetic microwires of distinct types. Thorough investigations were conducted utilizing fluxmetric, Sixtus-Tonks, and magneto-optical techniques. The magneto-optical examinations revealed transformation in the surface structure of the domain wall and facilitated the determination of the mechanism of external influence on the movement of domain walls in magnetic microwires.

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In this article, we study the effect of annealing temperature and applied stress on the magnetic properties of Fe71.80B13.27Si11.02Nb2.99Ni0.92 and Co65.34Si12.00B10.20Cr8.48Fe3.90Mo0.08 microwires. An anomalous behavior of the coercive field is observed while applying stress, indicating nontrivial changes in the microwire magnetic anisotropy. The effect of applied stimuli on the magnetic anisotropy and magnetostriction constant in both microwires is also discussed.

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As-prepared Fe-rich microwires with perfectly rectangular hysteresis loops present magnetization reversal through fast domain wall propagation, while the giant magnetoimpedance (GMI) effect in Fe-rich microwires is rather low. However, the lower cost of Fe-rich microwires makes them attractive for magnetic sensors applications. We studied the effect of conventional (furnace) annealing and Joule heating on magnetic-propertied domain wall (DW) dynamics and the GMI effect in two Fe microwires with different geometries. We observed that magnetic softness, GMI effect and domain wall (DW) dynamics can be substantially improved by appropriate annealing. Observed experimental results are discussed considering the counterbalance between the internal stresses relaxation and induced magnetic anisotropy associated with the presence of an Oersted magnetic field during Joule heating.

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In the current work, we illustrate the effect of adding a small amount of carbon to very common Co2MnSi Heusler alloy-based glass-coated microwires. A significant change in the magnetic and structure structural properties was observed for the new alloy Co2MnSiC compared to the Co2MnSi alloy. Magneto-structural investigations were performed to clarify the main physical parameters, i.e., structural and magnetic parameters, at a wide range of measuring temperatures. The XRD analysis illustrated the well-defined crystalline structure with average grain size (Dg = 29.16 nm) and a uniform cubic structure with A2 type compared to the mixed L21 and B2 cubic structures for Co2MnSi-based glass-coated microwires. The magnetic behavior was investigated at a temperature range of 5 to 300 K and under an applied external magnetic field (50 Oe to 20 kOe). The thermomagnetic behavior of Co2MnSiC glass-coated microwires shows a perfectly stable behavior for a temperature range from 300 K to 5 K. By studying the field cooling (FC) and field heating (FH) magnetization curves at a wide range of applied external magnetic fields, we detected a critical magnetic field (H = 1 kOe) where FC and FH curves have a stable magnetic behavior for the Co2MnSiC sample; such stability was not found in the Co2MnSi sample. We proposed a phenomenal expression to estimate the magnetization thermal stability, ΔM (%), of FC and FH magnetization curves, and the maximum value was detected at the critical magnetic field where ΔM (%) ≈ 98%. The promising magnetic stability of Co2MnSiC glass-coated microwires with temperature is due to the changing of the microstructure induced by the addition of carbon, as the A2-type structure shows a unique stability in response to variation in the temperature and the external magnetic field. In addition, a unique internal mechanical stress was induced during the fabrication process and played a role in controlling magnetic behavior with the temperature and external magnetic field. The obtained results make Co2MnSiC a promising candidate for magnetic sensing devices based on Heusler glass-coated microwires.

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In the current study we have obtained Co2FeSi glass-coated microwires with different geometrical aspect ratios, ρ = d/Dtot (diameter of metallic nucleus, d and total diameter, Dtot). The structure and magnetic properties are investigated at a wide range of temperatures. XRD analysis illustrates a notable change in the microstructure by increasing the aspect ratio of Co2FeSi-glass-coated microwires. The amorphous structure is detected for the sample with the lowest aspect ratio (ρ = 0.23), whereas a growth of crystalline structure is observed in the other samples (aspect ratio ρ = 0.30 and 0.43). This change in the microstructure properties correlates with dramatic changing in magnetic properties. For the sample with the lowest ρ-ratio, non-perfect square loops are obtained with low normalized remanent magnetization. A notable enhancement in the squareness and coercivity are obtained by increasing ρ-ratio. Changing the internal stresses strongly affects the microstructure, resulting in a complex magnetic reversal process. The thermomagnetic curves show large irreversibility for the Co2FeSi with low ρ-ratio. Meanwhile, if we increase the ρ-ratio, the sample shows perfect ferromagnetic behavior without irreversibility. The current result illustrates the ability to control the microstructure and magnetic properties of Co2FeSi glass-coated microwires by changing only their geometric properties without performing any additional heat treatment. The modification of geometric parameters of Co2FeSi glass-coated microwires allows to obtain microwires that exhibit an unusual magnetization behavior that offers opportunities to understand the phenomena of various types of magnetic domain structures, which is essentially helpful for designing sensing devices based on thermal magnetization switching.

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The rise of flexible electronics calls for efficient microbatteries (MBs) with requirements in energy/power density, stability, and flexibility simultaneously. However, the ever-reported flexible MBs only display progress around certain aspects of energy loading, reaction rate, and electrochemical stability, and it remains challenging to develop a micro-power source with excellent comprehensive performance. Herein, a reconstructed hierarchical Ni-Co alloy microwire is designed to construct flexible Ni-Zn MB. Notably, the interwoven microwires network is directly formed during the synthesis process, and can be utilized as a potential microelectrode which well avoids the toxic additives and the tedious traditional powder process, thus greatly simplifying the manufacture of MB. Meanwhile, the hierarchical alloy microwire is composed of spiny nanostructures and highly active alloy sites, which contributes to deep reconstruction (≈100 nm). Benefiting from the dense self-assembled structure, the fabricated Ni-Zn MB obtained high volumetric/areal energy density (419.7 mWh cm-3 , 1.3 mWh cm-2 ), and ultrahigh rate performance extending the power density to 109.4 W cm-3 (328.3 mW cm-2 ). More surprisingly, the MB assembled by this inherently flexible microwire network is extremely resistant to bending/twisting. Therefore, this novel concept of excellent comprehensive micro-power source will greatly hold great implications for next-generation flexible electronics.

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With the continuous miniaturization and integration of the semiconductor industry, micro/nanoscale integrated photonics has received extensive attention as a key technology for optical communication, optical storage, and optical interconnection. Here, a two-in-one device is reported with both unidirectional blue light emission and UV photodetection functions based on single trapezoidal PIN GaN microwire. By constructing a Fabry-Perot resonator cavity structure, the end-emitting blue light-emitting diode with a low turn-on voltage (≈0.97 V) and high color purity (full width at half maximum ≈22 nm) is implemented. Furthermore, benefiting from the slow growth rate of the semipolar planes on both sides of the trapezoidal microwire and the high diffuse reflectivity of the patterned substrate, the trapezoidal microwire sides can be used as a high-performance UV photodetector. In self-driven mode, the device exhibits a large responsivity (0.218 A W-1 ), high external quantum efficiency (83.31%) and fast response speed (rise/decay time of 0.48/0.98 ms). Finally, the prepared two-in-one device is successfully integrated into ambient light UV monitoring and feedback system and tested. This work provides a novel strategy to combine luminescence with photodetection, demonstrating high potential for applications, such as on-chip photonic integration, energy-saving communication and ambient light monitoring and feedback system.

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Amorphous microwires have attracted substantial attention in the past decade because of their useful technological applications. Their bistable magnetic response is determined by positive or negative magnetostriction, respectively. First-order reversal curves (FORC) are a powerful tool for analyzing the magnetization reversal processes of many-body ferromagnetic systems that are essential for a deeper understanding of those applications. After theoretical considerations about magnetostatic interactions among microwires, this work introduces a systematic experimental study and analysis of the FORC diagrams for magnetostrictive microwires exhibiting an individually bistable hysteresis loop, from a single microwire to sets of an increasing number of coupled microwires, the latter considered as an intermediate case to the standard many-body problem. We performed the study for sets of quasi-identical and different hysteretic microwires where we obtained the coercivity Hc and interaction Hu fields. In the cases with relevant magnetostatic interactions, FORC analysis supplies deeper information than standard hysteresis loops since the intrinsic fluctuations of the switching field generate a complex response. For sets of microwires with very different coercivity, the coercivity distributions of the individual microwires characterize the FORC diagram.

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We studied the magnetic properties of a glass-covered amorphous microwire that was stress-annealed at temperatures distributed along the microwire length. The Sixtus-Tonks, Kerr effect microscopy and magnetic impedance techniques have been applied. There was a transformation of the magnetic structure across the zones subjected to annealing at different temperatures. The annealing temperature distribution induces the graded magnetic anisotropy in the studied sample. The variety of the surface domain structures depending on the longitudinal location has been discovered. Spiral, circular, curved, elliptic and longitudinal domain structures coexist and replace each other in the process of magnetization reversal. The analysis of the obtained results was carried out based on the calculations of the magnetic structure, assuming the distribution of internal stresses.

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The piezoelectric properties of semiconductor micro/nanowires (M/NWs) are crucial for optimizing semiconductors' electronic structure and carrier dynamics. However, the dynamic characterization of the piezoelectric properties of M/NWs remains challenging. Here, a Kelvin probe force microscopy technique based on a dual-probe atomic force microscope is developed to achieve in situ piezoelectric potential measurements of dynamic bending MWs. This technique can not only characterize the surface potential on different crystal faces of ZnO MWs in a natural state through controllable axial rotation, but also investigate the piezoelectric potential of the dynamically bending flake-like ZnO MW at different points and under different strain loads. The results show that the surface potentials of different faces/positions of the ZnO MWs are varied significantly, and determine that the quasi-static conditions piezo-strain factor of the flake-like ZnO MW is 0.28 V/%, while the factor was 0.14 V/% under low-frequency (⩽5 Hz) sinusoidal strain loading. This work provides a significant methodology to further study piezoelectric materials, and it aims to facilitate their applications in piezoelectric devices and systems.

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Fractals are quite normal in nature. However, fractal self-assembly of organic semiconductors remains challenging. Herein, we develop a facile solution assembly route to access organic microwires (MWs) comprising an oligo(p-phenylenevinylene) derivative (OPV-A) with and without branching. Instead of kinetically controlled ß-OPV-A microrods (MRs), thermodynamically favored α-OPV-A gives fractal branching MW patterns. As-prepared 9,10-dicyanoanthracene (DCA) alloyed assemblies function as seeds to allow for the heteroepitaxial growth of branching α-OPV-A MWs via either coassembly or two-step seeded growth. Consequently, fractal MWs with single- and multisite growth were both achieved, accompanied by tailorable branching densities and hierarchies. Thermodynamic control and a well-matched epitaxial relationship should be crucial to the formation of fractal MW patterns. Importantly, the aligned α-OPV-A MW array functions as a multichannel optical gain medium and exhibits low-threshold amplified spontaneous emission (ASE). The present work deepens the research into fractal self-assembly of functional organic semiconductors.

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Defective few-layered graphene mesostructures (DFLGMs) are produced from graphite flakes by high-energy milling processes. We obtain an accurate control of the generated mesostructures, as well as of the amount and classification of the structural defects formed, providing a functional material for microwave absorption purposes. Working under far-field conditions, competitive values of minimum reflection loss coefficient (RLmin) = -21.76 dB and EAB = 4.77 dB are achieved when DFLGMs are immersed in paints at a low volume fraction (1.95%). One step forward is developed by combining them with the excellent absorption behavior that offers amorphous Fe73.5Si13.5B9Cu1Nb microwires (MWs), varying their filling contents, which are below 3%. We obtain a RLmin improvement of 47% (-53.08 dB) and an EAB enhancement of 137% (4 dB) compared to those obtained by MW-based paints. Furthermore, a fmin tunability is demonstrated, maintaining similar RLmin and EAB values, irrespective of an ideal matching thickness. In this scenario, the Maxwell-Garnet standard model is valid, and dielectric losses mainly come from multiple reflections, interfacial and dielectric polarizations, which greatly boost the microwave attenuation of MWs. The present concept can remarkably enhance not only the MW attenuation but can also apply to other microwave absorption architectures of technological interest by adding low quantities of DFLGMs.