Structure Of Microwires Research Articles

Removal Forces of a Helical Microwire Structure Electrode.

(1) Background: Medical devices, especially neuromodulation devices, are often explanted for a variety of reasons. The removal process imparts significant forces on these devices, which may result in device fracture and tissue trauma. We hypothesized that a device's form factor interfacing with tissue is a major driver of the force required to remove a device, and we isolated helical and linear electrode structures as a means to study atraumatic removal. (2) Methods: Ductile linear and helical microwire structure electrodes were fabricated from either Gold (Au) or Platinum-Iridium (Pt-Ir, 90-10). Removal forces were captured from synthetic gel models and following chronic implantation in rodent and porcine models. Devices were fully implanted in the animal models, requiring a small incision (<10 mm) and removal via tissue forceps. (3) Results: Helical devices were shown to result in significantly lower maximal removal forces in both synthetic gel and rodent studies compared to their linear counterparts. Chronically (1 yr.), the maximal removal force of helical devices remained under 7.30 N, for which the Platinum-Iridium device's tensile failure force was 32.90 ± 2.09 N, resulting in a safety factor of 4.50. (4) Conclusions: An open-core helical structure that can freely elongate was shown to result in reduced removal forces both acutely and chronically.

Highly sensitive ammonia sensor based on a PMMA/PANI microwire structure.

In this paper, a highly sensitive ammonia (N H 3) sensor based on a polymethyl methacrylate/polyaniline (PMMA/PANI) microwire structure is designed and implemented. First, a micron-sized PMMA microwire was fabricated and connected with two tapered single-mode fibers to form a coupling structure; thus, the Mach-Zehnder (MZ) interference was successfully excited due to the good light conductivity of the PMMA. It was demonstrated that the coupling structure behaved with a high refractive index detection sensitivity of 3044nm/RIU. To make it sensitive to N H 3, the PANI was selected to mix with PMMA and then formed a micron-level PMMA/PANI fiber. The experimental results showed that the PMMA/PANI fiber can selectively sense N H 3 with a high sensitivity of 65.3pm/ppm. This proposed N H 3 sensor not only solves the problem of sensitive film shedding, but also possesses the advantages of good integration, high sensitivity, good selectivity, and short response time.

Ultraviolet sensing based on an in-fiber ZnO microwire constructed Mach–Zehnder interferometer

We propose a Mach–Zehnder interferometer based on an in-fiber ZnO microwire structure for ultraviolet sensing. The device undergoes femtosecond laser micromachining and chemical etching on a single-mode optical fiber initially, creating a microgroove that extends to half of the core’s depth, into which a single ZnO microwire is transferred. The ZnO microwire and the remaining core are used as the sensing arm and the reference arm, respectively, forming a Mach–Zehnder interferometer. To enhance the stability and the sensitivity, ZnO nanoparticles are filled into the microgroove after the ZnO microwire is transferred. The fabricated device exhibits a sensitivity of 0.86 nm/(W·cm−2) for ultraviolet sensing, along with a response time of 115 ns (rise time) and 133 µs (decay time), respectively. The proposed sensor exhibits good ultraviolet sensitivity, offering a novel approach for ultraviolet sensing technology.

Optical Properties and Photocatalytic Performance of Si/TiO2 Tandem Semiconductor Microwire Slurries

Semiconductor particle suspension reactors hold promise as a possible low-cost strategy for solar water-splitting, but they face several challenges that have inhibited their solar-to-hydrogen (STH) efficiencies. A tandem microparticle with a buried junction addresses some of these challenges and offers a pathway to high STH efficiency. As a slurry, the tandem microparticles need to be suspended and well dispersed with maximum light absorption for a minimal photoactive particle concentration. Herein, proof-of-concept Ni/np+-Si/FTO/TiO2 tandem microwire structures capable of unassisted solar water-splitting were investigated as a slurry using uplifting N2 carrier gas bubbles. Transmittance, reflectance, and absorptance of the slurry were characterized as a function of wavelength, bubble flowrate, and tandem microwire concentration using an integrating sphere. Notably, a slurry absorptance of 70–85% was achieved with only 1% of the solution volume filled with a photoactive material. Photochemical activity of the slurry was characterized with in situ monitoring of the photodegradation of methylene blue, including the effects of particle concentration, bubble flowrate, spectral mismatch, intermixed light scattering particles, and a back reflector.

Self-regulated parallel process 3-D array microfabrication with metal direct-write

Parallel process direct-write manufacturing of ultrahigh aspect ratio 3-D metal microstructures remains one of the ultimate challenges in 3-D manufacturing. Its development promises novel solutions for high density chip scale packaging and sorting that require precision microscale mechanical and electrical interfaces to microelectronics. Herein, we exploited a self-regulated growth mechanism revealed in the meniscus-confined direct-write electro-deposition to realize the parallel process fabrication of high-density area arrays of ultrahigh aspect-ratio metal microwire structures. We demonstrated the direct-write fabrication of an array of curvilinear metal spirals over 800 μm in height and 50 μm in array spacing, structurally and mechanically appropriate for high density wafer probe testing applications that cannot otherwise be fabricated with any other existing methods.

Field‐Induced Radial Junction for Dopant‐Free Crystalline Silicon Microwire Solar Cells with an Efficiency of Over 20%

AbstractRadial junctions on crystalline silicon (c‐Si) microwire structures considerably reduce the diffusion length of photoinduced minority carriers required for energy generation by decoupling light absorption and carrier separation in orthogonal spatial directions. Hence, radial junctions mitigate the need for high‐purity materials, and thus reduce the fabrication cost of c‐Si solar cells. In this study, the formation of dopant‐free radial junctions from atomic layer deposition (ALD) of Al2O3 on an n‐c‐Si microwire surface is reported. ALD‐Al2O3 generates a p+ inversion layer, which eventually forms the radial junction on the n‐c‐Si surface. The width of depletion region induced by the p+ inversion layer is calculated from PC1D simulation as 900 nm. The fabricated dopant‐free radial junction c‐Si solar cells exhibit a power conversion efficiency of 20.1%, which is higher than those of previously reported microwire‐based radial junction solar cells. Notably, internal quantum efficiencies of over 90% are obtained in the 300–980 nm wavelength region, thereby verifying the successful formation of radial junctions.

Torsion induced acceleration of domain wall motion in magnetic microwires

Abstract The effect of torsion-induced acceleration of domain-wall motion has been discovered in magnetic glass-covered microwires. Torsion-stress application causes a step-change increase in domain-wall velocity. The threshold character of the observed effect is related to the successive stress-induced appearance of spiral and elliptical types of domain structures. The theoretical analysis allows us to associate the stress-induced domain-structure transformation with a change of the relationship between the inner core and the outer shell of the magnetic structure in microwires.

A single InGaN/GaN multiple quantum wells microwire light-emitting diode with high efficiency current injection and spreading

Micro/nanowire light-emitting diodes have inspired considerable research interests due to their wide range of potential applications, such as in micro/nanoscale display, optical communication and optical logics. To realize a single wire light-emitting diode, however, it is usually faced with low-efficiency or wavelength uncontrollable. Herein, we report on an individual coaxial core/shell InGaN/GaN microwire light-emitting diode with tunable dual-/single-wavelength light emission, which can be feasibly realized by controlling growth rate of microwires using MOCVD. The unique cross-sectional morphologies of synthesized microwires can simplify the device fabrication process and are in favor of vertical current injection and spreading simultaneously. Thus, the microwire light-emitting diodes show advantages at the suppression of efficiency droop under large current injection, with a drop ratio of 19.6%, as increasing the injection current from 2.4 A cm−2 to 92.6 A cm−2. This study proposes a core/shell multiple quantum wells microwire structure to fabricate micro light-emitting diodes which may act as a reliable light source for micro/nanoscale integrated photonic systems.

CsPbBr3 interconnected microwire structure: temperature-related photoluminescence properties and its lasing action

Inorganic perovskite CsPbBr3 is a promising material for the next generation green-wavelength light-emitting devices.

Long‐Term Stable and Tunable High‐Performance Photodetectors Based on Perovskite Microwires

AbstractOraganolead halide perovskites (OHPs) present remarkable optoelectronic properties, and thus possess extensive applications in photovoltaic devices and photodetectors. However, the OHP‐based devices severely suffer from low environmental stability because of water invasion and oxygen erosion to the materials. In this work, this challenge is overcome by utilizing the unique advantages of the microwire structure. OHP microwires, which can be fabricated by simple and low‐cost dip coating method, present superior resistance to moisture as compare to conventional OHP films or nanowires, thanks to their combined properties of high‐crystallinity and low surface‐to‐volume ratio. Photodetectors based on the OHP microwires show outstanding long‐term stability over 90 d even stored with high relative humidity, which is among the highest stability according to the literature reports. Meanwhile, the photodetectors exhibit high and tunable sensory performance by adjusting the distribution of OHP microwires through changing the dip‐coating parameters, for example, the light‐to‐dark current ratio of the device can be over 20 000. The photodetectors with OHP microwaves deposited on polymer substrates also exhibit great mechanical flexibility. Therefore, this work reveals the unique advantages of the low‐cost and readily‐fabricated OHP microwires, and demonstrates their promising applications in optoelectronic devices by developing long‐term stable and tunable high‐performance photodetectors.

The change of domain structure of the amorphous microwire of Fe73.5Cu1Nb3Si13.5B9 composition under thermal treatment

The investigation on domain structure evolution under variation of magnetostriction, phase composition and internal stresses was provided. Glass-coated amorphous microwires of Fe73.5Cu1Nb3Si13.5B9 composition with positive magnetostriction were studied. The decrease of internal stresses and controlled crystallization leading to changes in the phase composition and reduction of magnetostriction were observed under different thermal treatment. The domain structure of the as-prepared and annealed microwires was studied by the method of magneto-optical indicator films. The estimation of the domain size was realized by Fourier transform from the domain contrast of magneto-optical images. The regularities of the influence of thermal treatment on the magnetic domain structure of microwires have been estimated.

2 μm Raman fiber laser based on a multimaterial chalcogenide microwire

We report a Raman fiber laser based on a multimaterial chalcogenide microwire. The microwire structure comprises a core of As38Se62, a cladding of As38S62, and a coating of poly-methyl methacrylate. The microwire is a robust, high confinement waveguide compatible with the mid-infrared. With the microwire inserted in a ring cavity, Raman laser oscillation at a wavelength of 2.025 μm occurs from synchronous pumping at a wavelength of 1.938 μm. The input peak power required to reach threshold is 4.6 W and the power slope efficiency is 4.5%. Numerical simulations are in good agreement with experimental results and predict chirp-free femtosecond pulses.

A long-range hybrid THz plasmonic waveguide with low attenuation loss

Numerical solutions are obtained for the proposed novel hybrid terahertz plasmonic waveguide structure, namely the silicon metal silicon (SMS) waveguide. It is shown that the SMS waveguide can overcome the diffraction limit while still maintaining a sizeable propagation length. The geometric dependence of the mode characteristics of this structure is analyzed in detail, showing strong confinement and low loss with propagation lengths exceeding 14mm at normalized mode areas of 1.72×10−2. By using the FEM method (Comsol), the guiding properties of the hybrid terahertz surface plasmon polariton (HTSPP) waveguide are numerically analyzed at the THz frequency, and a combination of double-structured comparisons of the best features of the terahertz plasmonic waveguide is made. Depending on the height used and how the mode confinement is measured, various modal designs, such as double microwire structures, are developed. The structures indicate that we verified the possibility of low attenuation loss of hybrid THz plasmonics propagation. The effective mode area Aeff, energy distribution, and propagation length Lp versus height for waveguides with Si microwire and SiO2 are shown. The numerical calculation results reveal a potential for use in applications such as optical force in trapping and transporting biomolecules, and in high-density integrated circuits.

Radial direct bandgap p-i-n GaNP microwire solar cells with enhanced short circuit current

We report the demonstration of dilute nitride heterostructure core/shell microwire solar cells utilizing the combination of top-down reactive-ion etching to create the cores (GaP) and molecular beam epitaxy to create the shells (GaNP). Systematic studies of cell performance over a series of microwire lengths, array periods, and microwire sidewall morphologies examined by transmission electron microscopy were conducted to shed light on performance-limiting factors and to optimize the cell efficiency. We show by microscopy and correlated external quantum efficiency characterization that the open circuit voltage is degraded primarily due to the presence of defects at the GaP/GaNP interface and in the GaNP shells, and is not limited by surface recombination. Compared to thin film solar cells in the same growth run, the microwire solar cells exhibit greater short circuit current but poorer open circuit voltage due to greater light absorption and number of defects in the microwire structure, respectively. The comprehensive understanding presented in this work suggests that performance benefits of dilute nitride microwire solar cells can be achieved by further tuning of the epitaxial quality of the underlying materials.

Vertical, capacitive microelectromechanical switches produced via direct writing of copper wires.

Three-dimensional (3D) direct writing based on the meniscus-confined electrodeposition of copper metal wires was used in this study to develop vertical capacitive microelectromechanical switches. Vertical microelectromechanical switches reduce the form factor and increase the area density of such devices in integrated circuits. We studied the electromechanical characteristics of such vertical switches by exploring the dependence of switching voltage on various device structures, particularly with regard to the length, wire diameter, and the distance between the two wires. A simple model was found to match the experimental measurements made in this study. We found that the electrodeposited copper microwires exhibit a good elastic modulus close to that of bulk copper. By optimizing the 3D structure of the electrodes, a volatile electromechanical switch with a sub-5 V switching voltage was demonstrated in a vertical microscale switch with a gap distance as small as 100 nm created with a pair of copper wires with diameters of ~1 μm and heights of 25 μm. This study establishes an innovative approach to construct microelectromechanical systems with arbitrary 3D microwire structures for various applications, including the demonstrated volatile and nonvolatile microswitches.

Imaging the Surface Domain Structure of Amorphous Glass-Coated Microwires by Bitter Colloid

The fast domain wall dynamics of amorphous glass-coated microwires can be changed drastically by properly selected annealing temperature. Here, the e ect of thermal annealing on the surface domain structure of microwires is examined. Imaging the surface domain structure by Bitter colloid revealed the periodic pattern in each studied sample. Thermal annealing of microwires results in the ve times increase of the domain wall velocity, as compared to the as-cast state. In uence of the surface domain structure on the fast domain wall propagation in microwires is discussed.

Vortex magnetic structure in circularly magnetized microwires as deduced from magneto-optical Kerr measurements

The magneto-optic Kerr effect has been employed to determine the magnetization process and estimate the domain structure of microwires with circular magnetic anisotropy. The diameter of microwires was 8 μm, and pieces 2 cm long were selected for measurements. The analysis of the local surface longitudinal and transverse hysteresis loops has allowed us to deduce a vortex magnetic structure with axial core and circular external shell. Moreover, a bamboo-like surface domain structure is confirmed with wave length of around 10 to 15 μm and alternating chirality in adjacent circular domains. The width of the domain wall is estimated to be less than 3 μm. Finally, closure domain structures with significant helical magnetization component are observed extending up to around 1000 μm from the end of the microwire.

The effect of mechanical stress on Ni63.8Mn11.1Ga25.1 microwire crystalline structure and properties

We studied structure and magnetic properties of Heusler alloy microwires. The dependence of the phase composition of the annealed microwires on the presence of glass coating has been found. The crystalline structure of the glass-coated samples is composed of two cubic crystalline phases of different density. The samples annealed without coating are in the single-phase state. The two-phase state is supposed to be caused by intrinsic stresses resulted from the action of opposite sign stresses in different microwire sections. The magnetic properties of the fabricated Heusler-type microwires differ from their bulk and thin film counterparts. Annealing of microwires considerably affect magnetic properties at room temperature. Unusual magnetic behavior is connected with two-phase structure of microwires.

Fast magnetization switching in Fe-rich amorphous microwires: Effect of magnetoelastic anisotropy and role of defects

We studied effect of magnetoelastic anisotropy and role of defects on domain wall (DW) dynamics and remagnetization process of magnetically-bistable Fe-rich microwires. We manipulated the magnetoelastic anisotropy applying the tensile stresses. Application of stresses resulted in decrease of the DW velocity v, and DW mobility S. Consequently, we observed certain correlation between the magnetoelastic energy and DW dynamics in microwires: decreasing the magnetoelastic energy, Kme, DW velocity can be increased. We are trying to reveal contribution of local defects on DW propagation in amorphous microwires. Below some critical magnetic field, Hn, determined by the microwires inhomogeneities, almost linear DW velocity, v on magnetic field, H, dependence is found. When the applied magnetic field exceeds Hn, new reverse domains can be nucleated and consequently tandem remagnetization mechanism can be realized. The role of defects existing in magnetically bistable microwires is related with nucleation of new reversed domains. Abrupt jumps on v(H) dependences correlate with defects existing in microwires. Magnetic field value, corresponding to such jump on v(H) dependences, correlates with the minimum nucleation field, which determines threshold between single and multiple domain wall propagation regimes. In the latter case, under the action of the magnetic field, a new domain can be spontaneously nucleated in front of the propagating head-to-head closure domain. In this way real structure of microwires limits single DW propagation regime.

Fabrication of p-Type Silicon Nanowire Arrays with a High Aspect Ratio Using Electrochemical and Alkaline Etching

We report on the fabrication of silicon nanostructures with a high aspect ratio that were created using a combination of electrochemical etching and alkaline etching. With this technique, we were able to fabricate nano- and/or micro-wire structures that are perfectly periodic over large areas of 3.14 cm2. After porous silicon was created by electrochemical etching, the effect of post-alkaline etching was investigated to determine how changes in the etching time, solution concentration and temperature of the etchant influenced the silicon morphology. As a result, periodic silicon wire arrays with good vertical alignment were obtained, and these arrays had a width of less than 500 nm and/or a high aspect ratio of more than 20.