Surface Of Microwires Research Articles

Amorphization of PrDy-FeCo-B microwire surface under nanosecond laser pulse

Micromagnets used in robotic mechanisms, actuators, electromotive devices, micro-engines require protection from chemically destructive factors. Improving micromagnets in the NdFeB family is particularly important. We found that laser-stimulated amorphization of the surface of PrDy-FeCo-B microwires can restore the amorphous structure from polycrystalline microwires under a single laser irradiation pulse of 1 mJ power and 120 ns duration, penetrating to a depth of 1 μm. The thermal exchange in the microwire causes rapid cooling of the laser-irradiated area. We imprinted periodic local magnetic labels of ∼10 μm in length using single laser pulse. Initially crystalline (PrDy)2(FeCo)14B1 microwires were locally transformed to an amorphous phase by laser irradiation. The alternating amorphous magnetic patterns are magnetized perpendicular to the microwire’s main axis.

Magnetic domain structure of iron-based microwires after removal of the glass shell by chipping and chemical etching

The magnetic domain structure of the surface of microwires with composition Fe73.9B13.2Si10.9C2 was studied by magnetic force microscopy. It has been found that the removal of glass shell by chipping leads to distortion of the original magnetic domain structure. Chemical etching of the glass shell makes it possible to observe the magnetic domain structure due to the stresses that have arisen due to the microwire production. In the absence of an applied magnetic field, a magnetic domain structure of the surface layer is observed, consisting of domain layers inclined to the microwire axis by 45 or 135 degrees. This structure has a shape close to a zigzag. The thickness of the domain layers is not constant and varies from 3 to 5 μm. It has been found that the application of a constant magnetic field along the microwire axis causes the formation of ring domain layers of various thicknesses (from 1 to 5 μm) with different orientations of the magnetic moment relative to the microwire surface. In a field of 60 oersteds along the axis of the microwire, the domain magnetic structure consists of only ring layers of domains. Magnetic field inversion leads to almost complete inversion of the observed domain structure. In this case, the complete removal of the magnetic field leads to the formation of a new domain structure of the surface layer. Such a structure is close in shape and position of the domains to the original one, but does not repeat it.

Bend Induced Magnetic Bistability in Amorphous Microwires

ABSTRACT Magnetic and magneto-optical studies were carried out in microwires that had been subjected to the bending annealing. A previously unobserved effect of bending-annealing-induced magnetic bistability was discovered. This effect is observed only in the region of the sample subjected to bending. The length of the longitudinal region of the sample, in which the effect of induced bistability takes place, depended on the bending radius. In contrast to the classical version of this effect, bending-induced bistability was accompanied by the rapid movement of the longitudinal domain wall in the microwire surface.

Surface energy in microwires. Review

The research involves using an analytical solution of the Gibbs–Tolman–Koenig–Buff equation to calculate the microwire surface tension. The classical theory of nucleation and the statistical theory of density were used to determine dependencies for the surface energy of a cylindrical particle. It was shown that within the linear theory, both approaches produce similar results. However, within the nonlinear theory, the results may differ. The article presents an analysis of the analytical solutions of equations for a cylindrical surface within the van der Waals linear and nonlinear theories

Novel in situ growing carbon nanocoils onto steel mesh as positive electrode and hexagonal-MoO3 micro-rod array onto carbon fabric as negative electrode for assembling dual-asymmetric supercapacitors with redox active gel eleectrolyte

Intrinsically functionalized carbon nanocoils (CNCs) are in-situ grown onto the microwire surface of stainless steel mesh (SS) in an alcohol flame. The CNCs are deposited without using any additional catalysts and the flame growth mechanism is proposed. Such a unique structure with functionalized CNCs directly growing onto SS micro-wires in the mesh current collector makes it an excellent binder-free CNC/SS electrode. It exhibits ultrahigh capacitance in a iron ion based redox active electrolyte, where an remarkable areal capacitance of 4160 mF/cm 2 at 20 mA/cm 2 can be achieved. Meanwhile, hexagonal MoO 3 microrods are grown vertically onto carbon fibers and their electrochemical behaviors in normal H 2 SO 4 electrolyte are investigated. Finally, novel dual-asymmetric supercapacitors (DASCs) with the configuration of CNC/H 2 SO 4 +PVA + Fe 2+/3+ //H 2 SO 4 +PVA/h-MoO 3 are assembled. The device exhibits an excellent areal capacitance of 1502 mF/cm 2 at 3 mA/cm 2 , and a remarkable ultrahigh energy density of 252.4 μW h/cm 2 at the power energy of 1.6 mW/cm 2 as well. The research is expected to promote the development of SCs with high energy density through the design and assembly of all their main components, including the direct growth of active materials onto current collectors and the appropriate utilizing the redox active gel electrolyte. • A facile method for growing carbon nanocoils on stainless steel mesh was developed. • The flame catalytic growth mechanism of CNCs on stainless steel mesh was proposed. • Arrays of vertical h-MoO 3 hexagonal micro-rods was grown onto carbon fabric. • Novel dual-asymmetric supercapacitor with redox active gel electrolyte was assembled. • Remarkable capacitance of 1.5F/cm 2 and energy density of 252.4 μWh/cm 2 was realized.

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.

Dielectrophoresis-based microwire biosensor for rapid detection of Escherichia coli K-12 in ground beef

By combining a functionalized microwire sensor with a dielectrophoresis (DEP) technique, a rapid and accurate detection method for bacterial pathogens was developed and demonstrated. The gold-tungsten microsensor (sensing diameter, 25 μm) was functionalized with specific Escherichia coli (E. coli) antibodies against surface antigens to capture E. coli bacterial cells from phosphate buffer saline (PBS) and ground beef. The DEP technique consisted of the application of a pin-type microwire and large base electrode under an alternating current (AC) electric field of 10 Vpp at a frequency of 3 MHz. Additionally, bovine serum albumin (BSA) was utilized as a blocking agent for the attachment of nonspecific proteins to the microwire surface to prevent false positive signals due to nonspecific binding. The resistance and fluorescent intensity (FI) demonstrated a linear relationship with the concentration of E. coli cells ranging from 103 to 107 CFU/mL. These results showed that DEP can be used as a reliable alternative for the detection of E. coli without a blocking effect minimizing the significant difference between PBS and ground beef.

Grain structure related inhomogeneous elastocaloric effects in Cu–Al–Mn shape memory microwires

An inhomogeneous elastocaloric effect has been found and investigated in the present Cu–Al–Mn shape memory microwires by using the combined technique of infrared thermography and electron backscatter diffraction. Upon unloading, a reversible temperature change of ~5 K has been detected within the 5 mm gauge length. Inhomogeneous temperature distribution can be directly observed on the surface of microwires through infrared thermography measurement. Different regions of the microwires, involving bi-crystalline, oligo-crystalline, single-crystalline and poly-crystalline grain architectures, display different eCE cyclic stability, which can be ascribed to the heterogeneous grain architectures, the discrepancy of grain orientation and the varied neighboring grain constraints.

Magnesium-based biodegradable microelectrodes for neural recording.

This article reports fabrication, characterization, degradation and electrical properties of biodegradable magnesium (Mg) microwires coated with two functional polymers, and the first in vivo evidence on the feasibility of Mg-based biodegradable microelectrodes for neural recording. Conductive poly(3,4‑ethylenedioxythiophene) (PEDOT) coating was first electrochemically deposited onto Mg microwire surface, and insulating biodegradable poly(glycerol sebacate) (PGS) was then spray-coated onto PEDOT surface to improve the overall properties of microelectrode. The assembled PGS/PEDOT-coated Mg microelectrodes showed high homogeneity in coating thickness, surface morphology and composition before and after in vivo recording. The charge storage capacity (CSC) of PGS/PEDOT-coated Mg microwire (1.72mC/cm2) was nearly 5 times higher than the standard platinum (Pt) microwire widely used in implantable electrodes. The Mg-based microelectrode demonstrated excellent neural-recording capability and stability during in vivo multi-unit neural recordings in the auditory cortex of a mouse. Specifically, the Mg-based electrode showed clear and stable onset response, and excellent signal-to-noise ratio during spontaneous-activity recordings and three repeats of stimulus-evoked recordings at two different anatomical locations in the auditory cortex. During 10days of immersion in artificial cerebrospinal fluid (aCSF) in vitro, PGS/PEDOT-coated Mg microelectrodes showed slower degradation and less change in impedance than PEDOT-coated Mg electrodes. The biodegradable PGS coating protected the PEDOT coating from delamination, and prolonged the mechanical integrity and electrical properties of Mg-based microelectrode. Mg-based novel microelectrodes should be further studied toward clinical translation because they can potentially eliminate the risks and costs associated with secondary surgeries for removal of failed or no longer needed electrodes.

Grain Structure Related Inhomogeneous Elastocaloric Effects in Cu-Al-Mn Shape Memory Microwires

An inhomogeneous elastocaloric effect (eCE) has been found and investigated in the present Cu-Al-Mn shape memory microwires by using combined technique of infrared thermography and electron backscatter diffraction. Upon unloading, a reversible temperature change of ~5 K has been detected within the 5 mm gauge length. Inhomogeneous temperature distribution can be directly observed on the surface of microwires through infrared thermography measurement. Different regions of the microwires, involving bi-crystalline, oligo-crystalline, single-crystalline and poly-crystalline grain architectures, display different eCE cyclic stability, which can be ascribed to the heterogeneous grain architectures, the discrepancy of grain orientation and the varied neighboring grain constraints.

Simulation of sputtering from an isolated conductor surrounded by a dielectric during plasma etching

We investigate the action of ion flows from a plasma onto the surface of a flat conductor lying on an insulator, with width less than the plasma Debye length. The model allows study of the processing with a steady state or pulsed potential on the microwire. The shape of pulses has been synthesized to provide the most homogeneous distribution of the etching rate over the microwire surface.

Rotation-Induced Macromolecular Spooling of DNA

Genetic information is stored in a linear sequence of base-pairs; however, thermal fluctuations and complex DNA conformations such as folds and loops make it challenging to order genomic material for in vitro analysis. In this work, we discover that rotation-induced macromolecular spooling of DNA around a rotating microwire can monotonically order genomic bases, overcoming this challenge. We use single-molecule fluorescence microscopy to directly visualize long DNA strands deforming and elongating in shear flow near a rotating microwire, in agreement with numerical simulations. While untethered DNA is observed to elongate substantially, in agreement with our theory and numerical simulations, strong extension of DNA becomes possible by introducing tethering. For the case of tethered polymers, we show that increasing the rotation rate can deterministically spool a substantial portion of the chain into a fully stretched, single-file conformation. When applied to DNA, the fraction of genetic information sequentially ordered on the microwire surface will increase with the contour length, despite the increased entropy. This ability to handle long strands of DNA is in contrast to modern DNA sample preparation technologies for sequencing and mapping, which are typically restricted to comparatively short strands resulting in challenges in reconstructing the genome. Thus, in addition to discovering new rotation-induced macromolecular dynamics, this work inspires new approaches to handling genomic-length DNA strands.

Size-dependent UV and gas sensing response of individual Fe2O3-ZnO:Fe micro- and nanowire based devices

In this work, the UV and gas sensing properties of single Fe-doped and Fe2O3-functionalized ZnO micro- and nanowires are reported. The influence of microwire diameter and concentration of Fe2O3 micro- and nanoparticles on the sensing properties of the fabricated devices was investigated. Results clearly reveal that sensors with a higher response can be obtained by a decrease in the diameter of micro- and nanowires and an increase of the Fe2O3 micro- and nanoparticle concentration on the surface of microwires. The enhanced sensing properties can be explained based on excellent charge separation properties of the formed Fe2O3/ZnO heterojunctions in the case of UV response which prolong the photocarrier lifetime and based on excellent catalytic properties of Fe2O3 in the case of gas sensing. The presented results demonstrate the importance of surface functionalization of single ZnO structures with other semiconducting oxide micro- and nanoparticles for the improvement of their sensing properties, i.e., UV and ethanol sensing, even for a single wire/rod with micro- and nanometric diameter.

Manipulation of Magnetic Domain Structures With Helical Magnetization in Magnetic Microwires

We report investigations on crossed magnetic field-induced transformation of surface domain structure in amorphous glass covered microwires. The study has been performed by a magneto-optical Kerr effect technique using optical microscopy. The existence of elliptic domain structure has been demonstrated experimentally. The formation of the domain structure with periodically inclined domain walls caused by the circular magnetic field was found in the surface of microwires.

Experimental demonstration of basic mechanisms of magnetization reversal in magnetic microwires

We report on the magneto-optical study of surface magnetization reversal in glass covered Co-rich microwires. Four different mechanisms of magnetization reversal were found to exist, depending on external magnetic field configuration. An analysis of the results obtained was performed using the theoretical model which proposes the existence of four magnetization states with different chirality. This model was developed previously to describe current-induced switching in wires with variable inner core radius. The co-existence of stable and meta-stable helical magnetic states on the microwire surface is the basic reason for the variety of mechanisms observed for the magnetization reversal.

Solution growth of ZnO microwires and grass architectures

• Au nanoparticles with different shapes and sizes were produced. • Au nanoparticles resulted in uniformly dispersed and standing ZnO microwires. • Au nanoparticles serve as heterogeneous nucleation sites for the ZnO microwires. • Au nanoparticles also resulted in ZnO grass architectures. In spite of extensive research in gold (Au) nanoparticles, it remains a challenge to synthesize structurally homogeneous sample-set with controlled morphologies. The latter critically affect the role of Au nanoparticles as a seed/catalyst for the growth of other nanostructures. Here, we systematically studied and quantified the growth of Au nanoparticles in a single-step chemical synthesis approach and observed the effects of growth temperature and duration, metal salt and surfactant concentration, and surfactant type. These parameters strongly influenced morphological evolution, distribution, and heterogeneities in the as-synthesized Au nanoparticles. Next, the synthesized Au nanoparticles were utilized for the growth of zinc oxide (ZnO) microwires in a solution growth approach. It was observed that Au nanoparticles on the substrate did not catalyze the growth of ZnO microwires but facilitated uniform dispersion of standing microwires. Supported by microscopic analysis, the proposed growth mechanism is heterogeneous nucleation of ZnO on the loosely bound Au nanoparticles on the substrates, favored by lattice match between the ZnO and Au. Based on this mechanism, Au nanoparticles only assisted in the initial stages of ZnO microwire growth. For longer growth duration (~10 h), over-deposition of ZnO from the solution on already grown wires led to their micron scale diameters as well as grass architectures and making the growth process independent of size and shape of the Au nanoparticles. The formation of ZnO grass architecture is due to attachment of Au nanoparticles on the growing microwire surface, which further served as a heterogeneous nucleation site for the ZnO growth. These Au nanoparticles detached from the Si wafer due to cleavage of Au S bonds or hydrolysis of Si O bonds on the thiolated Si wafer in presence of the ZnO growth precursor (hexamethylenetetramine) and conditions. As-synthesized Au nanoparticles and ZnO microwires were characterized by high-resolution transmission electron microscopy, scanning electron microscopy, and Raman spectroscopy.

Investigation of heat transfer around microwire in air environment using 3ω method

The 3ω principle is presented for the measurement of the heat transfer coefficient (h) based on natural convection model and heat conduction model. The 3ω technique is used at room temperature to measure h over the surfaces of microwires of the diameters 10–100 μm at horizontal and vertical orientations. The fitted results show that the heat loss from the microscale platinum wire to the air is dominated by heat conduction and the natural convection contribution is negligible. The comparison of the measured third harmonics for horizontal and vertical wires justifies that the orientation effect is negligible at microscales. The measured value of h is nearly two orders larger than that at macro scale and of the similar order to those from other literatures. Based on the 3ω principle, an explicit expression with a heat conduction shape factor is introduced and can predict the heat transfer coefficient reasonably in the validated range of frequency. Both the experimental results and the theoretical analysis conclude that the scale effect of heat transfer may be contributed to two factors: the effect of buoyancy, the driving force at microscales may be negligible; the heat loss is enhanced mainly by high ratio of surface to volume at microscales. It also shows the validation of the 3ω principle for thin wire if the heat loss to surrounding gas is dominated by heat conduction at microscale.

Oxidation of a platinum microwire surface applied in glucose detection

In this paper, we report the results of the surface oxidation of platinum (Pt) microwires in aqueous sulfuric acid (H 2 SO 4) solutions by using a cyclic voltammetry technique. The Pt microwire chips were scanned and applied with voltage potentials ranging from 0 to 1.4 V in the H 2 SO 4 solution with concentrations from 0.0003 to 0.0018 M to find out the optimized concentration of sulfuric acid for the oxidation process. The cyclic voltammetry (CV) measurements show the oxidation peak at a potential range from 1.1 to 1.2 V. This is the peak of the interfacial place exchange of chemisorbed O (O chem ) and surface Pt atoms, resulting in the formation of a quasi-3D surface PtO lattice comprising Pt 2+ and O 2−. The oxidized surface Pt microwires were then functionalized with a 3-aminopropyl triethoxy silane (APTES) and glucose oxidase (GOD) was immobilized onto the functionalized chips for further application in glucose detection. By using this process, Pt microwires have been used for the successful detection of glucose in solution with concentrations in the range of 4–20 mM.

The effect of surface domain structure on low-field microwave absorption of magnetic microwires

A model to describe the low-field microwave absorption of soft magnetic microwires is proposed. The field distributions inside a microwire and microwave absorption are found by means of a solution of Maxwell equations and the Landau–Lifshitz–Gilbert equation. It is shown that the microwave absorption field dependence is sensitive to a domain structure in a microwire surface region. The results obtained are applicable for both the amorphous microwires and the microwires consisting of a conducting nonmagnetic core and a soft magnetic shell.

Outer shell structure in nearly zero magnetostrictive amorphous microwires

Nearly zero magnetostrictive microwires have been proven to be very versatile, due to their extremely soft magnetic properties, the changes in their magnetization mechanism with dimensions, and the appearance of sensitive application-related effects, such as the large Barkhausen and the giant magnetoimpedance effects. Their sensitive magnetoimpedance response originates in the specific domain structure, composed of an inner core and an outer shell (OS), since the OS with a circumferential easy axis is the main region involved in the magnetoimpedance effect. The circumferential OS is believed to display a bamboolike structure with consecutive rings circumferentially magnetized in opposite directions. However, earlier theoretical studies predicted a uniformly magnetized OS as being energetically favored. This paper aims to clarify this contradiction. The variation of the magnetostatic energy from the bamboo domain to the uniformly magnetized state has been calculated and it has been found to be null. Therefore, a uniformly magnetized OS has lower energy due to the absence of domain walls. Calculation results are supported by magneto-optical Kerr effect surface domain images and surface hysteresis loops. For large values of the metallic nucleus diameter, as well as for microwires with the glass coating removed, the OS vanishes, being replaced with a surface region with helical magnetization, which expands toward the microwire surface.