Microwires Research Articles

Controllable Synthesis of Se Microwires and Mixed‐Dimensional Se/MoS2 Vertical Heterostructures for Nonlinear Optical Applications

AbstractSelenium (Se), as a typical elemental semiconductor, has garnered significant attention due to its excellent carrier mobility, outstanding photoconductivity, and broad spectral response. However, Se micro‐ and nanostructures exhibit inherently low nonlinear optical coefficients, necessitating substantial enhancement of their nonlinear optical properties. In this study, trigonal Se (t‐Se) microwires (MWs) and t‐Se/MoS2 mixed‐dimensional vertical heterostructures are synthesized using the atmospheric pressure vapor phase deposition method. the influence of precursor concentration on the growth of t‐Se MWs is systematically investigated, and computational fluid dynamics simulations are employed to elucidate the growth mechanism. Open‐aperture Z‐scan measurements reveal that the nonlinear optical properties of t‐Se/MoS2 mixed‐dimensional vertical heterostructures are significantly enhanced compared to those of t‐Se MWs and monolayer MoS2 nanosheets. First‐principles calculations based on density functional theory, along with surface potential measurements indicate that effective charge transfer across the interfaces of the vertical heterostructures is critical for enhancing their nonlinear optical properties. This study provides valuable insights into the development of next‐generation nonlinear optical materials and advanced devices.

Highly Polarization‐Sensitive Solar‐Blind Ultraviolet Photodetection Based on 1D Rb2CuCl3 Microwires

AbstractPolarization‐sensitive solar‐blind ultraviolet (UV) photodetectors are essential in both civilian and military applications. 1D perovskites derivative Rb2CuCl3 holds promise for polarization‐sensitive solar‐blind UV photodetectors due to its wide direct bandgap, anisotropic crystal structure, and long carrier lifetime. However, no studies on the polarization properties of Rb2CuCl3 are reported. Here, the electronic structural anisotropy of Rb2CuCl3 is confirmed by calculating the partial charge density distribution in the ac‐plane and bc‐plane. Then, the Raman‐active modes and corresponding atomic vibration modes are explored within the bc‐plane through joint experimental and theoretical Raman spectroscopy. Besides, angle‐resolved Raman, photoluminescence, and absorption spectroscopy reveal the intriguing anisotropic photoelectric characteristics of Rb2CuCl3 microwires (MWs). By using single Rb2CuCl3 MW as the photoactive layer, a polarization‐sensitive solar‐blind UV photodetector is fabricated, showing high photoresponsivity of 78 mA W−1 and photocurrent anisotropy ratio of ≈1.7 at 265 nm. Importantly, the proposed photodetectors without encapsulation exhibit excellent stability in ambient air, retaining the original photocurrent after two months, showcasing practical applicability. This study underscores the promise of Rb2CuCl3 for high‐performance polarization‐sensitive solar‐blind UV photodetectors, contributing valuable insights into its electronic structure, photoelectric properties, and practical applicability.

Single glass and polymer coated phosphate glass microwire photoactuators with instant response times and large actuating angles

Over the years significant scientific attention has been given towards the design of advanced photoactuating architectures as they are important elements for various optical tweezers, grippers, and soft robot applications. Most of the currently available photoactuators, rely on the existence of a free-space illumination pathway from the light sources to the device or on the employment of bendable optical fibers, while consisting of two or more elements, i.e. the photoactuating material and the substrate. Herein, we report on a facile method of preparing single-component pristine microwires (MWs) that exhibit photoactuating features upon utilizing a soft phosphate glass doped with silver nanoparticles (AgNPs), without the need of any additional photoactuating element. The developed photoactuators exhibited bending angles of around 110°, within a couple of seconds. In addition, we have fabricated double-component polymer-coated phosphate glass MWs photoactuators, upon employing PDMS coatings on the surface of the so-formed glass MWs. The introduction of the polymer component boosts the bending angle of the photoactuating device to over 200° within the a few seconds upon modest laser irradiation. The presence of AgNPs within the glass MWs, play a key role on the remarkable performance of the developed photoactuators, both in terms of actuating angles as well as of the respective response times, since they assist on the effective transmission of laser irradiation energy to thermal energy. The fabrication method reported here appears promising for the development of high-performance and low-cost free-space, as well as fiber-based photoactuators.

Postmelting Encapsulation of Glass Microwires for Multipath Light Waveguiding within Phosphate Glasses.

Glass waveguides are the fundamental component of advanced photonic circuits and play a pivotal role in diverse applications, including quantum information processing, light generation, imaging, data storage, and sensing platforms. Up to date, the fabrication of glass waveguides relies mainly on demanding chemical processes or on the employment of expensive ultrafast laser equipment. In this work, we demonstrate an advanced, simple, low-temperature, postmelting encapsulation procedure for the development of glass waveguides. Specifically, silver iodide phosphate glass microwires (MWs) are drawn from splat-quenched glasses. These MWs are then incorporated in a controlled manner within transparent silver phosphate glass matrices. The judicious selection of glass compositions ensures that the refractive index of the host phosphate glass is lower than that of the embedded MWs. This facilitates the propagation of light inside the encapsulated higher refractive index MWs, leading to the facile development of waveguides. Importantly, we substantially enhance the light transmission within the MWs by leveraging the plasmon resonance effects due to the presence of silver nanoparticles spontaneously generated owing to the silver iodide phosphate glass composition. Employing this innovative approach, we have successfully engineered waveguide devices incorporating either one or two MWs. Remarkably, the dual MW devices are capable of transmitting light of different colors and in multipath direction, rendering the developed waveguides outstanding candidates for extending the functionalities of diverse photonic and optoelectronic circuits, as well as in intelligent signaling applications in smart glass technologies.

Nonlinear optical response of strain-mediated gallium arsenide microwire in the near-infrared region.

Gallium arsenide (GaAs) semiconductor wires have emerged as potent candidates for nonlinear optical devices, necessitating bandgap engineering for an expanded operational wavelength range. We report the successful growth of strain-mediated GaAs microwires (MWs) with an average diameter of 1.1 μm. The axial tensile strain in these wires, as measured by X-ray diffraction and Raman scattering, ranges from 1.61 % to 1.95 % and from 1.44 % to 2.03 %, respectively. This strain condition significantly reduces the bandgap of GaAs MWs compared to bulk GaAs, enabling a response wavelength extension up to 1.1 μm. Open aperture Z-scan measurements reveal a nonlinear absorption coefficient of -15.9 cm/MW and a third-order magnetic susceptibility of -2.8×10-8 esu at 800 nm for these MWs. I-scan measurements further show that the GaAs saturable absorber has a modulation depth of 7.9 % and a nonsaturation loss of 3.3 % at 1050 nm. In laser applications, GaAs MWs have been effectively used as saturable absorbers for achieving Q-switched and dual-wavelength synchronous mode-locking operations in Yb-bulk lasers. These results not only offer new insights into the use of large diameter semiconductor wires but also expand the potential for applications requiring bandgap tuning.

The optimization of CuxO microwires synthesis for improvement in photoelectrochemical performance

One of the most important challenges in the fabrication of CuxO microstructures via the electrochemical method is formation of long, regular and well-packed microwires with good adhesion on the Cu substrate and to achieve better photoelectrochemical properties, which can be potentially applied in solar-driven water splitting and CO2 conversion to light hydrocarbons. In this paper, Cu2O photoelectrode has been fabricated by direct anodization of the Cu foil, then CuO microwires (MWs) was formed by calcination process. The effect of the applied potential (10–40 V), sodium fluoride content in the electrolyte (0.2–0.5% wt.) as well as calcination conditions (400–500 °C, 60–360 min) on the morphology, phase composition, optical and photoelectrochemical properties was investigated. The highest photocurrent response was −0.71 mA cm−2 for the sample 0.35%_10V_400 °C_60min with 0.83 μm length and 154 nm diameter. The mechanism of the photocurrent generation process in the presence of CuxO/Cu under UV–Vis irradiation was proposed.

Single-Crystalline Li2Sn(IO3)6 Microwires: Combining Optical-Waveguiding and Frequency-Doubling Functions.

High-quality single-crystalline Li2Sn(IO3)6 microwires (MWs) have been successfully prepared by using a facile hydrothermal method. The as-synthesized Li2Sn(IO3)6 MWs exhibit regular hexagonal prism morphology, excellent surface smoothness, and remarkable diameter uniformity. The optical propagation loss has been determined to be as low as 0.026 dB μm-1 at 785 nm wavelength, implying the low-loss optical waveguiding capability of the Li2Sn(IO3)6 MWs. The effective frequency-doubling conversions of the fundamental frequency light source in the wavelength range from 916 to 1560 nm have been observed, and the second-harmonic generation (SHG) conversion efficiency has been measured to be 2.1% with a 1560 nm fundamental pump source (pulse duration of 10 ns, and average power of 9.06 nW) transmitted through a 1.32-μm-diameter and 300-μm-length Li2Sn(IO3)6 MW. These intriguing optical waveguiding and strong SHG conversion capabilities of the Li2Sn(IO3)6 MWs suggest its potential applications for photonic devices in micrometer scale.

Negative temperature coefficient of ZnO microwires for cryogenic temperature sensing

Negative temperature coefficient (NTC) thermistors are expected to be developed at cryogenic temperature sensing. In this paper, a kind of cryogenic thermistor was developed based on NTC response of single crystal ZnO microwires (MWs). The current–voltage (I–V) characterization demonstrated a NTC response, which was temperature dependence of resistance that decreased with increasing temperature. A sensitive NTC response, especially at the cryogenic temperature range, was observed. The defects in ZnO MWs play an important role in NTC response; therefore, we studied the origin of NTC effect associated with defects to improve the recognition of relationship between defects and the NTC effect and further optimize the temperature sensor design for high performance. Annealing at 800 °C in air was undertaken to make a significant influence on the concentration of defects in as-grown sample, and a series of temperature-dependent features were investigated by photoluminescence, Raman, XPS, and EPR measurements. The results indicated the zinc interstitials to be effective donors for sensitive NTC effect at the cryogenic region. This study provides insight into the ZnO NTC effect and sensitive cryogenic sensing technology.

High‐Quality CsAg2I3Microwires Grown by Spatial Confinement Method for Self‐Powered UV Photodetectors

AbstractRecently, lead halide perovskites arouse intensive attentions in photoelectric fields owing to their low trap state density, high carrier mobility, large extinction coefficient, and low‐temperature solution processing technique. However, their future commercial development is severely hampered by the lead toxicity and instability. Although lead‐free metal‐halide perovskites recently have been extensively studied in optoelectronics, their low‐dimensional counterparts can further expand their novel optical and electronic properties for potential applications. In this work, the planar growth of one‐dimensional (1D) CsAg2I3 single‐crystal microwires (MWs) on diverse substrates by space‐confined method is reported. The growth kinetic process of CsAg2I3 single‐crystal MWs is elucidated by in situ observation. Furthermore, the CsAg2I3 single‐crystal MWs exhibit potential applications in ultraviolet light photodetectors as a photoactive layer. The fabricated heterojunction photodetector exhibits pronounced photoelectric performances working in self‐powered mode, including a specific detectivity of 2.09 × 108 Jones, a high responsivity of 26.5 mA W−1, and fast response speed of 258.43/289.32 ms under light illumination of 265 nm, due to the high crystallinity and effective photogenerated carrier transfer. This study provides a vital insight into the rational design of low‐dimensional perovskites for versatile optoelectronic applications.

High Responsivity and EQE of Single ZnO:Sb Microwire/Ti3C2Tx Heterojunction UV Photodetector

One-dimensional Sb-doped ZnO/Ti3C2Tx (ZnO:Sb/Ti3C2Tx) core–shell heterojunction microwires (MWs) have been fabricated in this work. The Mott–Schottky measurement confirms the p-type conductivity of the obtained ZnO:Sb MWs. The current–voltage (I–V) characteristics of the ZnO:Sb/Ti3C2Tx core–shell heterojunction show a well-defined rectification behavior with a rectification ratio of up to 1000. Photodetectors (PDs) based on a single ZnO:Sb/Ti3C2Tx core–shell heterojunction microwire exhibit a high ultraviolet (UV) response with ultrahigh responsivity (R) and an external quantum efficiency (EQE) of up to 29.2 A/W and 9920% at −1 V bias and under UV light (365 nm, 0.15 mW/cm2) irradiation. The high photocurrent of the PDs is driven by the increased Schottky barrier height of the distinct heterojunction and the extra external carrier injection. In addition, the PD exhibits satisfying self-power performance with an R of 40 mA/W and detectivity of 8.15 × 1011 Jones. This work provides a feasible reference direction for developing highly responsive microwire-based PDs.

Ultraviolet photodetector based on RbCu2I3 microwire

Copper-based halide perovskites have shown great potential in lighting and photodetection due to their excellent photoelectric properties, good stability and lead-free nature. However, as an important piece of copper-based perovskites, the synthesis and application of RbCu2I3 have never been reported. Here, we demonstrate the synthesis of high-quality RbCu2I3 microwires (MWs) by a fast-cooling hot saturated solution method. The prepared MWs exhibit an orthorhombic structure with a smooth surface. Optical measurements show the RbCu2I3 MWs have a sharp ultraviolet absorption edge with 3.63 eV optical band gap and ultra-large stokes shift (300 nm) in photoluminescence. The subsequent photodetector based on a single RbCu2I3 MW shows excellent ultraviolet detection performance. Under the 340 nm illumination, the device shows a specific detectivity of 5.0 × 109 Jones and a responsivity of 380 mA·W−1. The synthesis method and physical properties of RbCu2I3 could be a guide to the future optoelectronic application of the new material.

Metal Microwires Functionalized with Cell-Imprinted Polymer for Capturing Bacteria in Water

Molecularly imprinted polymers (MIPs) and cell-imprinter polymers (CIPs) have emerged as synthetic recognition elements in biomimetic sensors. In this paper, we have conducted a parametric study to optimize a bulk polymerization methodology for uniform functionalization of stainless steel microwires (MWs) with CIPs comprising single to fourplex combinations of functional monomers (FMs). MWs are widely used in biosensors, and their functionalization with single-FM MIPs has been demonstrated. Complex MIPs comprising multiple FMs have shown enhanced selectivity toward microorganisms, but their coating on MWs has yet to be shown. Moreover, imprinting microorganisms into these coatings has not been reported. In our studies, solvent, FM, cross-linker-to-FM ratio, polymerization temperature, and time were found to significantly influence the thickness and uniformity of CIP coatings on MWs. Reproducible CIP coatings with a thickness of 2.2 ± 0.4 μm, imprinted with E. coli OP50 as the template, were achieved. E. coli rebinding assays demonstrated a 76 ± 10% capture efficiency in a suspension with an initial bacteria count of 104 CFU/mL, using a 3 cm long CIP-MW with an optimized fourplex CIP composition, while the capture efficiency obtained by using a single-monomer CIP composition was 30 ± 5%. Our results indicated a higher binding capacity of fourplex CIP-MWs to target bacteria, while nonsignificant binding was obtained using single-monomer CIP-MWs. The addition of N-vinylpyrrolidone significantly increased the binding performance due to its hydrophobic–hydrophilic functional groups interacting with counterparts on the surface of bacterial cells. The developed CIP-MWs can be integrated with microfluidic sensing systems as low-cost and stable working electrodes for future transduction of CIP-target binding events to an electrical read-out in CIP-based electrochemical biomimetic sensors.

Fractal Branched Microwires of Organic Semiconductor with Controlled Branching and Low-Threshold Amplified Spontaneous Emission

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 β-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.

Generation of Defective Few-Layered Graphene Mesostructures by High-Energy Ball Milling and Their Combination with FeSiCuNbB Microwires for Reinforcing Microwave Absorbing Properties

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.

Flexible self-powered solar-blind Schottky photodetectors based on individual Ga2O3 microwire/MXene junctions

Flexible solar-blind Schottky photodetectors made of individual β-Ga2O3 microwires (MWs) and Ti3C2Tx (MXene) on a PET substrate are designed.

Spraying Perovskite Intermediate Enabling Inch‐Scale Microwire Film Fabrication for Integration Compatible Efficient‐Photodetectors Array

AbstractMetal halide perovskite microwires (MWs) have emerged as promising photoactive materials for highly efficient photodetectors (PDs). However, large‐scale MWs film fabrication is still a formidable challenge for achieving integration compatible perovskite PDs arrays, owing to precipitation and structure crushing of MWs during deposition and annealing. Herein, a strategy of fabrication of inch‐scale perovskite MWs films is presented by depositing perovskite intermediate suspension through spray‐coating, which addresses the trade‐off present between the high flatness of MWs film and its large‐scale fabrication. The single crystalline perovskite MWs weave a film with high enough flatness rendering narrow performance distribution of high efficiency on the 7 × 7 PDs arrays. The formamidinium lead iodide (FAPbI3) PDs arrays show average responsivity and detectivity of (1.60 ± 0.46) A W−1 and (1.49 ± 0.50) × 1012 Jones. The methanaminium lead iodide (MAPbI3) PDs arrays show average responsivity and detectivity of (0.065 ± 0.046) A W−1 and (2.54 ± 0.77) × 1011 Jones. The champion PDs based on FAPbI3 MWs film and MAPbI3 MWs film show detectivity of 1.26 × 1013 and 9.67 × 1011 Jones, which are much higher than that of corresponding polycrystalline films and located on the top ranking of similar devices.

Electrical properties of 2H-Si microwire grown by mixed-source hydride vapor phase epitaxy

Hexagonal 2H polytypes of Si (2H-Si) exhibit promising mechanical and optical properties owing to their crystal structures with quasi-direct bandgap characteristics. However, few studies have investigated the electrical properties of 2H-Si semiconductors. In this study, we used a hot-probe measurement to determine the doping type of 2H-Si microwires (MWs) prepared by hydride vapor-phase epitaxy (HVPE). It was found that the 2H-Si MWs had unintentional n-type characteristics. For the first time, a heterojunction PN diode with n-type 2H-Si MW and p-type Si (100) was fabricated. According to the current–voltage and capacitance–voltage measurements, the n-type doping concentration of the unintentionally doped 2H-Si MWs was 4.3–9.5 × 1015 cm−3 and the electron mobility was 260–580 cm2/V·s.

High performance solar-blind ultraviolet photodetector based on ITO/β-Ga2O3 heterostructure

The authors report an indium tin oxide (ITO) decorated solar-blind deep ultraviolet photodetectors (PDs) based on high quality β-Ga2O3 single crystal microwires (MWs). An ultrahigh photo-to-dark current (I photo/I dark) ratio ∼107 of the PDs has been realized. Compared with In/β-Ga2O3/In metal-semiconductor-mental (MSM) PD, the device with ITO as the interlayers between In and β-Ga2O3 show excellent performances, such as the high responsivity of 1720.2 A W−1 and 438.8 A W−1 under 260 nm illumination with reverse and forward bias, respectively. In addition, the device exhibited a very low dark current as low as 2.0 × 10−13 A and a photocurrent up to 1.0 × 10−6 A at the bias of −6 V (under 1.95 mW cm−1@260 nm). The rise and fall time of the device were 0.5 s and 0.2 s, which was significantly faster than MSM structure. Moreover, the device exhibited an ultrahigh solar-blind/visible rejection ratio (R 260 nm/R 400 nm) of 1.09 × 105, a detectivity D* of 1.23 × 1014 Jones and the external quantum efficiency of 4180.3%. The excellent performances of the PDs are attributed to the improved carrier separating process at the ITO/β-Ga2O3 interfaces and the reduced carrier trapping behavior induced by the β-Ga2O3 surface states. The introduction of ITO between MWs and the electrodes is of great significance for the application of β-Ga2O3 based detectors.

Switch type PANI/ZnO core-shell microwire heterojunction for UV photodetection

In this study, single crystal ZnO microwires (MW) with size of ∼5.4 mm × 30 μm are prepared through a chemical vapor deposition technique at high temperature (1200 °C). Subsequently, p-type conducting polyaniline (PANI) polymers with different conductivities are densely coated on part of the ZnO MW to construct organic/inorganic core-shell heterojunction photodetectors. The hetero-diodes reach an extremely high rectification ratio (I +3V /I -3V ) of 749230, and a maximum rejection ratio (I 350nm /I dark ) of 3556 (at -3 V), indicating great potential as rectified switches. All the heterojunction devices exhibit strong response to ultraviolet (UV) radiation with high response speed. Moreover, the obvious photovoltaic behavior can also be obtained, allowing the device to operate as an independent and stable unit without externally supplied power. Under 0 V bias voltage, the self-powered photodetector shows a maximum responsivity of 0.56 mA W −1 and a rapid response speed of 0.11 ms/1.45 ms (rise time/decay time). Finally, a finite difference time domain (FDTD) simulation is performed to further demonstrate the interaction mechanism between the incident light field and the hexagonal cavity, which strongly supports the enhancement of the light absorption in whispering-gallery-mode resonator.

A (CH3)2CNHCH3PbBr3/CH3NH3PbBr3 core-shell heterostructure fabricated by an in situ a-site reaction for fast response 1D perovskite photodetectors.

Benefitting from their long carrier diffusion lengths, low trap densities and high carrier mobilities, metal halide perovskites are of great value in the field of energy and optical communications. Herein, we propose a reversible organic cation reaction for (CH3)2CNHCH3PbBr3/CH3NH3PbBr3 core-shell microwires (MWs), in which (CH3)2CNHCH3PbBr3 grow on bulk CH3NH3PbBr3 in acetone and then convert back to CH3NH3PbBr3 on the surface with the action of water. The core-shell MWs present excellent stability for more than 454 days with over 80% humidity. Moreover, the employed core-shell heterostructure significantly increases the photoluminescence lifetime and improves the rise/recovery response. The (CH3)2CNHCH3PbBr3/CH3NH3PbBr3 core-shell heterostructure demonstrates excellent stability and fast response (2.8 ms/0.8 ms), which is anticipated to find comprehensive applications in future optical communication of one-dimensional devices.