Aligned Arrays Research Articles

Diameter dependence of the UV light detecting performance of InGaN/GaN nanorods array photodetector

Vertically aligned InGaN/GaN nanorod arrays with multiple quantum wells (MQWs) was prepared via inductively coupled plasma (ICP) followed by a further anisotropic wet etching method. It was demonstrated that the sizes of nanorods could be easily regulated in the ranges of 330–1090 nm by simply controlling the ICP etch parameters. The morphology characterisation results indicated that these nanorods are of straight and smooth appearance, and the length of nanorods is about 4 μm. Ultraviolet (UV) detectors based on nanorods arrays with different diameters were fabricated, which exhibited fast response/recovery speed and good response. The UV detecting performance was getting better with the decrease of nanorods diameter, which may be caused by the suppression of the dark current. This work provides an efficient route for fabricating the large-scale vertical aligned MQWs nanorods array and developing their fascinating applications.

Large‐Area, Solution‐Processed, Hierarchical MAPbI3 Nanoribbon Arrays for Self‐Powered Flexible Photodetectors

AbstractOrganic–inorganic perovskites with micro‐/nanostructures exhibit outstanding optical and electrical properties, thus attracting increased attention as components of high‐performance optoelectronic devices, but the fabrication of complex micro‐/nanostructured perovskites shows limited success. This study describes the fabrication of hierarchical methylammonium lead iodide (MAPbI3) nanoribbon (NR) arrays with controlled internal nanorod structures by simple spin‐coating with solvent treatment process and investigates the suitability of these arrays for high‐performance and multifunctional photodetectors. In the UV‐to‐800‐nm range, photodetectors based on the hierarchical MAPbI3 NR arrays exhibit specific detectivities 18.1–23.7 times higher than those of photodetectors based on MAPbI3 films due to the effective photon management and reduced charge trap states in the hierarchical MAPbI3 NR arrays. The solution‐processed hierarchical MAPbI3 NRs can be fabricated on various substrates including ultrathin polyimide, which facilitates the development of flexible photodetectors with highly stable photoresponse under bending strain. Furthermore, the ferroelectricity and the highly anisotropic alignment of MAPbI3 NR arrays allow multifunctional photodetectors capable of self‐powered and polarization‐sensitive light detection, respectively. The strategy used to fabricate hierarchical organic–inorganic perovskite NR arrays is believed to be applicable to other types of perovskites and can probably be used to construct various optoelectronic devices based on hierarchical nanostructures.

Interdigitated Electrode‐Based Triboelectric Sliding Sensor for Security Monitoring

AbstractSecurity monitoring and precaution for private information and property plays a key role in the smart home system. In this work, a triboelectric nanogenerator‐based active sliding sensor is demonstrated which can monitor the position, displacement, velocity, and direction of a contact sliding objects. The device consists of a mover and a stator which operate in sliding mode. Two aligned column arrays of copper electrodes are coated on the substrate as the mover, while two interdigitated copper electrode pairs with relative position shift are coated under a polytetrafluoroethylene film as the stator. The experimental results show that a single device can generate a voltage of about 5 V at a resistance load of 60 MΩ at a sliding velocity of 0.5 m s–1. The sliding sensor can detect an ultralow velocity in 0.001 m s–1 as well as the sliding direction of the mover. The sensor can be fixed on the drawer and door to detect the motion parameters which are sent to a remote client application for security monitoring in smart home systems. The proposed sliding sensor has great potential in the Internet of things, personal motion feature recognition, and meandering trajectory tracking.

Impact of aligned carbon nanotubes array on the magnetostatic isolation of closely packed ferromagnetic nanoparticles

We investigate the influence of carbon nanotubes (CNT) aligned array on the magnetic properties of ensemble of densely packed Co nanoparticles (NPs) embedded inside CNT. Each CNT contains only one nanosized Co. Such a special structure was formed by catalyst chemical vapor deposition (CCVD) activated by current discharge plasma and hot filament. The Co NPs, previously deposited onto SiO2/Si substrate, acted as a catalyst. By varying the parameters of the CCVD process, we were able to also sputter the substrate instead of CNT growth. Co NPs were used as a mask and the structure of Si-based nanocones with Co NPs on the top of each cone was formed. Exhaustive investigation of the structural, morphology and crystalline properties of Co nanoparticles were performed. The magnetic properties of two kinds of samples, Co on the Si-based nanocone and Co inside CNT, were differ drastically. In the former case, the magnetic anisotropy of thin-film-type has been observed with large magnetic domains. Whereas for the Co-CNT samples ferromagnetic NPs were magnetically isolated. It was established that the magnetic anisotropy of nanosized Co plays more dominant role than the dipole interaction between Co NPs. The role of the CNT container in this is discussed.

Improving the efficiency of wind farms via wake manipulation

AbstractWind turbine farms suffer from wake losses, where the downstream turbines generate less power, and/or the leading turbines are throttled to reduce the downstream power losses. In this paper, we focus on possible external modifications that can enhance the wind turbines' performance when they are operating in a farm environment. In particular, this study is interested in enhancing the performance of the downstream turbines in wind farms. The idea is to move each turbine's wake down and away from subsequent turbines. This goal is achieved by using stationary external airfoils that are placed in proximity to the rotating blades. A number of different designs are tested and the design concepts are tested using Reynolds‐Averaged Navier‐Stokes simulations of an aligned array of 2 wind turbines. The turbines are modeled as actuator disks with axial induction and are placed in a velocity field that is modeled as a turbulent atmospheric boundary layer. It is found that fixed external airfoils can enable partial or full power recovery at turbine separations of as small as 3 rotor diameters downstream. We will also demonstrate that some devices can also improve the performance of the upstream turbine. The physical reasons for these power recovery phenomena are discussed.

Blown bubble assembly of ultralong 1D bismuth sulfide nanostructures with ordered alignment and shape control

Recently, semiconducting chalcogenide nanostructures have attracted intense attention due to their excellent properties and broad applications, especially metal chalcogenides in the form of A2(V)B3(VI). Here we synthesized one-dimensional (1D) bismuth sulfide (Bi2S3) nanostructures with a length of more than 100 μm via a one-step hydrothermal method, and found that the reaction temperature and the alkali concentration play vital roles in the morphology of the 1D nanostructures. Since the as-synthesized Bi2S3 nanostructures were disordered in powder form, it is necessary to align them with ordered orientation and uniform distribution before further application. A blown bubble method was specifically applied to align these ultralong 1D nanostructures, and the assembly mechanism was also deeply analyzed, including the drift of nanostructures in the bubble film thickness direction, the relationship between (nanowire) NW spacing and array density, and the angle deviation of aligned arrays assembled from different bubble solutions. Interestingly, the initial straight Bi2S3 NWs could also be converted into buckled nanosprings (NSs) with regular pitches during the assembly process, and different NS formation stages were observed. A possible deformation mechanism or load bearing model of the wavy NS was proposed and verified, and the Young’s modulus of an individual NW was figured out for the first time. After annealing under a N2 atmosphere, the aligned Bi2S3 NWs embedded in the bubble film were exposed, and the clean arrays were fabricated into functional optoelectronic devices such as photodetectors with a high performance.

Humidity sensor based on micro optical fiber array fabricated by electrospinning

This paper reports a new type of humidity sensor based on aligned microfibers array waveguides with high specific surface area for the sensing region. The MNF array is fabricated by electrospinning and light can be efficiently coupled into them. The results indicate that the microfiber waveguides have uniform diameter and smooth morphology. Simultaneously, the microfiber array present obvious humidity sensing properties through strong evanescent fields for the humidity of 35–85 RH % with short response time, good linearity, stability and repeatability. Significantly, this idea provides an efficient and simple way to achieve a large number of optical waveguides array in microscopic scale with excellent optical characteristics and the microfibers could find wide applications in various micro or nano scale photonic and sensitive devices.

Fabrication and evaluation of controllable deposition distance for aligned pattern by multi-nozzle near-field electrospinning

To mass-volume fabricate micro- and nano-scales aligned pattern, multi-nozzle near-field electrospinning (NFES) direct-writing technology is well proposed as a high-efficiency method in electrohydrodynamic (EHD) printing process. However, the interference effect among adjacent nozzles and coupling effect of various parameters have restricted to investigate deposition characteristic of multi-nozzle NFES and control EHD multi-jet deposition accuracy. In order to improve the accuracy of EHD multi-jet deposition with high-efficiency printing process, the experimental result compared with theoretical method were discussed. In this work, the influence of multi-nozzle geometry distribution and electrospinning parameters on deposition characteristic was studied with multi-nozzle NFES setup, and nozzles were in linear array. The deposition distance and homogeneity of aligned nanofibers were measured and explained with coefficient of dispersion on electric field among nozzles by simulation. Moreover, deposition distance of multi-nozzle NFES process was evaluated by modified theoretical derivation based on our previous studies. The modified theoretical derivation showed a good agreement with experiment results, and indicated that multi-nozzle NFES could accurately and efficiently direct-write aligned array pattern in future.

Aligned Carbon Nanotube Synaptic Transistors for Large-Scale Neuromorphic Computing.

This paper presents aligned carbon nanotube (CNT) synaptic transistors for large-scale neuromorphic computing systems. The synaptic behavior of these devices is achieved via charge-trapping effects, commonly observed in carbon-based nanoelectronics. In this work, charge trapping in the high- k dielectric layer of top-gated CNT field-effect transistors (FETs) enables the gradual analog programmability of the CNT channel conductance with a large dynamic range ( i. e., large on/off ratio). Aligned CNT synaptic devices present significant improvements over conventional memristor technologies ( e. g., RRAM), which suffer from abrupt transitions in the conductance modulation and/or a small dynamic range. Here, we demonstrate exceptional uniformity of aligned CNT FET synaptic behavior, as well as significant robustness and nonvolatility via pulsed experiments, establishing their suitability for neural network implementations. Additionally, this technology is based on a wafer-level technique for constructing highly aligned arrays of CNTs with high semiconducting purity and is fully CMOS compatible, ensuring the practicality of large-scale CNT+CMOS neuromorphic systems. We also demonstrate fine-tunability of the aligned CNT synaptic behavior and discuss its application to adaptive online learning schemes and to homeostatic regulation of artificial neuron firing rates. We simulate the implementation of unsupervised learning for pattern recognition using a spike-timing-dependent-plasticity scheme, indicate system-level performance (as indicated by the recognition accuracy), and demonstrate improvements in the learning rate resulting from tuning the synaptic characteristics of aligned CNT devices.

Hierarchical Arrays of Cesium Lead Halide Perovskite Nanocrystals through Electrophoretic Deposition.

The suppression of halide ion exchange between CsPbBr3 and CsPbI3 nanocrystals achieved through capping with PbSO4-oleate has enabled us to deposit different perovskite nanocrystals as aligned arrays on the electrode surfaces without intermixing of species. The electrophoretic deposition of PbSO4-oleate-capped CsPbX3 (X = Cl, Br, I) nanocrystals suspended in hexane solution on mesoscopic TiO2 films allows the design of controlled architecture with single or multiple layers of perovskite films. The hierarchy in the assembly of these nanocrystals is seen first through the linearly organized nanocrystals in hexane followed by the deposition of larger linear rods ∼500 nm in length. Since most of the photophysical properties of nanocrystals are retained in these aligned arrays, we can design films with tunable luminescence including white color. The electrophoretic deposition of layered films of perovskites in a controlled fashion opens up new ways to design tandem perovskite solar cells and tunable display devices.

Effectiveness of short and straight carbon nanotubes on dispersion state and static/dynamic mechanical properties of woven glass fibre-reinforced polymer laminates

This study reports about the dispersibility of short, straight and pristine multi-walled carbon nanotubes (pCNTs) in epoxy and their effectiveness on the mechanical properties of three-phased GF/epoxy/pCNT laminates. These nanotubes were produced by arc discharge method and had an average aspect ratio (l/d) of 100. Glass fibre-reinforced polymer samples with four different weight fractions of these nanotubes (0.5, 1.0, 1.5 and 2.0 wt.% of the total matrix system) were fabricated and tested for their thermo-mechanical and mechanical properties. These carbon nanotubes with small aspect ratio contributed well to the strengthening mechanism due to their homogeneous dispersion. Fractography revealed that these nanotubes formed aligned arrays that minimized entanglements between the individual tubes, thus leading to lesser agglomerates up to 1.5 wt.% of carbon nanotube loading. However, the samples modified with 2.0 wt.% of nanotubes had lesser individual tubes and more of their aggregates. Unmodified glass fibre-reinforced polymer samples had a glass transition temperature (Tg) of 139.2℃, whereas addition of 1.5 wt.% of multi-walled carbon nanotubes increased the same to 160℃. Similarly, these specimens witnessed about 21% and 34% enhancement in tensile and flexure strength over the control samples, respectively. However, these trends dropped at 2.0 wt.% carbon nanotube loading owing to nanotubes aggregation but were higher than those of the neat epoxy composite. Samples containing carbon nanotubes witnessed higher fatigue life which proves that multi-walled carbon nanotubes with smaller aspect ratio are capable of obstructing fatigue crack growth.

Probing of polymer to carbon nanotube surface interactions within highly aligned electrospun nanofibers for advanced composites

By electrospinning poly(ethylene oxide) (PEO)-blended sodium dodecyl sulfate (SDS) functionalized carbon nanotube (CNT) solutions, we engineered single- and double-walled nanotubes into highly aligned arrays. CNT alignment was measured using electron microscopy and polarised Raman spectroscopy. Mechanical tensile testing demonstrates that a CNT loading of 3.9 wt% increases the ultimate tensile strength and ductility of our composites by over a factor of 3, and the Young's modulus by over a factor of 4, to ∼260 MPa. Transmission electron microscopy (TEM) reveals how the aligned nanotubes provide a solid structure, preventing polymer chains from slipping, as well as polymer crystallisation structures such as ‘shish-kebabs’ forming, which are responsible for the improved mechanical properties of the composite. Differential scanning calorimetry (DSC) and small angle X-ray scattering (SAXS) reveals micellar and hexagonal columnar structures along the axis of the fibers, some of which are associated with the presence of the CNT, where these hexagonal structures are associated with the SDS functionalization on the CNT surfaces. This work demonstrates the benefits of CNT alignment within composites, revealing the effectiveness of the electrospinning technique, which enables significantly improved functionality, increasing the utility of the composites for use in many different technological areas.

Large-area Scanning Probe Nanolithography Facilitated by Automated Alignment and Its Application to Substrate Fabrication for Cell Culture Studies

Scanning probe microscopy has enabled the creation of a variety of methods for the constructive ('additive') top-down fabrication of nanometer-scale features. Historically, a major drawback of scanning probe lithography has been the intrinsically low throughput of single probe systems. This has been tackled by the use of arrays of multiple probes to enable increased nanolithography throughput. In order to implement such parallelized nanolithography, the accurate alignment of probe arrays with the substrate surface is vital, so that all probes make contact with the surface simultaneously when lithographic patterning begins. This protocol describes the utilization of polymer pen lithography to produce nanometer-scale features over centimeter-sized areas, facilitated by the use of an algorithm for the rapid, accurate, and automated alignment of probe arrays. Here, nanolithography of thiols on gold substrates demonstrates the generation of features with high uniformity. These patterns are then functionalized with fibronectin for use in the context of surface-directed cell morphology studies.

Large-area Scanning Probe Nanolithography Facilitated by Automated Alignment and Its Application to Substrate Fabrication for Cell Culture Studies.

Scanning probe microscopy has enabled the creation of a variety of methods for the constructive ('additive') top-down fabrication of nanometer-scale features. Historically, a major drawback of scanning probe lithography has been the intrinsically low throughput of single probe systems. This has been tackled by the use of arrays of multiple probes to enable increased nanolithography throughput. In order to implement such parallelized nanolithography, the accurate alignment of probe arrays with the substrate surface is vital, so that all probes make contact with the surface simultaneously when lithographic patterning begins. This protocol describes the utilization of polymer pen lithography to produce nanometer-scale features over centimeter-sized areas, facilitated by the use of an algorithm for the rapid, accurate, and automated alignment of probe arrays. Here, nanolithography of thiols on gold substrates demonstrates the generation of features with high uniformity. These patterns are then functionalized with fibronectin for use in the context of surface-directed cell morphology studies.

1 × 25 LCOS-based wavelength selective switch with flexible passbands and channel selection

Abstract Wavelength-selective-switching based reconfigurable optical add-drop multiplexers are the essential components of current and next generation dynamic optical networks. A proof-of-concept 1 × 25 wavelength selective switch is demonstrated experimentally based on liquid crystal on silicon (LCOS) technology and 2-foptical system. Each of the input C-band wavelength channel can be independently selected and switched into arbitrary output ports. The channel passband and channel spacing can be adjusted flexibly by applying holograms onto an LCOS chip. The insertion loss for polarized beam ranges from 5.4 to 7.5 dB for 1–20 output ports and increases up to 9.6 dB at side ports for 100 GHz spaced ITU-T channels over the C-band. The general channel crosstalk is below −20 dB. The minimum resolution of center frequency for each channel is 5 GHz (0.04 nm). The performance can be further improved by using an LCOS chip with smaller pixel pitch, higher-quality optical components and accurate alignment of the fiber-lenslet array.

Draw Spinning of Wafer‐Scale Oxide Fibers for Electronic Devices

AbstractThe fabrication of functionalized 1D oxide fibers with accurate control of orientation, location, and number is highly demanded and challengeable based on current techniques, which hinder their practical application in opto/electronic devices. Herein, a rapid and simple method is developed to directly draw the oxide fibers from its polymer solution over large area. The draw‐spinning method enables the accurate positioning of individual fiber and the construction of complex patterns, holding great potentials in fiber‐based electronics. The assembled field‐effect transistors (FETs) based on single indium oxide (In2O3) fiber exhibit excellent current modulation capability with a high on/off current ratio of 106. Adjusting the number of fibers within the channel, the device performance can be modulated. Moreover, the draw‐spinning technique is applied to fabricate highly aligned fiber arrays by using brush pen. The FETs based on aligned In2O3 fiber arrays exhibit superior current‐driven capability compared with the devices with limited number of fibers. Their further integrations on high‐permittivity dielectric layer show improved device performance at an operating voltage of 4 V. This method is scalable and can be implemented easily to fabricate various functional fibers in both laboratory and industrial manufacturing.

Fabrication of IrO2 decorated vertical aligned self-doped TiO2 nanotube arrays for oxygen evolution in water electrolysis

To fabricate effective and stable OER electrode in water electrolysis, self-doped TiO2 nanotube arrays which has a higher electrical conductivity than pristine TiO2 nanotube arrays was used as the support for loading IrO2. The self-doped TNTA was fabricated by a simple electrochemical reduction of TNTA in neutral electrolyte solution, and then IrO2 nano particles were deposited by pulse electro-deposition method. The cyclic voltammetric behavior, electrical conductivity and micro structure of self-doped TNTA prepared at different reduction potential were characterized to obtain an optimal performance, and self-doped TNTA prepared under −1.9 V (vs. Ag/AgCl) shows the best electrochemical performance. After depositing IrO2, the OER activity and stability of new electrodes were also determined. Due to the enhanced electrical conductivity of support, the mass activity of IrO2/self-doped TNTA are 50 times higher than IrO2/TNTA. The OER stability of new electrode was evaluated under constant current of 5 mA/cm2, IrO2/TNTA and IrO2/Ti were also tested for comparison. A higher stability of IrO2/self-doped TNTA electrode is observed than the other two electrodes, and XPS studies indicate a lower oxidation state of Ir in IrO2/self-doped TNTA, this shows a possible interactions between IrO2 and the new support.

Printable Zn2GeO4 Microwires Based Flexible Photodetectors with Tunable Photoresponses

AbstractPrinted electronics have drawn considerable attention due to their unique features and broad applications in future portable and wearable electronic devices. Herein, a near‐field direct‐printing method is used to realize a precise manipulation of microwires in the level of the individual wire for depositioning in a desired position and direction. High‐performance flexible photodetectors are fabricated on printed aligned Zn2GeO4 microwires arrays, which show excellent photoresponse, stability, and uniformity toward UV light irradiation. Studies find that the photocurrents can be easily tuned by adjusting the number of printed microwires, enabling a potential application in printable imaging sensors. Patterned flexible photodetector arrays are also fabricated with a high sensitivity (≈4 × 103), precise manipulation, tunable photoresponses, and a good tolerance toward mechanical deformations. This work paves the way toward efficient fabrication of printable electronic device and facilitates their practical applications in future printed electronics, such as flexible and wearable functional devices, electronic textiles, transistors, and circuits.

Scalable Direct Writing of Lanthanide-Doped KMnF3 Perovskite Nanowires into Aligned Arrays with Polarized Up-Conversion Emission.

The use of one-dimensional nano- and microstructured semiconductor and lanthanide materials is attractive for polarized-light-emission studies. Up-conversion emission from single-nanorod or anisotropic nanoparticles with a degree of polarization has also been discussed. However, microscale arrays of nanoparticles, especially well-aligned one-dimensional nanostructures as well as their up-conversion polarization characterization, have not been investigated yet. Herein, we present a novel and facile paradigm for preparing highly aligned arrays of lanthanide-doped KMnF3 (KMnF3:Ln) perovskite nanowires, which are good candidates for polarized up-conversion emission studies. These perovskite nanowires, with a width of 10 nm and length of a few micrometers, are formed through the oriented attachment of KMnF3:Ln nanocubes along the [001] direction. By the employment of KMnF3:Ln nanowire gel as nanoink, a direct-writing method is developed to obtain diverse types of aligned patterns from the nanoscale to the wafer scale. Up-conversion emissions from the highly aligned nanowire arrays are polarized along the array direction with a polarization degree up to 60%. Taking advantage of microscopic nanowire arrays, these polarized up-conversion emissions should offer potential applications in light or information transportation.

Confined Shear-Based Alignment of Carbon Nanotubes for Thin Film Transistors

Individual semiconducting single-walled carbon nanotubes (s-SWCNTs) exhibit the high charge-carrier mobility, current carrying capacity, and sensitivity needed for applications based on thin-film transistors (TFTs) such as flexible electronics, displays, and sensors. However, assembling s-SWCNTs into aligned arrays to exploit the exceptional electronic properties of this material has been a major roadblock toward the integration of s-SWCNTs into electronic devices. Here, we are able to use confined shear-based alignment to fabricate aligned arrays of s-SWCNTs across arbitrarily large substrates. In this study, we demonstrate that large amounts of shear can be used to align s-SWCNTs from solution by forcing s-SWCNT ink at high volumetric flow rates through 20 - 100 µm tall channels on SiO2 substrates. We use Raman spectroscopy to quantify the ratio of the Raman G band (~1590 cm-1) to the Si peak (~520 cm-1) of our films. This ratio provides a measure of the amount of s-SWCNTs deposited. We study the deposition from three concentrations of ink (~70, 35, and 7 µg mL-1) while varying the volume of ink used at a set shear rate of 3.2*105 s-1. The G/Si ratio behavior is similar for each concentration. Initially, there is a steep increase in the G/Si ratio up to 100 µL of ink, after which, the G/Si ratio increases linearly with increasing volume of ink. Polarized Raman spectroscopy is used to quantify the disorder in the film. We show that for the s-SWCNT ink concentrations used in this study, the concentration does not affect the degree of alignment in the aligned s-SWCNT films and that the shear rate is the main factor affecting the alignment. Assuming the s-SWCNTs are oriented within a Gaussian angular distribution, from polarized Raman spectroscopy, the angular width of distribution was measured to be σ = 30° for a shear rate of 3.2*105 s-1 regardless of ink concentration and volume. This degree of alignment makes this technique non-ideal for fabricating devices with small channel lengths for high-performance applications such as logic or radio-frequency devices. However, for long-channel devices, there must be some amount of disorder in the s-SWCNT films to allow for charge percolation. This means this shear alignment technique is ideal for fabricating films for long-channel devices such as TFTs. Here, we fabricate transistors from films of shear-aligned s-SWCNTs and study the effect of degree of alignment on the transistor performance. Because of the simplicity of this technique, we are able to scale the deposition of aligned s-SWCNTs to arbitrarily large areas as long as the high shear rate is maintained. This makes the technique ideal for large-area scaling in industry applications. As a demonstration, we show the large-area, uniform alignment of s-SWCNTs via confined shear-based alignment across a 4” wafer.