Nanowire Hybrid Structure Research Articles

Sn/InAs Josephson Junctions on Selective Area Grown Nanowires with in Situ Shadowed Superconductor Evaporation.

Superconductor-semiconductor nanowire hybrid structures are useful in fabricating devices for quantum information processing. While selective area growth (SAG) offers the flexibility to grow semiconductor nanowires in arbitrary geometries, in situ evaporation of superconductors ensures pristine superconductor-semiconductor interfaces, resulting in strong induced superconductivity in the semiconducting nanowire. In this work, we used high-aspect-ratio SiOx dielectric walls to in situ evaporate islands of superconductor tin on in-plane InAs SAG nanowires. Our technique enables customization in the designs of such hybrid nanostructures, while simultaneously performing the nanowire and superconductor growth without breaking vacuum. Using this technique, we grew super(S)-normal(N)-super(S), NS, and SNSNS junctions. We performed cryogenic electron transport measurements revealing the presence of gate and field tunable supercurrents. We further measured the superconducting gap and critical fields in the hybrid nanostructures and the crossover from 2e to 1e periodicity in the SNSNS junctions as a proof of the usability of these hybrid nanostructures.

A neuromorphic bionic eye with filter-free color vision using hemispherical perovskite nanowire array retina

Spherical geometry, adaptive optics, and highly dense network of neurons bridging the eye with the visual cortex, are the primary features of human eyes which enable wide field-of-view (FoV), low aberration, excellent adaptivity, and preprocessing of perceived visual information. Therefore, fabricating spherical artificial eyes has garnered enormous scientific interest. However, fusing color vision, in-device preprocessing and optical adaptivity into spherical artificial eyes has always been a tremendous challenge. Herein, we demonstrate a bionic eye comprising tunable liquid crystal optics, and a hemispherical neuromorphic retina with filter-free color vision, enabled by wavelength dependent bidirectional synaptic photo-response in a metal-oxide nanotube/perovskite nanowire hybrid structure. Moreover, by tuning the color selectivity with bias, the device can reconstruct full color images. This work demonstrates a unique approach to address the color vision and optical adaptivity issues associated with artificial eyes that can bring them to a new level approaching their biological counterparts.

Fabrication and characterization of low-sheet-resistance and stable stretchable electrodes employing metal and metal nanowire hybrid structure

Stretchable electrodes with high stretching capability and low sheet resistance were developed using a metal/silver nanowires (AgNWs)/metal hybrid structure on a poly-dimethylsiloxane substrate. A low sheet resistance around 100 mΩ square−1 was achieved using the hybrid structures of Ag/AgNWs/Ag and Cu/AgNWs/Cu electrodes. The stretching capability under single and multi-cycling strain conditions was greatly improved due the AgNWs in-between top and bottom metal electrodes. The random connection of AgNWs generates new current path over the various cracks and wavy structures of the metal electrodes, which improve the initial resistance, the stretching capability under single strain up to 16%, and the resistance stability under 100 times cycling strain for the electrodes. Using a simple resistor model, it was shown that the hybrid structure is effective to improve the stretching capability of the stretchable metal electrodes due to the random connection of AgNWs in-between the metal electrodes.

Optimal Co(OH)₂ Nanowire Contents in Graphene Nanosheet Electrode on Its Electrochemical Performance of Supercapacitor.

Graphene/Co(OH)₂ nanowire composite films were successfully synthesized using a simple three-step treatment, and the effect of the Co(OH)₂ nanowire content on the electrochemical properties of the composite films was studied in this study. One-dimensional Co(OH)₂ nanowires were homogeneously embedded and dispersed between the prepared graphene papers, forming a layered graphene/Co(OH)₂ nanowire hybrid structure. These composite films exhibited better electrochemical properties than the previously reported graphene composites with carbon spheres such as graphene/CNT composites. These graphene composites were fabricated using the same method we used in this study but without the addition of Co(OH)₂ nanowires. The addition of a small amount of Co(OH)₂ to reduced graphene oxide (rGO) (RGO:Co(OH)₂=5:1) yielded thick paper-like rGO/Co(OH)₂ sandwiches, which showed an excellent specific capacitance of 1032.57 Fg-1 at a scan rate of 5 mVs-1. These results indicate the potential of these composites for the development of highly capacitive energy storage devices for practical applications.

Fabrication of a Combustion-Reacted High-Performance ZnO Electron Transport Layer with Silver Nanowire Electrodes for Organic Solar Cells.

Herein, a new methodology for solution-processed ZnO fabrication on Ag nanowire network electrode via combustion reaction is reported, where the amount of heat emitted during combustion was minimized by controlling the reaction temperature to avoid damaging the underlying Ag nanowires. The degree of participation of acetylacetones, which are volatile fuels in the combustion reaction, was found to vary with the reaction temperature, as revealed by thermogravimetric and compositional analyses. An optimized processing temperature of 180 °C was chosen to successfully fabricate a combustion-reacted ZnO and Ag nanowire hybrid electrode with a sheet resistance of 30 Ω/sq and transmittance of 87%. A combustion-reacted ZnO on Ag nanowire hybrid structure was demonstrated as an efficient transparent electrode and electron transport layer for the PTB7-Th-based polymer solar cells. The superior electrical conductivity of combustion-reacted ZnO, compared to that of conventional sol-gel ZnO, increased the external quantum efficiency over the entire absorption range, whereas a unique light scattering effect due to the presence of nanopores in the combustion-derived ZnO further enhanced the external quantum efficiency in the 450-550 nm wavelength range. A power conversion efficiency of 8.48% was demonstrated for the PTB7-Th-based polymer solar cell with the use of a combustion-reacted ZnO/Ag NW hybrid transparent electrode.

1-D Metal Nanobead Arrays within Encapsulated Nanowires via a Red-Ox-Induced Dewetting: Mechanism Study by Atom-Probe Tomography.

Metal nanoparticle arrays are excellent candidates for a variety of applications due to the versatility of their morphology and structure at the nanoscale. Bottom-up self-assembly of metal nanoparticles provides an important complementary alternative to the traditional top-down lithography method and makes it possible to assemble structures with higher-order complexity, for example, nanospheres, nanocubes, and core-shell nanostructures. Here we present a mechanism study of the self-assembly process of 1-D noble metal nanoparticles arrays, composed of Au, Ag, and AuAg alloy nanoparticles. These are prepared within an encapsulated germanium nanowire, obtained by the oxidation of a metal-germanium nanowire hybrid structure. The resulting structure is a 1-D array of equidistant metal nanoparticles with the same diameter, the so-called nanobead (NB) array structure. Atom-probe tomography and transmission electron microscopy were utilized to investigate the details of the morphological and chemical evolution during the oxidation of the encapsulated metal-germanium nanowire hybrid-structures. The self-assembly of nanoparticles relies on the formation of a metal-germanium liquid alloy and the migration of the liquid alloy into the nanowire, followed by dewetting of the liquid during shape-confined oxidation where the liquid column breaks-up into nanoparticles due to the Plateau-Rayleigh instability. Our results demonstrate that the encapsulating oxide layer serves as a structural scaffold, retaining the overall shape during the eutectic liquid formation and demonstrates the relationship between the oxide mechanical properties and the final structural characteristics of the 1-D arrays. The mechanistic details revealed here provide a versatile tool-box for the bottom-up fabrication of 1-D arrays nanopatterning that can be modified for multiple applications according to the RedOx properties of the material system components.

C and O doped BN nanoflake and nanowire hybrid structures for tuneable photoluminescence

Abstract C and O doped BN nanoflakes and hybrid nanoflake-nanowire structures were synthesized in N2+H2 environment using plasma-enhanced hot filament chemical vapour deposition with solid B4C as boron and carbon precursor. Structure and chemical composition of the C and O doped BN nanoflakes and hybrid nanoflake-nanowire hybrid structures were systemically studied using advanced characterization instruments including high resolution transmission electron microscope, micro-Raman spectroscope, Fourier transform infrared spectroscope, X-ray diffractometer, field emission scanning electron microscope, and X-ray photoelectron spectroscope. The obtained results evidence that the C and O doped BN nanowires nucleate and grow directly on the tops of C and O doped BN nanoflakes due to the presence of dangling bonds on the surfaces of tips of C and O doped BN nanoflakes, which were formed by the ion bombardment in plasma. The photoluminescence (PL) properties of C and O doped BN nanoflakes and C and O doped BN nanoflake-nanowire hybrid structures were studied at room temperature using a micro-Raman system with the 325 nm line of He-Cd laser as the excitation source. The results of PL measurements indicate that the PL properties of C and O doped BN nanoflake-nanowire hybrid structures significantly change with the length of C and O doped BN nanostructures due to the interface zones caused by the nanowire length. Thus, the PL properties can be efficiently tuned by the length of nanowires. These achievements can contribute to the synthesis of novel BN-based hybrid nanostructures and the development of the next generation BN-based optoelectronic nanodevices.

Enhanced room-temperature NO2 gas sensing with TeO2/SnO2 brush- and bead-like nanowire hybrid structures

We have synthesized two highly sensitive, room-temperature operating TeO2/SnO2 gas sensors with hierarchical nanowire structures. One is a brush-like nanostructure, from a two-step thermal vapor-transport route, and the other one is a TeO2/SnO2 bead-like nanostructure, from annealing of the former. The TeO2/SnO2 nanostructures exhibit a greatly enhanced room-temperature gas-sensing response compared to pristine TeO2 nanowires in the sequence: TeO2/SnO2 bead-like structure > brush-like structure > pristine TeO2 nanowire. The response of the TeO2/SnO2 bead-like structure is in a range of 10 to 20 against NO2 gas of ppm levels (3–100 ppm) at room temperature. This compares favorably to the response, smaller than 2, for the pristine TeO2 nanowires. Interestingly, the TeO2/SnO2 bead-like structure exhibits a typical n-type gas-sensing behavior, in contrast to the p-type behavior from the brush-like and the pristine TeO2 structures. Possible hybrid growth and sensing mechanisms are discussed.

ZnO nanorod/porous silicon nanowire hybrid structures as highly-sensitive NO2 gas sensors at room temperature.

ZnO nanorod/porous silicon nanowire (ZnO/PSiNW) hybrids with three different structures as highly sensitive NO2 gas sensors were obtained. PSiNWs were first synthesized by metal-assisted chemical etching, and then seeded in three different ways. After that ZnO nanorods were grown on the seeded surface of PSiNWs using a hydrothermal procedure. ZnO/PSiNW hybrids showed excellent gas sensing performance for various NO2 concentrations (5-50 ppm) at room temperature, and the electrical resistance change rate reached as high as 35.1% when responding to 50 ppm NO2. The distinct enhancement was mainly attributed to the faster carrier transportation after combination, the increase in gas sensing areas and the oxygen vacancy (VO) concentration. Moreover, the p-type gas sensing behavior was explained by the gas sensing mechanism and the effect of VO concentration on gas sensing properties was also discussed concerning the photoluminescence (PL) spectra performance.

Electrical Tuning of Surface Plasmon Polariton Propagation in Graphene–Nanowire Hybrid Structure

We demonstrate a dynamic surface plasmonic modulation based on graphene-nanowire (grapheme-NW) hybrid structures in the visible light range. A static modulation depth of as high as 0.07 dB/μm has been achieved experimentally. Through careful simulation and systematical experimental investigation, we found that the dual-confinement effect of charge density and electromagnetic energy around the vicinity of the NW will dramatically enhance the light-matter interaction and increase the Fermi level shifting, which are the key roles for bringing the optical response of the device to the visible range. The carrier concentration near the vicinity of a Ag NW is estimated to reach 0.921×10(14) cm(-2) after applying more than 25 V voltages, which is enough to shift the Fermi level for visible light. Furthermore, the modulation behaviors near the Dirac point of monolayer graphene and the singularity of gap-induced bilayer graphene are investigated. Calculated optical conductivity as a function of Fermi level predicts a minimum value near the Dirac point, which is consistent with the experimental results.

Decorating Semiconductor Silver-Tetracyanoquinodimethane Nanowires with Silver Nanoparticles from Ionic Liquids

Hybrid semiconducting silver-tetracyanoquinodimethane (AgTCNQ) nanowires decorated with Ag nanoparticles have been synthesized at room temperature in the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate. Hydroquinone was applied to reduce Ag+ and TCNQ to silver nanoparticles, and TCNQ–, respectively, under ambient conditions. AgTCNQ nanowires were formed via spontaneous electrolysis between Ag metal nanoparticles and TCNQ, and reaction between Ag+ and TCNQ–. Microscopic, spectroscopic, and X-ray characterizations all confirmed the formation of crystalline Ag nanoparticle–AgTCNQ nanowire hybrid structures. The ionic liquid was used as a reaction medium, but also as a stabilizing (or blocking) agent to control the nucleation and growth rate of AgTCNQ wires.

Graphene-silver nanowire hybrid structure as a transparent and current spreading electrode in ultraviolet light emitting diodes

We report a device that combines graphene film and Ag nanowires (AgNWs) as transparent and current spreading electrodes for ultra-violet (UV) light emitting diode (LED) with interesting characteristics for the potential use in the deep UV region. The current-voltage characteristics and electroluminescence (EL) performance show that graphene network on AgNWs well-operates as a transparent and current spreading electrode in UV LED devices. In addition, scanning electron microscopy and EL images exhibit that graphene film act as the protection layer of AgNWs layer as well as a transparent conducting network, by bridging AgNWs.

Carbon fiber–ZnO nanowire hybrid structures for flexible and adaptable strain sensors

We report the flexible piezotronic strain sensors fabricated using carbon fiber-ZnO nanowire hybrid structures by a novel and reliable method. The I-V characteristic of the sensor shows high sensitivity to external strain due to the change in Schottky barrier height (SBH), which has a linear relationship with strain. This fabricated strain sensor has a quick, real-time current response under both static and dynamic mechanical loads. The change in SBH resulted from the strain-induced piezoelectric potential is investigated by band gap theory. In this work we develop a new feasible method to fabricate a flexible strain sensor within the fabric adapted to textile structures, able to measure their strain.

Graphene–nanowire hybrid structures for high-performance photoconductive devices

Graphene–CdS nanowire (NW) hybrid structures with high-speed photoconductivity were developed. The hybrid structure was comprised of CdS NWs which were selectively grown in specific regions on a single-layer graphene sheet. The photoconductive channels based on graphene–CdS NW hybrid structures exhibited much larger photocurrents than graphene-based channels and much faster recovery speed than CdS NW network-based ones. Our graphene–CdS NW structures can be useful because they were much faster than commercial CdS film-based photodetectors and had photocurrents large enough for practical applications.

Synthesis of High Crystallinity ZnO Nanowire Array on Polymer Substrate and Flexible Fiber-Based Sensor

Well aligned ZnO nanowire (NW) arrays are grown on Kevlar fiber and Kapton film via the chemical vapor deposition (CVD) method. These NWs have better crystallinity than those synthesized through the low-temperature hydrothermal method. The average length and diameter of ZnO NWs grown on Kevlar fiber can be controlled from 0.5 to 2.76 μm and 30 to 300 nm, respectively. A flexible ultraviolet (UV) sensor based on Kevlar fiber/ZnO NWs hybrid structure is made to detect UV illumination quantificationally.

Antireflection properties and solar cell application of silicon nanostructures

Silicon nanowire arrays (SiNWAs) are fabricated on polished pyramids of textured Si using an aqueous chemical etching method. The silicon nanowires themselves or hybrid structures of nanowires and pyramids both show strong anti-reflectance abilities in the wavelength region of 300–1000 nm, and reflectances of 2.52% and less than 8% are achieved, respectively. A 12.45% SiNWAs-textured solar cell (SC) with a short circuit current of 34.82 mA/cm2 and open circuit voltage (Voc) of 594 mV was fabricated on 125 × 125 mm2 Si using a conventional process including metal grid printing. It is revealed that passivation is essential for hybrid structure textured SCs, and Voc can be enlarged by 28.6% from 420 V to 560 mV after the passivation layer is deposited. The loss mechanism of SiNWA SC was investigated in detail by systematic comparison of the basic parameters and external quantum efficiency (EQE)of samples with different fabrication processes. It is proved that surface passivation and fabrication of a metal grid are critical for high efficiency SiNWA SC, and the performance of SiNWA SC could be improved when fabricated on a substrate with an initial PN junction.

Synthesis of carbon coated silica nanowires

Carbon coated silica nanowire hybrid structures were directly synthesized by a chemical vapor deposition method using ethanol as the precursor. The morphology and structural properties of the nanostructures were investigated. It was found that, in the sample prepared at a relative lower temperature (1185 °C), the carbon shell was composed of orderly graphitic layers, whereas the carbon shell on those fabricated at higher temperature (1236 °C) was amorphous. Moreover, the thickness of the amorphous carbon shell increased with increasing reaction temperature and reaction time.

Microfibre–nanowire hybrid structure for energy scavenging

A self-powering nanosystem that harvests its operating energy from the environment is an attractive proposition for sensing, personal electronics and defence technologies. This is in principle feasible for nanodevices owing to their extremely low power consumption. Solar, thermal and mechanical (wind, friction, body movement) energies are common and may be scavenged from the environment, but the type of energy source to be chosen has to be decided on the basis of specific applications. Military sensing/surveillance node placement, for example, may involve difficult-to-reach locations, may need to be hidden, and may be in environments that are dusty, rainy, dark and/or in deep forest. In a moving vehicle or aeroplane, harvesting energy from a rotating tyre or wind blowing on the body is a possible choice to power wireless devices implanted in the surface of the vehicle. Nanowire nanogenerators built on hard substrates were demonstrated for harvesting local mechanical energy produced by high-frequency ultrasonic waves. To harvest the energy from vibration or disturbance originating from footsteps, heartbeats, ambient noise and air flow, it is important to explore innovative technologies that work at low frequencies (such as <10 Hz) and that are based on flexible soft materials. Here we present a simple, low-cost approach that converts low-frequency vibration/friction energy into electricity using piezoelectric zinc oxide nanowires grown radially around textile fibres. By entangling two fibres and brushing the nanowires rooted on them with respect to each other, mechanical energy is converted into electricity owing to a coupled piezoelectric-semiconductor process. This work establishes a methodology for scavenging light-wind energy and body-movement energy using fabrics.

Chemical Conversion Reaction between CdS Nanobelts and ZnS Nanobelts by Vapor Transport

Single-crystalline wurtzite CdS nanobelts are completely converted into single-crystalline wurtzite ZnS nanobelts by Zn vapor transport (at 800 °C). In contrast, the ZnS nanobelts are not completely transformed into CdS nanobelts by Cd vapor transport but yield Cd-doped (up to 60%) ZnS nanobelts (at 1000 °C). This result indicates that the conversion reaction of the CdS nanobelts into the ZnS nanobelts takes place more efficiently, as compared to the opposite reaction. At temperatures lower than the conversion temperature, a CdS−ZnO nanobelt−nanowire hybrid structure grew, in which the ZnO nanowires were aligned in the [0001] direction of the CdS nanobelts. We suggest that the conversion reaction of the wurtzite CdS structure proceeds preferentially through their polar (001) planes.