High Aspect Ratio ZnO Nanowires Research Articles

Size-controllable zinc oxide nanowires fabricated via the combination of die-casting and oxidation process

Herein, we demonstrate a facile approach in the fabrication of one-dimensional ZnO nanowires (NWs) from the vacuum die-casting method in assistance with anodic aluminum oxide (AAO) template. The casting method enables molten Zn to embed uniformly over the AAO nanomould under high pressure and temperature of 500 °C. Besides, the significant influence of the oxidation time and temperature stimulates the ZnO NWs growth inside the AAO nanochannels. The oxidation in the nanochannels was profoundly controlled by the inward diffusion of oxygen atoms and the ZnO grows perpendicular towards the surface which obeys the parabolic law. The TEM and XRD results revealed the ZnO wurtzite crystalline structure with preferential orientation along the c-axis. The relationship between ZnO geometry and function of oxidation parameters is demonstrated by microscopic and spectroscopic analysis. The obtained NWs from the chemical etching process resulted in high crystalline, homogeneous, and high-aspect ratio ZnO NWs in relationship with the AAO pore dimension. Further, the as-prepared ZnO NWs electrical properties were measured in a four-electrode system through the single nanowire device fabricated by FIB. The obtained current-voltage characteristic curves exhibited hysterias loop in consequence with the space charge limited current effect of ZnO NW, which confirms its potential to be used in practical electronic applications.

A facile hydrothermal approach for the density tunable growth of ZnO nanowires and their electrical characterizations

Controlling properties of one-dimensional (1D) semiconducting nanostructures is essential for the advancement of electronic devices. In this work, we present a low-temperature hydrothermal growth process enabling density control of aligned high aspect ratio ZnO nanowires (NWs) on seedless Au surface. A two order of magnitude change in ZnO NW density is demonstrated via careful control of the ammonium hydroxide concentration (NH4OH) in the solution. Based on the experimental observations, we further, hypothesized the growth mechanism leading to the density controlled growth of ZnO NWs. Moreover, the effect of NH4OH on the electrical properties of ZnO NWs, such as doping and field-effect mobility, is thoroughly investigated by fabricating single nanowire field-effect transistors. The electrical study shows the increase of free charge density while decrease of mobility in ZnO NWs with the increase of NH4OH concentration in the growth solution. These findings show that NH4OH can be used for simultaneous tuning of the NW density and electrical properties of the ZnO NWs grown by hydrothermal approach. The present work will guide the engineers and researchers to produce low-temperature density controlled aligned 1D ZnO NWs over wide range of substrates, including plastics, with tunable electrical properties.

Controlled facile fabrication of plasmonic enhanced Au-decorated ZnO nanowire arrays dye-sensitized solar cells

Facile controlled formation of well-dispersed Au-nanoparticles (Au-NPs) decorated on high aspect ratio ZnO nanowires (NWs) was demonstrated. Au-NPs decorated ZnO NWs obtained exhibited a significant enhancement of 75% in power conversion efficiency (PCE) of dye-sensitized solar cells (DSSCs) performance. Superior PCE of 1.01% achieved was attributed to the surface plasmon resonance (SPR) effect of Au-NPs near 520nm which promoted improved dye light absorption resulting in more electrons generation as indicated in the significant increment of the short circuit current density, JSC. SPR phenomenon was further supported by a distinctive extinction spectra obtained.

Mechanisms involved in the hydrothermal growth of ultra-thin and high aspect ratio ZnO nanowires

Hydrothermal synthesis of ZnO nanowires (NWs) with tailored dimensions, notably high aspect ratios (AR) and small diameters, is a major concern for a wide range of applications and still represents a challenging and recurring issue. In this work, an additive-free and reproducible hydrothermal procedure has been developed to grow ultra-thin and high AR ZnO NWs on sol-gel deposited ZnO seed layers. Controlling the substrate temperature and using a low reagent concentration (1mM) has been found to be essential for obtaining such NWs. We show that the NW diameter remains constant at about 20–25nm with growth time contrary to the NW length that can be selectively increased leading to NWs with ARs up to 400. On the basis of investigated experimental conditions along with thermodynamic and kinetic considerations, a ZnO NW growth mechanism has been developed which involves the formation and growth of nuclei followed by NW growth when the nuclei reach a critical size of about 20–25nm. The low reagent concentration inhibits NW lateral growth leading to ultra-thin and high AR NWs. These NWs have been assembled into electrically conductive ZnO nanowire networks, which opens attractive perspectives toward the development of highly sensitive low-cost gas- or bio-sensors.

Determining the diffusion mechanism for high aspect ratio ZnO nanowires electrodeposited into anodic aluminum oxide

ZnO nanowires electrodeposited into anodic aluminum oxide (AAO) templates exhibit a high filling ratio and aspect ratio. A diffusion mechanism, which depends on electrodeposition parameters is proposed.

Erratum to: “Synthesis of high aspect ratio ZnO nanowires with an inexpensive handcrafted electrochemical setup”

Erratum to: “Synthesis of high aspect ratio ZnO nanowires with an inexpensive handcrafted electrochemical setup”

Synthesis of high aspect ratio ZnO nanowires with an inexpensive handcrafted electrochemical setup

In this work, high aspect ratio zinc oxide nanowires are synthesized using templated one-step electrodeposition technique. Electrodeposition of the nanowires is done using a handcrafted electronic system. Nuclear track-etched polycarbonate membrane is used as a template to form the high aspect ratio nanowires. The result of X-ray diffraction and scanning electron microscopy shows that nanowires with a good crystallinity and an aspect ratio of more than 30 can be achieved in a suitable condition. The height of electrodeposited nanowires reaches to about 11 μm. Based on the obtained results, high aspect ratio ZnO nanowires can be formed using inexpensive electrodeposition setup with an acceptable quality.

A Simple Method for Production of High Aspect Ratio ZnO Nanowires with Uniform Structure for NO2 Gas Sensors

A Simple Method for Production of High Aspect Ratio ZnO Nanowires with Uniform Structure for NO₂ Gas Sensors

ZnO Nanowires Grown on Carbon Cloth for Flexible Cold Cathode

Nanostructures grown on carbon cloth are recently attracted great interests for flexible field emitter and cold cathode. In this paper, we report high-aspect ratio ZnO nanowires grown on carbon cloth by a low-temperature solution chemical approach that can be used as a flexible and high performance cold cathode. The carbon cloth is covered by outward-grown ZnO nanowires uniformly and densely with spiny structures. The hybrid structures exhibits a turn-on electrical field of 4.36 V/microm and a field enhancement factor of 1157, which benefit from the high-aspect ratios of both ZnO nanowires and carbon cloth. These results demonstrate a low cost and scalable approach for flexible cold cathode lighting and field emission display.

Morphology and electrical properties of high aspect ratio ZnO nanowires grown by hydrothermal method without repeated batch process

We propose a growth method to obtain ZnO nanowires with very high aspect ratios which involves adding ammonium chloride without repeated batch process. The ZnO nanowires with a length of over 13.6 μm and an aspect ratio of about 97 were grown by the proposed method. Nanogenerators based on the prepared ZnO nanowires were fabricated and their electrical properties were characterized as a function of aspect ratio to verify the changes in the piezoelectric potential. We obtained a maximum current density of ∼1.6 μm/cm2 by applying a compressive force to the nanogenerator using a linear motor.

Effect of nanosphere monolayer on the morphology of ZnO nanowires grown by hydrothermal method

Very high aspect ratio ZnO nanowires have been prepared by a novel nanosphere assisted hydrothermal method. The wires were synthesized on a ZnO seed layer, which was covered by a monolayer of Stöber silica nanoparticles. The so formed nanowires were ca. 30nm in width and up to 7μm in length in contrast with the thicker (60nm) and shorter (0.85μm) ones grown without nanoparticle film under identical conditions. Larger nanoparticles result in shorter nanowires, but the diameter of the nanowires is not affected by the particle diameter in the investigated size range (240–450nm). The thin nanowires show superior photoresponse upon exposure to 360nm UV light compared to those grown without cap layer.

PH-Dependent Toxicity of High Aspect Ratio ZnO Nanowires in Macrophages Due to Intracellular Dissolution

High-aspect ratio ZnO nanowires have become one of the most promising products in the nanosciences within the past few years with a multitude of applications at the interface of optics and electronics. The interaction of zinc with cells and organisms is complex, with both deficiency and excess causing severe effects. The emerging significance of zinc for many cellular processes makes it imperative to investigate the biological safety of ZnO nanowires in order to guarantee their safe economic exploitation. In this study, ZnO nanowires were found to be toxic to human monocyte macrophages (HMMs) at similar concentrations as ZnCl(2). Confocal microscopy on live cells confirmed a rise in intracellular Zn(2+) concentrations prior to cell death. In vitro, ZnO nanowires dissolved very rapidly in a simulated body fluid of lysosomal pH, whereas they were comparatively stable at extracellular pH. Bright-field transmission electron microscopy (TEM) showed a rapid macrophage uptake of ZnO nanowire aggregates by phagocytosis. Nanowire dissolution occurred within membrane-bound compartments, triggered by the acidic pH of the lysosomes. ZnO nanowire dissolution was confirmed by scanning electron microscopy/energy-dispersive X-ray spectrometry. Deposition of electron-dense material throughout the ZnO nanowire structures observed by TEM could indicate adsorption of cellular components onto the wires or localized zinc-induced protein precipitation. Our study demonstrates that ZnO nanowire toxicity in HMMs is due to pH-triggered, intracellular release of ionic Zn(2+) rather than the high-aspect nature of the wires. Cell death had features of necrosis as well as apoptosis, with mitochondria displaying severe structural changes. The implications of these findings for the application of ZnO nanowires are discussed.

Growth of ZnO Nanowires by MOCVD: Fundamental Role of the Substrate

ZnO is a unique material that exhibits semiconducting and piezoelectric dual properties. Moreover the possibility of growing ZnO with a nanowire structure opens ways for promising applications in different fields such as solar cells, biosensors or UV detectors. This work reports the relationship between the properties of the substrate and the growth of high aspect ratio ZnO nanowires by pulsed injection Metal Organic Chemical Vapor Deposition (MOCVD). Indeed we demonstrate that the morphology of the substrate surface is one of the fundamental parameter for the nanowires growth without any catalyst. We have investigated various substrates (glass, silicon, SnO2, SiC,...) and have shown that for identical experimental conditions the material deposited can be either textured thin film, randomly orientated nanowires or vertically aligned nanowires.

High Aspect-Ratio ZnO Nanowires Based Nanoscale Field Effect Transistors

High aspect-ratio ZnO nanowires were grown onto the copper foil, in a large-quantity, by non-catalytic thermal evaporation method. The detailed morphological observations revealed that the diameters and lengths of as-grown nanowires are in the range of 60-100 nm and 10-30 microm, respectively exhibiting a very high-aspect ratio. Detailed structural characterizations confirmed that the as-grown nanowires are well crystalline and possess a wurtzite hexagonal phase, grown along the c-axis direction in preference. The presence of a sharp and strong UV emission at 381 nm in the room temperature photoluminescence (PL) spectrum affirmed that the obtained nanowires have good optical properties. The electrical transport properties of the as-grown nanowires was explored by fabricating the field effect transistors (FETs) using a single ZnO nanowire. From the fabricated single ZnO nanowire based FET, the electron carrier density and field effect mobility were estimated to be approximately 6.7 x 10(13) cm(-3) and approximately 3.8 cm2/Vs, respectively.

Non-catalytic growth of high aspect-ratio ZnO nanowires by thermal evaporation

High-density and high aspect-ratio ZnO nanowires were grown on Si(100) substrates by the thermal evaporation of metallic zinc powder without the use of metal catalysts or additives. The as-grown nanowires had diameters in the range of 60–100 nm with lengths 5–15 μm. Detailed structural characterization indicated that the obtained nanowires are single-crystalline with a perfect hexagonal facet and surfaces. The room temperature PL spectrum exhibited strong UV emission, affirming that the as-grown products have good optical properties. The possible growth mechanism for the formation of hexagonal-faceted and perfect surface ZnO nanowires is also discussed.