Growth Of Zinc Oxide Nanowires Research Articles

Playing with Dimensions: Rational Design for Heteroepitaxial p–n Junctions

A design for a heteroepitaxial junction by the way of one-dimensional wurzite on a two-dimensional spinel structure in a low-temperature solution process was introduced, and it's capability was confirmed by successful fabrication of a diode consisting of p-type cobalt oxide (Co(3)O(4)) nanoplate/n-type zinc oxide (ZnO) nanorods, showing reasonable electrical performance. During thermal decomposition, the 30° rotated lattice orientation of Co(3)O(4) nanoplates from the orientation of β-Co(OH)(2) nanoplates was directly observed using high-resolution transmission electron microscopy. The epitaxial relations and the surface stress-induced ZnO nanowire growth on Co(3)O(4) were well supported using the first-principles calculations. Over the large area, (0001) preferred oriented ZnO nanorods epitaxially grown on the (111) plane of Co(3)O(4) nanoplates were experimentally obtained. Using this epitaxial p-n junction, a diode was fabricated. The ideality factor, turn-on voltage, and rectifying ratio of the diode were measured to be 2.38, 2.5 V and 10(4), respectively.

Gas Sensing Properties of Interconnected ZnO Nanowires

In this report, the structural, morphological, and gas-sensing properties of nanostructured thin films made of interconnected zinc oxide (ZnO) nanowires were studied. This paper is the first demonstration of functional devices based on such nanowires. Interconnected nanowires were grown via a two-stage process using, spray pyrolysis for the deposition of a ZnO seed layer on glass substrates, followed by a hydrothermal method for the growth of interconnected ZnO nanowires. Samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques. Characterization of the films revealed that they were populated with interconnected ZnO nanowires, approximately ~20-30 nm in width with a hexagonal wurtzite structure after heat treatment. Samples were evaluated for NO2 gas sensing applications, and exhibited a considerable change in surface conductivity when exposed to N O2 at 200 °C. The influence of temperature between 65-260 °C on N O2 response of the developed sensors will be presented and discussed.

Zinc Oxide Nanowire Based Hydrogen Sensor On SOI CMOS Platform

Here we report on the successful low-temperature growth of zinc oxide nanowires (ZnONWs) on silicon-on- insulator (SOI) CMOS micro-hotplates and their response, at different operating temperatures, to hydrogen in air. The SOI micro-hotplates were fabricated in a commercial CMOS foundry followed by a deep reactive ion etch (DRIE) in a MEMS foundry to form ultra-low power membranes. The micro-hotplates comprise p+silicon micro-heaters and interdigitated metal electrodes (measuring the change in resistance of the gas sensitive nanomaterial). The ZnONWs were grown as a post-CMOS process onto the hotplates using a CMOS friendly hydrothermal method. The ZnONWs showed a good response to 500 to 5000ppm of hydrogen in air. We believe that the integration of ZnONWs with a MEMS platform results in a low power, low cost, hydrogen sensor that would be suitable for handheld battery- operated gas sensors.

Coarse-grained kinetic scheme-based simulation framework for solution growth of ZnO nanowires

Kinetic Monte Carlo (KMC)-based stochastic model is used to understand the growth of zinc oxide nanowires from aqueous solution containing chemical precursors and capping agent. Through a hydrothermal growth mechanism, the average diameter of zinc oxide wires obtained is around 300 nm, whereas the length is order of several micrometers. Our Monte Carlo algorithm is based on the continuous-time Monte Carlo algorithm of Bortz, Kalos and Lebowitz (BKL) methodology. Both reactions and diffusion mechanisms assigning stochastic probabilities have been simulated. In algorithm, the ZnO atoms were treated as individual particles which diffuse in solution substrate and interact with other type of atoms. Once attached with growing nanowires, the diffusion rate of ZnO atom is considerably reduced. Since in a KMC algorithm each atom can be represented individually therefore, internal noise is automatically incorporated.

Enhanced Lateral Growth of Zinc Oxide Nanowires on Sensor Chips

We have adapted a simple concept analogous to substrate tilting used in common chemical vapor deposition processes to enhance the lateral growth of zinc oxide nanowires for bridging two adjacent electrodes in sensor chips. The chips were placed at elevated positions to avoid reactant depletion due to the existence of a diffusion boundary layer atop the horizontal substrate support. We show that the nanowire bridging is much improved and better than that reported in the literatures. As a result, the sensor chip sensitivity is also enhanced as compared with the previously reported data.

Screw Dislocation-Driven Epitaxial Solution Growth of ZnO Nanowires Seeded by Dislocations in GaN Substrates

In the current examples of dislocation-driven nanowire growth, the screw dislocations that propagate one-dimensional growth originate from spontaneously formed highly defective "seed" crystals. Here we intentionally utilize screw dislocations from defect-rich gallium nitride (GaN) thin films to propagate dislocation-driven growth, demonstrating epitaxial growth of zinc oxide (ZnO) nanowires directly from aqueous solution. Atomic force microscopy confirms screw dislocations are present on the native GaN surface and ZnO nanowires grow directly from dislocation etch pits of heavily etched GaN surfaces. Furthermore, transmission electron microscopy confirms the existence of axial dislocations. Eshelby twist in the resulting ZnO nanowires was confirmed using bright-/dark-field imaging and twist contour analysis. These results further confirm the connection between dislocation source and nanowire growth. This may eventually lead to defect engineering strategies for rationally designed catalyst-free dislocation-driven nanowire growth for specific applications.

Growth of high-quality ZnO nanowires without a catalyst

In this study, an efficient method to achieve a wide range of high-quality zinc oxide (ZnO) nanostructures through zinc powder evaporation at lower temperatures is developed. ZnO nanowires could be synthesized on n-type silicon substrates by a simple thermal-evaporation technique without a catalyst at 550, 600, and 650 °C. Samples are annealed in wet oxygen and ambient argon gases. Surface morphology, crystallinity, and optical properties of the ZnO nanowires are examined by scanning electron microscopy, X-ray diffraction, and photoluminescence measurement. The optimum temperature for synthesizing high-density, long ZnO nanowires was determined as 650 °C. The possible growth mechanism of ZnO nanowires is also proposed.

A New Method for the Growth of Zinc Oxide Nanowires by MOCVD using Oxygen‐Donor Adducts of Dimethylzinc

AbstractThe oxygen donor adducts of dimethylzinc [Me2Zn(L)] (L = tetrahydrofuran, tetrahydropyran, or furan) are used without pre‐reaction with oxygen for the growth of ZnO by liquid injection metal‐organic (MO)CVD over the temperature range 350–550 °C. Vertically‐aligned ZnO nanowires are deposited in a narrow temperature range centered on ∼500 °C. At other deposition temperatures, the ZnO films show continuous polycrystalline morphologies. At room temperature, the ZnO nanowires exhibit intense near band‐edge photoluminescence (PL) at emission energies of 3.26 to 3.28 eV, and show minimal defect‐related visible emission. Analysis of the ZnO nanowires by Auger electron spectroscopy (AES) shows that they are of high purity, with carbon not detected at an estimated detection limit of 0.5 at.‐%.

Templated one step electrodeposition of high aspect ratio n-type ZnO nanowire arrays

High aspect ratio Zinc Oxide (ZnO) nanowires (NWs) were synthesized by template based one-step electrochemical deposition (OSECD) technique. The electro-reduction of hydroxide ions in the presence of Zn(2+) ions within Zn(NO(3))(2) is involved in the growth of ultra thin NWs arrays. Field Emission Scanning Electron Microscopy (FESEM) images revealed that the growth rates of different crystal faces, (0 0 0 1) and (0 0 0 1), were different at different deposition potential for the high aspect ratios ZnO NWs arrays. The n-type semiconductor conductivity of ZnO NWs was ascertained by a Hot-Probe approach. X-ray diffraction results demonstrated that the grown ZnO NWs had wurtzite crystal structure with unit cell parameters a=2.93 A, c=5.45 A and a deterioration of preferred (1 0 1) orientation is observed at more negative deposition potentials. Small angle X-ray scattering (SAXS) results evidenced that the NW arrays grown at -1.2 V have higher fraction of larger crystallites. Micro-Raman spectroscopy analysis showed that the variation in E(2) (high) vibration mode at 435 cm(-1) is coupled with an increase in electro acceptor oxygen atoms incorporated within ZnO NWs at -1.2 V.

Effects of Seed Layer Characteristics on the Synthesis of ZnO Nanowires

Single crystalline zinc oxide (ZnO) nanowires were synthesized on sputter‐deposited ZnO seed layers via hydrothermal reactions in an equimolar (20 mM) aqueous solutions of Zn(NO3)2·6H2O and C6H12N4 at 90°C. The sputter‐deposited ZnO seed layers were prepared to exhibit different crystalline structures in order to examine their effects on the growth of ZnO nanowires. It was found that the nanowire diameter depends on the size of the (002) grains of the seed layer. This is attributed to the epitaxially growth of the nanowires from the columnar grains of the seed layer which is shown by the TEM analysis.

Anomalous nucleation of gold nanoparticles on silicon substrate and monitoring the growth of ZnO nanowires on such structures

Nucleation of a gold catalyst on a (100) oriented silicon substrate was extensively investigated. An anomalous mechanism of nucleation was observed in the grain formation of gold nanoislands. The chemical vapour deposition method was employed to grow zinc oxide nanowires. Zinc powder and oxygen gas were used as reaction sources for the growth. Different shaped ZnO nanowires were obtained for different nucleation mechanisms. The nucleation mechanism and growth evolution were monitored by scanning electron microscopy and atomic force microscopy.

Transport Limited Growth of Zinc Oxide Nanowires

Vertical arrays of crystalline zinc oxide (ZnO) nanowires grown on various substrates find applications in dye-sensitized and hybrid organic/inorganic bulk-heterojunction solar cells. The ability to grow dense nanowires at high rates and the fundamental understanding of the growth process are important for these applications. Herein, we show that heterogeneous growth of ZnO nanowires on substrates seeded with ZnO nanoparticles in an aqueous solution of methenamine and zinc nitrate is mass transport limited. Mass transport limited growth leads to an inverse relationship between the nanowire dimensions (height and diameter) and the nanowire number density. This mass transport limitation also leads to nonuniform growth near the boundaries between seeded and unseeded regions. Stirring the reaction solution increases the nanowire growth rate. Experimental results were interpreted within the framework of two simple but nontrivial models of the solution phase species transport and the nanowire growth. Additional...

Strain-Driven Growth of Zinc Oxide Nanowires on Sapphire: Transition from Horizontal to Standing Growth

Recently, we showed large-scale fabrication of field-effect transistors from horizontal ZnO nanowires (NWs) on a-plane sapphire. Here, in examining the cross sections of such nanodevices, we use high-resolution transmission electron microscopy (HRTEM) and large-angle, convergent-beam electron diffraction (LACBED). We show how horizontally grown ZnO NWs influence their underlying sapphire surface and how substrate influences the growth directionality of the NWs. As a NW grows on sapphire, the substrate experiences a compressive strain of ≈7% in its [0001]sap direction (along the width of a NW) to minimize its lattice mismatch with the ZnO NW. Accordingly, ZnO expands along its width to improve its lattice match with the sapphire. The growth direction of (11̅00) is suggested to be the direction that produces a lower lattice strain between ZnO and sapphire. Analyses of NW/sapphire interfaces show that single-crystal NWs grow epitaxially and semicoherently with many fewer misfit dislocations than theoretically expected. We attribute the formation of fewer dislocations at the interface to local relaxation of zinc oxide strain into the sapphire surface. This relaxation is in agreement with the observed deformation of the sapphire underneath the NWs. We also define a critical NW thickness beyond which the growth mode changes from horizontal to standing. Results indicate that below this thickness, gold nanodroplets partially wet both sapphire and ZnO crystals. Above the critical thickness, gold preferentially wets the ZnO nanocrystal, and formation of misfit dislocations at the interface becomes energetically favorable. Combination of these two effects is used to explain the observed change in the growth modes of the NWs.

Quantitative Investigation of the Factors Affecting the Hydrothermal Growth of Zinc Oxide Nanowires

AbstractZinc oxide (ZnO) nanowires (NWs) are receiving significant industrial and academic attention for a variety of novel electronic, optoelectronic and MEMS device applications due to their unusual combination of physical properties, including being optically transparent, semiconducting and piezoelectric. Hydrothermal growth is possible at significantly lower temperatures (and hence lower thermal budgets) compared with other NW growth methods, such as chemical vapour deposition. In this context, the hydrothermal growth of ZnO NWs on seeded substrates immersed in equimolar zinc nitrate/HMTA aqueous solution was investigated. NWs were grown on polished silicon (001) substrates, and the solution concentrations, temperatures and growth times were varied. Importantly, the NW diameter was found to depend only on concentration during hydrothermal growth for times up to 4 hours. The average diameter was 14 nm in 0.005 M solution and increased up to a maximum 150 nm at 0.07 M, when the NWs formed a continuous polycrystalline film. Concentration and temperature were all found to affect the axial growth rate of NWs in the [0001] direction. The growth rate was constant up to 4 hours (200 nm hr-1) for constant conditions (81 oC, 0.025 M). The growth rate was found to increase approximately linearly with concentration at a rate of 7840 nm M-1 hr-1 up to 0.06 M (81 oC solution). The growth rate also increased linearly with temperature at a rate of 4.9 nm hr-1 K-1 (0.025 M solution). This indicates that growth takes place close to the equilibrium point, found by linear regression to be 36 oC for 0.025 M solution.

电泳法排列ZnO纳米线

The synthesis of zinc oxide (ZnO) nanowires is achieved by vapor phase transportation (VPT) method. The designed quartz tube, whose both ends are narrow and the middle is wider, is used to control the growth of ZnO nanowires. Dielectrophoresis (DEP) method is employed to align and manipulate ZnO nanowires which are ultrasonic dispersed and suspended in ethanol solution. Under the dielectrophoretic force, the nanowires are trapped on the pre-patterned electrodes, and further aligned along the electric field and bridge the electrode gap. The dependence of the alignment yield on the applied voltage and frequency is investigated.

Ultrashort Pulse Manipulation of ZnO Nanowire Growth

A procedure of femtosecond pulse laser irradiation was incorporated into the synthesis of zinc oxide (ZnO) nanowires in aqueous solutions to investigate the photo-initiated heterogeneous nucleation induced by the irradiation and the associated nanowire growth. Elongated ZnO nanowires with smooth planes and end tips were successfully grown following the irradiation process and subsequent hydrothermal treatments in a catalyst-free environment, compared to aggregated flower-like nanostructures with porous and rough surfaces, grown from homogeneous nucleation without laser irradiation. Studies using femtosecond laser systems at 1 kHz and 250 kHz repetition rates show that the pulse energy is critical in the heterogeneous nucleation process for the growth of ZnO nanowires. A minimum threshold pulse energy, 200 microJ/pulse for the 1 kHz system and 2.4 microJ/pulse for 250 kHz, is observed beyond which well-defined and individually separated nanowires were grown. Thermal effect caused by the 250 kHz repetition rate provides a counter-balance to the low pulse energy required for the growth process. XRD analysis of the nanowires reveals a hexagonal structure while photoluminescence shows emission at about 385 nm. The overall results show that the pulse energy is critical for heterogeneous nucleation while the irradiation duration affects the density of nucleation, which together with the hydrothermal treatment temperature influence the growth rate and thus the morphology of the nanowires.

Growth of high-quality, uniform c-axis-oriented zinc oxide nano-wires on a-plane sapphire substrate with zinc oxide templates

High-quality, vertically aligned zinc oxide (ZnO) nano-wires were grown by the vapour-transport method on (112¯0) (a-plane) sapphire substrate covered by a uniform ZnO nano-crystalline seed layer which was deposited in a preceding growth step via simple chemical vapour deposition. A thin layer of close-packed nano-seeds with an average size of 12nm was formed rapidly on the substrate by sublimation and thermal decomposition of zinc acetate dihydrate as the precursor at moderate temperatures and pressures. Subsequently, growth of ZnO nano-wires was performed by a carbo-thermal vapour-transport method yielding nano-wires with high reproducibility and homogeneity. The as-grown, c-axis-oriented nano-wires exhibit excellent luminescence properties and perfect alignment with respect to the substrate surface.

Large-area self-catalysed and selective growth of ZnO nanowires

A simple procedure to selectively grow zinc oxide nanowires (ZnO NWs) on a large scalewithout any catalyst is reported. The process is based on the use of a zinc metal layerdeposited onto substrates before the NW growth. The zinc layer, which becomes liquid atthe synthesis temperature, favours the correct local conditions for a selectivegrowth of pure ZnO NWs in an effective area of several square centimetres (up to20 cm2 in our laboratory-scale reactor). The proposed method is suitable for patterned ZnO NWsynthesis.

Tribological characteristics of ZnO nanowires investigated by atomic force microscope

Zinc oxide (ZnO) nanowires have attracted great interest in nanodevices. In this work, the tribological characteristics of vertically grown ZnO nanowires obtained by metalorganic chemical vapor deposition were investigated by using an atomic force microscope (AFM). The ZnO nanowires were slid against flattened silicon and diamond-coated AFM probes under 50–150 nN normal force while monitoring the frictional force. The wear of the ZnO nanowires was observed by a scanning electron microscope and quantified based on Archard’s wear law. Also, the wear debris accumulated on the silicon probe was analyzed by using a transmission electron microscope (TEM). The results showed that the wear of ZnO nanowires slid against the silicon probe was extremely small. However, when the ZnO nanowires were slid against the diamond-coated probe, the wear coefficients ranged from 0.006 to 0.162, which correspond to the range of severe wear at the macroscale. It was also shown that the friction coefficient decreased from 0.30 to 0.25 as the sliding cycles increased. From TEM observation, it was found that the ZnO wear debris was mainly amorphous in structure. Also, crystalline ZnO nanoparticles were observed among the wear debris.

Mechanisms of Self-Catalyst Growth of Agave-like Zinc Oxide Nanostructures on Amorphous Carbons

Agave-like zinc oxide (ZnO) nanowire arrays are self-assembled on amorphous carbons using thermal chemical vapor transport and condensation without any metal catalysts. Experimentally, a study is performed to clarify the nucleation and growth of the unique nanostructures. Theoretically, a thermodynamic approach is proposed to address the self-assembly of agave-like ZnO nanowires on amorphous carbons. It is found that the physical and chemical origin of the nucleation aggregation and radial growth of agave-like ZnO nanowires is the immiscibility in the ZnO−carbon system.