Morphology Of ZnO Nanowires Research Articles

Synthesis of ZnO NWs via Thermal Evaporation Technique

Zinc oxide nanowires ZnONWs were successfully synthesized on glass slides. The synthesis was conducted firstly by the deposition of 12 µm a thin film of Zn metal by thermal evaporation. Secondly,the coated film was annealed at a temperature of 600 ºC in air for four hours to grow the ZnO nanowires. It have been observed that the produced nanowires were grown in a vertical orientation and having a high density, very long, and a minimal aspect ratio. The crystal structure and morphology of ZnO nanowires were investigated with X-ray diffraction (XRD) and scanning electron microscopy (SEM). The UV-visible spectrophotometer was also used to calculate the optical parameters from the absorption spectrum and show a band gap energy around 3.25 eV. The crystal structure of the material was revealed to be polycrystalline with a preferred orientation in the direction of [101]. Small average crystallite size was calculated about 17nm The wires can be measured to have a length of around 10 µm with diameters ranging from 50 to 100 nm. This could be used for gas sensor applications. In addition, this ZnONWs structure has a maximum transmittance (100%) which can be a good candidate for many optoelectronic apllications.

On the contact electrification mechanism in semiconductor–semiconductor case by vertical contact-separation triboelectric nanogenerator

With the speed of industrialization accelerating, the traditional energy is in the predicament of being exhausted. Humans urgently need a clean energy to maintain the peace and development. Triboelectric nanogenerator (TENG) is a tiny device that collects and converts the renewable energy, such as wind, vibration and tidal/blue energy, into electrical energy. As the most significant working principle of TENG, contact electrification (CE) has been broadly studied since it was documented thousands of years ago. A large number of related researches are reported. However, most of them are focused on the polymer materials, device structures and potential applications. There are few literatures about the mechanism of CE, especially in the semiconductor–semiconductor case. Semiconductor–semiconductor CE is a promising method to generate electricity, which has been used in many fields, such as the photodetector and displacement sensor. Therefore, it is necessary to establish a serious and detailed theory in order to deeply explain the underlying mechanisms of semiconductor–semiconductor CE. In this work, a novel Fermi level model based on energy band theory is proposed to illustrate the semiconductor–semiconductor CE mechanism. By assembling a ZnO/Si vertical contact-separation (CS) mode TENG, the charge transfer introduced by CE is systematically measured. According to the energy band theory and TENG governing equation, the experimental data is qualitatively and quantitatively analyzed. Moreover, the effects of different concentrations of growth solutions on the morphology of ZnO nanowires and the Fermi level difference between ZnO and Si are explored as well. Results show that it is the Fermi level difference that dominates the short circuit transfer charge amount and direction of semiconductor–semiconductor CE mechanism. Our work can be applied to understand the CE mechanism in semiconductor–semiconductor case and broaden the application prospects of semiconductor-based TENG.

Glucose biosensor electrode fabrication based on CuO /ZnO nanostructures

Zinc oxide nanowires (ZnO NWs) were successfully synthesized by Zn-metal evaporation and deposition of a thin metal film about 20 µm on quartz substrates. Followed by the subsequent oxidation process in the air at 550 oC for 4h. Copper oxide nanoparticles (CuO NPs) were then deposited on ZnO NWs, using the drop-casting technique. The crystal structure and morphology of ZnO nanowires were investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM). The results of XRD confirmed that the ZnO has the Wurtizite polycrystalline structure along [101] direction. The SEM images revealed that the highest density of ZnO nanowires was distributed over a large area of the substrate with many wrinkles. The current response to glucose of the CuO/ZnO/Qz electrode gives a linear dependence range from 50 µM to 500 µM of glucose. The typical sample of CuO/ZnO NWs was used for a glucose biosensor electrode. It was found that CuO NPs layer on ZnO NWs has well improved the performance of the electrode and increased the electrocatalytic ability towards glucose oxidation.

Short beam shear behaviour of ZnO nanowire reinforced glass/epoxy composites

Abstract This paper describes the short beam shear (SBS) test properties of plain and ZnO nanowire reinforced unidirectional glass/epoxy composites. A simple low temperature hydrothermal process was used to synthesize ZnO nanowires on glass fabrics. Two different annealing conditions were used for seeding of ZnO nanoparticles which were then grown into ZnO single crystalline nanowires. The morphology of ZnO nanowires was found to be more uniform in the case of fabrics treated with extended annealing cycle. Both plain and ZnO nanowire coated fabrics were then used to fabricate glass/epoxy composites using hand lay-up technique. Short beam shear (SBS) test was performed to evaluate the interlaminar shear strength (ILSS) of composite samples, wherein the induced delamination damages were studied under scanning electron microscope. The results showed that while the ZnO nanowire reinforcement reduced the delamination resistance of composites, it improved the delamination damage tolerance.

Enhanced Ultra-violet Photodetection Based on a Heterojunction Consisted of ZnO Nanowires and Single-Layer Graphene on Silicon Substrate

In this study, heterojunction photoelectric devices based ZnO nanowires were fabricated on p-Si substrate with and without single-layer graphene as insert layer. ZnO nanowires and graphene were prepared by hydrothermal method and chemical vapor deposition respectively. The effect of insert layer on the morphology of ZnO nanowires was very weak as can be seen from scanning electron microscope and X-ray diffraction. Raman scattering showed that the graphene prepared was a single-layer structure. The ultraviolet detection performance of photodetectors with single graphene insert layer was much better than that of photodetectors without single graphene insert layer. The ultraviolet irradiation sensitivity of photodetectors with single graphene insert layer was up to 1071 which was improved 7 times than that of photodetectors without single graphene insert layer. Moreover, photodetectors with single graphene insert layer had faster response time (1.02 s) and recovery time (0.34 s).

Tunable Morphology and Doping of ZnO Nanowires by Chemical Bath Deposition Using Aluminum Nitrate

Mastering the properties of ZnO nanowires grown by the low temperature chemical bath deposition (CBD) is of crucial importance but is still challenging. We show that the shape, dimensions, and doping of ZnO nanowires can simultaneously be tuned by the addition of aluminum nitrate in the standard chemical system using zinc nitrate, hexamethylenetetramine, and ammonia in aqueous solution. The formation and doping mechanisms of ZnO nanowires are thoroughly investigated by combining chemical, structural, and optical analyses with in situ pH measurements correlated with thermodynamic simulations. We reveal that the electrostatic interactions of Al(OH)4– complexes with the positive m-plane sidewalls of ZnO nanowires at a given pH favor their adsorption as capping agents, reducing the radial growth and promoting the elongation, while favoring the aluminum uniform incorporation. Importantly, the aluminum doping is found to be thermally activated above the low temperature of 200 °C under oxygen atmosphere, as indicated by the occurrence of six related additional modes in the range of 200–900 cm–1 in temperature-dependent Raman spectroscopy. These findings show that CBD using aluminum nitrate is of high potential for tuning both the morphology of ZnO nanowires and their physical properties via the aluminum doping, which paves the way for their more efficient use into sensing, electronic, and optoelectronic devices on both flexible and rigid substrates.

Solution-Processed One-Dimensional ZnO@CdS Heterojunction toward Efficient Cu2ZnSnS4 Solar Cell with Inverted Structure.

Kesterite Cu2ZnSnS4 (CZTS) semiconductor has been demonstrated to be a promising alternative absorber in thin film solar cell in virtue of its earth-abundant, non-toxic element, suitable optical and electrical properties. Herein, a low-cost and non-toxic method that based on the thermal decomposition and reaction of metal-thiourea-oxygen sol-gel complexes to synthesize CZTS thin film was developed. The low-dimensional ZnO@CdS heterojunction nano-arrays coupling with the as-prepared CZTS thin film were employed to fabricate a novel solar cell with inverted structure. The vertically aligned nanowires (NWs) allow facilitating the charge carrier collection/separation/transfer with large interface areas. By optimizing the parameters including the annealing temperature of CZTS absorber, the thickness of CdS buffer layer and the morphology of ZnO NWs, an open-circuit voltage (VOC) as high as 589 mV was obtained by such solar cell with inverted structure. The all-solution-processed technic allows the realization of CZTS solar cell with extremely low cost.

Investigation on Nanostructure and Morphologies of ZnO Nanowires Prepared by Hydrothermal Method

In this study, we controlled nanostructure and morphologies of the vertically aligned zinc oxide nanowires (ZnO NWs) on 200 nm-thick zinc oxide seed layer. The ZnO nanowires were synthesized by the hydrothermal method at 90°C for 6 hours in the precursor solutions. The solutions with four different precursor concentrations of zinc nitrate and hexamethylenetetramine (HTMA) in distilled water were prepared at 5 to 20 mM. The effect of the precursor concentrations were systematically investigated based on the structural and morphologies of ZnO NWs. Most physical investigations were performed with grazing-incidence X-ray diffraction (GIXRD) and field-emission scanning electron microscopy (FE-SEM). From GIXRD, the peak intensity and full width at half maximum (FWHM) of the ZnO (002) were both increased as the precursor concentration was increased. It was also found that the diameter and length of the ZnO nanowires were increased with the increased precursor solution concentration. The average diameter and length of the ZnO NWs could be controlled from 60 to 135 nm and 0.39 to 1.73 μm, respectively.

Highly crystalline hydrothermal ZnO nanowires as photoanodes in DSCs

Vertically aligned ZnO nanowires (NWs) were prepared inside an autoclave by a hydrothermal procedure at temperatures above 100°C (HP). The effects of synthesis temperature and time on the morphology of ZnO NWs were carefully studied. The performance of HP ZnO NWs was compared with that of ZnO NWs grown by a conventional ambient pressure hydrothermal method at temperatures below 100°C (LP) as photoanodes in dye-sensitised solar cells (DSCs). HP ZnO NWs provided DSCs with more than two-fold higher power conversion efficiencies than LP ZnO NWs. Improved efficiencies are associated to the larger higher aspect ratio and improved crystallinity of HP ZnO NWs.

超长氧化锌纳米线的制备及其气敏性能和紫外传感应用研究

A simple and facial carbothermal reduction method was utilized to prepare ultra-long ZnO nanowires with lengths of about 100 μm,diameters of about 500 nm,aspect ratio up to 200 without usage of any catalyst and carrier gas. The effects of the positions of Si substrate,deposition time and the amount of reactant materials on the morphology of ZnO nanowires were studied. The gas sensing results of ZnO nanowires show that ZnO nanowire sensors have a good performance to alcohol with good selectivity,fast response and recovery at the working temperature of 350 ℃,and the detectable volume fraction is as low as 5 × 10- 6. In addition,a UV sensor based on ZnO nanowires was constructed through a simple and practical dielectrophoresis method. The photocurrent of the sensor increases about 13% under 365 nm UV illumination but has no changes under 254 nm UV irradiation, which indicates the good selectivity of the sensor.

Controlled synthesis of aligned ZnO nanowires and the application in CdSe-sensitized solar cells

According to the two-step hydrothermal method, ZnO nanowires (NWs) were successfully synthesized through the pretreatment of seeds in the NaOH/Zn(NO3)2 solution and the subsequent growth of ZnO NWs in the Zn(NO3)2/HMTA/PEI/NH4OH solution. The method overcomes the disadvantages in the fusion and tilt of NWs. The morphology of ZnO NWs was controlled through regulating the concentration of zinc acetate in the seed precursor and changing pretreatment time of ZnO seeds. SEM images show that the length of ZnO NWs increases with the increase of the volume ratio (Vgas:Vliquid) in the sealed system. The absorption spectra of the bulk solution confirm that decreasing vapor pressure can release more Zn2+ and accelerate the growth of NWs. The effect of vapor pressure on the growth of NWs was explained by the vapor–liquid equilibrium theory. With ZnO NW films synthesized in the three systems as the photoanodes, we fabricated CdSe quantum-dots-sensitized solar cells (QDSSCs) and tested photovoltaic (PV) performances. The result exhibits a remarkably enhanced short-circuit current density (Jsc) of 6.71mA/cm2 and power conversion efficiency (η) of 2.17%.

Effect of Growth Conditions on Morphology and Photoluminescence Properties of ZnO Nanowires Fabricated by Thermal Evaporation without a Metal Catalyst

We demonstrate that single crystalline ZnO nanowires with large length/diameter ratio are successfully grown on Si, glass, and Si with ZnO seed layer via simple thermal vapor deposition, without introducing any catalyst or additive. In this work, we study impact of growth conditions such as growth temperature, substrates, and ZnO seed layer on morphology and photoluminescence properties of ZnO nanowires, in terms of systematic characterizations. The investigations show that the growth temperatures have substantial effect on the morphology of ZnO nanowires, while substrates have low impact. And 700 °C is believed to be the optimized growth temperature among the series of temperatures. Moreover, ZnO seed layer plays an important role in the uniformity and reproducibility of ZnO nanowires growth. PL measurements for the ZnO nanowires exhibit two emission bands including a UV emission and a blue emission, respectively. Finally, the growth behavior of the ZnO nanowires is discussed based on the VS growth mechanism. Our resluts have made a positive progress toward improving control of the morphology of ZnO nanowires.

Facile synthesis of ZnO nanowires on FTO glass for dye-sensitized solar cells

Long and well-aligned ZnO nanowires were hydrothermally synthesized on FTO glass based on a ZnO seed layer which was prepared by spin-coating and annealing techniques. The effect of the growth solution refreshment on the morphology of ZnO nanowires was investigated and the possible mechanism was discussed. After refreshing the growth solution for 5 cycles, ZnO nanowires of ∼ 120 nm in diameter and ∼ 20 μm in length were obtained. The prepared ZnO nanowires were used as photoelectrodes in dye-sensitized solar cells (DSSCs), showing excellent photovoltaic performance. With the increase of growth cycles of ZnO nanowires, the photocurrent of DSSCs increased obviously due to the increased dye loading on the surface of ZnO nanowires. The results indicated that the long and well-aligned ZnO nanowires are promising for DSSCs application.

Controlled growth of well-aligned ZnO nanowire arrays using the improved hydrothermal method

Well-aligned ZnO nanowires were hydrothermally synthesized based on a facile method for preparing the ZnO seed layer which was derived from the combination of a sol—gel process and the spin-coating technique. The effect of the contents of growth solution and the growth duration on the morphology of ZnO nanowires has been investigated. The results indicated that long and vertically aligned ZnO nanowires could be obtained by adjusting the contents of ammonia and polyethyleneimine (PEI) in the growth solution. Under the optimized condition, the length of ZnO nanowires increased fast and almost linearly with the growth duration. After 10 h incubation, ZnO nanowires more than 25 μm in length were obtained. By combining the conventional photolithographic method with this hydrothermal approach, long and well-aligned ZnO nanowire arrays were selectively grown on the substrate. In addition, the bottom fusion at the foot of the nanowires has been obviously improved. The results demonstrated that the improved hydrothermal process is favorable to synthesize long and well-aligned ZnO nanowires, and possesses good process compatibility with the conventional photolithographic technique for preparing ZnO nanowire arrays. So it has great potential in applications such as display and field emission devices.

Tunable synthesis of ordered Zinc Oxide nanoflower-like arrays

A novel approach to fabricate an ordered array of ZnO nanoflowers, consisting of uniform polymer cores of 100s of nanometer diameter decorated with ZnO nanorods of 10s of nanometer diameter, is presented. The 2-stage method combines the formation of ZnO seed layer by pulsed laser deposition (PLD) onto a colloidally assembled polystyrene sphere monolayer and the subsequent hydrothermal growth of ZnO nanowires (NWs). The main advantages of this methodology are low cost and the large area scalability of perfectly ordered hierarchical structures. More importantly, the process enables a versatile control of dimensions and morphologies of ZnO NWs as well as control of the core diameter by changing the polystyrene sphere diameter. A strong improvement of light scattering by such arrays is observed, offering promise as building blocks in different types of solar cells and potentially useful for a wide variety of applications in optoelectronic devices.

Low Temperature Growth and Optical Properties of ZnO Nanowires Using an Aqueous Solution Method

ZnO nanowires were grown on indium tin oxide (ITO) coated glass substrates at a low temperature of 90 degrees C using an aqueous solution method. The ZnO seeds were coated on the ITO thin films by using a spin coater. ZnO nanowires were formed in an aqueous solution containing zinc nitrate hexahydrate (Zn(NO3)2 x 6H2O) and hexamethylenetetramine (C6H12N4). The pH value and concentration of the solution play an important role in the growth and morphologies of ZnO nanowires. The size of ZnO naonowires increased as the concentration of the solution increased. It was formed with a top surface of hexagonal and tapered shape at low and high pH values respectively. Additionally, the single crystalline structure and optical property of the ZnO nanowires were investigated using high-resolution transmission electron microscopy and photoluminescence spectroscopy.

The Periodic Instability of Diameter of ZnO Nanowires via a Self-oscillatory Mechanism

ZnO nanowires with a periodic instability of diameter were successfully prepared by a thermal physical vapor deposition method. The morphology of ZnO nanowires was investigated by SEM. SEM shows ZnO possess periodic bead-like structure. The instability only appears when the diameter of ZnO nanowires is small. The kinetics and mechanism of Instability was discussed at length. The appearance of the instability is due to negative feed-back mechanism under certain experimental conditions (crystallization temperature, vapor supersaturation, etc).

Annealing effects on the photoluminescence and morphology of ZnO nanowires

AbstractFor the fabrication of ZnO NWs, we have used Si wafers as smooth surface substrates. Gold was deposited on to the substrates with an electron beam evaporator, since it is known that gold particles can serve as the catalyst to grow ZnO NWs on substrates in Vapor‐Liquid‐Solid (VLS) method. In the VLS method, the mixture of ZnO powder and graphite was placed at 1100 °C and the substrates were at 800 °C in a two‐zone furnace. The reduction of ZnO of the source generates Zn vapor that diffuses to gold particles on Si substrates, and the oxidation of Zn‐Au alloy grows ZnO crystals. The gold deposited area has ZnO crystal growth and that the gold particles play the role of nucleation sites. ZnO crystals have the dimension of a few hundred nm wide and 2‐3 μm long under this particular condition. SEM, XRD, and PL have been used for characterization. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)