ZnO Arrays Research Articles

Highly dispersed graphene ribbons produced from ZnO–C core–shell nanorods and their use as a filler in polyimide composites

Long and few-layer thickness graphene ribbons (GRs) were fabricated through an efficient process from a well-ordered array of ZnO–C core–shell hexagonal nanorods that were formed by thermally heating zinc acetate dihydrate in a sealed chamber.

Photo-directed growth of Au nanowires on ZnO arrays for enhancing photoelectrochemical performances

Herein, we demonstrate that ZnO nanowire arrays could be rationally connected with each other by thin Au nanowires to construct a novel cross-linked hetero-structure by a simple photo-directed growth strategy, which exhibit much higher visible light photocurrent density than traditional Au nanoparticle/ZnO nanowire heterostructures.

Preparation and Photoelectric Properties of ZnO Arrays with Top Hollow Pits

Preparation and Photoelectric Properties of ZnO Arrays with Top Hollow Pits

Direct solution phase fabrication of ZnO nanostructure arrays on copper at near room temperature

Large-scale ZnO nanocone arrays were fabricated by using a [Zn(OH)4]2− solution consisting of Zn(NO3)2·6H2O and KOH on copper foil at near room temperature (~35 °C). The ZnO nanocones showed aligned growth on the downward surface when the copper foil floated in the solution. However, random growth of block-like microcrystals and microflowers composed of nanocones occurred on the upward surface if the foil was placed in the solution. In the [Zn(OH)4]2− solution, the growth of ZnO and Zn(OH)2 was a competitive process, the downward surface and the relatively high growth temperature were beneficial to the formation and growth of ZnO, and the pure and aligned ZnO arrays were obtained on the downward surface at 35 °C. Furthermore, the detailed growth behaviors of the crystals were discussed. We proposed that van der Waals epitaxy and Volmer–Weber growth accompanied by Ostwald ripening controlled the nucleation and growth of ZnO nanocone arrays on the downward surface of the copper foil, while oriented attachment and gravity deposition commanded the morphology on the upward surface in the solution.

Label-Free Detection of Hepatocellular Carcinoma Markers Based on Photoluminescence of Antibody-Conjugated ZnO Arrays

Hepatocellular carcinoma (HCC) is a malignant disease that is prevalent all around the world, especially in Asia. The combined detection of four common HCC markers, alpha-fetoprotein (AFP), carcinoembryonic antigen (CEA), carbohydrate antigen 125 (CA125) and 19-9 (CA19-9), can significantly improve the accuracy of early screening and diagnosis of this disease, which is very important for its effective treatment in a curable stage. In this article, hierarchical ZnO column arrays with core-shell structure were prepared, and specific antibodies of HCC markers were successfully conjugated onto ZnO arrays via the carbodiimide chemistry. The photoluminescence (PL) intensity of antibody-ZnO increased after HCC markers were bound. In the range of 0.5-15 ng/mL for AFP or CEA (or 0.5-15 U/mL for CA125 or CA19-9), the apparent linear relations between the PL enhancements and the concentrations of HCC markers offered simple standard curve for HCC detection in serum samples, indicating that the PL-enhanced antibody-ZnO arrays could be utilized in early clinical screening. A preliminary mechanism of PL intensity enhancement can be established based on this work.

Length‐Dependent Charge Generation from Vertical Arrays of High‐Aspect‐Ratio ZnO Nanowires

Aqueous chemical growth of zinc oxide nanowires is a flexible and effective approach to obtain dense arrays of vertically oriented nanostructures with high aspect ratio. Herein we present a systematic study of the different synthesis parameters that influence the ZnO seed layer and thus the resulting morphological features of the free-standing vertically oriented ZnO nanowires. We obtained a homogeneous coverage of transparent conductive substrates with high-aspect-ratio nanowire arrays (length/diameter ratio of up to 52). Such nanostructured vertical arrays were examined to assess their electric and piezoelectric properties, and showed an electric charge generation upon mechanical compressive stress. The principle of energy harvesting with these nanostructured ZnO arrays was demonstrated by connecting them to an electronic charge amplifier and storing the generated charge in a series of capacitors. We found that the generated charge and the electrical behavior of the ZnO nanowires are strictly dependent on the nanowire length. We have shown the importance of controlling the morphological properties of such ZnO nanostructures for optimizing a nanogenerator device.

Investigation on the Photovoltaic Performance of ZnO Nanoarrays Prepared by Chemical Bath Deposition and Hydrothermal Method

ZnO nanorod arrays were successfully prepared by chemical bath deposition (CBD) and hydrothermal method (HTM), respectively. The photovoltaic performance of ZnO nanoarrays as photoelectrodes in dye-sensitized solar cells (DSCs) was investigated. Experimental results show that ZnO seed crystals prepared by a sol-gol process have c axis orientation and consist of nanoparticles within the range of 50~100nm. The same particle size and orientation is well preserved in ZnO nanoarrays grown on the seed crystal layers. The photovoltaic performance of DSCs based on ZnO nanoarrays as the photoelectrodes is poor, due to the weaker adsorption bond force between ZnO and dye, and lower dye adsorption quantity. By contrast, the DSCs composed of ZnO arrays prepared by hydrothermal method have optimal performance, the corresponding short circuit photocurrent density (Jsc), open circuit voltage (Voc), fill factor (FF) and photoelectric conversion efficiency (η) are 4.89 mA/cm2, 0.650V, 0.39 and 1.25 %, respectively.

Polymer Crystallization as a Tool To Pattern Hybrid Nanostructures: Growth of 12 nm ZnO Arrays in Poly(3-hexylthiophene)

Well-ordered hybrid materials with a 10 nm length scale are highly desired. We make use of the natural length scale (typically 10-15 nm) of the alternating crystalline and amorphous layers that are generally found in semicrystalline polymers to direct the growth of a semiconducting metal oxide. This approach is exemplified with the growth of ZnO within a carboxylic acid end-functionalized poly(3-hexylthiophene) (P3HT-COOH). The metal-oxide precursor vapors diffuse into the amorphous parts of the semicrystalline polymer so that sheets of ZnO up to 0.5 μm in size can be grown. This P3HT-ZnO nanostructure further functions as a donor-acceptor photovoltaic system, with length scales appropriate for charge photogeneration.

Fabrication of Ni(OH)2 coated ZnO array for high-rate pseudocapacitive energy storage

The present communication reports on the first electrodeposition of Ni(OH)2 on ZnO array supported on Ni foam. When applied as a binder-free electrode material for pseudocapacitive energy storage, the resulting ZnO@Ni(OH)2 array exhibits a high specific capacitance of 2028Fg−1 at a current density of 10Ag−1 with good cycling stability. Meanwhile, the array exhibits a superb rate capability. Even at an extremely high current density of 100Ag−1, the array still shows a very high specific capacitance of 1059Fg−1.

Effect of Sn doping on structural, optical, electrical and wettability properties of oriented ZnO nanorod arrays

Herein we present a modified sol gel route for the one step fabrication of oriented ZnO nanorod arrays. The method is seed layer free, and nanorods directly attach to a substrate. We also present the effect of tin (Sn) content on the crystallinity, microstructural, optical and electrical properties of the ZnO nanorod arrays. Thermo gravimetric (TG) curves of gel precursors showed that most of the organic groups and other volatiles were removed at about 450 °C. X-ray diffraction patterns confirmed that the films were polycrystalline in nature with (002) preferred orientation. The texture coefficient, grain size, dislocation density and lattice parameters of the ZnO arrays were determined. The SEM micrographs revealed that the undoped and 1 at.%Sn doped films were composed of nanorods and the concentration of 2 at.%Sn doping hindered the rod like structure growth and modulated into granular nature. UV-visible transmission spectroscopy indicated that the transparency of the films increased with Sn content. On Sn doping, the films also exhibited a red shift and slight shrinkage of band gap. The electrical studies revealed that 1 at.% of Sn doping enhanced electrical conduction in ZnO films and beyond that the distortion caused in the lattice reduced the conductivity. The contact angle of the ZnO nanostructures varied between 91° and 115° depending upon the Sn content. Therefore, 1 at.%Sn doping into ZnO nanorods improves the crystallinity, electrical conductivity and water contact angle.

Synthesis and optical property of bouquet-like ZnO arrays

The unique bouquet-like ZnO arrays were successfully synthesized via a two-step route. First, flower-like ZnO arrays were prepared by a hydrothermal reaction. Then the bouquet-like structure was obtained by the selective etching of the ZnO nano-flowers in NaCl aqueous solution. Each ZnO bouquet was composed of many tube-like petals radiating from the center outwards. Based on the experimental evidences, a possible mechanism involving face-selective etching and defect-selective etching was proposed for the formation of bouquet-like ZnO arrays. It was found that the distribution of defects played a critical role in the structure of petals of ZnO bouquets. Photoluminescence (PL) spectrum of the bouquet-like ZnO arrays exhibited two emission bands, including a strong ultraviolet (UV) emission at 382nm and a weak visible emission band centered at 532nm.

Determination of sulfate-reducing bacteria with chemical conversion from ZnO nanorods arrays to ZnS arrays

This work presents a novel specific detection method for sulfate-reducing bacteria (SRB) based on sulfuration conversion from ZnO arrays to ZnS arrays. The sulfuration process was conducted in two steps. First, ZnO@ZnS intermediate nanocomposite arrays were formed by the sulfuration reaction between ZnO and sulfide, which is the characteristic enzymatic metabolism product of SRB. Next, unconverted ZnO cores were washed away in ammonia buffer solutions, leaving ZnS arrays on the surface of ITO substrates. The array conversion process can be used for SRB detection because the final state of ZnS arrays was highly related with the amount of accumulated sulfide, which was decided by the initial concentration of SRB. Electrochemical impedance spectroscopy has been used to optimize experimental conditions and detect SRB in aqueous solutions. This SRB detection method based on arrays conversion from ZnO to ZnS can avoid the use of biological recognition elements, which are expensive and easy to lose specific recognizing abilities. In addition, compared with the widely used MPN method which would take up to 15days to accomplish the detection process, the proposed method can shorten the detection time greatly.

High Density Metal Oxide (ZnO) Nanopatterned Platforms for Electronic Applications

ABSTRACTFabrication methodologies with high precision and tenability for nanostructures of metal and metal oxides are widely explored for engineering devices such as solar cells, sensors, non-volatile memories (NVM) etc. In this direction, metal and metal oxide nanopatterned arrays are the state-of-the-art platforms upon which the device structures are built where the tunable orderly arrangement of the nanostructures enhances the device performance. We describe here a coalition of fabrication protocols that employ block copolymer self-assembly and nanoimprint lithography (NIL) to obtain metal oxide nanopatterns with sub-100 nm spatial resolution. The protocols are easily scalable down to sub-50 nm and below.Nanopatterned arrays of ZnO created by using NIL assisted templates through area selective atomic layer deposition (ALD) and radio frequency (RF) sputtering find application in NVM and photovoltaics. We have employed NIL that produced nanoporous polymer templates using Si molds derived from block copolymer lithography (BCL) for pattern transfer into ZnO. The resulting ZnO nanoarrays were highly dense (8.6 x 109 nanofeatures per cm2) exhibiting periodic feature to feature spacing and width that replicated the geometric attributes of the template. Such nanopatterns find application in NVM, where a change in the density and periodicity of the arrays influences the charge storage characteristics. The above assembly and patterning protocols were employed to fabricate metal-oxide-semiconductor (MOS) capacitor devices for investigating application in NVM. Patterned ZnO nanoarrays were used as charge storage centres for the MOS capacitor devices. Preliminary results upon investigating the flash memory performance showed good flat-band voltage hysteresis window at a relatively low operating voltage due to high charge trap density.

Effects of nitrogen pressure during pulsed laser deposition on morphology and optical properties of N-doped ZnO nanostructures

Thin films, nanorod and nanopore arrays of N-doped ZnO (ZnO/N) have been prepared on quartz substrates, respectively, under different nitrogen pressures by pulsed laser deposition technique. The chemical bonds and nitrogen contents in the composition of ZnO/N nanostructures are characterized with X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy respectively, which confirm the implantation of nitrogen in ZnO. The optical properties of those ZnO/N nanostructures are studied with UV-visible transmission and photoluminescence measurements. The transparency of those ZnO/N nanostructures in visible range decreases when morphology varies from films, nanorods to nanopores. The photoluminescence of ZnO/N nanostructures at room temperature and low temperature of 4.6K reveals a blue-shift of photoluminescence peaks when the nitrogen pressure changes from 26.7 to 80.0Pa. Interestingly, we also observe that the dominated photoluminescence peaks of ZnO/N nanostructures at temperature of 4.6K are modulated with the nitrogen content in ZnO/N nanostructures.

Fabrication and photocatalytic activities of ZnO arrays with different nanostructures

Large-scale ZnO arrays with a series of morphologies, including nest-like, tower-like, and flower-like samples, have been successfully synthesized by a simple hydrothermal method. The morphologies of the obtained ZnO arrays can be conveniently tailored by changing seeding conditions. The samples were characterized using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence (PL) spectroscopy. Their PL spectra depend on their morphologies and defects density. The morphology-dependent photocatalytic performances were studied by analyzing the degradation of methylene blue (MB) in aqueous solution. The nest-like ZnO arrays exhibited higher photocatalytic activity than tower-like and flower-like ZnO arrays.

Enhanced photoelectrochemical performance of bridged ZnO nanorod arrays grown on V-grooved structure

Bridged ZnO nanorod arrays on a V-grooved Si(100) substrate were used as the photoanode of a photoelectrochemical (PEC) cell for water splitting. Photolithography followed by reactive ion etching was employed to create a V-grooved structure on a Si substrate. ZnO nanorod arrays were grown via a hydrothermal method. The light trapping and PEC properties are greatly enhanced using the bridged ZnO nanorod arrays on a V-grooved Si substrate compared with those on a flat one. Increased short circuit photocurrent density (JSC, 0.73 mA cm−2) and half-life time (1500 s) are achieved. This improved JSC and half-life time are 4 times and 10 times, respectively, higher than those of the ZnO nanorod arrays grown on a flat substrate. The overall PEC cell performance improvement for the V-groove grown ZnO array is attributed to the reduced light reflection and enhanced light trapping effect. Moreover, V-groove ZnO showed stronger adhesion between ZnO nanorod arrays and the substrate.

Comparative study of the ZnO and Zn1−xCdxO nanorod emitters hydrothermally synthesized and electrodeposited on p-GaN

Hydrothermal synthesis and electrodeposition are low-temperature and cost-effective growth techniques of high quality nanostructured active materials for opto-electronic devices. Here we report a hydrothermal seed layer-free and rapid synthesis (15min) of epitaxial nanorod arrays of ZnO on p-GaN(0001). The effects of hydrothermal (HT) versus electrochemical deposition (ECD) synthesis on the optical properties of ZnO nanorods/nanowires on p-GaN substrate are compared in details. For both types of layers, a strong photoluminescent UV-emission was found indicating the high quality of the synthesized ZnO layer. The hetero-structures were used for LED applications. With HT-ZnO and ECD-ZnO, UV-emission started at remarkably low forward voltage of 3.9–4.0V and 4.4V respectively and increased rapidly. Moreover, the LED structures showed a stable and repeatable electroluminescence. We propose for further studies a simple, efficient, seed layer-free and low temperature hydrothermal growth technique to fabricate high quality ZnO nanorods/p-GaN heterojunction LED nanodevices. It is also demonstrated that a single short wavelength emission can be shifted to the violet range with Cd-alloying of ZnO used for LED structure.

Surface structure and field emission properties of cost effectively synthesized zinc oxide nanowire/multiwalled carbon nanotube heterojunction arrays

A cost-effective and efficient approach for the synthesis of single-crystalline zinc oxide nanowires on vertically aligned multiwalled carbon nanotube (CNT) array is presented. ZnO nanowires are grown on the base of individual CNT through the low-temperature wet-chemical batch deposition technique, while the size and interspacing of the nanowires can be controlled by precursor concentration, growth temperature and time duration. The scanning electron microscopy image showed that the ZnO nanostructures are successfully grown on the CNT's surface uniformly. The produced nanostructures are characterized by x-ray diffraction, x-ray photoelectron spectroscopy and Raman spectroscopy. Also, field emission characteristics of the fabricated double-stage ZnO nanowire/CNT array are investigated and compared with the emission behaviour of CNT and ZnO nanowire arrays. The ZnO nanowire/CNT heterojunction array resulted in a low turn-on field of 1.5 V µm−1 and a threshold field of 4.5 V µm−1, which were lower than both the vertical CNT and ZnO arrays. The field emission properties and stability of the fabricated nanostructures also demonstrated great potential for field emission applications.

PREPARATION OF NANOCRYSTALLINE ZnO/TiO2 FILM AND ITS APPLICATION TO DYE-SENSITIZED SOLAR CELLS

Dye-sensitized solar cells (DSSCs) were built by using ZnO/TiO2 films as electrodes consisting of ZnO nanorod arrays coated with TiO2 nanoparticles (NPs) in sol or slurry form prepared by sol–gel methods. The addition of TiO2 sol to ZnO arrays resulted in an improvement of cell performance, but the cell efficiency was not high. The cell efficiency was more improved by coating of ZnO arrays with TiO2 slurry. The tetraethylammonium hydroxide surfactant was effective to control TiO2 NPs suspension between sol and slurry. The penetration of TiO2 sol or slurry into ZnO array was important, especially in the long nanorod array. The cell performance of ZnO/TiO2 electrode increased more by TiO2 slurry than by TiO2 sol because TiO2 sol shrank more during calcination.

Hybrid photoanode films based on sparse ZnO rod array-TiO2 nanoparticles in dye-sensitized solar cells

ZnO-TiO2 hybrid photoanodes were fabricated via the doctor-blade method by integrating vertically-grown sparse ZnO arrays with hydrothermal TiO2 nanoparticles. A special surface-coating technique was developed to deposit a thin TiO2 layer on the surface of ZnO rods. Microstructure, optical and photoelectrochemical performance of the hybrid photoanodes were investigated. The denser ZnO array exhibited bad filling behavior of nanoparticles in the interspace of ZnO rods, strong scattering and low conversion efficiency (0.27%). The sparser array showed a much better integrated microstructure, improved transmittance and high conversion efficiency (2.68%). The surface modification of ZnO rods by the TiO2 thin layer was found useful in improving the interfacial microstructure between the ZnO rod and the TiO2 bulk film, and the total conversion efficiency of 3.01% was achieved, higher than that of the pure TiO2 nanoparticle cell (2.93%). The increased scattering effects on the incident light, the enhanced electron transportation at TiO2/dye/electrolyte interface, and the inhabited recombination were responsible for this improvement.