Nanowhisker Arrays Research Articles

Anisotropic, biomorphic cellular Si3N4 ceramics with directional well-aligned nanowhisker arrays based on wood-mimetic architectures

Inspired by the transport behavior of water and ions through the aligned channels in trees, we demonstrate a facile, scalable approach for constructing biomorphic cellular Si3N4 ceramic frameworks with well-aligned nanowhisker arrays on the surface of directionally aligned microchannel alignments. Through a facile Y(NO3)3 solution infiltration into wood-derived carbon preforms and subsequent heat treatment, we can faultlessly duplicate the anisotropic wood architectures into free-standing bulk porous Si3N4 ceramics. Firstly, α-Si3N4 microchannels were synthesized on the surface of CB-templates via carbothermal reduction nitridation (CRN). And then, homogeneous distributed Y−Si−O−N liquid phase on the walls of microchannel facilitated the anisotropic β-Si3N4 grain growth to form nanowhisker arrays. The dense aligned microchannels with low-tortuosity enable excellent load carrying capacity and thermal conduction through the entire materials. As a result, the porous Si3N4 ceramics exhibited an outstanding thermal conductivity (TC, kR ≈ 6.26 W·m−1·K−1), a superior flexural strength (σL ≈ 29.4 MPa), and a relative high anisotropic ratio of TC (kR/kL = 4.1). The orientation dependence of the microstructure-property relations may offer a promising perspective for the fabrication of multifunctional ceramics.

Potential of zinc oxide nanowhiskers as antireflection coating in crystalline silicon solar cell for cost effectiveness

Antireflection coatings play an important role in enhancing the performance of crystalline silicon solar cells by increasing the light coupling into the active region of the devices. In this work we investigated the effects of seed layer thickness and growth time on the reflection properties of solution-grown zinc oxide nanowhiskers. Our results reveal the potential of zinc oxide nanowhiskers as antireflection coating in crystalline silicon solar cells as investigated herein. With this efficient antireflection coating, we have presented a hierarchical structure integrating zinc oxide nanowhisker arrays on silicon micropyramids for improving the energy conversion efficiency. This structure displays broadband reflection suppression in the 300–1200 nm range, with an integrated reflectance of 2.28%. A conversion efficiency of 13.3% was obtained, which is significantly high for large area (3″ × 3″) solar cell fabricated using zinc oxide nanowhiskers as the antireflection coating layer.

Hierarchically ordered arrays with platinum coated PANI nanowires for highly efficient fuel cell electrodes

A hierarchically ordered electrode architecture with crystallographically preferential growth of Pt nanowhisker arrays on PANI nanowire arrays demonstrates outstanding ORR and PEMFC performance.

Efficiency improvement of silicon solar cells enabled by ZnO nanowhisker array coating

An efficient antireflection coating is critical for the improvement of silicon solar cell performance via increased light coupling. Here, we have grown well-aligned ZnO nanowhisker (NW) arrays on Czochralski silicon solar cells by a seeding-growth two-step process. It is found that the ZnO NWs have a great effect on the macroscopic antireflection effect and, therefore, improves the solar cell performance. The ZnO NW array-coated solar cells display a broadband reflection suppression from 500 to 1,100 nm, and the minimum reflectance smaller than 3% can easily be achieved. By optimizing the time of ZnO NW growth, it has been confirmed that an increase of 3% relatively in the solar cell efficiency can be obtained. These results are quite interesting for the application of ZnO nanostructure in the fabrication of high-efficiency silicon solar cells.

Methane Gas Sensing Properties of the Zinc Oxide Nanowhisker-derived Gas Sensor

A low power methane gas sensor with microheater was fabricated by silicon bulk micromachining technology. In order to heat up the sensing layer to operating temperature, a platinum (Pt) micro heater was embedded in the gas sensor. The line width and gap of the microheater was 20 <TEX>${\mu}m$</TEX> and 4.5 <TEX>${\mu}m$</TEX>, respectively. Zinc oxide (ZnO) nanowhisker arrays were grown on a sensor from a ZnO seed layer using a hydrothermal method. A 200 ml aqueous solution of 0.1 mol zinc nitrate hexahydrate, 0.1 mol hexamethylenetetramine, and 0.02 mol polyethylenimine was used for growing ZnO nanowhiskers. Temperature distribution of the sensor was analyzed by infrared thermal camera. The optimum temperature for highest sensitivity was found to be <TEX>$250^{\circ}C$</TEX> although relatively high (64%) sensitivity was obtained even at as low a temperature as <TEX>$150^{\circ}C$</TEX>. The power consumption was 72 mW at <TEX>$250^{\circ}C$</TEX>, and only 25 mW at <TEX>$150^{\circ}C$</TEX>.

Self-assembly of well-ordered whisker-like manganese oxide arrays on carbon fiber paper and its application as electrode material for supercapacitors

Self-assembled well-ordered whisker-like manganese dioxide (MnO2) arrays on carbon fiber paper (MOWAs) were synthesized via a simple in situ redox replacement reaction between potassium permanganate (KMnO4) and carbon fiber paper (CFP) without any other oxidant or reductant addition. The CFP serves as not only a sacrificial reductant and converts aqueous permanganate (MnO4−) to insoluble MnO2 in this reaction, but also a substrate material and guarantees MnO2 deposition on the surface. The electrochemical properties were examined by cyclic voltammograms (CV), galvanostatic charge/discharge, and electrochemical impedance spectroscopy (EIS) in a three-electrode cell. According to the CV results, the ordered MOWAs yield high-capacitance performance with specific capacitance up to 274.1 F g−1 and excellent long cycle-life property with 95% of its specific capacitance kept after 5000 cycles at the current density of 0.1 A g−1. The high-performance hybrid composites result from a synergistic effect of large surface area and high degree of ordering of the ultrathin layer of MnO2 nanowhisker arrays, combined with the flexible CFP substrate and can offer great promise in large-scale energy storage device applications.

Growth of polyaniline nanowhiskers on mesoporous carbon for supercapacitor application

Vertically aligned polyaniline nanowhiskers (PANI-NWs) doped with (1R)-(−)-10-Camphorsulfonic acid (L-CSA) have been successfully synthesized on the external surface of ordered mesoporous carbon (CMK-3) by chemical oxidative polymerization. The specific surface area of the PANI-NWs/CMK-3 nanocomposite remains as high as 497 m 2 g −1 by removing mesoporous silica template after the polymerization of aniline. Structural and morphological characterizations of the nanocomposite were further investigated by XRD, FTIR and FE-SEM measurements. The result shows that the nanocomposite with 40 wt% PANI applying in supercapacitor devices possesses a large specific capacitance of 470 F g −1 and good capacitance retention of 90.4% is achieved after 1000 cycles at a current density of 1.0 A g −1. The synergistic effect of small PANI nanowhisker arrays and well-ordered mesoporous carbon endows the composite with high electrochemical capacitance and good cycling stability.

Hierarchical assembly of anatase nanowhiskers and evaluation of their photocatalytic efficiency in comparison to various one-dimensional TiO2 nanostructures

Well-crystallized anatase nanowhiskers were successfully grown from a Ti substrate via an anodization process followed by hydrothermal treatment. Progressive morphological and crystallographic evolution of anodic nanotubes to nanowhisker arrays was clearly elucidated. The morphology, crystallinity and optical properties of the final nanowhiskers were extensively investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), UV-Vis spectroscopy and photoluminescence (PL) techniques. The synthesized TiO2 photocatalyst exhibited excellent photodegradation of Acid Orange 7 (AO7), a common dye used in textile industries, under UV-A irradiation. Photocatalytic performance was evaluated against other TiO2 films of various 1D (one-dimensional) nanostructures, and benchmarked against a Degussa P25 TiO2 coated film. Owing to its unique morphology and monocrystalline defect-free lattice structure, the nanowhisker sample exhibited the highest photocatalytic efficiency. In view of presented experimental results, the 1D hierarchical nanowhisker architecture may find a variety of potential applications in solar cells, endoscopy and photonic devices, etc.

ZnO 나노휘스커 소재를 이용한 MEMS가스센서의 소비전력과 메탄 감응 특성 연구

A low power gas sensor with microheater was fabricated by MEMS technology. In order to heat up the gas sensing material to a operating temperature, a platinum(Pt) micro heater was built on to the micromachined Si substrate. The width and gap of microheater were and , respectively. ZnO nanowhisker arrays were fabricated on a sensor device by hydrothermal method. The sensor device was deposited with ZnO seeds using PLD systems. A 200 ml aqueous solution of 0.1 mol zinc nitrate hexahydrate, 0.1 mol hexamethylenetetramine, and 0.02 mol polyethylenimine was used for growthing ZnO nanowhiskers. The power consumption to heat up the gas sensor to a operating temperature was measured and temperature distribution of sensor was analyzed by a Infrared Thermal Camera. The optimum temperature for highest sensitivity was found to be although relatively high(64 %) sensitivity was obtained even at as low as . The power consumption was 72 mW at and was only 25 mW at .

Method for manufacturing zinc oxide nanowhisker arrays

Arrays of zinc oxide (ZnO) nanowhskers oriented perpendicularly to the surface of a substrate have been obtained by explosive laser evaporation of ZnO target on (0001)-oriented sapphire and unoriented silica, glass ceramic composite (Polycor), and glass substrates with magnetron-deposited ZnO sublayers layers. X-ray diffractograms of the nanowhisker arrays have been measured and features of their exciton luminescence have been studied.

ZnO Nanoarrays Film Grown by Forced-Hydrolysis-Initiated-Nucleation Technique and its Photo-Induced Electrical Property

Anhydrous zinc acetate pre-coated on the FTO substrate was served as a template layer, and ZnO nanowhisker arrays were simply and successfully fabricated by its forced-hydrolysis-initiated-nucleation of the layer in an aqueous solution at low temperature below 100 °C. The technique doesn’t need any expensive metal catalyst and high-temperature treatment. The density, diameter and length of whiskers were controllable by changing the deposition time. As-grown ZnO nanoarrays showed photo-induced electrical property. Enhanced photo-induced current (2.0~3.0  10-5 A) was detected under laser irradiation after DNA molecules labeled with dye molecules were loaded on the ZnO nanowhisker arrays.

Synthesis of highly conductive and transparent ZnO nanowhisker films using aqueous solution

Highly conductive and transparent ZnO nanowhisker films which can be used as transparent electrodes of optoelectronic devices have been produced at lower temperatures on modified conductive F-doped SnO 2 coated glass substrates in zinc nitrate-hexamethylenetetramine aqueous solutions with the addition of polyethylenimine. The crystal structure and morphology of ZnO nanowhiskers were characterized by X-ray diffraction and FE-SEM, respectively. The morphology of ZnO whiskers is dependent on the existence of surfactant polyethylenimine. The optical and electrical properties of the resultant porous films are discussed in terms of the crystal characteristics and microstructure. The films consisting of nanowhiskers with a height of 1 μm exhibited high transmittance of up to 85% in the visible range. The high monochromatic incident photo-electric conversion efficiency (IPCE) of about 50% indicated the excellent potential of ZnO electrodes based on nanowhisker arrays.

Interaction of optical radiation with GaAs nanowhisker arrays

We have studied the reflectivity spectra of doped GaAs nanowhiskers (NWs) with various morphologies, which were grown by molecular-beam epitaxy. It is established that the character of the reflectivity spectra of NWs is determined by the shape of nanocrystals. NWs with droplike and pointlike vertices differently interact with electromagnetic radiation. Laser radiation produces a spectraly selective action on the NW array, which leads to a change in the NW height and induces “caking” of their vertices, thus modifying the reflectivity of the sample. This phenomenon can be used for the creation of local microstructures with preset characteristics in large NW arrays.

Control of Crystal Growth of ZnO Nanowhiskers in Aqueous Solution and Synthesis of Transparent Nanoarrays

Transparent and porous ZnO nanowhisker arrays were prepared in 0.025 M zinc nitrate-hexamethylenetetramine aqueous solutions with the addition of polyethylenimine (PEI) at a low temperature. The effect of free zinc ion concentration was controlled by changing the immersing temperatures at which the pre-treated FTO substrates were got into the mixing solution such as 25°C, 75°C and 85°C. The free Zn ion concentration is a main factor for control of the transmittance. It was found that high Zn ion concentrations resulted in relative thick white and low transparent ZnO film, while the low concentrations gave high transparenency in the nanoarray. A transmittance of about 85% for porous ZnO films with thickness of 800 nm in the visible range was achieved.

Growth of GaAs nanowhisker arrays by magnetron sputtering on Si(111) substrates

The growth of GaAs nanowhisker (NW) arrays on Si(111) substrates by magnetron sputtering is demonstrated. The characteristic NW length is proportional to the effective thickness of a deposited layer and inversely proportional to the transverse whisker size at the top. The results are explained in terms of the diffusion model of NW growth.

Formation of GaAs nanowhisker arrays by magnetron sputtering deposition

The possibility is demonstrated of fabricating arrays of cone-shaped GaAs nanowhiskers with a surface number density of up to 109 cm-2, a characteristic height ranging from 300 to 10000 nm, and a transverse size of approximately 200 nm at the base and from 200 to 10 nm or smaller at the top. The characteristic height of GaAs nanowhiskers varies in direct proportion to the effective thickness of the deposited material layer and in inverse proportion to the transverse nanowhisker size at the top. The growth of GaAs nanowhiskers is studied as a function of the deposition rate, the temperature, and the crystallographic orientation of the substrate. From an analysis of the obtained dependences of the nanowhisker size on these parameters, it is concluded that GaAs nanowhiskers are formed through the diffusion mechanism.