Controllable synthesis of well‐aligned CuO nanotube arrays using porous alumina templates

In order to further enhance the performance of CuO in currently existing applications, well‐aligned CuO nanotube arrays with different diameters were fabricated. During the synthesis process, porous anodic alumina films were fabricated, and then the synthesis of CuO nanotube arrays was realized by using the obtained porous anodic alumina films as templates. The morphology and structure of the obtained products has been confirmed by field‐emission scanning electron microscopy, transmission electron microscopy and X‐ray diffraction measurements. Due to the large surface area of the synthesized products, the prepared CuO nanotube arrays may have potential applications in catalyzing and gas sensing area.     

Synthesis of highly‐ordered hierarchical ZnO nanostructures and their application in dye‐sensitized solar cells

In order to improve the performance of ZnO‐based solar cells, highly‐ordered hierarchical ZnO nanostructures were design and fabricated. The hierarchical nanostructures were grown on FTO (fluorine doped tin oxide, SnO₂:F) glass substrates via a facile, low‐temperature, and low‐cost chemical route. The morphology and structure of the obtained products has been confirmed by field‐emission scanning electron microscopy and X‐ray diffraction measurements. The performance investigation of the prepared dye‐sensitized solar cells (DSSCs) demonstrates that the hierarchical ZnO nanostructure‐based solar cell shows a higher short‐circuit current density compared with the ZnO nanowire counterpart. The enhanced current density may be due to the fact that the surface area of the hierarchical nanostructures is increased. These results indicate that hierarchical ZnO nanostructures are more suitable for the application as photoelectrode of DSSCs. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A low-temperature aqueous solution route to large-scale growth of ZnO nanowire arrays

A low-temperature template-free aqueous solution route has been successfully employed to fabricate large-scale arrays of highly oriented ZnO nanowires. It is found that the growth of the highly oriented ZnO nanowire arrays is dependent on the reaction time, leading to our proposal on the possible formation mechanism. The obtained ZnO nanowires are single crystalline and have a low defect concentration. Furthermore, the ZnO nanowires exhibit significant optical properties in photoluminescence (PL) emission spectroscopy and Raman spectrum, suggesting that they could find promising potential for opto-electronic application.     

ZnO超细纳米线阵列的制备及其电化学性能

以Zn(NO₃)₂· 6H₂O和C₆H₁₂N₄为原材料,采用二步水热法在碳纤维布上合成了形貌尺寸均匀的ZnO超细纳米线阵列。用 X 射线衍射(XRD)和扫描电镜(SEM)对其晶体结构和形貌进行了表征,利用恒流充放电测试等手段对其进行电化学性能测试。测试结果表明,材料表现出优异的电化学性能。在200 mA/g的电流密度下循环150次后,ZnO超细纳米线阵列仍然约有730 mAh/g的充放电比容量,库伦效率保持在95%以上。在1 200 mA/g的大倍率条件下,材料的充放电比容量依旧可达481 mAh/g左右,表现出十分良好的循环稳定性和可逆性能,是一种较为理想的锂离子电池负极复合材料。     

EDTA‐assisted synthesis of rose‐like ZnO architectures

Rose‐like ZnO nanostructures were prepared by a low‐temperature solution route with assistance of ethylenediaminetetraacetic acid disodium (EDTA‐2Na). The morphology of ZnO nanostructures was found to change from nanowire arrays to rose‐ and tower‐like architectures with increasing the molar ratio of EDTA‐2Na/Zn²⁺. Also, the shape evolution of ZnO nanostructures with time was observed from flat nanosheets to wrinkled nanosheets and to rose‐like nanostructures. EDTA‐2Na as a strong complexing agent was found to play a key role in the shape evolution. Photoluminescence spectra show that the rose‐like ZnO architectures have more defects than the nanowire arrays. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Facile fabrication of porous ZnO by a template free method

In this paper, a template free method has been employed to fabricate porous ZnO. Brick shaped precursor was first synthesized by a mild hydrothermal process. Accompanied with the decomposition of the precursor during the subsequent annealing treatment, porous ZnO with the inherited morphology of the precursor was obtained. The as‐prepared products were characterized by X‐ray diffraction (XRD) and scanning electron microscopy (SEM). It exhibited that the porous hierarchical frame consists of nano‐sheets with wurtzite‐type. The size of the pores as well as the size of the particles varied with the annealing temperature. Mechanism speculation showed that the crystal‐aggregation in the growth process of the precursor is the key to the establishment of pore structure. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and photoluminescence properties of ZnO nanowire arrays

In this paper we report a chemical method named coordination reaction method to synthesize ZnO nanowire arreys. ZnO nanowires with the diameter about 80nm were successfully fabricated in the channels of the porous anodic alumina (PAA) template by the above coordination reaction method. The microstructures of ZnO/PAA assembly were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X‐ray diffraction (XRD). The results showed that the ZnO nanowires can be uniformly assembled into the nanochannels of PAA template. The growth mechanism of ZnO nanowires and the conditions of the coordination reaction are discussed. Photoluminescence (PL) measurement shows that the ZnO/PAA assembly system has a blue emission band caused by the various defects of ZnO. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Fabrication and photocatalytic property of ZnO/SrTiO3 core/shell nanorod arrays

ZnO/SrTiO₃ core/shell nanorod arrays were fabricated by a facile two‐step method. ZnO nanorod arrays were first hydrothermally grown on Si substrate. Then, using liquid phase deposition method, SrTiO₃ were deposited onto the ZnO nanorods to form core/shell nanorod structures. The morphologies and structures of the products were characterized by scanning electron microscopy, transmission electron microscopy, and X‐ray diffraction. The photocatalytic behavior of the nanorod arrays was also examined through the photodegradation of methylene blue solution under UV irradiation. It was found that the core/shell nanorod arrays with deposition time of 10 min showed higher photocatalytic activity than bare ZnO nanorod arrays. This enhancement was attributed to the efficient charge separation at the ZnO/SrTiO₃ interface.     

Synthesis,characterization and electrical properties of hybrid Zn2GeO4–ZnO beaded nanowire arrays

We report the syntheses of vertically aligned, beaded zinc germinate (Zn₂GeO₄)/zinc oxide (ZnO) hybrid nanowire arrays via a catalyst-free approach. Vertically aligned ZnO nanowire is used as a lattice matching reactive template for the growth of Zn₂GeO₄/ZnO nanowire. The morphology and structure of the as-prepared samples were characterized using X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS). TEM studies revealed the beaded microstructures of the Zn₂GeO₄/ZnO nanowire. The thickness and microstructures of crystalline beads could be easily controlled by tuning the growth duration and temperature. The photoluminescence spectrum of the Zn₂GeO₄/ZnO nanowires is composed of two peaks, i.e., the ultraviolet (UV) peak and the defect peak. For longer treatment duration of the samples, both the UV and defect peak intensities decrease dramatically. One application of the as-prepared Zn₂GeO₄/ZnO nanowire is to use the nanowire as template for the growth of three-dimensionally (3D) aligned, high-density ZnO nanobranches en route to hierarchical structure. The study of field emission properties of the as-prepared samples revealed the low turn-on voltage and high current density electron emission from the 3D ZnO nanobranches as compared to the ZnO nanowires and Zn₂GeO₄/ZnO nanowires. Furthermore, the electrical transport behavior of single hybrid nanowire device indicates the formation of back-to-back Schottky barriers (SBs) formation at the contacts and its application in white-light response has been demonstrated.     

Electrical and sensory properties of zinc oxide – porous silicon nanosystems

Abstract

Zinc oxide nanostructures have been grown by electrochemical deposition on porous silicon–silicon substrate. The photoelectric and sensory properties of the obtained ZnO–porous silicon nanosystems were investigated in both DC and AC regimes. The obtained structures were characterized by photosensitivity in the 400–1100?nm wavelength range and by high sensitivity to moisture. Increase of relative humidity resulted in significant decrease of the electrical resistance and increase of the capacitance of the hybrid structures. To estimate the sensory properties of the ZnO–porous silicon nanostructures their adsorption sensitivity and dynamic characteristics were analyzed. Discovered features of the charge transport processes broaden the prospects of the semiconductor nanosystems application in gas sensors and photodetectors.     

Low temperature hydrothermal growth and optical properties of ZnO nanorods

Well‐faceted hexagonal ZnO nanorods have been synthesized by a simple hydrothermal method at relative low temperature (90°C) without any catalysts or templates. Zinc oxide (ZnO) nanorods were grown in an aqueous solution that contained Zinc chloride (ZnCl₂, Aldrich, purity 98%) and ammonia (25%). Most of the ZnO nanorods show the perfect hexagonal cross section and well‐faceted top and side surfaces. The diameter of ZnO nanorods decreased with the reaction time prolonging. The samples have been characterized by X‐ray powder diffraction (XRD) and scanning electron microscopy (SEM) measurement. XRD pattern confirmed that the as‐prepared ZnO was the single‐phase wurtzite structure formation. SEM results showed that the samples were rod textures. The surface‐related optical properties have been investigated by photoluminescence (PL) spectrum and Raman spectrum. Photoluminescence measurements showed each spectrum consists of a weak band ultraviolet (UV) band and a relatively broad visible light emission peak for the samples grown at different time. It has been found that the green emission in Raman measurement may be related to surface states. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

ZnO纳米线/纳米棒混合阵列的制备及其光致发光性能研究

使用无催化剂热蒸发法,在ZnO/Si薄膜衬底上制备了ZnO纳米线/纳米棒混合阵列.其中,纳米线的直径为10～20nm,纳米棒的直径为60～160 nn,二者混合在一起垂直生长于衬底表面.从衬底的上游到下游位置,混合,阵列中纳米线的含量逐渐下降,纳米棒逐渐增多.室温光致发光测试发现尺寸较小的纳米线阵列的紫外光发光强度比大尺寸纳米棒阵列高约5倍.持续激发光照射下,纳米线阵列的发光强度逐渐上升,停止光照后又逐渐下降到初始值,这可以用纳米线表面O2分子的解吸附和吸附过程来理解.     

ZnO纳米结构减反射层特性优化及对太阳能电池性能的影响

利用电化学沉积法在铜铟镓硒薄膜太阳能电池表面沉积一层ZnO纳米结构阵列减反射层.通过对沉积电位的操控,实现了对该纳米结构减反射层形貌、光学质量、反射率等特性的优化.在电池表面蒸镀电极后测试电池的电流电压曲线可知,相比于没有减反层的电池,沉积了纳米结构减反射层的电池利用氧化锌纳米结构的亚波长尺寸形成的蛾眼效应有效降低了表面光反射,增加光吸收,从而实现短路电流增加6.2;,电池效率提高了9.9;.     

水热法制备ZnO晶体及纳米材料研究进展

纳米ZnO材料是新型宽禁带半导体材料,具有优良的光学及电学性能,在太阳能电池电极及窗口材料、声表面波材料、光电材料、敏感材料等方面得到广泛应用.纳米ZnO材料性能与制备技术有很大关系,本文综合评述了水热法制备纳米ZnO材料研究现状,研究了其制备特点及制备机理,从纳米ZnO晶体、阵列或薄膜、粉体三个方面制备实例研究了水热制备方法,最后探讨了纳米ZnO材料发展前景.     

Solvothermal growth of highly oriented wurtzite‐structured ZnO nanotube arrays on zinc foil

ZnO nanotube arrays were synthesized on zinc foil by a simple solvothermal approach. In this approach, zinc foil was used not only as a substrate but also as a zinc‐ion source for the direct growth of ZnO nanotube arrays. X‐ray diffraction (XRD) analysis and Scanning electron microscope (SEM) images, indicated that the structure of the ZnO nanotube arrays on the zinc foil substrate was single‐crystalline with a wurtzite structure. The optical properties of the ZnO nanorod arrays were characterized by photoluminescence spectroscopies and Raman. Photoluminescence exhibited strong UV emission and a broad deep‐level (visible) emission emission at with 325 nm excitation. A possible mechanism is also proposed to account for the growth of the ZnO nanotube arrays. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Noncatalytic synthesis of carbon nanotubes by chemical vapor deposition

A new method is proposed to obtain uniform arrays of multiwall carbon nanotubes without catalysts. Nanotubes have been formed by carbon condensation from a hydrogen-methane gas mixture activated by a dc discharge. Structural and morphological investigations of the obtained material were performed by Raman spectroscopy, scanning and transmission electron microscopy, energy-dispersive X-ray analysis, and electron energy loss spectroscopy. It is shown that the obtained nanotubes contain no impurities that could act as catalysts. Based on these experimental data, it is concluded that the nanotube synthesis under study is noncatalytic. Possible mechanisms of this synthesis are considered.     

Template-guided growth of well-aligned ZnO nanocone arrays on FTO substrate

Well-aligned ZnO nanocone arrays (NCAs) were prepared on fluorine doped tin oxide (FTO) substrates using highly ordered ZnO nanorod arrays (NRAs) as templates to guide the growth via a hydrothermal method. In contrast, only disordered ZnO nanocones on FTO were obtained in the absence of the highly ordered ZnO nanorod templates. The well-aligned ZnO nanocone arrays were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), UV–visible absorption, and photoluminescence (PL) spectroscopies. It was found that the highly ordered ZnO NRAs pre-formed on FTO played a critical role in dictating the further growth of the well-aligned ZnO NCAs from them. Significantly, strong light-trapping effect was revealed for the well-aligned ZnO NCAs, which may find important applications in, e.g., photovoltaics.     

α‐Fe2O3 nanospindles loaded with ZnO nanocrystals: Synthesis and improved gas sensing performance

ZnO/α‐Fe₂O₃ nanocomposites were fabricated through a two‐step hydrothermal method. The morphology and composition of the as‐synthesized products were characterized by X‐ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), energy‐dispersive X‐ray spectroscopy (EDS), transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM). The gas sensing properties of the fabricated products were investigated towards ethanol, acetone, propanol, isopropanol, formaldehyde, chloroform and so on. The results demonstrated that the ZnO/α‐Fe₂O₃ nanocomposites exhibited excellent sensing properties and showed remarkably higher sensing responses and much lower optimum operating temperature compared to individual ZnO and α‐Fe₂O₃. In addition, the ZnO/α‐Fe₂O₃ nanocomposites have some selectivity for ethanol, propanol and isopropanol. The possible gas sensing mechanism was also proposed. Our studies demonstrate that our fabricated materials could be widely used in the future.     

Facile synthesis of silver‐nanobeadwire transparent conductive film by organic‐precursor paint reduction

A new facile process has been developed to synthesize silver nanowire transparent conductive films by reducing high‐aspect‐ratio, needle‐shaped silver carboxylates, prepared as the precursor, while retaining their morphology. Nanowire precursors are simply obtained by ultrasound irradiation when silver (I) oxide and carboxylic acids are used as starting materials. The aspect ratio of the precursors is increased when the ultrasound irradiation is followed by microwave irradiation. Silver nanowires can be easily obtained by reducing these precursors with hydrazine gas or irradiating them with Ar plasma for a short time. The morphology of the resulting nanowires is different from that of typical nanowires that have been reported. The nanowires have porous morphology, where small nanoparticles are connected to form nanobeadwire. The nanobeadwire is considered to increase the transparency of the film because of its rough morphology. This new method can synthesize silver nanobeadwires and fabricate the transparent conductive film simultaneously, in one‐step, so that it can significantly simplify manufacturing processes.     

Facile morphology‐controlled hydrothermal synthesis of flower‐like self‐organized ZnO architectures

Flower‐like self‐organized crystalline ZnO architectures were obtained through a facile and controlled hydrothermal process. As‐synthesized products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high‐resolution transmission electron microscopy (HRTEM), X‐ray diffraction (XRD), electron diffraction and UV‐Vis spectroscopy. XRD and electron diffraction results confirmed the obtained materials are pure wurtzite ZnO. The effects of different ratios of starting materials and solvent on the morphologies of ZnO hydrothermal products were also evaluated by SEM observations. It is suggested that the use of water, rather than ethanol as the solvent, as well as employing a precursor of Zn(Ac)₂ and 2NaOH (v/v) in hydrothermal reactions are responsible for the generation of specific flower‐like self‐assembled ZnO structures. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)