ZnO纳米线形态对其光致发光性能的影响

以多孔氧化铝膜为模板,电化学沉积出Zn纳米线,再通过高温氧化得到ZnO纳米线阵列。通过改变制备多孔氧化铝模板的工艺参数来改变模板纳米孔径,进而改变ZnO纳米线的直径,得到不同形态的ZnO纳米线阵列。应用X射线衍射仪、透射电子显微镜测试技术表征了ZnO纳米线的结构与形貌。结果发现,X射线衍射时会出现随ZnO纳米线直径增大衍射峰增多和增强的现象。采用荧光光谱仪测试样品的光致发光性能,通过Gaussian原理对谱峰的拟合分析了ZnO纳米线形态对其光致发光光谱的影响。结果表明,随着纳米线直径从30nm至60nm依次增大,其结晶性和化学计量比逐渐变好。近紫外区和蓝光区的发射峰随着纳米线直径的增大而蓝移,而纳米线直径为60nm的样品则出现随直径增大而红移的现象。结果可见,直径在55~60nm间的某点将是ZnO纳米线的结构和光致发光性能变化的临界点。     

A simple route to porous ZnO and ZnCdO nanowires

Porous ZnO nanowires were obtained in an inexpensive and simple way by thermally oxidizing ZnSe nanowires in air. The morphologies of the precursor and resulted nanowires are almost identical. X-ray diffraction and energy-dispersive X-ray spectroscopy reveal that the zinc blende ZnSe nanowires were transformed into wurtzite ZnO nanowires after oxidation. Transmission electron microscope measurements indicate that the ZnO nanowires are polycrystalline and are composed of nanoparticles and nanopores. ZnCdO nanowires, which were seldom reported previously, have also been prepared in this way. Just like the ZnO nanowires, the ZnCdO nanowires also show the porous structure. Photoluminescence studies on both ZnO and ZnCdO nanowires show intense near-band edge emissions at room temperature. The transition from one kind of nanowires to another by simple thermal oxidization described in this paper may be applicable to some other compound semiconductors and may open a practical route to yield nanowires.     

Synthesis and Characterization of ZnO Nanowires

Zinc oxide is a wide bandgap (3.37 eV) semiconductor with a hexagonal wurtzite crystal structure. ZnO prepared in nanowire form may be used as a nanosized ultraviolet light-emitting source. In this study, ZnO nanowires were prepared by vapor-phase transport of Zn vapor onto gold-coated silicon substrates in a tube furnace heated to 900 ?C. Gold serves as a catalyst to capture Zn vapor during nanowire growth. Size control of ZnO nanowires has been achieved by varying the gold film thickness…     

Synthesis and characterization of ZnO nanowires by thermal oxidation of Zn thin films at various temperatures

In this research high-quality zinc oxide (ZnO) nanowires have been synthesized by thermal oxidation of metallic Zn thin films. Metallic Zn films with thicknesses of 250 nm have been deposited on a glass substrate by the PVD technique. The deposited zinc thin films were oxidized in air at various temperatures ranging between 450 °C to 650 °C. Surface morphology, structural and optical properties of the ZnO nanowires were examined by scanning electron microscope (SEM), X-ray diffraction (XRD), energy dispersive X-ray (EDX) and photoluminescence (PL) measurements. XRD analysis demonstrated that the ZnO nanowires has a wurtzite structure with orientation of (002), and the nanowires prepared at 600 °C has a better crystalline quality than samples prepared at other temperatures. SEM results indicate that by increasing the oxidation temperature, the dimensions of the ZnO nanowires increase. The optimum temperature for synthesizing high density, ZnO nanowires was determined to be 600 °C. EDX results revealed that only Zn and O are present in the samples, indicating a pure ZnO composition. The PL spectra of as-synthesized nanowires exhibited a strong UV emission and a relatively weak green emission.     

Hydrothermal synthesis and optical study of bunches of ZnO nanowires

Bunches of ZnO nanowires have been synthesized by hydrothermal process with the assistance of cetyltrimethylammonium bromide. The obtained bunches of ZnO nanowires are hexagonal wurtzite structures, and they exhibit orange visible emission ~600 nm. It seems the orange emission ~600 nm is due to the presence of Zn(OH)₂ on the surface of ZnO nanowires. On the basis of material information provided by X-ray diffraction, scanning electron microscopy and photoluminescence, a growth mechanism is proposed for the formation of bunches of ZnO nanowires.     

Wire-shaped electrode of CdSe-sensitized ZnO nanowire arrays for photoelectrochemical hydrogen generation

We combined CdSe nanoparticles and ZnO nanowire arrays to demonstrate a wire-shaped electrode for photoelectrochemical hydrogen generation illuminated with AM 1.5 spectrum. An array of ZnO nanowires was grown vertically and radially outward from a Cu-wire mesh substrate. CdSe nanoparticles were attached to the surface of the orientated ZnO nanowires. Such wire-shaped electrode with radially outward orientated CdSe/ZnO nanowires provided improved electrolyte mass transport and minimized loss of incident photons. CdSe/ZnO nanowires were formed in all directions over the Cu wire, leading to low incident-light-angle dependence. For photoelectrochemical hydrogen generation under one-sun irradiation, the wire-shaped electrode device outperformed the planar-shaped electrode device by at least 30%.     

Preparation of ZnO Nanowires and Study of Surface‐adsorbate Interaction by Fourier‐Transform Infrared Spectroscopy

To study the surface‐adsorbate properties of ZnO nanowires, a hydrothermal method was modified to grow ZnO nanowires directly on ZnSe, which were then characterized by attenuated total reflection infrared (ATR‐IR) spectroscopy. To prepare ZnO nanowires directly on ATR sensing element of ZnSe, ZnO seed layers were first formed by annealing of ZnO seeds on ZnSe surfaces. The ZnO seed layers then were exposed to growth solution, forming ZnO nanowires directly on the ATR crystals. The interaction properties of the resulting surfaces were studied by an ATR‐IR method. The diameter, length and distribution of the ZnO nanowires can be tuned by adjusting the growth conditions, particularly the growing time and the concentrations of reagents. Two surfaces, namely Zn‐rich and Zn‐O ion‐pair surfaces were studied in detail for their adsorption properties toward compounds bearing different functional groups. By examination of several volatile organic compounds (VOCs), it was found that the Zn‐rich surface is less selective and interacts with compounds bearing the functional groups of amino and hydroxyl. The Zn‐O ion‐pair surface is more selective and a much stronger interaction was observed with non‐aromatic amino compounds. These results indicate that the improving of the selectivity of a ZnO‐based sensing device can be achieved by tuning the surface structure of the ZnO nanomaterials.     

硫化锌与硫化锌/氧化锌异质结纳米线的化学气相沉积法制备与表征

介绍一种利用石墨还原快速制备大量硫化锌纳米线的方法,并分别合成了超晶格型、双轴型、核/壳型的硫化锌/氧化锌异质结纳米线。所合成的硫化锌纳米线存在六方纤锌矿和立方闪锌矿两种晶型,纳米线长度达几十微米,直径在20-50 nm,直径均匀且产量很高。在具有双轴型的硫化锌/氧化锌异质结中,首次发现具有超结构特征的氧化锌。HRTEM分析表明,硫化锌/氧化锌超晶格异质结界面为ZB-ZnS(111)∥ZnO(0001),而核/壳型异质结界面为W-ZnS(0001)∥ZnO(0001),这三个晶面分别为各自晶体的极性面,即所合成的硫化锌/氧化锌异质结中极性面相互平行。对ZnS 和ZnS/ZnO 异质结的生长机制进行了探讨,并对硫化锌纳米线与硫化锌/氧化锌异质结的光学性质进行了分析。     

Luminescence Property and Synthesis of Sulfur-doped ZnO Nanowires by Electrochemical Deposition

"Sulfur-doped zinc oxide (ZnO) nanowires were successfully synthesized by an electric field-assisted electrochemical deposition in porous anodized aluminum oxide template at room temperature. The structure, morphology, chemical composition and photoluminescence properties of the as-synthesized ZnO:S nanostructures were investigated. X-ray diffraction and the selected area electron diffraction results reveal that the as-ynthesized products are single phase with hexagonal wurtzite structure with a highly preferential orientation in the (101) direction. Transmission electron microscopy observations indicate that the nanowires are niform with an average diameter of 70 nm and length up to several tens of micrometers. X-ray photoelectron pectroscopy further reveals the presence of S in the ZnO nanowires. Room-temperature photoluminescences observed in the sulfur-doped ZnO nanowires which exhibits strong near-band-edge ultraviolet peaks at 378 and 392 nm and weak green emissions at 533 and 507 nm. A blue emission at 456 nm and violet emissions at around 406, 420, and 434 nm were also observed in the PL spectrum for the as-synthesized ZnO:S nanowires. The PL spectrum shows that S-doping had an obvious effect on the luminescence property of typical ZnO nanowires."     

Attachment-driven morphology evolvement of rectangular ZnO nanowires

The rectangular cross-sectional ZnO nanowires were synthesized in a solution method. An attachment-driven growth mechanism was proposed for the morphology evolvement of ZnO nanocrystals from nanoparticles to nanoplates and eventually to nanowires. Due to the pileup attachment of the nanoplates to recrystallize into nanowires, unique one-dimensional (1D) ZnO nanowires with the rectangular cross section were obtained, which is different from those nanowires in the previous reports. It is the first time the evidence that "oriented attachment" can occur not only for nanoparticles but also for nanoplates was obtained, suggesting that "oriented attachment" is an intrinsic behavior for nanosized materials. According to the growth model proposed based on the direct TEM observations, ZnO nanocrystals can be easily controlled as nanoparticles, nanoplates, or nanowires by tuning the synthetic parameters.     

采用高分子自组装ZnO纳米线及其形成机理

介绍了一种能在各种晶面的硅衬底上制备垂直于衬底取向生长的ZnO纳米线阵列的新方法. 该法采用高分子络合和低温氧化烧结反应, 以聚乙烯醇(PVA)高分子材料作为自组装络合载体来控制晶体成核和生长. 首先通过PVA侧链上均匀分布的极性基团羟基(—OH)与锌盐溶液中的Zn²⁺离子发生络合作用, 然后滴加氨水调节络合溶液pH值为8.5±0.1, 使络离子Zn²⁺转变为Zn(OH)₂, 再将硅片浸入此溶液中, 从而在硅衬底表面得到较均匀的Zn(OH)₂纳米点, 随后在125 ℃左右Zn(OH)₂纳米点通过热分解转化为ZnO纳米点, 其后在420 ℃烧结过程中衬底上的ZnO纳米点在PVA高分子网络骨架对其直径的限域下逐渐取向生长成ZnO纳米线, 并且烧结初期PVA碳化形成的碳通过碳热还原ZnO为Zn, 再在氧气氛中氧化为ZnO的方式在纳米线顶端形成了催化活性点, 促进了纳米线顶端ZnO的吸收. 烧结后碳逐渐氧化被完全去除. 采用场发射扫描电镜(FE-SEM)、透射电镜(TEM, HR-TEM)和X射线衍射(XRD)对纳米线的分析结果表明, ZnO纳米线在硅衬底上分布均匀, 具有六方纤锌矿结构, 并且大多沿[0001]方向择优取向生长, 直径为20～80 nm, 长度可从0.5至几微米. 提出了聚合物控制ZnO结晶和形貌的网络骨架限域模型以解释纳米线的生长行为.     

Controlled growth of semiconducting oxides hierarchical nanostructures

Semiconducting ZnO hierarchical nanostructure, where ZnO nanonails were grown on ZnO nanowires, has been fabricated under control experiment with a mixture of ZnO nanopowders and Sn metal powders. Sn nanoparticles are located at or close to the tips of the nanowires and the growth branches, serving as the catalyst for the vapor-liquid-solid growth mechanism. The morphology and microstructure of ZnO nanowire and nanonail were measured by scanning electron microscopy and high-resolution transmission electron microscopy. The long and straight ZnO nanowires grow along [0001] direction. ZnO nanonails are aligned radially with respect to the surface the ZnO nanowire. The long axis direction of nanonails forms an angle of ∼30° to the [0001] direction.     

Synthesis and Photocatalytic Activity of One-dimensional ZnO-Zn2SnO4 Mixed Oxide Nanowires

Mixed oxide photocatalysts, ZnO-Zn2SnO4 (ZnO-ZTO) nanowires with different sizes were prepared by a simple thermal evaporation method. The ZnO-ZTO nanowires were characterized with a scanning electron microscope, X-ray diffraction, high-resolution transmission electron microscopy, energy-dispersive spectrometer, and X-ray photoelectron spectrThe photocatalytic activity of the ZnO-ZTO mixed nanowires were studied by observing the photodegradation behaviors of methyl orange aqueous solution. The results suggest that the ZnO-ZTO mixed oxide nanowires have a higher photocatalytic activity than pure ZnO and Zn2SnO4 nanowires. The photocatalyst concentration in the solution distinctly affects the degradation rate, and our results show that higher photodegradation efficiency can be achieved with a smaller amount of ZnO-ZTO nanowire catalyst, as compared to the pure ZnO and ZTO nanowires. Moreover, the photocatalytic activity can also be enhanced by reducing the average diameter of the nanowires. The activity of pure ZnO and ZTO nanowires are also enhanced by physically mixing them. These results can be explained by the synergism between the two semiconductors.     

ZnO纳米线的电化学制备研究

High-quality ZnO nanowires have been synthesized at relatively low temperature via one-step electrochemical anodization technique. In this method, Zn sheet acted as the anode and Pb sheet served as the counter electrode, and the complex solution of HF-C₂H₅OH-H₂O was used as electrolyte. ZnO nanowires were characterized by Field Emission Scanning Electron Microscopy (FE-SEM), Transmission Electron Microscopy (TEM) and Selected Area Electron Diffraction (SAED) and X-ray Diffraction (XRD). The results show that the nanowires were wurtzite crystalline ZnO, and the ZnO nanowires with the diameters of 70 nm and 30～40 nm were obtained by adjusting preparation conditions, respectively.     

Vertically well aligned P-doped ZnO nanowires synthesized on ZnO-Ga/glass templates

Vertically well aligned P-doped ZnO nanowires were prepared on ZnO-Ga/glass templates at 550 degrees C by reactive evaporation without metal catalysts and the nanowires were found to be single crystalline with the würtzite structure, oriented in the c-axis direction; the P-doping shortened the physical lengths of the ZnO nanowires without changing their diameter, and furthermore, the introduction of P atoms resulted in a much weaker and broader ZnO band edge emission.     

Comparative structure and optical properties of Ga-, In-, and Sn-doped ZnO nanowires synthesized via thermal evaporation

ZnO nanowires doped with a high concentration Ga, In, and Sn were synthesized via thermal evaporation. The doping content defined as X/(Zn + X) atomic ratio, where X is the doped element, is about 15% for all nanowires. The nanowires consist of single-crystalline wurtzite ZnO crystal, and the average diameter is 80 nm. The growth direction of vertically aligned Ga-doped nanowires is [001], while that of randomly tilted In- and Sn-doped nanowires is [010]. A correlation between the growth direction and the vertical alignment has been suggested. The broaden X-ray diffraction peaks indicate the lattice distortion caused by the doping, and the broadening is most significant in the case of Sn doping. The absorption and photoluminescence of Sn-doped ZnO nanowires shift to the lower energy region than those of In- and Ga-doped nanowires, probably due to the larger charge density of Sn.     

One-step electrodeposition of Ag-decorated ZnO nanowires

A new route for synthesizing Ag-decorated ZnO nanowires (NWs) on conductive glass substrates using a one-step electrodeposition technique is described here. The structural, optical, and photoelectrochemical properties of Ag-decorated ZnO nanowires were studied in detail using techniques such X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, UV-visible spectroscopy, photoluminescence, and photoelectrochemical measurements. Both pure and Ag-decorated ZnO nanowires were found to crystallize in the wurtzite structure, irrespective of their Ag contents. Increasing the Ag content from pure ZnO NWs to 3% Ag ZnO NWs decreases the photoluminescence intensity, shifts the optical band gap to the red, and increases the photocurrent up to threefold. This behavior was attributed to the surface plasmon resonance effect induced by the Ag nanoparticles, which inhibits charge recombination and improves charge transport on the ZnO surface.     

Zinc nanowires synthesized on a large scale by a simple carbothermal process

Metallic Zn nanowires have been synthesized by a new carbothermal reduction route in which ZnO and Eucalyptus sp. tar pitch were used as source materials. This simple practical procedure was capable of producing Zn nanowires in large quantities without reoxidation. This process was carried out in inert atmosphere, without vacuum or catalyst, at temperatures (800–900 °C) lower than those required in the carbothermal reduction of ZnO with graphite. A comparative study was performed using graphite that is traditionally used as a ZnO reducer, under the same experimental conditions, however, no reaction was observed. The new process involves the pyrolysis of biopitch to obtain a highly reactive coke and the reduction of ZnO with the release of Zn_(v) for the growth of Zn_(s) nanowires. The resulting Zn nanowires were characterized by X-ray diffractometry, energy-dispersive spectroscopy and scanning electron microscopy. Differential thermal analysis and thermogravimetric analysis coupled with infrared analysis techniques were used in an effort to understand the underlying mechanism and establish the best ratio biopitch/ZnO to be used. This paper presents the characterization of the as-synthesized nanowires and discusses the main reactions involved in their production.     

Simplifying patterning process of ZnO nanowires by one step development and etching process

We present herein a simple protocol of growing a patterned ZnO nanowire by etching of ZnO seed layer in the tetramethyl ammonium hydroxide (TMAH) solution. The ZnO seed layer was fabricated by sol–gel method using zinc acetate solution and patterned by using photolithographic method. Patterned ZnO seed layer as etched in the TMAH solution, followed by growth of ZnO nanowires by hydrothermal method. Remarkable point of present ZnO seed layer patterning is that development of UV-exposed photoresist and etching of ZnO seed layer is subsequently processed in aqueous TMAH solution without interruption. The grown ZnO nanowires were analyzed using XRD patterns to exhibit high purity and degree of crystallinity, and showed very good pattern fidelity.     

ZnO-聚苯胺同轴纳米线及其列阵的制备和表征

以阳极氧化铝膜 (AAO)作模板 ,制备聚苯胺 (PANI)纳米管和PANI纳米管列阵 ;同时利用溶胶_凝胶法制备ZnO_PANI同轴纳米线和同轴纳米线列阵 .PANI纳米管和ZnO_PANI同轴纳米线的形貌通过透射电子显微镜表征 .PANI纳米管的外径约 3 0nm ,内径约 1 0nm ;ZnO_PANI同轴纳米线直径约 60nm .实验发现 ,较之ZnO纳米线 ,同轴AAO模板中纳米线列阵的可见光发射谱带兰移 ,强度显著增强 ,这可能和PANI链上的NH基团与表面Zn2 +离子之间的相互作用有关 ,以及由于ZnO纳米微粒在PANI上富集、PANI的光生载流子部分转移给ZnO微粒所致 .实验还发现分散在NaOH溶液中的同轴纳米线 ,其可见光发射谱带比AAO模板中同轴纳米线的谱带兰移更甚