One-dimensional ZnO nanostructure arrays: synthesis and characterization

One-dimensional ZnO nanostructure arrays such as nanowires, nanonails, and nanotrees, have been synthesized by oxygen assisted thermal evaporation of metallic zinc on a quartz substrate over a large area. Morphological evolution of ZnO nanostructures at different time scales and different positions of the substrates have been studied by electron microscopy. A self-catalyzed vapor-liquid-solid (VLS) process is believed to be responsible for the nucleation and subsequently a vapor-solid process is operative for further longitudinal growth. The photoluminescence spectrum showed a weak UV and a broad green emission peak at 3.25 and 2.49 eV, respectively. The latter was attributed to the presence of zinc interstitial defects. Electrical resistivity as a function of temperature showed activated mechanisms to be present. The electrical response of the ZnO nanonail arrays to different gases (CO, NO2, and H2S) indicated that there could be possible application as gas sensors for this material.     

Simple solvothermal route to synthesize ZnO nanosheets, nanonails, and well-aligned nanorod arrays

ZnO nanosheets, nanonails, and well-aligned nanorods were fabricated on Zn foils by a solvothermal approach using ethanol as the solvent. A lower synthesis temperature and a shorter time period favor the formation of nanosheets. By optimizing the synthesis temperature and time period, ZnO nanonails with a hexagonal cap and a long stem could be produced. A higher temperature was not favorable to produce uniform and smooth nanorods. Well-aligned ZnO nanorod arrays were produced with diameters within 100-250 nm and lengths up to approximately 6 microm when NaOH was added to the solvent. By optimizing the reaction parameters, the morphology, size, and orientation of the nanoforms could be tailored. The ZnO nanorods exhibit an excitonic strong UV emission and a defect-related broad green emission at room temperature. The defect-related green emission band decreased with the improvement of the degree of alignment of the nanorods.     

Enhanced ultraviolet emission from ZnS-coated ZnO nanowires fabricated by self-assembling method

A simple chemical route for ZnS-coated ZnO nanowires with preferential (002) orientation is reported. Sodium sulfide and zinc nitrate were employed to supply S and Zn atoms at 60 degrees C to form ZnS-coated ZnO nanowires structures. Electron diffraction measurement shows that the ZnO/ZnS core-shell nanostructure is single crystalline. Interesting features are found in the photoluminescence (PL) spectra of ZnS-coated ZnO nanostructures. After coating, the UV emission of nanorods is dramatically enhanced at the expense of the green emission. The core/shell structure with higher band gap shell material and reduced surface states should be responsible for this PL enhancement.     

Morphology-controlled synthesis of ZnO nanostructures by a simple round-to-round metal vapor deposition route

One-dimensional ZnO nanostructures with different morphologies have been successfully synthesized through a simple round-to-round metal vapor deposition route at 550 degrees C with a zinc powder covered indium film as the source material. The structures and morphologies of the products were characterized in detail by using X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Studies found that the morphology of the products can be easily tuned from one experimental round to another. Possible growth mechanisms for the formation of one-dimensional ZnO nanostructures with different morphologies are discussed. Photoluminescence studies show that there are sharp UV emission and broad defect-related green emissions for the products obtained in all experimental rounds. Relative intensity of the UV emission to defect-related emissions gradually increased from one experimental round to another.     

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.     

Structure and opto-electrochemical properties of ZnO nanowires grown on n-Si substrate

Zinc oxide (ZnO) nanostructures have attracted great attention as a promising functional material with unique properties suitable for applications in UV lasers, light emitting diodes, field emission devices, sensors, field effect transistors, and solar cells. In the present work, ZnO nanowires have been synthesized on an n-type Si substrate using a hydrothermal method where surfactant acted as a modifying and protecting agent. The surface morphology, electrochemical properties, and opto-electrochemical properties of ZnO nanowires are investigated by using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), cyclic voltammetry, and impedance spectroscopy techniques. The cycling characteristics and rate capability of the ZnO nanowires are explored through electrochemical studies performed under varying electrolytes. The photo response is observed using UV radiation. It is demonstrated that crystallinity, particle size, and morphology all play significant roles in the electrochemical performance of the ZnO electrodes.     

Sn掺杂ZnO半导体纳米带的制备、结构和性能

在无催化剂的条件下, 利用碳热还原反应气相沉积法制备出了高产率单晶Sn掺杂ZnO纳米带. XRD和TEM研究表明纳米带为结晶完好的纤锌矿结构, 生长方向沿[0001], EDS分析表明纳米带中Sn元素含量约为1.9%. 室温光致发光谱(PL)显示掺锡氧化锌纳米带存在强的绿光发射峰和较弱的紫外发射峰, 谱峰峰位中心分别位于494.8 nm和398.4 nm处, 并对发光机制进行了分析. 这种掺杂纳米带有望作为理想的结构单元应用于纳米尺度光电器件领域.     

一种新颖的ZnO纳米结构的自组装合成及发光性能

采用水热法制备了花生状ZnO微米棒, 通过XRD, EDX和FE-SEM等技术分析了其物相组成、形貌及尺寸; 通过变温荧光光谱测试及对所得谱图的高斯拟合研究了该ZnO微米棒的荧光性能, 并将其在300 K时所得的谱图与常规室温荧光谱图进行了比较. XRD, EDX及FE-SEM测试结果表明, 该产物为长约10 μm, 直径约2 μm的花生状六方纤锌矿ZnO微米棒; 荧光测试结果表明, 该ZnO微米棒有紫外峰、紫峰和绿峰3个发光峰, 当温度从8 K升至300 K时, 各峰的强度均有所减弱, 同时紫外峰出现蓝移, 绿峰出现红移, 紫峰峰位出现特殊的“S”形(红移-蓝移-红移)移动. 并对各峰的产生及随温度变化的规律进行了探讨.     

Synthesis and Optical Properties of Ce-doped ZnO

ZnO nanorods were synthesized using the sol-gel method, and the effects of annealing temperature and Ce doping on the morphologies and optical properties of ZnO nanostructures were investigated in detail. The XRD measurements showed that the as-synthesized ZnO nanostructures had a hexagonal wurtzite structure. SEM images showed that uniform nanorods formed at 900 °C. Photoluminescence measurements showed an ultraviolet emission peak and a relatively broad visible light emission peak for the samples sintered at different temperatures. The UV emission peak bathochromically shifted when the annealing temperature rose from 850 to 1000 °C. Ce doping decreased the synthesized temperature of the ZnO nanorods to 500 °C, and the UV peaks hypsochromically shifted.     

Raman scattering and efficient UV photoluminescence from well-aligned ZnO nanowires epitaxially grown on GaN buffer layer

Optical phonon confinement and efficient UV emission of ZnO nanowires were investigated in use of resonant Raman scattering (RRS) and photoluminescence (PL). The high-quality ZnO nanowires with diameters of 80-100 nm and lengths of several micrometers were epitaxially grown through a simple low-pressure vapor-phase deposition method at temperature 550 degrees C on the precoated GaN(0001) buffer layer. The increasing intensity ratio of n-order longitudinal optical (LO) phonon (A(1)(nLO)/E(1)(nLO)) with increasing scattering order in RRS reveals the phonon quantum confinement as shrinking the diameter of ZnO nanowires. The exciton-related recombination near the band-edge transition dominate the UV emissions at room temperature as well as at low temperature that exhibits almost no other nonstoichiometric defects in the ZnO nanowires.     

Fabrication of 3D rotor-like ZnO nanostructure from 1D ZnO nanorods and their morphology dependent photoluminescence property

A facile and eco-friendly sonochemical route to fabricate well-defined dentritic (rotor-like) ZnO nanostructures from 1D ZnO nanorods without alloying elements, templates and surfactants has been reported. Phase and structural analysis has been carried out by X-ray diffraction (XRD) and Fourier Transform Infra-Red (FTIR) spectroscopy, showed the formation of hexagonal wurtzite structure of ZnO. Scanning electron microscopic (SEM) study showed the formation of rotor-like ZnO nanostructure having a central core which is surrounded by side branches nanocones. Transmission electron microscopic (TEM) study showed that these nanocones grow along [0001] direction on the six {01–10} planes of central core ZnO nanorods. A plausible formation mechanism of rotor-like ZnO nanostructures was studied by SEM which indicates that the size and morphology of side branches can be controlled by adjusting the concentration of OH^? ions and time duration of growth. The photoluminescence (PL) spectrum of the synthesized rotor-like ZnO nanostructures exhibited a weak ultraviolet emission at 400 nm and a strong green emission at 532 nm recorded at room temperature. The influence of morphology on the origin of green emission was discussed in detail. The results suggested a positive relationship among polar plane, oxygen vacancy and green emission.     

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.     

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."     

Synthesis of europium-doped zinc oxide micro- and nanowires

Single crystalline Eu³⁺-doped wurtzite ZnO micro- and nanowires were synthesized by a chemical vapor deposition method (CVD). The nanostructures were grown by autocatalytic mechanism at walls of an alumina boat. The structure and properties of the doped ZnO is fully characterized by X-ray diffraction (XRD), energy-dispersive X-ray spectrometry (EDX), scanning and transmission electron microscopy (SEM and TEM), and photoluminescence (PL) methods. The synthesis was carried out for 10 min giving vertically aligned nanowires with mean diameter of 50–400 nm and with length of up to several microns. The nanowires were grown along ±[0001] direction. The concentration of Eu³⁺ dopant in the synthesized nanowires was varied from 0.7 to 0.9 at %. The crystal structure and microstructures of the doped nanomaterials were discussed and compared with undoped ZnO. The photoluminescence spectra show that emission of doped samples were shifted towards orange-red region (2.02 eV) relative to undoped zinc oxide nanostructures (2.37 eV) due to Eu³⁺ intraionic transitions from ZnO/Eu.     

等离子体增强MOCVD法生长ZnO薄膜

利用等离子体增强MOCVD法生长出 ZnO薄膜，用X射线衍射谱观察到位于 2θ34．56°处（0002）的衍射峰，表明ZnO沿c方向呈柱状生长．通过荧光光谱，观察到来自于激子的高强度的近带边紫外光发射（375um）．紫外发射光强度与深能级复合发射光强度比高达 193，显示出材料的高质量，并通过原子力显微镜加以验证．为了实现高阻ZnO薄膜，利用高温富氧分段退火和用N2 气进行掺氮两种方法生长高阻ZnO薄膜．结果表明，电阻率由0．65 Ω·cm分别升高到1100 Ω·cm（分段退火）和5×104Ω·cm（掺氮）．进一步比较发现，掺氮的样品不仅电阻率高，而且光荧光特性好，显示出更高的薄膜质量．     

Synthesis and synchrotron light-induced luminescence of ZnO nanostructures: nanowires, nanoneedles, nanoflowers, and tubular whiskers

ZnO nanostructures, including single-crystal nanowires, nanoneedles, nanoflowers, and tubular whiskers, have been fabricated at a modestly low temperature of 550 degrees C via the oxidation of metallic Zn powder without a metal catalyst. Specific ZnO nanostructures can be obtained at a specific temperature zone in the furnace depending on the temperature and the pressure of oxygen. Scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and X-ray diffraction (XRD) studies show that ZnO nanostructures thus prepared are single crystals with a wurtzite structure. X-ray excited optical luminescence (XEOL) from the ZnO nanostructures show noticeable morphology-dependent luminescence. Specifically, ZnO nanowires of around 15 nm in diameter emit the strongest green light. The morphology of these nanostructures, their XEOL, and the implication of the results will be discussed.     

砷掺杂的ZnO纳米线的发光特性

在GaAs基底上制备了高质量的直径为10～100 nm、长度约几个微米的As掺杂ZnO纳米线. 扫描电镜、EDX分析及透射电镜分析显示, ZnO纳米线具有较好的晶态结构. 对As掺杂前后的ZnO纳米线进行光学特性测量, 结果表明, ZnO纳米线在385 nm处有较强的紫外发光峰, 在505 nm左右有较弱的蓝绿发光峰; As掺杂较大地改变了ZnO纳米线的发光性质, 使本征发光峰移到393 nm处, 蓝绿发光强度有了很大程度的提高.     

Systematic investigation on morphologies, forming mechanism, photocatalytic and photoluminescent properties of ZnO nanostructures constructed in ionic liquids

In this contribution, a series of shape-controllable ZnO nanostructures were synthesized in ionic liquids by a simpler, only one-step, low-temperature route, and characterized by XRD, XPS, TEM, HRTEM, SAED, EDXA, SEM, FTIR, surface area measurement and photoluminescence. We mainly investigate the effect of cations of ionic liquids on the shape of ZnO nanostructures and the forming mechanism of ZnO nanostructures in ionic liquids, as well as the luminescent property and photocatalytic activity for the degradation of Rhodamine B. The results show that the longer alkyl chain at position-1 of the imidazole ring of the ionic liquid will hinder the ZnO nanostructures from growing longer, and the hydrogen bonds may play a crucial role for the directional growth of the 1D nanocrystals. The photoluminescent study shows that the as-obtained ZnO nanostructures exhibit a unique green emission, indicating the existence of oxygen vacancies in the ZnO nanostructures. Importantly, the as-obtained ZnO nanostructures prepared in different ionic liquids show strong size/shape-dependent photocatalysis activity for degradation of Rhodamine B, and the well-dispersed homogeneous ZnO nanoparticles and nanowires display high photocatalytic activity. The investigation of photodegradation kinetics of Rhodamine B indicates that the photodegradation process obeys the rule of a first-order kinetic equation ln( C(0)/ C) = kt. This is the first systematic investigation on the relationship between the structure of ionic liquids and the morphology of ZnO nanostructures.     

Synthesis of ZnO nanobundles via Sol–Gel route and application to glucose biosensor

ZnO nanobundles were fabricated by Sol–Gel route. The as-prepared ZnO nanobundles were characterized by XRD, FE-SEM, TEM and PL. ZnO nanobundles structure are composed of many nanorods of about 80 nm in diameter and 0.6 μm in length. It showed weaker UV emission and stronger green emission. A glucose biosensor was constructed using these ZnO nanobundles as supporting materials for glucose oxidase (GO_X) loading by chitosan-assisted cross-linking technique. The biosensor exhibits a high affinity, high sensitivity, and fast response for glucose detection. These results demonstrate that zinc oxide nanostructures have potential applications in biosensors.     

Hydrothermal synthesis and humidity sensing property of ZnO nanostructures and ZnO-In(OH)3 nanocomposites

Prism- and raspberry-like ZnO nanoparticles and ZnO-In(OH)(3) nanocomposites were prepared by template free hydrothermal method. XRD investigations and microscopic studies showed that pill-like In(OH)(3) particles with body-centered cubic crystal structure formed on the surface of ZnO nanoparticles resulting in increased specific surface area. TEM-EDX mapping images demonstrated that not only nanocomposite formation took place in the course of the synthesis, but zinc ions were also built into the crystal lattice of the In(OH)(3). However, only undoped In(OH)(3) was found on the surface of the pill-like particle aggregates by XPS analyses. The raspberry- and prism-like ZnO particles exhibit strong visible emission with a maximum at 585 and 595 nm, respectively, whose intensity significantly increase due to nanocomposite formation. Photoelectric investigations revealed that photocurrent intensity decreased with increasing indium ion concentration during UV light excitation, which was explained by increase in visible fluorescence emission. QCM measurements showed that morphology of ZnO and concentration of In(OH)(3) had an influence on the water vapor sensing properties.