Structural, optical, and magnetic characterization of Co and N co-doped ZnO nanopowders

Co and N co-doped ZnO nanopowders with Co and N concentration 4, 6, and 8 mol% were synthesized by sol–gel method. Powder X-ray diffraction reveals that Co and N co-doped ZnO crystallize in wurtzite structure having space group C _6v . Photo-luminescence studies show the reduction in band gap with increase in concentration of dopants. Micro Raman studies show the red shift for 1LO phonon peak with increase in doping, generally credited to the stress caused by lattice mismatch due to N doping in ZnO. X-ray absorption spectroscopy reveals that Co replaces the Zn atoms and N replace the O atoms in the host ZnO lattice. Magnetic studies show that Co and N co-doped ZnO nanopowders exhibit ferromagnetic character at room temperature.     

Microwave sintering of ZnO nanopowders and characterization for gas sensing

Thick ?lm gas sensors based on ZnO nanopowders were fabricated by using microwave sintering. The surface and cross section morphologies were characterized by ?eld-emission scanning electron microscopy (FE-SEM). The stability of the microstructure was studied by impedance spectroscopy. The results showed that the shape of the nanoparticles was not changed through microwave sintering, and the thick films had the more dense microstructures than that by muffle oven sintering. The resistance-temperature characteristic and the responses to toluene, methanol and formaldehyde revealed that the microwave sintering technique could effectively control the growth of ZnO nanoparticles, realize the uniform sintering of thick film, gain the stable microstructure and improve the response of sensor. In addition, the formative mechanism of the thick film microstructure was proposed according to microwave sintering mechanism.     

Starch-stabilized synthesis of ZnO nanopowders at low temperature and optical properties study

Zinc oxide nanoparticles (ZnO–NPs) were synthesized via the sol–gel method in starch media. Starch was used as a stabilizer to control of the mobility of zinc cations and then control growth of the ZnO–NPs. Because of the special structure of the starch, it permits termination of the particle growth. Thermogravimetry analysis (TGA) was applied on dried gel to obtain the certain calcination temperature(s) of the ZnO–NPs. The dried gel was calcined at different temperatures of 400, 500, and 600 °C. Several techniques such as X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FTIR), and high-magnification transmission electron microscopy (TEM) were used to characterize the ZnO–NPs. The ZnO–NPs calcined at different temperatures exhibited a hexagonal (wurtzite) structure with sizes from 30 to 50 nm. The optical properties of the prepared samples were investigated using UV–vis spectroscopy. The results showed that starch is a suitable stabilizer in the sol–gel technique, and this method is a reasonable and facile method to prepare ZnO–NPs for large-scale production.     

Li-Cu共掺杂ZnO纳米薄膜的溶胶凝胶法制备

采用溶胶-凝胶法,通过调整氯化锂和氯化铜的摩尔比在不同基片上制备了不同Li-Cu共掺杂浓度的ZnO薄膜.利用X射线衍射仪、扫描电子显微镜、透射电子显微镜、紫外可见光分光光度计和伏安特性测试等表征了薄膜的结晶状况、表面形貌及光电特性.结果表明:所得Li-Cu共掺杂ZnO薄膜为六角纤锌矿多晶结构,有CuO杂质相生成.随Li和Cu摩尔比增加,共掺杂ZnO薄膜结晶度增强,晶粒长大,样品表面不平整度增加.CuO颗粒的出现,使得共掺杂ZnO薄膜透射率降低,透光性较差.Li与Cu摩尔比为1∶1时,共掺杂ZnO薄膜的综合导电性最好.     

Refractory metal nanopowders: Synthesis and characterization

Refractory nanometals have been the subject of interest for the past two decades in order to manufacture compact materials with dramatically improved mechanical properties for aerospace, military, chemical and metallurgical applications. The interest in nanomaterials has led to the development of many synthetic methods for their fabrication. In this review the challenges, synthesis methods and the characteristics of refractory metal nanopowders of IV–VI sub-group of the periodic table are discussed. Special attention is paid to salt-assisted combustion reaction (SACR) as a promising technique for the large-scale production of refractory metal nanopowders.The current paper will: (1) focus on the synthesis methods, morphology and physical–chemical characteristics of metal nanopowders; (2) present the specific feature of the salt-assisted combustion reaction, combustion parameters and macro-kinetic aspects of chemical reactions in the powder bed; and (3) demonstrate the perceptiveness of the fabrication route for the mass production of nanosized powders.     

Excitonic luminescence in ZnO nanopowders and ceramics

Fast photoluminescence spectra in the spectral region of 3.1–3.45 eV in ZnO and ZnO:Al ceramics were studied at 14 and 300 K. Ceramics with grains smaller than 100 nm were sintered from nanopowders by high pressure (8 GPa) and low temperature (350 °C). Ceramics with grain sizes 1–5 μm were sintered at 1400 °C. It is shown that excitonic luminescence spectra depend on the ceramics grain size, post preparing annealing and doping. The excitonic luminescence decay time was faster than 2 ns and the afterglow at 30 ns was 0.05%.     

Controlled mechanochemically assisted synthesis of ZnO nanopowders in the presence of oxalic acid

In this study, the ZnO nanopowders were synthesized by mechanochemical processing with a successive thermal decomposition reaction. The initial reactants mixture of zinc chloride and oxalic acid was milled from 30 min to 4 h and thermally treated for 1 h at 450 °C. The influence of both, oxalic acid and the duration of milling, on the crystal structure, average crystallite size, average particle size, and the morphology of ZnO nanopowders were investigated. The qualitative analysis was performed using X-ray diffraction and Raman spectroscopy techniques. While the XRD analysis shows perfect long-range order and pure wurtzite structure of the synthesized ZnO powders, Raman spectroscopy indicates a different middle-range order; in addition, according to Raman spectra, it is found that lattice defects and impurities introduced in ZnO crystal structure depend on milling duration, in spite of applied thermal treatment. The particle size distribution was measured by laser diffraction, whereas the morphology of the powders was determined by scanning electron microscopy. Impurity contamination was studied using inductively coupled plasma analysis. The obtained results showed that the applied two-step method is appropriate for the synthesis of high crystalline ZnO nanopowders, with uniform spherical particles with diameter between 20 and 50 nm. Profound effect of aqueous solution of oxalic acid to prevent agglomeration of final product is presented.     

Single step synthesis of nanocrystalline ZnO via wet-milling

In this work, we describe the effect of milling speed on the formation, crystallite size, and lattice parameter of nanocrystalline ZnO in a single step process that is based on wet-milling of metallic Zn in distilled water. The samples were characterized by XRD, TEM, and FTIR spectra. The analyses reveal that although the 150 rpm milled sample exhibits imprints of Zn (OH)₂, 200, 250, 300, and 350 rpm milled samples possess the standard hexagonal ZnO wurtzite structure. The crystallite size and lattice parameters of the samples were calculated from the XRD patterns by applying the Maud refinement procedure. According to the results, average crystallite size of the ZnO nanocrystals is in the range of 27.3-31.4 nm depending on the milling speed.     

简单水热法制备棒状纳米氧化锌及其表征

以Zn(NO3)2和NaOH为原料,在不使用任何添加剂的条件下,采用水热合成法在不同的合成时间和合成温度下制备棒状纳米ZnO颗粒。通过X射线衍射(XRD)、透射电镜(TEM)、光致发光谱(PL)、电导率测试对样品进行表征。结果表明,所制备的纳米ZnO粉末具有六方红锌矿结构并沿(101)面择优生长;随着合成时间和温度的增加,样品的纯度逐渐增加;合成时间为25h,温度为200℃时,样品的结晶最好,样品基本成棒状,平均直径约为30～40nm,长度约为300～400nm、电阻率最大,且在376nm和500～600nm处有明显发射现象。深入分析了上述结果的形成原因。     

Aqueous combustion synthesis and characterization of ZnO powders

New organic fuels (β-alanine, valine, zinc acetate and acrylamide) have been successfully tested for the preparation of nanocrystalline ZnO powders via aqueous combustion synthesis. In all cases, ZnO resulted directly from the combustion process and no subsequent annealing was required. Properties of the as-prepared ZnO powders were investigated and it was found that morphology, specific surface area, crystallite size and cumulative volume of pores are determined by the used fuel. A correlation has been found between the total volume of generated gases, adiabatic temperature, the amount of ZnO and the characteristics of the resulting powders. Largest surface area (42.0 m² g⁻¹) and smallest ZnO crystallite size (21 nm) were obtained for acrylamide.     

Microwave synthesis and characterization of ZnO with various morphologies

ZnO micro- and nanostructures with a variety of morphologies have been synthesized using Zn(NO₃)₂·6H₂O and pyridine by a microwave-assisted aqueous solution method at 90 °C for 10 min. The pyridine has a significant influence on the morphology of ZnO. Various morphologies of ZnO (hexagonal columns, linked hexagonal needles, hollow structures, and hexagonal nanorings) were obtained by adjusting the concentration of pyridine. The effect of the type of other alkaline additive (aniline and triethanolamine) on the morphology of ZnO was also investigated. The products were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM).     

Low temperature solution synthesis and characterization of ZnO nano-flowers

Synthesis of flower-shaped ZnO nanostructures composed of hexagonal ZnO nanorods was achieved by the solution process using zinc acetate dihydrate and sodium hydroxide at very low temperature of 90 °C in 30 min. The individual nanorods are of hexagonal shape with sharp tip, and base diameter of about 300-350 nm. Detailed structural characterizations demonstrate that the synthesized products are single crystalline with the wurtzite hexagonal phase, grown along the [0 0 0 1] direction. The IR spectrum shows the standard peak of zinc oxide at 523 cm⁻¹. Raman scattering exhibits a sharp and strong E₂ mode at 437 cm⁻¹ which further confirms the good crystallinity and wurtzite hexagonal phase of the grown nanostructures. The photoelectron spectroscopic measurement shows the presence of Zn, O, C, zinc acetate and Na. The binding energy ca. 1021.2 eV (Zn 2p_3/2) and 1044.3 eV (Zn 2p_1/2), are found very close to the standard bulk ZnO binding energy values. The O 1s peak is found centered at 531.4 eV with a shoulder at 529.8 eV. Room-temperature photoluminescence (PL) demonstrate a strong and dominated peak at 381 nm with a suppressed and broad green emission at 515 nm, suggests that the flower-shaped ZnO nanostructures have good optical properties with very less structural defects.     

N-doped ZnO nano-arrays: A facile synthesis route, characterization and photoluminescence

Field emission scanning electron microscopy (SEM) investigation reveals that array-orderly novel nanostructures, which are nanorods with many nanoparticles on the surfaces, have been synthesized at low temperature (162 °C) via a one-step in-situ process in solution. High resolution transmission electron microscope (HRTEM) and energy-dispersive X-ray spectroscopy (EDS), coupled with X-ray powder diffraction (XRD) patterns and X-ray photoelectron spectra (XPS), reveal that the as-obtained products possess crystalline structure of N-doped ZnO. The room temperature photoluminescence (PL) spectrum has also been examined to explore the optical property. The present synthesis method possesses several advantages, which would be significant to be studied deeper in the future. It is also envisioned that this method could provide a new approach to synthesize ZnO:N and other ZnO-based adulterants at low temperature.     

Fe-C纳米粉体的制备及特性

在50%CH4 20%H2 30%Ar,总压为2×104Pa的混合气氛下,用直流电弧等离子体蒸发纯Fe制备了Fe-C纳米粉体.用XRD、TEM、HRTEM、XPS、VSM、化学分析和氧含量分析等测试手段对粉体进行了分析.结果表明,在50%CH4 20%H2 30%Ar的混合气氛下制备的粉体形貌接近类球形,平均粒度50nm,粒子具有核壳结构,核为Fe-C,壳为4nm左右的碳膜.在温度低于300℃时,在50%CH4 20%H2 30%Ar气氛下制备的纳米粉体抗氧化性比在50%H2 50%Ar气氛下制备的强,饱和磁化强度为151.8Am2/kg,比在纯CH4气氛下制备的106.3Am2/kg大.     

Structural and luminescence properties of pure and Al-doped ZnO nanopowders

Pure and Al doped zinc oxide nanopowders have been synthesized by sol-gel route. This is a simple and inexpensive method permitting to obtain a very small grain size powders. Zinc acetate dehydrate was first dissolved in a mixture of 2-methoxyethanol and mono-ethanolamine (MEA) solution, were used as a solvent and stabilizer respectively and doped with a quantity of aluminum nitrate, varying from 0 to 10 mol%. The obtained gel is then calcinated in air at 500 °C. The samples are characterized by XRD, SEM and photoluminescence (PL) studies. The XRD results indicate that pure and Al-doped ZnO powders are solid solutions crystallizing in pure würtzite structure, and consisted of a mixture of nanoparticles with grain size between 23 and 36 nm. The grain size decreases strongly with increasing Al concentration and reaches its lowest value at 5 mol% Al. The PL spectra show that the most important establishment is that the powders show luminescence peaks from green to ultraviolet light, and thus can be used to manufacture transmitters using these emissions. The peaks connected to the blue luminescence are the most intense, and they are generated by transitions involving (Zn_i). The SEM images show a formation of pebbles with sizes decreasing with Al concentration and a morphology evaluating, qualitatively, from pebbles without cavities to highly porous ones.     

纳米氟硼酸钾粉末的制备及表征

探讨了高能球磨法制备纳米KBF4粉末的工艺过程及影响因素.通过选择合适的球磨工艺及表面活性剂,以普通KBF4粉末为原料成功制备出粉末的粒度均径为81.2nm、比表面积为28.26m2/g的纳米级KBF4粉末.分别采用BET比表面积测试法、X射线小角度散射法(SAXS)及扫描电镜对纳米KBF4粉末进行了表征.     

Microwave plasma synthesis of silver nanopowders

Silver nanopowder was synthesized by the microwave plasma synthesis method. The effect of feeding rate of precursor raw material to the average particle size and crystallinity were studied. The microwave plasma unit can be modified to prepare silver nanopowder with polymeric coating. The silver nanopowder was characterized by means of transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDAX) and X-ray diffraction (XRD).     

Fabrication and characterization of n-type aluminum-boron co-doped ZnO on p-type silicon (n-AZB/p-Si) heterojunction diodes

In this paper, the growth of n-type aluminum boron co-doped ZnO (n-AZB) on a p-type silicon (p-Si) substrate by sol–gel method using spin coating technique is reported. The n-AZB/p-Si heterojunctions were annealed at different temperatures ranging from 400 to 800 °C. The crystallite size of the AZB nanostructures was found to vary from 28 to 38 nm with the variation in annealing temperature. The band gap of the AZB decreased from 3.29 to 3.27 eV, with increasing annealing temperature from 400 to 700 °C and increased to 3.30 eV at 800 °C probably due to the formation of Zn₂SiO₄ at the interface. The band gap variation is explained in terms of annealing induced stress in the AZB. The n-AZB/p-Si heterojunction exhibited diode behavior. The best rectifying behavior was exhibited at 700 °C.