Structure and optical properties of ZnO:V thin films with different doping concentrations

A series of ZnO thin films doped with various vanadium concentrations were prepared on glass substrates by direct current reactive magnetron sputtering. The results of the X-ray diffraction (XRD) show that the films with doping concentration less than 10 at.% have a wurtzite structure and grow mainly along the c-axis orientation. The residual stress, estimated by fitting the XRD diffraction peaks, increases with the doping concentration and the grain size also has been calculated from the XRD results, decreases with increasing the doping concentration. The surface morphology of the ZnO:V thin films was examined by SEM. The optical constants (refractive index and extinction coefficient) and the film thickness have been obtained by fitting the transmittance. The optical band gap changed from 3.12 eV to 3.60 eV as doping concentration increased from 1.8 at.% to 13 at.% mol. All the results have been discussed in relation with doping concentration.     

CuO/ZnO复合纳米树阵列的制备及光学特性

通过热氧化法在铜基板上制备CuO纳米线,采用凝胶法制备ZnO/CuO复合纳米树阵列。通过扫描电镜(SEM)、X射线衍射(XRD)、光致发射光谱对样品结构、形貌、光学特性进行表征。结果表明,CuO/ZnO纳米树形貌规整完美,在CuO纳米线上二次生长的ZnO纳米棒具有各向晶体生长性质,CuO/ZnO复合纳米树在可见光区域出现了优越的发光性能;以甲基橙为模拟污染物,通过光催化测试表明,CuO/ZnO复合纳米树还具有卓越的光催化性能。     

Template-free solvothermal synthesis of ZnO nanoparticles with controllable size and their size-dependent optical properties

ZnO nanoparticles (NPs) have been synthesized via a facile and template-free solvothermal method. The size of ZnO NPs could be tailored by adjusting the ratio of ethanol to ethylene glycol (EG). Their structure and morphology have been investigated. The as-prepared samples are monodispersed ZnO NPs with controllable sizes of about 24.2, 18.9 and 14.7 nm. The cathodoluminescence (CL) spectra of the samples show that the relative intensity ratio of the visible emission peak at 500-650 nm to the band-edge UV emission peak at 380 nm increases as the particle size decreases. Sample with smaller crystallites would have larger surface area and more oxygen vacancy defects, thus it exhibits higher visible emission peak. The UV-vis absorption spectrum indicates the band gap variation of the ZnO NPs with their size. Moreover, the size-dependent blue shifts of both the CL emission and the UV-vis absorption spectra reveal the effect of quantum confinement.     

Effects of different complexing agents on the physical properties of ZnO nanoparticles

ZnO nanoparticles have been synthesised via a co-precipitation method using different complexing agents. X-ray diffraction (XRD) analysis revealed that ZnO nanoparticles were composed of a single hexagonal wurtzite phase. Transmission electron microscopy (TEM) analysis indicates that the samples prepared without any complexing agent have slight agglomeration characteristics presenting a prismatic morphology and a wider size distribution from 22 to 72?nm, which provides good material packing density. However, samples synthesised using urea and glycine are similar and show spherical-like morphology. XRD and TEM analyses indicate that complexing agents also have an important role in the size of the ZnO nanoparticles, where the average particle size of 47 and 22?nm were obtained using urea and glycine, respectively.     

The microstructure and its properties of Ni3Al based composite

 Composites of B-doped ductile Ni₃Al alloy matrix with no-oxide WC ceramic powders were produced by mechanical alloying, half-sintering and build-up welding. WC powders form non-continuous hardening phases, which are distributed in Ni₃Al matrix, wetting well with the matrix. The hardness and the structure stability are retained to temperatures of at least 850°C. After build-up welding, most of the NiAl phase left after sintering was changed into other phases and some graphite was precipitated in the matrix. The sand-laden water wear test showed expected results. Received: 12 October 1998/Accepted: 2 November 1998     

Shed light on submerged DC arc discharge synthesis of low band gap gray Zn/ZnO nanoparticles: Formation and gradual oxidation mechanism

Synthesis of colloidal metal oxides with controllable size and morphology is burgeoning field of research in nanoscience. Low band gap gray Zn/ZnO colloidal nanoparticles were fabricated by plasma-liquid interaction of DC arc discharge in water. Scanning electron microscopy, X-ray diffraction and UV–vis spectroscopy were employed for morphology, crystal structure and optical characterizations respectively. Optical emission spectroscopy was used to investigate the plasma properties during the synthesis and formation mechanism of nanoparticles. Nanoparticles with different size and shape were fabricated only by adjusting discharge current during synthesis without introducing any chemical agent. Electric discharge current was set to 20, 50, 100 and 150?A during synthesis. Estimated values of plasma excitation energies were 2.41, 2.66, 2.86 and 3.04?eV and diameter size of nanoparticles were 63, 42, 37 and 29?nm for these applied currents respectively. Synthesized nanoparticles were dark gray as prepared and became more transparent gradually getting white color finally. XRD and UV–vis results revealed that the oxidation process was time dependent. The colloidal nanoparticles composed of two metal and metal-oxide phase and white crystalline ZnO was achieved after complete oxidation process. These results provided a flexible and versatile method to synthesize metal oxide nanoparticles with controlled composition.     

Surfactant assisted solvothermal synthesis of ZnO nanoparticles and study of their antimicrobial and antioxidant properties

This study demonstrated a solvothermal method of growth of three different morphologies of zinc oxide nanoparticles(ZnO NPs): i) flower-like nanorod and nanoflakes, ii) assembled hierarchical structure,and iii) nano granule. Oleic acid(C_(18)H_(34)O_2), gluconic acid(C_6H_(12)O_7) and tween 80(C_(64)H_(124)O_(26)) were used as surfactant/capping/reducing agent for the formation of different morphologies of nanoparticles.The as-synthesized ZnO NPs were characterized by different physicochemical techniques such as UV–vis(UV–vis) spectroscopy, X-ray diffraction(XRD), fourier transform infrared spectroscopy(FTIR), field emission scanning electron microscopy(FE-SEM), energy dispersive X-ray(EDX) analysis and dynamic light scattering(DLS) studies. Further, the antioxidant and antimicrobial activity of these nanostructures was evaluated. The antioxidant activity of these nanostructures was assessed via 2,2-diphenyl,1-1 picrylhydrazyl(DPPH), 2,2-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid)(ABTS) and H_2O_2 free radical scavenging activity. The in vitro antimicrobial activity of the obtained nanostructures was demonstrated against both gram negative(Escherichia coli) and gram positive(Staphylococcus aureus) bacterial genera.This study revealed antioxidant and antimicrobial properties of different structures of ZnO NPs suggesting their biomedical and industrial applications.     

不同形貌纳米ZnO的合成及其光催化性能研究

以Zn(NO3)2·6H2O和NH4HCO3为原料,采用直接沉淀法制备了不同形貌和微观结构的纳米氧化锌。详细研究了反应终点pH值及沉淀前驱物的后处理方式等对粉体的晶体结构、形貌、粒径分布和团聚状况的影响。通过调节反应条件可分别获得网络状或颗粒状纳米氧化锌;光催化降解实验结果表明,网络状纳米氧化锌的光催化性能优于纳米颗粒状产物,而且该网络状和颗粒状纳米氧化锌的光催化活性均明显优于商品光催化剂P25。     

Fabrication of BaTiO3/Cu composite by reducing Cu2O under nitrogen atmosphere

BaTiO₃–Cu ferroelectric/metal composite was successfully fabricated by sintering Cu₂O-added BaTiO₃ pellet under nitrogen gas flow. In the results of XRD analysis of the sintered body, it was found that cuprous oxide was reduced to copper in the atmosphere of 100 ml/min nitrogen gas flow, but was not reduced and remained as itself in air. Lattice parameter changes of the specimens sintered at 1280 °C in 100 ml/min nitrogen gas flow indicated that solubility limit of cuprous oxide (Cu₂O) into BaTiO₃ is thought to be less than 1 wt%. The melt from cuprous oxide is thought as a good sintering aid to densify BaTiO₃. In this experiment, we determined the optimum sintering condition to get BaTiO₃–Cu ferroelectric/metal composite with more than 95% of relative density. From the results of DTA and TG analysis, cuprous oxide is considered to dissociate into copper and oxygen gas and form the eutectic melt of BaTiO₃–Cu at around 900 °C in more than 50 ml/min nitrogen flow rate atmosphere. Received: 29 October 2001 / Reviewed/Accepted: 3 November 2001     

纳米硅镶嵌氮化硅薄膜的制备及非线性光学性质研究

采用射频磁控反应溅射法结合热退火处理技术制备纳米硅镶嵌氮化硅(nc-Si/SiNx)复合薄膜.通过X射线能谱(EDS)、红外光谱(IR)、X射线衍射(XRD)及紫外-可见吸收光谱(UV-vis)的测定,对薄膜进行了组分、键合状态、结构及光学带隙的表征.采用皮秒激光运用单光束Z扫描技术开展了对该复合薄膜的非线性光学性质的研究,测得其三阶非线性折射率系数和非线性光吸收系数分别为10-8esu和10-8m/W量级,并将薄膜这种三阶光学非线性增强的原因归因于量子限域效应.     

A new model for the analysis of composite steel – concrete slab and beam structures with deformable connection

 In this paper a solution to the bending problem of reinforced concrete slabs stiffened by steel beams with deformable connection including creep and shrinkage effect is presented. The adopted model takes into account the resulting inplane forces and deformations of the plate as well as the axial forces and deformations of the beam, due to combined response of the system. The analysis consists in isolating the beams from the plate by sections parallel to the lower outer surface of the plate. The forces at the interface producing lateral deflection and inplane deformation to the plate and lateral deflection and axial deformation to the beams are related with the interface slip through the shear connector stiffness. Any distribution of connectors along the interface and any linear or non-linear load–slip relationship or partial shear connection for the shear connectors can be handled. The creep and shrinkage effect relative with the time of the casting and the time of the loading of the plate is taken into account. The solution of the arising plate and beam problems, which are nonlinearly coupled, is achieved using the analog equation method (AEM). The adopted model compared with those ignoring the inplane forces and deformations, approaches more reliable the actual response of the plate–beams system. Moreover, it permits the evaluation of the shear forces at the interfaces, the knowledge of which is very important in the design of composite steel–concrete structures. Received: 21 June 2002 / Accepted: 5 March 2003     

A study on defect controlled morphology of Organic/Inorganic composite nanofibers with different heat flow rates

One dimensional nanofibers of organic and inorganic materials have been used in filters, optoelectronic devices, sensors etc. It is difficult to obtain ultra fine fibers of inorganic materials having lengths in the order of millimeter as they tend to break during formation due to thermal and other mechanical stresses. In this study, we have investigated the mechanism to prevent the defect formation and the breaking ZnO nanofibers by using optimized heat flow rates. ZnO nanofibers were obtained by heat treating the PVA composites fibers formed by electrospinning. The morphology and structural characteristic of prepared samples were investigated by Scanning electron microscopy and X-ray diffraction. It was found that the morphology of the composite and annealed nanofibers could be influenced by the concentration of the polymer content and heat flow rate during thermal treatment respectively. A lower concentration favors the formation of defects along the fiber and the number of defects reduces when the concentration is increased. The reasons for the formation of defects and their reduction, and the observed structural changes of ZnO nanofibers during heat treatment are also discussed.     

衬底温度对磁控溅射法制备ZnO薄膜结构及光学特性的影响

采用射频反应磁控溅射法在玻璃衬底上制备了具有c轴高择优取向的ZnO薄膜,利用X射线衍射仪、扫描探针显微镜及紫外分光光度计研究了生长温度对ZnO薄膜的结构及光学吸收和透射特性的影响.结果表明,合适的衬底温度有利于提高ZnO薄膜的结晶质量;薄膜在紫外区显示出较强的光吸收,在可见光区的平均透过率达到90%以上,且随着衬底温度的升高,薄膜的光学带隙减小、吸收边红移.采用量子限域模型对薄膜的光学带隙作了相应的理论计算,计算结果与实验值符合得较好.     

Synthesis of ZnO/Zn2SiO4/SiO2 composite pigments with enhanced reflectance and radiation-stability under low-energy proton irradiation

ZnO/Zn₂SiO₄/SiO₂ composite pigments with nano-sized α-Zn₂SiO₄ interface phase were synthesized by a simple solid-state reaction method. It was found that the composite pigments exhibit significant improvement on the spectral reflectance and the proton radiation-stability compared with the pure ZnO pigment. The investigations have demonstrated that the enhancements on the spectral reflectance and the radiation-stability are attributed to the introduction of willemite Zn₂SiO₄ interface phase on the surface of ZnO matrix particles. In addition, the enhancement mechanisms of radiation-stability for ZnO/Zn₂SiO₄/SiO₂ composite pigments were discussed.     

Effects of optical band gap energy,band tail energy and particle shape on photocatalytic activities of different ZnO nanostructures prepared by a hydrothermal method

The dependence of the crystallite size and the band tail energy on the optical properties, particle shape and oxygen vacancy of different ZnO nanostructures to catalyse photocatalytic degradation was investigated. The ZnO nanoplatelets and mesh-like ZnO lamellae were synthesized from the PEO₁₉-b-PPO₃ modified zinc acetate dihydrate using aqueous KOH and CO(NH₂)₂ solutions, respectively via a hydrothermal method. The band tail energy of the ZnO nanostructures had more influence on the band gap energy than the crystallite size. The photocatalytic degradation of methylene blue increased as a function of the irradiation time, the amount of oxygen vacancy and the intensity of the (0 0 0 2) plane. The ZnO nanoplatelets exhibited a better photocatalytic degradation of methylene blue than the mesh-like ZnO lamellae due to the migration of the photoelectrons and holes to the (0 0 0 1) and (0 0 0 −1) planes, respectively under the internal electric field, that resulted in the enhancement of the photocatalytic activities.     

Analysis of optical properties of TiO2 nanoparticles and PAN/TiO2 composite nanofibers

The aim of the study was the production of thin composite nanofibrous mats PAN/TiO₂ nanoparticles using the electrospinning method from solution of PAN/TiO2/DMF. TiO₂ nanoparticles were obtained using sol-gel method. To prepare sol mixture, organic alkoxides precursor of titanium isopropoxide and water solution were used. Calcination of TiO-gel and following milling were carried out to obtain nanoparticles of TiO₂ rutile phase. In order to analyze the structure of the obtained particles, we used X-ray diffraction analysis (XRD) and energy dispersive spectrometer (EDS). Analysis of the morphology and chemical composition of the resulting composite nanofibers were carried out using a scanning electron microscope (SEM) with EDS. The analysis of the optical properties and the energy band structure prepared nanoparticles and thin composite nanofibrous mats were determined by spectral analysis of the absorbance as a function of the energy of radiation obtained using a UV–Vis spectrophotometer.     

Enhanced structural and optical properties of ZnO nanopowder with tailored visible luminescence as a function of sodium hydroxide to zinc sulfate mass ratio

ZnO nanopowders of tailored particle sizes were synthesized using a simple wet chemical method, by controlling the mass ratio of the precursors. The physical properties were investigated as a function of OH^?/Zn²⁺ mass ratio (x). The structural properties of the synthesized nanoparticles (NPs) are studied using X-ray diffraction (XRD). XRD patterns show pure wurtzite structure. Microstructural parameters dependence on x ratio was studied based on Williamson-Hall model. We notice an increase in crystallite size (17–24?nm) and a decrease in strain values when the x ratio increases (0.5–1.4). The best crystallinity corresponds to the higher mass ratio. Indeed, for x?=?1.4 we obtain the largest crystallite size, the lowest strain and stacking faults. The TEM images support the XRD results. Raman spectra confirm the purity of the synthesized ZnO powder. Furthermore, the optical properties were examined by UV–vis and Photoluminescence as a function of precursor’s ratio. Absorption data show a band gap red-shift of the ZnO-NPs with increase in particle’s size. Moreover, we found that the ZnO-NPs luminescence in the visible range can be engineered by changes of x ratio. This constitutes an advantage for the use of ZnO-NPs in different wavelength areas in optoelectronic applications covering UV-Blue-Green domain for the LED design, sensors…     

理论研究ZnO掺杂Al;Ga;In电子结构与光学属性(英文)

计算了Ga、Al、In掺杂对ZnO体系电子结构和光学性质的影响.所有计算都是基于密度泛函理论(DFT)框架下的第一原理平面波超软赝势方法.计算结果表明:Ga、AI、In掺杂在ZnO中占据了Zn位置,为n型浅施主掺杂,导带底引入了大量由掺杂原子贡献的导电载流子,明显提高了体系的电导率.同时,光学带隙展宽,且向低能方向漂移,可作为优良的透明导电薄膜材料.同时,计算结果为我们制备基于ZnO透明导电材料的设计与大规模应用提供了理论依据,也为监测和控制ZnO透明导电材料的生长过程提供了可能性.     

On probabilistic viscous incompressible flow of some composite fluids

 The perturbation-based stochastic finite element formulation for the viscous incompressible fluid flow with heat transfer is proposed below. Analyzed viscoelastic fluid contains elastic spherical particles with randomly treated radii and total number in the fluid volume; these random variables are defined using their expected values and variances. Starting from these parameters and statistically described fluid viscosity, the probabilistic moments of the effective viscosity for a fluid with these suspensions are derived thanks to the second order perturbation second central probabilistic moment approach. So defined random effective fluid is next studied in the incompressible isobaric Couette flow between parallel plates, where the heat transfer effects are included. Defining boundary velocities and temperatures by their first two moments, the expected values and cross-covariances of the relevant homogenized fluid state functions are calculated. The engineering application of the approach can be modeling of polymers in fluid state (during their processing), reinforced with rubber particles to strengthen the entire composite as well as in general computational simulation of the composite fluids. The stochastic methodology applied to fluids with random solid suspensions can be extended on random flows with stochastic bubbles as well as multiphase coupled flow problems, where partially saturated media are considered [7], too. The main value of the stochastic approach is that it creates the opportunity to determine reliability indices, quite analogously to the research in the domain of solids and structures made of composites. Received 20 October 2001 / Accepted 15 February 2002     

Tribological improvement of aluminium infiltrated with zirconia nanoparticles

Aluminium matrix-zirconia nanoparticles-reinforced composites were prepared by the infiltration technique. The metallic matrix for these composites stabilizes the tetragonal phase of zirconia at low temperature (450 °C) whereas at 610 °C a mixture of tetragonal and monoclinic was obtained. The wear resistance of zirconia-modified aluminium was significantly improved due to the presence of the ceramic nanoparticles embedded into the matrix. Received: 13 March 2000 / Reviewed and accepted: 20 July 2000