Positron annihilation characterization of nanocrystalline ZnO

Nanocrystalline (average crystal size ∼ 3–4 nm) ZnO have been prepared by chemical route. Employing positron annihilation techniques these nanocrystalline ZnO have been characterized. Positron annihilation lifetime spectroscopy indicates the presence of large number of vacancy defects at the surface of these nanocrystaline ZnO. A large percentage of positronium formation has been observed in this nanocrystalline wide band gap semiconductor.     

Preparation and characterization of polyaniline-copper composites by electrical explosion of wire

Polyaniline-copper composites with a polyacrylic acid (PAA) were synthesized by electrical explosion of wire. Polyaniline (PANI) and PAA were put into the explosion medium, deionized water (DIW) and ethanol, stirred for 24 hrs and sonicated for 2 hrs. These solutions were used as base liquids for explosion process to fabricate Cu nanoparticle. Optical absorption in the UV-visible region of PANI and PANI/PAA-Cu composites was measured in a range of 200-900 nm. X-ray diffraction was used to analyze the phase of the composites. XRD pattern showed the PANI was amorphous and copper was polycrystalline. Two phases of Cu and Cu2O were formed in aqueous solution while single Cu phase was obtained in ethanol solution. Field emission scanning electron microscope was used to observe the microstructure of the composites. The synthesized composites were extensively characterized by Fourier Transform Infrared (FTIR) spectroscopy and electrical measurements.     

Synthesis and x-ray diffraction characterization of nanocrystalline ZnO obtained by Pechini method

Nanocrystalline zinc oxide powders were successfully prepared by Pechini method. The polymeric precursors were prepared using zinc acetate and a mixed solution of citric acid and ethylene glycol as a chelating agent and reaction medium respectively. The polymeric precursors were calcined at temperatures from 500 to 900°C for 1 h. The resulting powders were characterized by x-ray powder diffraction, thermogravimetry, and Fourier-transform infrared spectroscopy. Well-crystallized zinc oxide was obtained at low-temperature about 500°C. The average crystallite size was estimated as 47–73 nm in the range of 500–900°C and the lattice parameters were compatible with the values found in literature. The text was submitted by the authors in English.     

Synthesis and optical characterization of ZnO and ZnO:Al nanocrystalline films obtained by the sol-gel dip-coating process

Zinc oxide is obtained by the sol-gel process. The precursor solution was deposited on quartz substrates by dip-coating. The as-deposited films are transformed into nanocrystalline pure or aluminium-doped ZnO after thermal treatment. The microstructure was studied by X-ray diffraction and the nanocrystallite size was estimated using Scherrer equation. The optical transmittance in the visible region is between 83 and 91%. A direct absorption edge is observed with bandgap energies between 3.27 and 3.31 eV for the undoped samples, and between 3.30 and 3.35 eV for the Al doped ZnO. These values correlate well with the nanocrystal sizes following two different laws for the undoped and doped samples, due to Moss-Burstein shift. The visible transmittance also increases for higher bandgap energies. The UV transmittance is greater than 50% due to the small thickness of the films, which for the undoped samples is proportional to the number of layers.     

Synthesis and optical properties of nanocrystalline V-doped ZnO powders

This paper reports the synthesis and optical properties of nanocrystalline powders of V-doped ZnO (i.e. Zn_0.95V_0.05O, Zn_0.90V_0.10O, and Zn_0.85V_0.15O) by a simple sol–gel method using metal acetylacetonates of Zn and V and poly(vinyl alcohol) as precursors. Structure of the prepared samples was studied by X-ray diffraction, FTIR spectroscopy, and selected-area electron diffraction (SAED) analysis. The morphology of the powders revealed by SEM and TEM was affected by the amount of V, causing the formations of both nanoparticles and nanorods in the Zn_0.95V_0.05O sample, nanorods in the Zn_0.90V_0.10O sample, and nanoparticles in the Zn_0.85V_0.15O sample. The optical properties of the samples were investigated by measuring the UV–VIS absorbance and photoluminescence spectra at room temperature. All the samples exhibited UV absorption at below 400 nm (3.10 eV) with a well-defined absorbance peak at around 364 nm (3.41 eV) and 288 nm (4.31 eV). The band gap of the V-doped samples shows a decrease with increasing V concentration. The photoluminescence spectra of all the samples showed a strong UV emission band at 2.98 eV, a weak blue band at 2.82 eV, a week blue–green band at 2.56 eV, and a weak green band at 2.34 eV, which indicated their high structural and optical quality.     

Magnetic and optical properties of Mn doped ZnO nanocrystalline films

We have investigated the properties of Mn-doped ZnO nanocrystalline film growing on zinc foil by the hydrothermal method. X-ray photoelectron spectroscopy shows that the manganese ions exist as Mn2+ in the film. From UV-vis spectra, we observe a red shift in wavelength of absorption and greater reflectivity due to the Mn ion incorporation in ZnO lattices. The photoluminescence spectrum of the Mn-doped ZnO film shows two strong new blue peaks centered at 424 nm and 443 nm, besides the UV emission peak owing to the band gap of ZnO semiconductor. The magnetic property of the Mn-doped ZnO exhibits a room temperature ferromagnetic characteristic with a saturation magnetization (Ms) of 0.3902 x 10(-3) emu/cm3 and a coercive field of 47 Oe. We suggest that the blue emission of the Mn-doped ZnO film corresponds to the electron transition from the level of interstitial Zn and Mn to the valence band. The defects brought about by Mn ion incorporation are the main cause of the room temperature ferromagnetic property.     

Effect of pyrolysis temperature on structural,microstructural and optical properties of nanocrystalline ZnO powders synthesised by ultrasonic spray pyrolysis technique

In this article, we report on the effect of pyrolysis temperature on structural, microstructural and optical properties of nanocrystalline ZnO powder synthesised by ultrasonic spray pyrolysis (USP) technique. Powder samples P1, P2 and P3 were prepared at various pyrolysis temperatures (temperature of 2nd zone) of 973, 1073 and 1273?K, respectively. Phases were identified and crystallite sizes were calculated from X-ray diffraction (XRD) diagrams. The morphology and size of ZnO nanocrystallites associated with nanopowder were studied using transmission electron micrograph (TEM). It revealed that the powder consisted of crystallites ranging in size from 9 to 20?nm. These values were matching with the crystallite sizes calculated from XRD. Both XRD and TEM studies of ZnO nanopowders showed that the crystallite sizes increased with an increase in the pyrolysis temperature. The synthesised nanopowders exhibited direct band gap (E _g) in the range 3.37–3.40?eV.     

Electrical conduction properties of Co-doped ZnO nanocrystalline thin films

The temperature dependent conductivity behavior of 15% Co and 25% Co-doped ZnO nanocrystalline thin films prepared by spin-coating method was examined. It was found that the conductivity shows a change when the Co concentration varies from 15 to 25%. The observed increase of conductivity with increasing Co concentration was interpreted through the grain boundary conduction model. The temperature dependent conductivity of the films was analyzed in term of formulas in consistence with grain boundary conduction model. With rising temperature for 25% Co doped ZnO, a transition from the region in which crystallites are only partially depleted to the region in which the crystallites are entirely depleted was observed around 375 K. Some improtant electrical parameters were determined for the films.     

Generation and characterization of nano aluminium powder obtained through wire explosion process

In the present study, nano aluminium particles were produced by wire explosion process (WEP) in nitrogen, argon and helium atmospheres. Thus produced nano particles were characterized through certain physico-chemical diagnostic studies using wide angle X-ray diffraction (WAXD) and by energy dispersive analysis by X-rays (EDAX). The size and shape of the powder were analysed by using transmission electron microscopic (TEM) studies. The particle size distribution studies were performed by adopting log-normal probability distribution. The relationship between size of the particle generated in the explosion process and the type of inert gas/pressure was analysed. The mechanisms of nano particle formation, the factors which can aid the process of formation of nano particle in the wire explosion process were analysed. It is realized that energy deposited to the conductor and duration of current flow have major impact on particles produced by this process.     

Generation of nano aluminium powder through wire explosion process and its characterization

The nano aluminium particles were produced in different ambience by the wire explosion process. The influence of pressure in the exploding wire chamber on the size of the particles was analyzed. Certain physico-chemical diagnostic studies, viz., wide angle X-ray diffraction (WAXD), thermo-gravimetric differential thermal analysis (TG–DTA) studies were carried out to characterize the produced nano aluminium powder. The compositions of the material were characterized through the energy dispersive analysis by X-ray (EDAX) results. The size of the particles was measured using transmission electron microscope (TEM) studies and particle size distribution analyses were carried out by adopting log-normal distribution. The mechanism of formation of nano powder by wire explosion technique was explained in detail.     

Deposition of nanocrystalline ZnO thin films on p-Si by novel galvanic method and application of the heterojunction as methane sensor

Undoped nanocrystalline n-ZnO thin films were deposited by a novel galvanic technique at room temperature on p-Si 〈100 〉 substrates to fabricate ZnO–Si heterojunctions. The I–V characteristics were studied at different temperatures with two different metallic contacts e.g., gold and palladium–silver (26%), in air and in presence of different concentrations (0.1, 0.5 and 1%) of methane gas. A shift in I–V characteristics in presence of methane was observed. The sensitivity and response time were studied at different temperatures (30 through 350 °C). Pd–Ag (26%) catalytic contacts showed much improved sensor performance.     

Magnetic properties of iron nanoparticles prepared by exploding wire technique

Nanoparticles of iron were prepared in distilled water using very thin iron wires and sheets, by the electro-exploding wire technique. Transmission electron microscopy reveals the size of the nanoparticles to be in the range 10 to 50 nm. However, particles of different sizes can be segregated by using ultrahigh centrifuge. X-ray diffraction studies confirm the presence of the cubic phase of iron. These iron nanoparticles were found to exhibit fluorescence in the visible region in contrast to the normal bulk material. The room temperature hysteresis measurements upto a field of 1.0 tesla were performed on a suspension of iron particles in the solution as well as in the powders obtained by filtration. The hysteresis loops indicate that the particles are superparamagnetic in nature. The saturation magnetizations was approximately 60 emu/gm. As these iron particles are very sensitive to oxygen a coating of non-magnetic iron oxide tends to form around the particles giving it a core-shell structure. The core particle size is estimated theoretically from the magnetization measurements. Suspensions of iron nanoparticles in water have been proposed to be used as an effective decontaminant for ground water.     

Preparation and characterization of ZnS nanocrystalline thin films by low cost dip technique

Nanocrystalline ZnS semiconducting nanopowder and thin films have been deposited by simple low cost technique based on combination of dip coating and thermal reaction process. The deposited films and the prepared nanopowder have been characterized in the structurally, optically and electrically point of views. The effect of preparation conditions has been also optimized for good quality films. X-ray diffraction analysis performed the ZnS cubic phase in the reaction temperatures in the range 473–593 K. Above 593 K mixed cubic and hexagonal crystallographic phases have been resolved. Crystallite size and micro strain have been calculated to be 2.65 and 0.011 nm, respectively. The deposited film surface and cross section morphologies show that neither cracks nor peels have been observed and good film adhesion with the substrate was performed. Energy dispersive X-ray measurements of the film agree well with the calculated concentrations of the precursor components. Optical measurements confirm the optical characteristics of nanocrystalline ZnS film such as absorption and dispersion properties. Copper doped ZnS reduces the band gap while indium doped ZnS increases the band gap. Electrical characterization shows that copper doped ZnS increases the resistivity by one order of magnitude due to electron compensation process while indium doped ZnS decreases the resistivity three orders of magnitude due to increase of the carriers concentration. Hot probe thermoelectric quick test of ZnS:Cu and ZnS:In show opposite sign of thermoelectric voltage due to bipolar p and n types, respectively.     

Fe的不同掺杂量对ZnO薄膜光致发光的影响

采用射频磁控溅射在玻璃衬底上制备了不同掺杂量的Fe-ZnO薄膜,分析不同掺杂量对薄膜光学性能的影响.利用X射线衍射仪(XRD)和原子力显微镜(AFM)研究Fe-ZnO薄膜的微观结构和形貌结构.Fe-ZnO薄膜光致发光(PL)性质的研究发现,发光峰主要有蓝光发射和绿光发射,蓝光发射主要是由于电子从导带向锌空位形成的浅受主能级上的跃迁;绿光发射是由于电子从氧空位到锌空位的能级跃迁及导带底到氧错位缺陷能级的跃迁.由透射谱和吸收谱分析,Fe-ZnO薄膜在可见光区的平均透过率为66%,掺杂量为2%Fe的薄膜的禁带宽度最接近于ZnO的禁带宽度.     

Deposition and characterization of PEDOT/ZnO layers onto PET substrates

ZnO thin films of different thicknesses were deposited by pulsed direct-current magnetron sputtering onto poly(ethylene terephthalate) (PET) substrates and afterwards poly 3, 4-ethylenedioxythiophene:polystyrenesulfonate (PEDOT:PSS) was spin-coated onto the ZnO film. Spectroscopic ellipsometry in the Vis–fUV energy range (1.5–6.5 eV), X-ray diffraction and atomic force microscopy were used to reveal the properties of the deposited films. The size of crystallites increased from 5.1 to 7.4 nm, whereas the crystallinity of the ZnO films has been improved. The influence of different ZnO thickness on the optical properties of the PEDOT:PSS layer was studied as well. As the thickness of ZnO films increased, the surface roughness increased but the energy gap decreased after a critical thickness. Concerning the consequences to the PEDOT:PSS optical properties, no major changes occurred in the transition energies.     

Preparation and properties of ZnO thin films deposited by sol-gel technique

Zinc oxide (ZnO) thin films were deposited on (100) Si substrates by sol-gel technique. Zinc acetate was used as the precursor material. The effect of different annealing atmospheres and annealing temperatures on composition, structural and optical properties of ZnO thin films was investigated by using Fourier transform infrared spectroscopy, X-ray diffraction, atomic force microscopy and photoluminescence (PL), respectively. At an annealing temperature of 400°C in N₂ for 2 h, dried gel films were propitious to undergo structural relaxation and grow ZnO grains. ZnO thin film annealed at 400°C in N₂ for 2 h exhibited the optimal structure and PL property, and the grain size and the lattice constants of the film were calculated (41.6 nm, a = 3.253 ? and c = 5.210 ?). Moreover, a green emission around 495 nm was observed in the PL spectra owing to the oxygen vacancies located at the surface of ZnO grains. With increasing annealing temperature, both the amount of the grown ZnO and the specific surface area of the grains decrease, which jointly weaken the green emission. Translated from Journal of Lanzhou University (Natural Science), 2006, 42(1): 67–71 [译自: 兰州大学学报 (自然科学版)]     

Structure and gas sensing properties of nanocrystalline Fe-doped ZnO films prepared by spin coating method

Nanocrystalline Fe-doped ZnO films were obtained by spin coating, using zinc acetate and iron acetate as starting materials and N,N-dimethylformamide as solvent. Characteristic XRD patterns indicate that the films under study are single phase with the ZnO-like wurtzite structure. There are not any secondary phases and Fe²⁺ as well as Fe³⁺ substitutes for Zn²⁺ of ZnO host. Atomic force microscopy analysis revealed that the studied films are characterized by high-density columnar structure and the incorporation of Fe atoms into the ZnO lattice modified the surface morphology. The sensitivity, at three different gases, was investigated and it was observed that acetone is the test gas that produces the most significant changes in the electrical resistance of all studied samples. Experimental results indicate that the optimum operating temperature increases for Fe-doped ZnO films by comparison with the undoped one. Also, the values of sensitivity were found to depend on the dopant concentration in ZnO films.     

Synthesis and characterization of Cu-Sn oxides nanoparticles via wire explosion method with surfactants,evaluation of in-vitro cytotoxic and antibacterial properties

In this study, Cu-Sn oxides nanoparticles (CSO NPs) were synthesized via explosion of Sn-coated Cu wires in aqueous solution with and without surfactants. The physicochemical properties of the synthesized nanoparticles were characterized using XRD, FTIR, SEM, TEM and HRTEM techniques. In vitro cytotoxicity of NPs against L929 cell lines was observed. Potential antibacterial activity of CSO NPs against Gram-positive and Gram-negative bacteria was explored. TEM microstructural observations depicted the core-shell structure of plate-like CSO NPs synthesized in water. TEM and FTIR analysis confirmed the presence of PEG and L-cysteine at the surface of NPs prepared in surfactants. Accurate microstructural analysis of these NPs verified the positive effects of adding surfactants on the refinement of CSO NPs as well as changing its morphology. In vitro test showed that small amount of NPs (less than 80 μg/ml) have no cytotoxicity effect. Moreover, results showed that the Cu-Sn oxides nanoparticles synthesized in the surfactant agents presented a great antibacterial properties due to lower size of NPs, higher oxide concentrations as well as existence of polymer on the surface that could induce the ROS mechanism for attacking more bacteria. Synthesizing in presence of PEG showed more efficient antibacterial activity than L-cysteine because of combined effect of CuO and attachment of PEG to the surface of NPs.     

Deposition, characterization and biological application of epitaxial Li:ZnO/Al:ZnO double-layers

Double-layers of lithium doped ZnO (LZO) and aluminum doped ZnO (AZO) are grown on r-cut sapphire (r-Al₂O₃) crystal substrates by pulsed-laser deposition. The epitaxial double-layers are a-axis lattice oriented to the substrate. The LZO/AZO/r-Al₂O₃ samples have high optical transmission in the visible range and a bandgap energy of E_g = 3.28 eV according to the absorption edge of ZnO. The AZO bottom layers are electrically conductive (resistivity at room temperature ρ ~ 10^− 3 Ω cm) and LZO top layers are highly resistive (ρ ≥ 10⁵ Ω cm). Acoustic shear mode resonances in r-Al₂O₃ are excited by employing electric fields to the piezoelectric LZO layer (frequency interval 1.5-3 GHz). For biological applications, Madin-Darby canine kidney cells are cultivated on Platinum coated LZO/AZO/r-Al₂O₃ samples. Osmotic pressure applied to the cells increases or reduces the cell volume depending on the osmolarity of the medium.     

脉冲激光沉积ZnO及其掺杂薄膜的研究

本文用脉冲激光沉积（PLD）法在SiO2基片上制备了ZnO薄膜和Zn1-xMnxO薄膜。X射线衍射、原子力显微镜、紫外-可见分光光度计对ZnO薄膜的测试结果表明：薄膜具有（103）面的择优取向，表面比较平坦；SiO2基片上制备的薄膜在387nm附近存在明显的吸收边，且薄膜的吸收对基片温度变化不明显。通过对Zn1-xMnxO薄膜的吸收光谱分析得出：Mn离子的掺杂改变了ZnO薄膜的禁带宽度，随Mn离子的掺杂量的增加，薄膜禁带宽度增加；薄膜的光吸收也从直接跃迁过渡为间接跃迁过程。