Fabrication, sintering and electrical properties of cobalt oxide doped Gd0.1Ce0.9O2 − δ

Ceria-based electrolytes have been widely researched in intermediate-temperature solid oxide fuel cell (SOFC), which might be operated at 500~600 °C. Gd0.1Ce0.9O1.95(GDC10) powders were prepared by a modified chemical co-precipitation process with Gd(NO3)3 and Ce(NO3)3 as precursors, and ammonia and hydrogen peroxide as precipitants. The precursors of GDC10 were fired at 350 °C for 2 h, then the fluorite structure cerias were identified by X-ray diffraction. The powders are well crystallized, with the size about 5 nm and surface area of 148.3 m2/g. Loading 1mol% cobalt oxide as additive, the GDC10 were succeeded to densify at 950 °C by liquid phase sintering mechanism. The grain size of 1CoGDC10 is small, about 100 nm. The electrical conductivity of samples sintered at 950 °C is about 0.01S/cm at 600 °C. The existence of cobalt oxide and smaller grain size of 1CoGDC10 don't affect the electrical conductivity.     

Influence of mesoporous substrate morphology on the structural, optical and electrical properties of RF sputtered ZnO layer deposited over porous silicon nanostructure

Morphological, optical and transport characteristics of the RF sputtered zinc oxide (ZnO) thin films over the mesoporous silicon (PS) substrates have been studied. Effect of substrate porosity on the grain growth and transport properties of ZnO has been analyzed. Physical and optical properties of ZnO-PS structures were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), atomic force microscopy (AFM), and photoluminescence (PL) spectroscopy. Our experimental results indicate that on changing porosity of the PS substrates, regularity of the spatial distribution of the ZnO nanocrystallites can be controlled. While the morphology and grain size of ZnO depended strongly on the morphology and pore size of the PS substrates, the rectifying factors of the metal semiconductor junction were found to be different by a factor of 3. The deposition of semiconducting oxides on such mesoporous substrates/templates offers the possibility to control their properties and amplify their sensing response.     

A mathematical model to predict the grain size of nanocrystalline CdS thin films based on the deposition condition used in the sol–gel spin coating method

Design of experiment (DOE) based on central composite design (CCD) has been employed for the development of a mathematical model correlating the important process parameters like thiourea concentration (U), annealing temperature (A), rotational speed (S), and annealing time (T) of the spin coating process for the preparation of CdS thin films. The experiments were conducted as per the design matrix. Nanocrystalline CdS thin films have been prepared using cadmium nitrate and thiourea as precursors by sol gel spin coating method using the results of the mathematical model. The prepared CdS films have been characterized and the crystal structure and grain size of the samples were analyzed using X-ray diffraction technique. The adequacy of the developed models was checked by analysis of variance (ANOVA) technique. The accuracy of prediction has been carried out by conducting confirmation test. Using this model, the main effect of process parameters on grain size of CdS films have been studied. These parameters were optimized to obtain minimum grain size using the Microsoft excel solver. The results have been verified by depositing CdS films using the optimized conditions. These films have been characterized using X-ray diffraction technique and the grain size is found to be 8.8 nm. The high resolution transmission electron microscopy (HRTEM) analysis showed the grain size of the prepared CdS film to be ∼7 nm. UV–vis spectroscopy analysis revealed that CdS films exhibited quantum confinement effect.     

Plasma-based sputtering of indium tin oxide for the application of photovoltaic cells

Transparent and conducting indium tin oxide (ITO) thin films were deposited on soda lime glass substrates by RF plasma magnetron sputtering at room temperature. The effect of thickness (100, 200 and 300?nm) on the physical (structural, optical, electrical) properties of ITO thin films was investigated systematically. It is observed that with an increase in thickness, the X-ray diffraction data indicate polycrystalline films with grain orientations predominantly along (222) and (400) directions; the average grain size increases from 10 to 30?nm; the optical band gap increases from 3.68 to 3.73?eV and the transmission decrease from 80% to 70% . Four-point probes show a low resistivity (2.4×10^?5?Ω?cm) values for film with a thickness 300?nm. Present work shows that the ITO is a promising transparent conductive oxide material for the solar cell application.     

Ferromagnetism of zinc oxide nanograined films

The reasons for the appearance of ferromagnetic properties of zinc oxide have been reviewed. It has been shown that ferromagnetism appears only in polycrystals at a quite high density of grain boundaries. The critical size of grains is about 20 nm for pure ZnO and more than 40 μm for iron-doped zinc oxide. The solubility of manganese and cobalt in zinc oxide increases significantly with a decrease in the size of grains. The dependences of the saturation magnetization on the concentrations of cobalt, manganese, and ion are nonmonotonic. Even if the size of grains is below the critical value, the ferromagnetic properties of zinc oxide depend significantly on the texture of films and the structure of amorphous intercrystallite layers.     

Structural and optical properties of nanophase zinc oxide

Nanophase zinc oxide samples were synthesized by a two-step solid-state reaction method. The phase structure and microstructure were investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The vibrational Raman spectra were compared with those from the bulk and their grain size dependence was also examined. Their photoelectric behavior was studied by X-ray photoelectron spectroscopy (XPS). The peaks at 1044.5 and 1021.4 eV were recorded as corresponding to the respective binding energies of Zn 2p_1/2 and Zn 2p_3/2, and the photoelectron spectrum of O 1s in the as-prepared powder was located at 531.2 eV. A strong visible emission centered at 580 nm was clearly observed in the nanosized zinc oxide at room temperature. Photoluminescence (PL) spectra were investigated as a function of grain size after different heat treatments. The origin of the luminescence is attributed to the recombination of electrons in singly occupied oxygen vacancies with photoexcited holes in the valence band. Received: 30 June 2001 / Accepted: 20 February 2002 / Published online: 3 June 2002 RID="*" ID="*"Corresponding author. Fax: +86-25/359-5535, E-mail: mszhang@nju.edu.cn     

Inverse Hall–Petch like behaviour in a mechanically milled nanocrystalline Al5Fe2 intermetallic phase

In the present investigation, the indentation study on the high-energy ball-milled nanocrystalline Al₅Fe₂ intermetallic compound has established the inverse Hall–Petch (IHP) behaviour. The structural characterisation of the milled powder particles by X-ray diffraction (XRD) and transmission electron microscopy has shown the evolution of nanocrystalline phase. Micro-indentation measurements have revealed the increase in hardness with decreasing grain size, reaching to a maximum of 9.0 ± 0.3 GPa up to a grain size of 32 ± 4 nm, followed by a decrease. The decrease in hardness with further refinement, an indication of grain size softening, demonstrates the IHP-like behaviour. The deviation from the Hall–Petch behaviour has been discussed using various models based on the dislocations and grain boundary-mediated processes. From the analysis, it appears that the model based on mesocopic grain boundary sliding phenomena is more appropriate to account for the observed grain size softening.     

Studies of iron and iron oxide layers by electron spectroscopes

Thin iron oxide layers prepared “in situ” in the ultra high vacuum on polycrystalline iron substrate were investigated by electron spectroscopy methods—X-ray photoelectron spectroscopy (XPS) and elastic peak electron spectroscopy (EPES), using spectrometer ADES-400. The texture and the average grain size of the iron substrate foil have been examined by glancing angle X-ray diffraction (XRD). Qualitative and quantitative estimation of investigated oxide layers was made using (i) the relative sensitivity factor XPS method, (ii) comparison of binding energy shifts of Fe 2p photoelectron line and (iii) non-linear fitting procedure of Fe 2p photoelectron lines.Both, sputter-clean polycrystalline iron substrate and finally grown Fe_2.2O₃ layer, were investigated by the EPES method to measure the electron transport parameters used for quantitative electron spectroscopy, such as the electron inelastic mean free path (IMFP) values. The IMFPs were measured in the electron kinetic energy range 200-1000 eV with the Cu standard. The surface excitation parameters using Chen and Werner et al. approaches were evaluated and applied for correcting these IMFPs. The discrepancies between the evaluated parameters obtained using the above quantitative and qualitative approaches for characterising the iron oxide layers were discussed.     

氧化铝/氧化镧X射线衍射及拉曼光谱研究

当钢中氧化铝夹杂物的尺寸过大、棱角分明,在线材拉拔为钢丝的过程中可视为主要的裂纹源,会严重影响钢材性能,细化或去除钢中夹杂物备受重视。由于钢中合金元素添加量相对于钢液较小,并在实验及分析的中间过程中存在误差,使用放大夹杂物反应的思路,研究了在高温1 600 ℃时,不同比例稀土氧化镧粉末和氧化铝粉末的添加量对夹杂物的物相变化、尺寸大小的影响。对高温箱式炉设定程序进行升温、保温、随炉冷却,使用X射线衍射仪、拉曼光谱仪测试结果分析了镧铝氧化物的具体变化过程。结果表明：随着La₂O₃添加量的不断增加,最先生成LaAl₁₁O₁₈相,其次为LaAl₁₁O₁₈,LaAlO₃相,峰强减弱,半高宽增加,晶粒尺寸变小,随后LaAl₁₁O₁₈特征峰消失,只剩下LaAlO₃相,且并无新相生成。结合H-W平均晶粒尺寸数学模型计算R2分别为0.990 25,0.962 59,0.987 1和0.989 76,且1#样品到4#样品晶粒尺寸分别为6.08,2.88,7.67和4.75 μm,2#样品晶粒尺寸最小,3#样品晶粒尺寸最大,表明合适的氧化镧和氧化铝配比可以促进形核并缩小晶粒尺寸。通过拉曼光谱分析得出,随着Al₂O₃配比的减少,观察拉曼位移在4 385 cm-1处拉曼特征峰消失,结合XRD图谱可以判定该处为LaAl₁₁O₁₈相。3#-4#曲线在拉曼位移为3 564～3 642和4 461～5 554 cm-1处出现拉曼特征峰,结合2#曲线以及XRD图谱可知,生成新的LaAlO₃相,且3#样品和4#样品的不同配比对拉曼峰强无太大影响,也没有出现新的特征峰。通过放大钢中需要针对性研究的物质,分析了氧化镧粉末添加后对氧化铝粉末改性的演变过程。研究结果可对实际炼钢过程中解决氧化铝夹杂物改性的问题提供参考。     

Cobalt Modification of Thin Rutile Films Magnetron-Sputtered in Vacuum

Using X-ray phase analysis, atomic force microscopy, and secondary ion mass-spectrometry, the phase formation and component distribution in a Co–TiO₂ film system have been investigated during magnetron sputtering of the metal on the oxide and subsequent vacuum annealing. It has been found that cobalt diffuses deep into titanium oxide to form complex oxides CoTi₂O₅ and CoTiO₃. A mechanism behind their formation at grain boundaries throughout the thickness of the TiO₂ film is suggested. It assumes the reactive diffusion of cobalt along grain boundaries in the oxide. A quantitative model of reactive interdiffusion in a bilayer polycrystalline metal–oxide film system with limited solubility of components has been developed. The individual diffusion coefficients of cobalt and titanium have been determined in the temperature interval 923–1073 K.

     

Electrical and optical properties of ZnO films grown by molecular beam epitaxy

Zinc oxide (ZnO) films have been grown on sapphire by molecular beam epitaxy (MBE), and it is found that the grain size of the ZnO films increased with increasing the growth temperature. Photoluminescence (PL) study shows that the intensity ratio of near-band-edge emission to deep-level-related emission (NBE/DL) of the ZnO is significantly enhanced with increasing the growth temperature, and the dependence of the carrier mobility on the growth temperature shows very similar trend, which implies that there is a community factor that determines the optical and electrical properties of ZnO, and this factor is suggested to be the grain boundary. The results obtained in this paper reveal that by reducing the grain boundaries, ZnO films with high optical and electrical properties may be acquired.     

Evolution of structural and magnetic properties of sputtered nanocrystalline Co thin films with thermal annealing

Ultrafine grain films of cobalt prepared using ion-beam sputtering have been studied using X-ray diffraction (XRD), X-ray reflectivity (XRR), atomic force microscopy (AFM) and magneto-optical Kerr effect (MOKE) measurements. As-prepared films have very smooth surface owing to the ultrafine nature of the grains. Evolution of the structure and morphology of the film with thermal annealing has been studied and the same is correlated with the magnetic properties. Above an annealing temperature of 300 °C, the film gradually transforms from HCP to FCC phase that remains stable at room temperature. A significant contribution of the surface energy, due to small grain size, results in stabilisation of the FCC phase at room temperature. It is found that other processes like stress relaxation, grain texturing and growth also exhibit an enhanced rate above 300 °C, and may be associated with an enhanced mobility of the atoms above this temperature. Films possess a uniaxial anisotropy, which exhibits a non-monotonous behaviour with thermal annealing. The observed variation in the anisotropy and coercivity with annealing can be understood in terms of variations in the internal stresses, surface roughness, and grain structure.     

Sensing of LPG with nanostructured zinc oxide thin films grown by spray pyrolysis technique

Nanostructured zinc oxide thin films were prepared by spray pyrolysis technique using Zn(NO₃)₂·6H₂O as the precursor solution. The resulting films were investigated by X-ray diffraction and scanning electron microscopy to know crystal structure, size of crystallites and surface morphology. The films have been found to be polycrystalline zinc oxide, possessing hexagonal wurtzite crystal structure and nanocrystallite with grain size of approximately 30-35 nm. The LPG sensing performance of the films has been investigated at various concentrations of LPG in air at operating temperatures varying from 225 to 400 °C. At 325 °C the maximum responses of 46.3% and 48.9% have been observed, respectively, for concentrations of 0.8 and 1 vol% of LPG in air (1 vol% of LPG in air corresponds to 50% LEL of LPG in air). The recovery time has been found to be less than the response time for all concentrations of LPG. A possible reaction mechanism of LPG sensing has been proposed.     

Deposition of nanostructured crystalline and corrosion resistant alumina film on bell metal at low temperature by rf magnetron sputtering

Aluminium oxide films deposited by rf magnetron sputtering for protective coatings have been investigated. The alumina films are found to exhibit grainy surface microstructure. The grain size, structure and density depend on different system parameters such as argon and/or oxygen flow rate and applied rf power etc. The effect of transition of the discharge from metallic to reactive mode on the surface characteristics of the alumina film is studied. X-ray diffractometry reveals that in poisoned mode of sputtering and under optimized power and pressure, crystalline alumina film can be grown. Different system conditions are optimized for corrosion resistant aluminium oxide films with good adhesion properties. Nanostructured alumina film is obtained at lower pressure (8 × 10⁻⁴ to 9 × 10⁻⁴ Torr) by rf reactive magnetron sputtering.     

Finite size effects on the structural and magnetic properties of sol–gel synthesized NiFe2O4 powders

Nanoparticles of nickel ferrite have been synthesized by the sol–gel method and the effect of grain size on its structural and magnetic properties have been studied in detail. X-ray diffraction (XRD) studies revealed that all the samples are single phasic possessing the inverse spinel structure. Grain size of the sol–gel synthesized powders has been determined from the XRD data and the strain graph. A grain size of 9 nm was observed for the as prepared powders of NiFe₂O₄ obtained through the sol–gel method. It was also observed that strain was induced during the firing process. Magnetization measurements have been carried out on all the samples prepared in the present series. It was found that the specific magnetization of the nanosized NiFe₂O₄ powders was lower than that of the corresponding coarse-grained counterparts and decreased with a decrease in grain size. The coercivity of the sol–gel synthesized NiFe₂O₄ nanoparticles attained a maximum value when the grain size was 15 nm and then decreased as the grain size was increased further.     

强辐射源用铜纳米线阵列靶的结构与性能

 采用多孔阳极氧化铝（AAO）模板脉冲电沉积法制备了强辐射源用铜纳米线阵列靶,并用扫描电子显微镜（SEM）、能谱（EDS）和X射线衍射（XRD）对其进行了结构表征。结果表明：去除AAO模板后铜纳米线平均直径比去除AAO模板前的平均孔径大32%,长度缩短5%。对电沉积2 000 s的样品进行铜纳米线长度分布表征,结果显示:距离模板圆心越远,铜纳米线越长。与超短脉冲激光相互作用实验结果表明:纳米线平均长度在18~50 μm范围内,铜Kα光子产额先随纳米线长度增加而增加,当长度大于33 μm时,铜Kα光子产额开始下降。     

Synthesis and analysis of ZnO and CdSe nanoparticles

Zinc oxide and cadmium selenide particles in the nanometer size regime have been synthesized using chemical routes. The particles were capped using thioglycerol in case of ZnO and 2-mercaptoethanol in case of CdSe to achieve the stability and avoid the coalescence. Zinc oxide nanoparticles were doped with europium to study their optical properties. A variety of techniques like UV-Vis absorption spectroscopy, X-ray diffraction (XRD), photoluminescence (PL), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR) and transmission electron microscopy (TEM) were used to carry out structural and spectroscopic characterizations of the nanoparticles.     

Characterisation of advanced metal particle recording media pigments

Advanced metal particle (MP) pigments used in high density digital storage applications on flexible substrates have been characterised using a wide range of techniques. We have examined the chemical composition of the particles and find that the core consists of an iron–cobalt alloy in a structure BCC, analogous to that of α-Fe. Surface layers on the particle used to provide oxidation resistance, have been found to contain some form of oxides of Co, Al and Y as well as iron oxide which we find to be in a spinel form. From Mössbauer spectroscopy we have determined the proportion of the iron atoms in the oxide layer and find that by controlling the percentage of Y in the surface, a much thinner oxide layer results with a corresponding increase in the overall saturation magnetisation. From high resolution TEM images we have determined the particle size of each sample and compared those values with those obtained from X-ray line broadening. We find that in each case the X-ray ‘size' is about a quarter of the physical size excluding the oxide layer. This indicates the polycrystalline character of the particles and the crystallite size is in broad agreement with the activation volume of magnetisation reversal determined from an analysis of magnetic viscosity in the materials. These results are indicative of incoherent magnetisation reversal in the particles which may account for the lower than expected coercivity values in such pigments.     

Effects of Interface Roughness on Interlayer Coupling in Fe/Cr/Fe Structure

Effect of interface roughness on antiferromagnetic coupling between Fe layers in a Fe/Cr/Fe trilayer, with Cr layer having a wedge form has been studied. All the samples have been deposited simultaneously on substrates having different roughness, thus it is being considered that there is no variation in the morphological features like grain size and grain texture of the films. Measurements have been done as a function of Cr spacer layer thickness and the peak value of antiferromagnetic coupling strength is compared among different trilayers, thus any influence of spacer layer thickness fluctuation from sample to sample has also been avoided. The samples are characterized by X-ray reflectivity (XRR) and magneto-optic Kerr effect (MOKE). XRR results show that the roughness of the substrate is not replicated at the successive interfaces. Antiferromagnetic coupling between Fe layers decreases with the increase of roughness of Fe/Cr/Fe interfaces.