Characterization and structure study of the anodic oxide film on Zircaloy-4 synthesized using NaOH electrolytes at room temperature

Thick crystalline zirconium oxide films were synthesized on Zircaloy-4 substrates by anodic oxidation at room temperature in NaOH solution with a stable applied voltage (300 V). The film is approximately 4.7 μm in thickness. The XPS and SEM analysis shows that the film is a three-layer structure in water, hydroxide and oxide parts. The thickness of that order is ∼0.01 μm, ∼1 μm, ∼3.7 μm, respectively. The oxide layer is composed of tetragonal and monoclinic phases with the volume ratio about 0.2. Furthermore, the thick anodic film acts as a barrier to oxygen and zirconium migrations. It effectively protects zirconium alloys against the worse corrosion. An extremely low passive current density of ∼0.018 μA/cm² and a low oxidation weight gain of ∼0.411 mg/cm² were also observed in the films.     

High-temperature Auger electron spectroscopy of Zircaloy-4

The near-surface region of Zircaloy-4 (Zry-4) has been probed using Auger electron spectroscopy (AES). In particular, the behavior of impurity (sulfur) and alloying (tin) elements has been monitored as a function of annealing temperature and time. High-temperature AES experiments above 900 K are reported, with a primary focus on changes in the S(LMM) Auger feature that overlaps with the primary Zr(MNV) transition. We find that the sulfur content of the near-surface region increases linearly with annealing time at higher temperatures. Tin is the only alloying element whose Auger signal intensity significantly exceeds the noise level at these temperatures.     

Linear assemblies of aged CdS particles and cationic porphyrin in multilayer films

Multilayer films of CdS particles and meso-tetra-(4-trimethylaminophenyl)porphyrin cobalt iodide (CoTAPPI) were fabricated via layer-by-layer self-assembly technique. UV-vis absorption spectra, fluorescence spectra and SEM images were used to compare the differences between the films prepared from freshly synthesized nanoparticles and from aged particles. SEM images show the aged CdS particles and CoTAPPI in the multilayer film, assembling in a linear structure. The mechanism of dipole-dipole interaction was presented to explain linear formation.     

SEM扫描云纹法的相移技术研究

提出一种扫描电镜(SEM)扫描云纹法的相移新技术,通过SEM系统控制电镜电子束扫描线移动,对获取的云纹图像实现0-2π范围内的四步相移,从而获得了更高的位移测量灵敏度。同时对SEM扫描云纹法的测量原理以及相移实验技术的原理进行了详细的阐述。并将该技术应用到电子封装试件栅的相移分析中。实验结果证明了该方法的可行性,该方法为微米云纹法的条纹处理提供了一种新途径。     

Effect of aluminum substitution on the structural and magnetic properties of cobalt ferrite synthesized by sol-gel auto combustion process

Aluminum substituted cobalt ferrite powders (CoFe_2−xAl_xO₄) with varying composition from 0.0 to 1.0 in the step of 0.2 have been obtained by sol-gel auto combustion technique using citric acid as a fuel. The metal nitrate to fuel ratio was maintained 1:4 throughout the synthesis of CoFe_2−xAl_xO₄. The thermal analysis of as prepared samples is done by TGA technique. The compositional stoichiometry of the prepared samples is confirmed by Energy dispersive X-ray analysis technique. Single phase cubic spinel structure and nano phase structure of the synthesized powders were confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The crystallite size of 16-26 nm was obtained using Scherrer formula. SEM analysis shows the formation of uniform grain growth. The grain size obtained from SEM results is of the order of 30 nm. Maximum specific surface area was observed to be of the order of 52 m²/gm. The highest value of saturation magnetization and coercivity was observed for pure cobalt ferrite sample and it decreases as the aluminum content x increases. A strong co-relation between the saturation magnetization and aluminum content was observed. The decrease in magnetic properties is due to the substitution of aluminum ions in place of Fe³⁺.     

A TEM study of the stability of intermetallic precipitates in Zircaloy nuclear reactor components

Transmission electron microscopy (TEM) has been used to characterise the radiation-induced changes in Zr(Cr,Fe)₂ intermetallic precipitates present in Zircaloy-2 and -4 nuclear reactor components. The results show that the precipitates become completely amorphous at low fluences (<1 × 10²⁴ n·m⁻²) during low temperature neutron irradiation (about 330 K) with no associated chemical composition change. At higher temperatures (about 573 K), a duplex amorphous-crystalline structure is produced. The precipitates retain a crystalline core surrounded by a peripheral amorphous layer that advances inwards with increasing fluence. The amorphous outer layer is coincident with a depletion of Fe that is dispersed into the surrounding hcp -phase matrix. Subsequent post-irradiation heat-treatment below the amorphous phase recrystallisation temperature results in the back-diffusion of Fe into the precipitates.     

Oxidation of Zircaloy-4 by H2O followed by molecular desorption

The interaction of H₂O with Zircaloy-4 (Zry-4) is investigated using Auger electron spectroscopy (AES) and temperature programmed desorption (TPD) methods. Following adsorption of H₂O at 150 K the Zr(MNV) and Zr(MNN) Auger features shift by ∼6.5 and 4.5 eV, respectively, indicating surface oxidation. Heating H₂O/Zry-4 results in molecular desorption of water at both low and high temperatures. The low-temperature desorption is attributed to ice multilayers, whereas, three overlapping high-temperature features are presumably due to recombinative desorption. This high-temperature desorption begins before the surface oxide is dissolved, continues upon its removal, and is atypical for water/metal systems. Unexpectedly, no significant desorption of hydrogen is observed near 400 K, as is typically observed following O₂ adsorption on Zr-based materials. However, we do observe that H₂O adsorption on Zry-4 surfaces roughened by argon ion sputtering results in H₂ desorption.     

Preparation, structures and photoluminescent enhancement of CdWO4-TiO2 composite nanofilms

For the first time, Cadmium tungstate (CdWO₄)-TiO₂ composite nanofilms on a glass substrate were prepared by means of the dip-coating technique, in which collodion was used as a dispersant and film-forming agent. The films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermo gravimetric and thermal analyses (TG/DTA), FTIR and photoluminescence (PL) methods, respectively. SEM and XRD characterization of these films indicated that CdWO₄ particles crystallized in a monoclinic wolframite-type structure whereas TiO₂ particles were Anatase phase; and both of them were well distributed in the nanofilms. FTIR spectra proved the presence of CdWO₄ on the nanofilms. Photoluminescent results showed that the emitting peak of CdWO₄ films blue shifted slightly relative to that of CdWO₄ crystal. Moreover, the PL intensity of CdWO₄-TiO₂ composite nanofilm was much higher than that of CdWO₄ nanofilm. We ascribed that the introduction of TiO₂ should be responsible for the PL enhancement.     

Auger electron spectroscopic study of CO2 adsorption on Zircaloy-4 surfaces

We investigate the adsorption of CO₂ onto Zircaloy-4 (Zry-4) surfaces at 150, 300 and 600 K using Auger electron spectroscopy (AES). Following CO₂ adsorption at 150 K the graphitic form of carbon is detected, whereas upon chemisorption at 300 and 600 K we detect the carbidic phase. As the adsorption temperature is increased, the carbon Auger signal increases, whereas the oxygen signal decreases. Adsorption at all three temperatures results in a shift of the Zr Auger features, indicating surface oxidation. The effect of adsorbed CO₂ on the Zr(MVV) and Zr(MNV) transitions depends on adsorption temperature and is less pronounced at higher temperatures. On the other hand, changes in the Zr(MNN) feature are similar for all three adsorption temperatures. The changes in the Zr Auger peak shapes and positions are attributed to oxygen from dissociated CO₂, with the differences observed at various temperatures indicative of the diffusion of oxygen into the subsurface region.     

Dissolution patterns caused by chemical etching of Al–Co–Cu and Al–Co–Ni decagonal quasicrystals with a HF–HNO3–H2O solution

Dissolution patterns essential for Al–Co–Cu and Al–Co–Ni decagonal quasicrystals (d-QCs) have been investigated in detail by chemical etching using a HF–HNO₃–H₂O solution followed by scanning electron microscopy (SEM) observations. The chemical etching of definite surface areas of the samples, which are either normal or parallel to the tenfold axes, using a solution with HF–HNO₃–H₂O (1?:?5?:?4 in volume ratio; 0°C; 5–10?min), produces a large number of microfacet pits of decagonal prismatic shape. In addition, the same etching test in combination with SEM observations was carried out on a deformed sample of the Al–Co–Ni d-QC, which had been subjected to concentrated mechanical stress at an elevated temperature of 850°C by means of the Vickers indentation technique. The morphological features of the resulting micropits and their possible origins are discussed on the basis of results obtained by SEM observations.     

Ionic conduction and phase separation studies in P(VdF-HFP))-LiClO4-dedoped polyaniline nanofiber composite polymer electrolytes — II: Effect of incorporation of PC and DEC

In the present work, ionic transport and interfacial stability of dedoped (insulating) polyaniline (PAni) nanofibers dispersed P(VdF-HFP) based nanocomposite gel polymer electrolytes have been investigated. Samples of P(VdF-HFP)-(PC+DEC)-LiClO₄-x wt. % dedoped PAni nanofibers (x = 0, 2, 4, 6, 8, 10) are prepared by conventional solution casting technique. By analysis of SEM, XRD and impedance spectroscopy results it has been demonstrated that the incorporation of up to 6 wt. % of dedoped PAni nanofibers to P(VdF-HFP)-(PC+DEC)-LiClO₄ polymer electrolyte system significantly enhances the ionic conductivity and interfacial stability of the electrolyte system. Above that concentration phase separation of PAni nanofibers is observed leading to decrease in ionic conductivity. The aggregated phase decreases the porosity, which results in lower ionic conductivity as confirmed by SEM. Experiments on the interfacial stability reveals that the stability of polymer electrolytes containing nanofibers is better than that of nanofiber free polymer electrolytes.     

Co3O4-ZnO hierarchical nanostructures by electrospinning and hydrothermal methods

A new hierarchical nanostructure that consists of cobalt oxide (Co₃O₄) and zinc oxide (ZnO) was produced by the electrospinning process followed by a hydrothermal technique. First, electrospinning of a colloidal solution that consisted of zinc nanoparticles, cobalt acetate tetrahydrate and poly(vinyl alcohol) was performed to produce polymeric nanofibers embedding solid nanoparticles. Calcination of the obtained electrospun nanofiber mats in air at 600 °C for 1 h, produced Co₃O₄ nanofibers with rough surfaces containing ZnO nanoparticles (i.e., ZnO-doped Co₃O₄ nanofibers). The rough surfaced nanofibers, containing ZnO nanoparticles (ZnNPs), were then exploited as seeds to produce ZnO nanobranches using a specific hydrothermal technique. Scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were employed to characterize the as-spun nanofibers and the calcined product. X-ray powder diffractometery (XRD) analysis was used to study the chemical composition and the crystallographic structure.     

Electrochemical and mechanical properties of nanochitin-incorporated PVDF-HFP-based polymer electrolytes for lithium batteries

Nanocomposite polymer electrolytes (NCPE) composed of poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP) and chitin for different concentrations of LiClO₄ have been prepared by a hot-press technique. The prepared NCPE films were subjected to XRD, SEM, FTIR and tensile analyses. The thermal stability of NCPE membrane was investigated by TG-DTA. Ionic conductivity studies have also been made as a function of lithium salt concentration for different temperatures ranging from 0 to 80 °C. The polymeric membrane comprising PVDF-HFP/chitin/LiClO₄ of ratio 75:20:5 (wt.%) offered maximum ionic conductivity. Thermal study reveals that these membranes are stable up to 260 °C.     

Structure, thermal and transport properties of PVAc-LiClO4 solid polymer electrolytes

The lithium ion conducting solid polymer electrolytes (SPE) based on PVAc-LiClO₄ of various compositions were prepared by solution casting technique. Structure and surface morphology characterization were studied by X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) measurements, respectively. Thermal and conductivity behavior of polymer-salt complexes were studied by employing differential scanning calorimetry (DSC) and ac impedance measurements, respectively. XRD and SEM analyses indicate the amorphous nature of the polymer-salt complexes. DSC measurements show decrease in T_g with the increase in LiClO₄ concentrations. The bulk conductivity of the PVAc:LiClO₄ polymer electrolytes was found to vary between 7.6×10⁻⁷ and 6.2×10⁻⁵ S cm⁻¹ at 303 K with the increase in salt concentration. The temperature dependence of the polymer electrolyte complexes appear to obey Arrhenius law.     

Preparation and properties of spray-deposited ZnIn2Se4 nanocrystalline thin films

Zinc indium selenide (ZnIn₂Se₄) thin films have been deposited onto amorphous and fluorine doped tin oxide (FTO)-coated glass substrates using a spray pyrolysis technique. Aqueous solution containing precursors of Zn, In, and Se has been used to obtain good quality deposits at different substrate temperatures. The preparative parameters such as substrate temperature and concentration of precursors solution have been optimized by photoelectrochemical technique and are found to be 325 °C and 0.025 M, respectively. The X-ray diffraction patterns show that the films are nanocrystalline with rhombohedral crystal structure having lattice parameter a=4.05 Å. The scanning electron microscopy (SEM) studies reveal the compact morphology with large number of single crystals on the surface. From optical absorption data the indirect band gap energy of ZnIn₂Se₄ thin film is found to be 1.41 eV.     

Photoconductivity and photoluminescence in chemically deposited films of (Cd0.95-Pb0.05)S: CdCl2,Ce

The results of photoconductivity (PC), photoluminescence (PL), optical absorption spectra, XRD and SEM studies are presented for (Cd_0.95-Pb_0.05)S: CdCl₂,Ce films prepared by chemical bath deposition technique. PC gains ∼10⁷ are found in doped films. PL emission spectrum is found in red region which is related to 5d to 4f transition in Ce. Films prepared at 60°C show better PC while those prepared at room temperature (RT) show better PL. Optical absorption studies show reduction in band gap due to addition of PbS. A peak due to Ce is also observed in absorption spectrum. XRD studies show the presence of both CdS and PbS. SEM studies show presence of microcrystals, cluster of grains along with some rod type structures.     

HFCVD法制备纳米晶体碳化硅薄膜中氢流量对晶粒尺寸的影响

以甲烷、硅烷和氢气为反应气体,采用热丝化学气相沉积(HFCVD)法在单晶硅衬底上沉积纳米晶体碳化硅(SiC)薄膜.通过X射线衍射(XRD)和扫描电子显微镜(SEM)分别对SiC薄膜的晶体结构和表面形貌进行分析.实验发现氢气流量对碳化硅薄膜晶粒尺寸有很大影响,当氢气流量从10SCCM变化到300SCCM时,薄膜晶粒的平均尺寸将由较大的400 nm左右减小到40 nm左右.     

N型4H-SiC同质外延生长

利用水平式低压热壁CVD (LP-HW-CVD) 生长系统,台阶控制生长和衬底旋转等优化技术,在偏晶向的4H-SiC Si(0001) 晶面衬底上进行4H-SiC同质外延生长,生长温度和压力分别为1550℃和10⁴ Pa,用高纯N₂作为n型掺杂剂的4H-SiC原位掺杂技术,生长速率控制在5μm/h左右.采用扫描电镜(SEM)、原子力显微镜(AFM),傅里叶变换红外光谱(FTIR)和Hg/4H-SiC肖特基结构对同质外延表面形貌、厚度、掺杂浓度以及均匀性进行了测试.实验结果表明,4H-SiC同质外延在表面无明显缺陷,厚度均匀性1.74%, 1.99% 和1.32%(σ/mean),掺杂浓度均匀性为3.37%,2.39%和2.01%.同种工艺条件下,样品间的厚度和掺杂浓度误差为1.54%和3.63%,有很好的工艺可靠性. 关键词： 4H-SiC 同质外延生长 水平热壁CVD 均匀性     

Phase shifting SEM moiré method

A new phase shifting scanning electron microscope (SEM) moiré method is proposed in this paper. The phase shifting technique is realized in four steps from 0 to 2π by shifting electron beam in the y-axis direction controlled by the SEM system. It is successfully applied to determine the residual strain of a deformed holographic grating with a frequency of 1200 lines/mm in an electronic package. As a further application, it is used to measure the virtual strain of a MEMS structure with a 5000-line/mm grating and to determine the phase distribution of a SEM moiré formed with a 6000-line/mm grating fabricated by electron beam lithography. The experiments show the feasibility of this method. It provides a new way for disposal of fringes pattern in sub-micro moiré method.     

Silane decorated metallic nanorods for hydrophobic applications

A novel technique to modify a metallic surface for anti-icing applications is presented. An oblique angle deposition (OAD) technique has been used to fabricate metallic nanorods of Aluminum and Tungsten on a glass substrate. A conformal coating of a silane has been applied using a molecular vapor deposition technique. The resulting surface has shown a static contact angle of 134° with the water droplet. SEM, AFM and XPS have been used to study the surface modification. This is a highly promising approach for anti-icing applications due to its scalability at a very low cost.