Crystal structure of iron-oxide nanoparticles synthesized from ferritin

We have investigated the crystal structure of nanosized iron-oxide by X-ray diffraction (XRD), extended X-ray absorption fine structure measurements at the iron K-edge as well as by transmission electron microscopy (TEM). Iron-oxide nanoparticles were produced by thermal treatment of horse spleen ferritin molecules. The structure of these particles was compared to α-Fe₂O₃ and γ-Fe₂O₃ nanopowder references. The thermal treatment of a submonolayer film of ferritin molecules results in pure γ-Fe₂O₃ nanoparticles, while for films above a certain thickness α-Fe₂O₃ and γ-Fe₂O₃ coexist, exhibiting two different crystallite sizes. TEM shows a characteristic particle diameter of ~7 nm for γ-Fe₂O₃ resulting from thermal treatment of monolayers, consistent with the crystallite size of the γ-phase as obtained from XRD measurements on multi-layered samples. XRD shows the α-Fe₂O₃ phase to be characterized by a crystallite size of ~34 nm.     

一氧化碳合成金刚石薄膜的形貌和结构分析

利用微波等离子体化学气相沉积(MPCVD)技术，采用偏压增加成核(BEN)、两步生长的方法在一氧化碳(CO)和氢气(H₂)的环境下制备了金刚石薄膜. 利用扫描电子显微镜(SEM)、Raman光谱仪和透射电子显微镜(TEM)对金刚石薄膜的形貌和结构进行了分析. 研究发现金刚石晶粒在第一步成核及生长的过程中产生了层错和孪晶，而在第二步的生长过程中产生的层错和孪晶很少，最终形成的金刚石晶粒外表面比较光滑，包含有近五次对称或者平行的片状的孪晶，并可以观察到少量的位错. 而在样品的边缘由于等离子体的不均匀产生了比样品中心成核密度低的区域. 在这个区域中，发现了一个新的非金刚石的碳结构.     

A DFT study on the structure and radical scavenging activity of newly synthesized hydroxychalcones

Quantum‐chemical computations based on the density functional theory have been employed to study the relation between the structure and the radical scavenging activity of six newly synthesized hydroxychalcones. The three main working mechanisms, hydrogen atom transfer (HAT), stepwise electron‐transfer‐proton‐transfer, and sequential‐proton‐loss‐electron‐transfer (SPLET), were investigated, and the O–H bond dissociation enthalpy, ionization potential, proton dissociation enthalpy, and electron transfer energy parameters were computed in the gas phase and in solvents using PCM model. The geometry structure, radical, electron character, and the frontier molecular orbital were analyzed to explore the key factors that influence the radical scavenging activity of the hydroxychalcones. Results indicated that 3,4‐dihydroxychalcone (6) possessing the catechol functionality is expected to be more efficient hydrogen atom and proton donor than others. The theoretical results confirm the important role of the B‐ring and shed light on the role of the o‐dihydroxy (catechol) moiety in the antioxidant properties of hydroxychalcones. In addition, the calculated results are in good agreement with experimental values. It was found that HAT is the most favored mechanism for explaining the radical‐scavenger activity of hydroxychalcone in the gas phase, whereas SPLET mechanism is thermodynamically preferred pathway in aqueous solutions. Copyright © 2012 John Wiley & Sons, Ltd.     

Effect of lateral structure parameters of SiGe HBTs on synthesized active inductors

The effect of lateral structure parameters of transistors including emitter width, emitter length, and emitter stripe number on the performance parameters of the active inductor(AI), such as the effective inductance Ls, quality factor Q,and self-resonant frequency ω_0 is analyzed based on 0.35-μm Si Ge Bi CMOS process. The simulation results show that for AI operated under fixed current density JC, the HBT lateral structure parameters have significant effect on Ls but little influence on Q and ω_0, and the larger Ls can be realized by the narrow, short emitter stripe and few emitter stripes of Si Ge HBTs. On the other hand, for AI with fixed HBT size, smaller JCis beneficial for AI to obtain larger Ls, but with a cost of smaller Q and ω_0. In addition, under the fixed collector current IC, the larger the size of HBT is, the larger Ls becomes, but the smaller Q and ω_0 become. The obtained results provide a reference for selecting geometry of transistors and operational condition in the design of active inductors.     

Aggregate structure and crystallite size of platinum nanoparticles synthesized by ethanol reduction

Monodispersed platinum (Pt) nanoparticles were synthesized from reducing hydrated hydrogen hexachloroplatinic acid (H₂PtCl₆·nH₂O) with ethanol in the presence of polyvinylpyrrolidone (PVP) as a steric stabilizer. Concentration of both PVP and ethanol influenced the aggregate structure and crystallite size of the nanoparticles. When the molar ratio of monomeric unit of PVP to Pt, i.e., [PVP]/[Pt], was one, the synthesized Pt particles coagulated pronouncedly into an inter-connected particulate network or self-organized into spherical superstructures with an apparent diameter ranging from 60 to 80 nm, depending on the ethanol concentration. The geometry and structure of these complex aggregates were characterized by fractal analysis. Fractal dimensions of 2.13–2.23 in three dimensions were determined from the Richardson’s plot, which suggests that a reaction-limited cluster–cluster aggregation model (RCLA) was operative. The Pt colloids became apparently more stable when the [PVP]/[Pt] ratio was increased greater than 20. Crystallite size of the Pt nanoparticles was found to increase linearly with the ethanol concentration as the [PVP]/[Pt] was held at one. This suggests that the reduction rate of PtCl₆ ²⁻ ions in solution is critically important to the synthesized crystallite size.     

Formation of nano-hydroxyapatite on recombinant human-like collagen fibrils

Mineralization of recombinant human-like collagen is an important biomaterial for bone tissue engineering. Features of the formation of nano-hydroxyapatite on recombinant human-like collagen surface were investigated by SEM, XRD, FTIR and TEM. Formation mechanism of the nano-crystals is also discussed. The nano-HA is about 6–25 nm in size and with their c-axis parallel to the fibrils orientation.     

Effect of cooling conditions on the magnetic structure of multiferroic BiFeO3 synthesized by mechanical activation

We have studied the nuclear quadrupole interactions (NQI) of the ¹⁴N, ¹⁷O and ²H nuclei in the nucleobases cytosine, adenine, guanine and thymine in the free state as well as when they are bonded to the sugar ring in DNA, simulated through a CH₃ group attached to the nucleobases. The nucleobase uracil, which replaces thymine in RNA, has also been studied. Our results show that there are substantial indirect effects of the bonding with the sugar group in the nucleic acids on the NQI parameters e ² qQ/h and η. It is hoped that measurements of these NQI parameters in DNA will be available in the future to compare with our predictions. Our results provide the conclusion that for any property dependent on the electronic structures of the nucleic acids, the effects of the bonding between the nucleobases and the nucleic acid backbones have to be included.     

Nanophases in mechanochemically synthesized AgI-CuI system: structure, phase stability and phase transitions

Nanoscale crystallites of Ag-rich (Ag_1−xCu_xI, x=0.05, 0.10, 0.15 and 0.25), Cu-rich (Cu_1-yAg_yI, y=0.05, 0.10, 0.15 and 0.25) and intermediate Ag_1-xCu_xI (x=0.50) solid solutions and end members AgI, CuI with sizes in the range of 46-13 nm were synthesized by attrition at ambient temperature in a soft mechanochemical reaction (MCR) of Ag, Cu and I. Monophasic γ-AgI (zincblende, ) with disordered Ag⁺ sublattice and the crystallite size of about ∼31 nm was realized in the case of Ag_0.75Cu_0.25I (x=0.25) composition. Lattice parameter decreases linearly from 649 to 604 pm with increasing Cu concentration in the AgI-CuI system validating Vegard's law. Smallest size (∼13 nm) agglomerated nanocrystals were realized in the Cu-rich composition Cu_0.75Ag_0.25I (), while unagglomerated uniform-sized (∼17 nm) and spherical shape nanocrystallites of Ag_0.50Cu_0.50I () with maximum strain were synthesized for sensor applications using MCR. Differential scanning calorimetry study shows the systematic changes in the phase transition temperature with Cu substitution. Ag-rich composition posses less enthalpy (ΔH (x or Cu=0.05, 0.10, 0.15, 0.25)=6.0, 6.11, 6.6, 6.3 in kJ/mol) and entropy (ΔS (y or Ag=0.05, 0.10, 0.15, 0.25)=14.15, 14.1, 15.03, 13.6 in J/mol K) when compared to undoped AgI () implying greater thermal stability of γ-phase due to Cu-strengthened Ag-I bond. Enhanced entropy () in Cu_0.75Ag_0.25I (Cu-rich) solid solutions relative to CuI () indicates Ag-induced cation disorder. Fifteen percent Ag-doped CuI (Cu_0.85Ag_0.15I) nanocrystals apparently behave like microscopic p-n junctions with currents in the range of 10⁻⁶-10⁻⁸ A characterized by a non-linear I-V curve.     

SYNGRAT,an electrooptically controlled tunable filter with a synthesized grating structure

A new design for a single-stage filter, calledsyn thesizedgrat ing structure (SYNGRAT), is presented and investigated theoretically. It is shown that, even for weak electrooptical effects, the tuning range can be as high as 450 channels for a channel separation of 1 nm. The electrooptically synthesized grating structure gives full control of the filter characteristics in terms of channel separation, side-lobe suppression and coupling efficiency over a very large tuning range. Efficient side-lobe suppression can be used to reduce the crosstalk. This concept gives new freedom of functionality and flexibility.     

Parameters effects on the surface morphology and structure of Nd:YAG nanopowders synthesized by co-precipitation method

In recent years, many attempts are made to produce Nd:YAG rods from its nanopowders instead of single crystals because of difficulties and complications of the crystal growth. The quality of new rods is strongly depended on the grain size and agglomeration amount of primary nanopowders. Co-precipitation method is one of the applicable methods to produce Nd:YAG powders with nano sizes; however, with usual co-precipitation method, the grains size are large and the agglomeration amount is high yet. This method contains different steps and parameters that any change of them leads in grains morphological and structural variations. This article’s purpose was to report the effect of different experimental parameters on controlling the quality of the Nd:YAG nanopowders. Some chemical and physical variations on usual co-precipitation method were designed based on particle growth process analysis and performed. By analyzing the result of performed experiments on the grains properties, a modified co-precipitation method could be achieved. This modified method allows the synthesizing of pure YAG powders with smaller grain size and lower agglomeration in comparison with usual co-precipitation technique. It is claimed that this modified method can be applied for a large number of materials produced by the usual co-precipitation technique.     

Rh的芳基化合物与含氮芳基卤代物交叉偶联反应机理研究

利用密度泛函理论(DFT)研究了Rh的芳基化合物与含氮芳基卤代物交叉偶联过程催化循环的微观反应机理.在B3LYP/6-31+G(d)基组水平上(Rh、I采用了赝势基组Lan L2DZ)优化了反应过程中所有化合物的几何构型并计算了频率,通过能量、频率和振动方式确定了中间体和过渡态的真实性.此外,在同等基组水平上还运用了分子中的原子理论讨论了成键临界点的电荷密度的变化,运用了自然键轨道理论讨论了键的性质与轨道间的相互作用.为了提高计算精度,在6-311++G(d,p)基组水平上计算了反应机理中所有物质在气相及溶剂化下的单点能,得到与6-31+G(d)基组计算相同的结论 .结论表明Rh(Ⅰ)起到了有效的催化作用,且计算所得结论与实验结果相符合.     

Effect of thermal annealing on the structure and magnetism of Fe-doped ZnO nanocrystals synthesized by solid state reaction

High purity Fe₂O₃/ZnO nanocomposites were annealed in air at different temperatures between 100 and 1200 °C to get Fe-doped ZnO nanocrystals. The structure and grain size of the Fe₂O₃/ZnO nanocomposites were investigated by X-ray diffraction 2θ scans. Annealing induces an increase of the grain size from 25 to 195 nm and appearance of franklinite phase of ZnFe₂O₄. Positron annihilation measurements reveal large number of vacancy defects in the interface region of the Fe₂O₃/ZnO nanocomposites, and they are gradually recovered with increasing annealing temperature. After annealing at temperatures higher than 1000 °C, the number of vacancies decreases to the lower detection limit of positrons. Room temperature ferromagnetism can be observed in Fe-doped ZnO nanocrystals using physical properties measurement system. The ferromagnetism remains after annealing up to 1000 °C, suggesting that it is not related with the interfacial defects.     

Rh的芳基化合物与含氮芳基卤代物交叉偶联反应机理研究

利用密度泛函理论(DFT)研究了Rh的芳基化合物与含氮芳基卤代物交叉偶联过程催化循环的微观反应机理。在B3LYP/6-31+G(d) 基组水平上(Rh、I采用了赝势基组LanL2DZ)优化了反应过程中所有化合物的几何构型并计算了频率,通过能量、频率和振动方式确定了中间体和过渡态的真实性。此外,在同等基组水平上还运用了分子中的原子理论讨论了成键临界点的电荷密度的变化,运用了自然键轨道理论讨论了键的性质与轨道间的相互作用。为了提高计算精度, 在6-311++G(d,p) 基组水平上计算了反应机理中所有物质在气相及溶剂化下的单点能, 得到与 6-31+G(d) 基组计算相同的结论。结论表明Rh(Ⅰ)起到了有效的催化作用,且计算所得结论与实验结果相符合。     

Chemistry, structure and electrochemistry of new lithium intercalation compounds synthesized via low temperature techniques

The present work exemplifies the interest of using the soft chemistry route to obtain high performance cathodic materials for rechargeable lithium batteries. Significant progress may be made either in obtaining new compounds or in providing improvements to the electrochemical performance of oxides already known. Two synthesis ways are developed in our laboratory: the sol-gel process and precipitation reactions. The electrochemical behaviour of three main groups of Li intercalation compounds is investigated and discussed in relation with the specific chemical and structural properties induced by the synthesis way. Paper presented at the 4th Euroconference on Solid State Ionics, Renvyle, Galway, Ireland, Sept. 13–19, 1997     

The influence of the metalloid species on the electronic structure of disordered transition-metal-metalloid alloys

The results of x-ray emission investigations of the electronic structure of Fe-Si and Fe-P disordered alloys are presented. Relying on the analysis of the spectrum parameters and data available in the literature, a qualitative model of the electronic-structure formation in disordered Fe-P alloys is proposed. The model allows one to account for the concentration dependence of the average magnetic moment per iron atom in the disordered systems investigated.     

Formation, structure and nonlinear optical properties of carbon nanoparticles synthesized by pulsed laser ablation

Carbon nanoparticles were prepared by pulsed laser ablation in argon gas for studying their formation, properties and applications. The nanoparticles were produced at different background pressures and different substrate temperatures, respectively. Micro-Raman spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to analyze the samples. Nonlinear optical limiting properties of the carbon nanoparticles were characterized using nanosecond laser pulses. Uniform carbon nanoparticles can be synthesized in a background gas for nonlinear optical applications. PACS 61.46.+w; 81.07.-b; 78.20.-e     

A comprehensive overview on the structure and comparison of magnetic properties of nanocrystalline synthesized by a thermal treatment method

This study reports the simple synthesis of MFe₂O₄ (where M=Zn, Mn and Co) nanostructures by a thermal treatment method, followed by calcination at various temperatures from 723 to 873 K. Poly(vinyl pyrrolidon) (PVP) was used as a capping agent to stabilize the particles and prevent them from agglomeration. The pyrolytic behaviors of the polymeric precursor were analyzed by use of simultaneous thermo-gravimetry analyses (TGA) and derivative thermo-gravimetry (DTG) analyses. The characterization studies were conducted by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Fourier transform infrared spectroscopy (FT-IR) confirmed the presence of metal oxide bands for all the calcined samples. Magnetic properties were demonstrated by a vibrating sample magnetometer (VSM), which displayed that the calcined samples exhibited different types of magnetic behavior. The present study also substantiated that magnetic properties of ferrite nanoparticles prepared by the thermal treatment method, from viewing microstructures of them, can be explained as the results of the two important factors: cation distribution and impurity phase of α-Fe₂O₃. These two factors are subcategory of the preparation method which is related to macrostructure of ferrite. Electron paramagnetic resonance (EPR) spectroscopy showed the existence of unpaired electrons ZnFe₂O₄ and MnFe₂O₄ nanoparticles while it did not exhibit resonance signal for CoFe₂O₄ nanoparticles.     

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.