Synthesis of lanthanum–strontium manganites by oxalate-precursor co-precipitation methods in solution and in reverse micellar microemulsion

Nanostructured lanthanum–strontium manganites were synthesized using two different co-precipitation approaches, one in bulk solution, and the other in reverse micelles of CTAB/1-hexanol/water microemulsion. In both cases, precursor cations were precipitated by using oxalic acid. The properties of the materials synthesized by using these two methods were compared in order to reveal potential advantages of the microemulsion-assisted approach. The influence of the annealing conditions on the properties of synthesized manganites was investigated by using X-ray diffraction, transmission electron microscopy, differential thermal analysis, thermogravimetric analysis and magnetic measurements.     

Electrodeposition of aligned arrays of ZnO nanorods in aqueous solution

We report electrodeposition of ZnO nanorods from aqueous solution at low temperature (～80 ^°C). The substrates used were thin films of silver grown on glass by thermal evaporation. Nanorods were grown by electrodeposition from aqueous solution of Zinc Nitrate and Hexamethylenetetramine (HMT). The growth process lasts for up to 4 h and the optimum potential for growth of nanorods was ?0.8 V. The nanorods have a well-defined hexagonal morphology and have a Wurtzite structure. The nanorods were characterized by different techniques and have a band gap of 3.08 eV. The width of nanorods has a bimodal distribution.     

Critical anomaly in the viscosity of a nonionic micellar solution

The critical enhancement in the viscosity has been examined using a low-shear rotational viscometer for a nonionic micellar solution of tetraethylene glycol n-decylether (C₁₀E₄) in water. The estimated value ø=0.041±0.005, which characterizes the temperature dependence of the viscosity very close to its critical point of mixing, is in excellent agreement with that predicted by the dynamical universality for a fluid.     

Facile synthesis and characterization of glass/cobalt core/shell composite spheres with tunable shell morphologies

Polyhedral cobalt microcrystals assembled on hollow glass spheres are successfully synthesized by a facile and easy-control hydrothermal reduction process, and thus hierarchical glass/cobalt core/shell composite hollow spheres are fabricated with low-density (0.96 g cm⁻³). By properly tuning the process conditions and the component of the reaction solution, a series of composite spheres with gradient in morphologies of the shell layer can be prepared. Based on a series of contrast experiments, the probable formation mechanism of the core/shell hierarchical structures is proposed. The magnetic properties of the products are studied and the results demonstrate that the composite spheres present ferromagnetic properties related to the special shell morphologies. The composite hollow spheres thus obtained may have some promising applications in the fields of low-density magnetic materials, conduction, and catalysis, etc. This work provides an additional strategy to prepared core/shell composite spheres with tailored shell morphology and magnetic properties.     

Facile synthesis and characterization of Co nanoplatelets with tunable dimensions via solution reduction process

Plate-like Co nanoparticles with different sizes were synthesized by solution reduction process. The size of Co nanoplatelets can be tuned by varying the concentration of CoCl₂·6H₂O and the dosage of N₂H₄·2H₂O. The Co nanoplatelets with the different size all exist in both fcc and hcp crystal structures. The normal direction of the nanoplatelets is perpendicular to the (002) planes of hcp phase or to the (111) planes of fcc phase. The saturation magnetizations of the samples are lower than the corresponding bulk value. The coercivities of the samples vary with the phase content and the particle size. The shape control mechanism was discussed.     

Structure, morphology and electrochemistry of doped lithium cobalt oxides

The structure, morphology and electrochemical performance of LiCoO₂ powders doped with various trivalent cations such as M³⁺=Ni³⁺, Al³⁺, and B³⁺ have been investigated. X-ray diffraction patterns and FTIR data show that LiCo_1−yNi_yO₂ oxides display a solid solution in the whole range 0≤y≤1, while the solubility limit of LiCo_1−yAl_yO₂ and LiCo_1−yB_yO₂ materials is about y=0.35. Electrochemical features of LiCo_1−yNi_yO₂ cathode materials show remarkable stability in their charge-discharge profiles. Aluminum substitution also stabilizes the two-dimensional framework and induces an increasing average cell potential than for LiCoO₂. The overall capacity of the LiCo_1−yB_yO₂ oxides has been reduced due to the sp metal substitution, however, a more stable charge-discharge cycling characteristic has been observed when electrodes are charged up to 4.4 V as compared to the performances of the native oxides. Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000.     

Magnetic properties and surface morphology of layered In2Se3 crystals intercalated with cobalt

The magnetic properties of layered Co _x In₂Se₃ crystals electrochemically intercalated with cobalt in an external magnetic field and without a magnetic field and the morphology of the van der Waals surfaces of layers of these crystals have been investigated. It has been found that the ferromagnetic ordering at room temperature is observed only for Co _x In₂Se₃ crystals intercalated in an external magnetic field. These crystals are nanocomposite materials that consist of a layered matrix and arrays of nanorings and nanowires formed from Co nanocrystals on the van der Waals surfaces of the In₂Se₃ layers. Cobalt nanocrystals in Co _x In₂Se₃ crystals have a pyramidal equilibrium shape, which is characteristic of the face-centered cubic crystal structure, and their geometrical sizes are of the order of a few nanometers. The specific features of self-organization of cobalt magnetic nanostructures on the van der Waals surfaces of layered semiconductor crystals during their electrolytic intercalation in a magnetic field and the magnetic properties of these structures have been considered.     

Coherent light with tunable polarization from single-pass free-electron lasers

Tunable polarization over a wide spectral range is a required feature of light sources employed to investigate the properties of local symmetry in matter. In this Letter, we provide the first experimental characterization of the polarization of the harmonic light produced by a free-electron laser and demonstrate a method to obtain free-electron laser harmonics with tunable polarization. Experimental results are successfully compared with theory. Our findings can be expected to have a deep impact on the design and realization of experiments requiring full control of light polarization.     

Strain relaxation and surface morphology of high indium content InAlAs metamorphic buffers with reverse step

Low-temperature step-graded high indium content InAlAs (In% = 0.75) metamorphic buffer layers with reverse step layer grown on GaAs substrate by molecular beam epitaxy are investigated in this paper. The composition and the strain relaxation of the top InAlAs layer are determined by high-resolution triple-axis X-ray diffraction measurements, which show that the top InAlAs layer is nearly fully relaxed and the growth parameters for these samples have little influence on the strain relaxation ratio. Surface morphology is observed by reflection high-energy electron diffraction pattern and atomic force microscopy. The surface morphology is found to depend strongly on both the growth temperature and the As flux. Compared with other samples, the sample growth under the optimized conditions has the smallest value of root mean square surface roughness. Furthermore, the ω − 2θ and ω scans of the triple-axis X-ray diffraction and transmission electron microscopy result also show the sample grown under the optimized conditions has good crystalline quality.     

Zinc silicates with tunable morphology by surfactant assisted sonochemical route suitable for NUV excitable white light emitting diodes

The cationic surfactants assisted ultrasound route was used to prepare Dy³⁺ doped Zn₂SiO₄ nanophosphors. The final products were characterized by powder X-ray diffraction (PXRD), ultraviolet visible spectroscopy, scanning electron microscopy, transmission electron microscopy and photoluminescence. Orthorhombic phase of Zn₂SiO₄:Dy³⁺ (JCPDS card No. 35-1485) was confirmed from PXRD. It was evident that the morphology of spherical and broom like structures were obtained with epigallocatechin gallate (EGCG) and cetyltrimethylammonium bromide (CTAB) surfactants respectively. Further the size and agglomeration of the products were varied with surfactants concentration, sonication time, pH and sonication power. The probable formation mechanisms to obtain various micro/nano superstructures were discussed. The characteristic PL peaks were observed at 484, 574 and 666 nm due to the electronic transitions ⁴F_9/2 → ⁶H_j (j = 15/2, 13/2, 11/2) of Dy³⁺ ions upon excited at NUV pumping wavelength of 350 nm [⁶H_15/2 → ⁶P_7/2 (⁴M_15/2)]. The Judd–Ofelt intensity parameters and radiative properties were estimated by using PL emission data. The photometric studies indicated that the obtained phosphors could be promising materials in white light emitting diodes (wLED’s). The present synthesis route was rapid, environmentally benign, cost-effective and useful for industrial applications such as solid state lighting and display devices.     

Temporal oscillations of the shear stress and scattered light in a shear-banding-shear-thickening micellar solution

The results of optical and rheological experiments performed on a viscoelastic solution (cetyltrimethylammonium bromide + sodium salicylate in water) are reported. The flow curve has a horizontal plateau extending between two critical shear rates characteristic of heterogeneous flows formed by two layers of fluid with different viscosities. These two bands which also have different optical anisotropy are clearly seen by direct observation in polarized light. At the end of the plateau, apparent shear thickening is observed in a narrow range of shear rates; in phase oscillations of the shear stress and of the first normal stress difference are recorded in a shearing device operating under controlled strain. The direct observation of the annular gap of a Couette cell in a direction perpendicular to a plane containing the vorticity shows that the turbidity of the whole sample also undergoes time dependent variations with the same period as the shear stress. However no banding is observed during the oscillations and the flow remains homogeneous.     

On uniqueness of solution of a reverse problem of magnetic location

An analysis of solution uniqueness for a problem of magnetic dipole localization based on known values of magnetic field strength vectors at two points is presented. It is shown that a usage of two triples (pairs) of sensors is sufficient to solve a 3D (2D) problem of arbitrary magnetic dipole localization with a satisfactory number of crude errors.     

Coherent and tunable radiation with power enhancement from surface plasmon polaritons

Surface plasmon polaritons excited by an electron beam can be transformed into coherent and tunable light radiation waves with power enhancement in the simple structure of a metal film with a dielectric medium loading. In this paper, the process of the radiation transformation of this radiation, and the dependencies of the radiation characteristics on the parameters of the structure and the electron beam are studied in detail. The radiation power enhancement is greatly influenced by the beam energy and the film thickness in the infrared to ultraviolet frequency region. Up to 122 times radiation power enhancement and 6.5% radiation frequency tuning band can be obtained by optimizing the beam energy and the parameters of the film.     

Dark pulses with tunable repetition rate emission from fiber ring laser

We demonstrated the experimental observation of the dark pulses with tunable repetition rate from an erbium-doped fiber ring laser. A considerable length of high nonlinear fiber is incorporated into the fiber ring laser to enhance the nonlinear intensity. In our experiment, both bright and dark pulses can be observed under the conditions of appropriately setting of the device in the cavity. Further study showed that the dark pulse is formed due to the cross coupling between two different lasing wavelengths. Particularly, dark pulse-train with multiple repetition rates was observed from the laser cavity and the repetition rate switchable operation can be realized by simply adjusting the polarization controller (PC) in the cavity. The operation of multiple repetition rates of dark pulses was further experimentally investigated and detected as a result of pulse splitting of each component with different wavelength.     

Electrodeposition of nanostructure objects with pentagonal symmetry

It is shown that electrodeposition can be used to obtain hollow metallic nanoparticles with pentagonal symmetry and unique properties. This technique seems to be promising for producing fundamentally new nanomaterials in the form of films, coatings, and powders, and also for making nanofilters.     

Synthesis of Co-Cu-Zn doped Fe3O4 nanoparticles with tunable morphology and magnetic properties

Co-Cu-Zn doped Fe₃O₄ nanoparticles can be successfully synthesized using a simple method. The particles in the size range 20−400 nm with different regular shapes i.e. sphere-like, regular hexane and tetrahedron are controllably achieved by changing the metal ion concentration. Compared to pure Fe₃O₄ without dopants, Co-Cu-Zn doped Fe₃O₄ nanoparticles exhibit better microwave absorbing properties at 2−18 GHz. Among three Co-Cu-Zn doped Fe₃O₄ nanoparticles with different morphologies, tetrahedral Co-Cu-Zn doped Fe₃O₄ nanoparticles represent a better dielectric loss in high frequency range. This work is believed the first known report of Co-Cu-Zn doped Fe₃O₄ nanoparticles with tunable morphology and magnetic properties through the hydrothermal process without using any organic solvents, organic metal salts or surfactants.     

NaCl稀溶液结晶的分形形态研究

通过光学显微镜观察NaCl稀溶液在玻璃基底上快速蒸发结晶形成了完整的立方晶体、DLA凝聚体和形状复杂的凹凸状结晶3种形貌.对复杂的凹凸状结晶进行分析,认为不完整的NaCl小晶粒构成了一个个微小的生成元,以随机Koch曲线的生长方式自组织地顺次相互连接起来,指出此类结晶符合随机Koch曲线,是远离平衡态下的自组织现象.通过改变观测尺度求维数的方法,得到分形维数是1.15±0.06,与Koch曲线相近.