Synthesis, structure, and magnetic behavior of a new gadolinium thiosilicate: Gd4[SiS4]3

Single crystals of the title compound were prepared from the elements by a solid state reaction in an iodine atmosphere. Data collection were carried out using a STOE image plate detector at 293 K. The compound crystallizes in the space group P2₁/n of the monoclinic system isotypically to Tb₄[SiS₄]₃ with four formular units in cells of dimensions: a=986.7(2) pm, b=1099.69(19) pm, c=1646.2(4) pm, β=102.67(3)°. The corresponding residual (all data) for the refined structure is 3.09%.The magnetic behavior of the compound was investigated on powdered samples in a temperature range between 1.7 and 300 K. The deviations from the Curie-behavior could be interpreted by the molecular field approach.     

Nanoparticle Formation Mechanism in CVD Reactor with Ionization of Source Vapor

A new chemical vapor deposition (CVD) method, called ionization CVD, was developed, to produce non-agglomerated nanoparticles in which reactant gases are charged. A sonic-jet corona discharger was used as an ionizer in the developed nanoparticle generator. For a tetraethylorthosilicate (TEOS)/O₂ chemical system, SiO₂ nanoparticles were prepared. All particles formed by the ionization CVD were charged unipolarly. SEM micrographs of particles showed that the repulsive Coulombic force between charged particles reduces their coagulation rate and produces non-agglomerated nanoparticles that have a relatively high number concentration and small size. An external field was used to collect the charged particles onto Si wafers. These collected samples indicated that the deposition of charged particles could be controlled by the external electric field. Particle concentration measurement with a condensation nucleus counter at various TEOS concentrations suggested the particle formation mechanism in the ionization CVD was an ion-induced nucleation.     

Thin films of metal-organic compounds and metal nanoparticle-embedded polymers for nonlinear optical applications

Thin films based on two very different metal-organic systems are developed and some nonlinear optical applications are explored. A family of zinc complexes which form perfectly polar assemblies in their crystalline state are found to organize as uniaxially oriented crystallites in vapor deposited thin films on glass substrate. Optical second harmonic generation from these films is investigated. A simple protocol is developed for thein-situ fabrication of highly monodisperse silver nanoparticles in a polymer film matrix. The methodology can be used to produce free-standing films. Optical limiting capability of the nanoparticle-embedded polymer film is demonstrated     

Magneto-optical spectroscopy of carbon nanotubes

We review our recent optical experiments on single-walled carbon nanotubes in high magnetic fields. The data revealed magnetic-field-induced optical anisotropy as well as broadening, splittings, and shifts of interband absorption and photoluminescence peaks. Quantitative comparison with theoretical predictions based on the Aharonov–Bohm effect is presented.     

Synthesis of nanoparticles in an atmospheric pressure glow discharge

Nanopowders are produced in a low temperature, non-equilibrium plasma jet (APPJ), which produces a glow discharge at atmospheric pressure, for the first time. Amorphous carbon and iron nanoparticles have been synthesized from Acetylene and Ferrocene/H₂, respectively. High generation rates are achieved from the glow discharge at near-ambient temperature (40–80°C), and rise with increasing plasma power and precursor concentration. Fairly narrow particle size distributions are measured with a differential mobility analyzer (DMA) and an aerosol electrometer (AEM), and are centered around 30–35 nm for carbon and 20–25 nm for iron. Particle characteristics analyzed by TEM and EDX reveal amorphous carbon and iron nanoparticles. The Fe particles are highly oxidized on exposure to air. Comparison of the mobility and micrograph diameters reveal that the particles are hardly agglomerated or unagglomerated. This is ascribed to the unipolar charge on particles in the plasma. The generated particle distributions are examined as a function of process parameters.     

Bulk, Surface and Morphological Features of Nanostructured Tin Oxide by a Controlled Alkoxide-Gel Path

SnO₂ particles and films were prepared by following a common sol–gel preparative route using tin (IV) alkoxide as the starting compound; the xerogels were thermally treated at 300, 500 and 700°C. The materials were characterized for phase composition-crystallinity, by X-ray diffraction, and for surface area and porosity, by N₂ adsorption isotherms. Both structural and morphological characterizations showed, at all temperatures, the formation of nanostructured SnO₂. By cyclic voltammetry and by electrochemical impedance spectroscopy the typical semiconductive behaviour of nanostructured materials was observed; the presence of Sn surface states with lower valence with respect to Sn(IV) was supported by both impedance and XPS analyses performed, also, in the valence band region. The isoelectric point (i.e.p.) of the material and its dependence on the temperature of calcination was obtained by means of electrophoretic mobility determinations as a function of the solution pH.M. Ionita: On leave from the Faculty of Industrial Chemistry, Applied Physical Chemistry and Electrochemistry Department, University Politechnica of Bucharest     

Suppression of particle generation in a plasma process using a sine-wave modulated rf plasma

Sine-wave modulated rf plasma has been used to control particle generation and growth in a plasma-enhanced chemical vapor deposition of silicon dioxide thin films using TEOS/O₂. The density and the size of particles generated in the plasma are greatly reduced when the plasma is modulated with sine-wave modulation at low modulation frequency (<1000 Hz). In addition, particle contamination on the films is significantly reduced also for nanoparticles, and the film growth rates at the range of modulation frequencies where particle generation are greatly reduced do not decrease appreciably. Compared to its counterpart pulse-wave modulation plasma, the sine-wave modulation plasma has demonstrated a better performance in terms of reduction of particle generation and film contamination, and of film growth rate. Thus, the sine-wave modulation plasma has shown as a promising method to be applied in the production of thin film with a high deposition rate and a low particle contamination.     

Spin wave spectrum of a magnonic crystal with an internally structured defect

We report a theoretical investigation of the spin wave spectrum of a magnonic crystal with a defect. The latter is considered as either a single or double layer with parameters (the values of the uniaxial anisotropy and/or layer thickness) different from those of the constituent layers of the magnonic crystal. It is shown that, depending upon the parameters of the defect, the spectrum may contain either one or several additional discrete (localized) modes within the magnonic band gaps, or even a mini-band of those.     

聚集效应对银纳米粒子的二阶非线性光学特性的影响研究

运用超瑞利散射(HRS)技术,对由KNO3诱导聚集的银纳米粒子的二阶光学非线性特性进行了实验研究.通过粒子尺寸测量和透射电镜观察，表明银纳米粒子的聚集方式为链状聚集.当聚集体平均尺寸为120nm时，银纳米粒子聚集体的HRS信号强度比聚集前增大了约15倍.分析表明，聚集导致银纳米粒子表面电场极化强度的增强和极化分布的改变，并通过表面和体贡献机理对二阶非线性极化过程产生影响. 关键词： 银纳米粒子 超瑞利散射 二阶光学非线性 聚集