A new approach to diffusion-like relaxation processes

We measured the time decay of the electric field in two dielectric non-crystalline solids and the data were analyzed in the framework of a new theoretical approach. It is observed that the application of this approach allows identifying different regimes in the relaxation process. At long times the dynamics end up by following a power law decay, which suggests the existence of a scale property in the interaction that defines the state of the materials and also the possibility of defining an invariant. We check the stability of this invariant under different time intervals, which means also a low dependence of it on noisy data.     

A possible new approach to the better understanding of crystallization kinetics

Literature data dealing with the structure of solutions, solubility of tiny particles, and the organization of small colloidal particles in solutions were summarized to support the evidence that the growth units in the crystallization by precipitation are identical with clusters or primary particles. These growth units may self-organize themselves in a kind of a three-dimensional network surrounding the growing crystals or secondary particles. This colloidal concept was used to explain qualitatively some experimental facts observed in the controlled double jet precipitation of sparingly soluble salts.     

A new theoretical description for anomalous birefringence of phase-separated glasses

Theoretical relationships between anomalous birefringence and microstructure of phase-separated glasses are proposed based on light scattering by particles and self-consistent effective-medium theory. A phase-separated and stretched glass generally has positive anomalous birefringence because the positive birefringence produced by form anisotropy of the secondary phase particles is larger than the negative birefringence produced by the distribution anisotropy of the particles. A postpulling heat-treated glass has negative birefringence because the form anisotropy decays and the distribution anisotropy remains. The magnitude of the anomalous birefringence increasesin particle size, particle size distribution variance, volume fraction of secondary phase, and uniaxial load. Results obtained by the theoretical model are consistent with available experimental results.     

A new approach to modification of polyelectrolyte capsule shells by magnetite nanoparticles

A new method for modifying polyelectrolyte capsule shells by magnetic nanoparticles is proposed: the in situ synthesis of magnetite by chemical condensation. The capsule cores were spherical calcium carbonate microparticles, while polymer shells were prepared using the layer-by-layer electrostatic adsorption of polyallylamine and polystyrene sulfonate. After in situ synthesis, nanoparticles of different shapes are formed on the capsule shell; the main crystalline phase of nanoparticles is magnetite. The thus obtained nanocomposite capsules are highly sensitive to external magnetic fields.     

A new equation for the temperature dependence of density of saturated aqueous solutions of electrolytes

A new empirical three-parameter equation d = d₀ exp[β′(T – T₀)²] (where β′, d₀, and T₀ are constants for a salt) has been proposed to describe the dependence of density d (g/ml³) of saturated aqueous solutions of electrolytes on temperature T (K) in the whole range of temperature in which solubility increases or decreases with an increase in temperature.     

Total pressure dependence of doping element incorporation during the chemical vapour deposition of epitaxial silicon

Starting from the literature on doping element incorporation at atmospheric and lower pressures the partial pressure of the dopants available within the deposition system is selected as a uniform basis of reference for the total pressure dependence of the doping element incorporation. It is shown that also at reduced pressures the incorporation equilibria of phosphor and arsenic, the author previously derived from the temperature dependence of the doping element incorporation may be used.     

An approximation to the description of growth of coherent precipitates

The tree-dimensional growth of a spherical coherent particle in an isotropic infinite matrix is considered in the frame of the stationary solution of the classical diffusion equation applying WAGNERS approximation in a varied manner and taking into account both the concentration dependence of the diffusion constant D and the influence of elastic energy. From the obtained results qualitative conclusions are drawn on the stability of the precipitates during the OSTWALD-ripening process in dependence on their size. The evaluations doubtlessly confirm the higher stability and the favoured growth of the larger precipitates.     

A new approach to thin film crystal silicon on glass: Biaxially-textured silicon on foreign template layers

We propose a new approach to growing photovoltaic-quality crystal silicon films on glass. Other approaches to film Si focus on increasing grain size in order to reduce the deleterious effects of grain boundaries. Instead, we propose aligning the silicon grains biaxially (both in and out of plane) so that (1) grain boundaries are ‘low-angle’ and have less effect on the electronic properties of the material and (2) subsequent epitaxial thickening is simplified. They key to our approach is the use of a foreign template layer that can be grown with biaxial texture directly on glass by a technique such as ion-beam-assisted deposition or inclined substrate deposition. After deposition of the template layer, silicon is then grown aligned to the template and subsequently thickened. Here, we outline this new approach to silicon on glass, describe initial experimental results and discuss challenges that must be overcome.     

A variational approach to cellular crystal growth

The variational method is applied to the study of crystal growth from melt under the condition that the boundary between the liquid and solid phases has a cellular structure. The surface energy of the interface is taken into account.     

A new approach of creating Au‐Sn solder bumps from electroplating

A homogeneous melting eutectic Au/Sn solder bump for laser chip application has been developed. The under‐bump metallization consists of a Ni wetting layer, a plating seed layer of Pt/Au/Ti multi‐layer scheme. The solder is electroplated as a sequence of Ni, Au and Sn layers. The bump can be exposed to multi‐step reflow cycles. The reflow of the solder as plated starts with a phase forming process in the solid state which results in an eutectic‐like phase and the near eutectic dand z phases. The dand z phases dissolve during the liquid state stage of the reflow at temperatures between 300 and 350 °C. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Multicell model of La<Subscript>3</Subscript>Ga<Subscript>5</Subscript>GeO<Subscript>14</Subscript> crystal: A new approach to the description of the short-range order of atoms

The multicell model alternative to the model of mixed atomic sites used now is proposed for a single crystal of La₃Ga₅GeO₁₄ belonging to the langasite family. The multicell consists of four unit cells. In three identical cells of the structure, atoms adapt to the Ge atom occupying one of the two 2d positions on the threefold symmetry axis. In the fourth cell, atoms surround the Ge atom located at the 1a position. The multicell model allows one to study the short-range order of atoms by the methods of classical structure analysis based on Bragg scattering. Four high-resolution data sets measured at 295 and 111.5 K are used in the study. The results are obtained with high relative precision (space group P321, Z = 1; at 295 K a = 8.2020(6) Å and c = 5.1065(6) Å, R/wR = 0.81/0.73% for 3829 unique ref lections; at 111.5 K a = 8.1939(1) Å and c = 5.1022(4) Å, R/wR = 0.85/0.76% for 3880 reflections).     

A new method for the growth of GaAs epilayer at low H2 pressure

A method of growing thin GaAs epitaxial layers has been perfected by working under low hydrogen pressure. Layers of good crystalline quality can be obtained with a growth rate of 0.1 μm/min for temperatures ranging from 520 to 750°C and pressures ranging from 25 to 600 Torr. By working under low pressure, the various substrate-layer and layer-layer impurity profiles are more abrupt than at atmospheric pressure. Autodoping can be eliminated thus permitting the use of very low resistivity tellurium doped substrates. Good quality microwave components have been realized with the layers obtained by this technique.     

A statistical description of dislocation mobility at stresses close to the threshold of unlocking from the atmosphere of adsorbed impurities

A model is developed to describe the effect of impurities adsorbed by dislocation cores on the dislocation mobility in materials with a high potential relief (Peierls barriers). It is shown that the statistical fluctuations in the impurity distribution, which are due to the adsorption randomness, significantly change the conditions of dislocation kink formation. This model explains and describes the qualitative phenomenon experimentally found in semiconductor crystals: the immobilization of dislocations at stresses σ below a certain threshold value σ _unl (σ < σ _unl ). An analytical solution is obtained based on an analogy with the well-studied and urgent problem of calculating the ruin probability for insurance or other financial companies in the mathematical theory of mass service. A slight generalization of the methods developed in the theory made it possible to calculate the degree of “spread” of the threshold stress due to the random character of impurity distribution as well.     

Time dependence of electrical resistance at high pressure in some tellurium based amorphous alloys

Electrical resistance measurements are reported for amorphous In₂₀Te₈₀ and Cu₂₅Au₅Te₇₀ alloys up to a pressure of 80 Kbar using a Bridgman anvil apparatus and a four lead arrangement to measure resistances. The amorphous samples are produced by liquisol quenching. The resistance shows time dependent changes which are analysed in detail. The contention that there is a pressure-induced transformation from the amorphous to the crystalline phase is confirmed by X-ray diffraction of samples recovered after they were pressurised to 35 Kbar in a hydrostatic environment.     

A novel approach to Au@SiO2 core-shell spheres

A novel synthesis method was described to prepare Au@SiO₂ core-shell spheres, using a commercial gold colloid and tetraethyl orthosilicate as the precursors. The synthesis concept was based on surface modification of the gold nanoparticles with a binary system of surfactants, or using both of 2-Mercapto-ethanol and (3-Aminopropyl)-trimethoxysilane together, and the Stöber processing. The shape and size, and silica coatings of the resultant particles were investigated by transmitting electron microscopy (TEM). The Au@silica core-shell spheres, each containing a single gold nanoparticle or an aggregate of several gold nanoparticles at the center, could be prepared.     

Application of a microrheology technique to measure the viscosity of disodium cromoglycate liquid crystal

Although the science of rheology is well established, some important challenges still persist to measure the viscoelastic properties of complex fluids, such as biological solutions and liquid crystals (LC). In this work, we present a method, based on the calculation of the step length of Brownian particles, to measure the effective local viscosity sensed by microscopic objects in the LC host. This approach allowed us to quantify the anisotropy of the viscosity, and it could also be extended to measure the local viscosity in other nonhomogeneous media. We also present a new guided light dark-field microscopy technique that was used to track particles during our experiments.     

Percolation of polar nanoregions: A dynamic approach to the ferroelectric phase transition

The percolative nature of the ferroelectric phase transition in a potassium tantalate niobate (KTN) crystal is studied using time domain dielectric spectroscopy. A relaxation process linked to the off-center niobium ions is observed. The dynamic nature of this relaxation shows well defined temperature regimes in which it progresses from independent (Arrhenius) to cooperative (Vogel–Fulcher–Tammann) behavior. A recursive fractal model was applied in order to interpret the data obtained from the dielectric measurements. The structural parameters, ν and μ, derived from the correlation functions, enable the investigation of the onset of the phase transition in terms of the fractal dimensions of the polarization excitation.