The transportation of brine inclusions in rock salt in a temperature field of a heat source

There are three kinds of brine inclusions in a natural crystal of halite, as follows: a) inclusion totally filled with brine; b) inclusions partially filled with brine and gas (SORBY inclusions) and c) inclusions totally filled with gas. Type a) and b) migrate in the crystal under the influence of a temperature gradient. Type c) inclusions do not move. This paper deals with the question whether the migration causes tracks in the crystal or not. In general, no tracks are caused directly by the motion of inclusions. However, there are some phenomena which can be explained as tracks. The reasons of these phenomena are examined and described.     

Photo-induced phenomena in chalcogenide glass: Comparison with those in oxide glass and polymer

Two topics, the both being related with localized states in non-crystalline solids, are studied. One is a comparison of photo-induced phenomena in oxide, chalcogenide, and organic materials. Despite of different inorganic and organic structures, there exist many similarities in photo-induced phenomena, which can be ascribed to excitation of localized electronic states. The other topic concerns photo-induced phenomena induced by linear and non-linear excitation. A result on As₂S₃ demonstrates that band-gap excitation by one- and two-photon processes provides different changes. It is suggested that the two-photon process occurs resonantly at around localized states in amorphous materials, and the process plays important roles in the structural change.     

Aggregation model for the gelation of a sol starting from the processing conditions

A stochastic computational model for the gelation of a sol is explained and tested for the case of neutral silica aerogels. The computational model produces the final structure of the sol after gelation, using two of the several physical phenomena occurring during gelation of sols. Diffusion, represented by Brownian motion, is modeled by a random walk, and chemical reactions are incorporated through a stochastic aggregation model using a probability function; the latter determined in terms of the processing conditions based on the knowledge of the cluster formation energies. The two phenomena are coupled by a Monte Carlo simulation. The analysis of the connected structure and its functionality is demonstrated for neutral silica aerogels. It is shown how the gelation process can be controlled to obtain different structures for different application requirements. The only parameters required by the model are the density and the processing conditions. The results of the model show that those parameters strongly affect the structure of the generated samples. Therefore, processing conditions could be selected to produce aerogels with structures tailored to specific applications, which would constitute a major achievement in aerogel fabrication.     

Nonstoichiometry in oxides

Nonstoichiometry phenomena have been extensively studied in oxide systems. It is proposed that some models developed for oxides could be usefully extended for understanding nonstoichiometry in other systems.

Many aspects of nonstoichiometry are closely connected with order-disorder phenomena. The broad field of nonstoichiometric compounds extends from variable composition phases with randomly distributed point defects (entropy controlled systems) to sets of discrete intermediate sompounds, each corresponding with a fully ordered state resulting from assimilation or annihilation of defects (enthalpy controlled systems). Between these two extreme cases, one finds intermediate situations such as clusters with a short range order, shear structures with possibly swinging shear planes, coherent intergrowths and infinitly adaptive structures in which any composition, even irrational, corresponds with an unique ordered structure.     

Transport phenomena analysis for boron CVD in a horizontal cold-wall reactor

The transport phenomena in a horizontal cold-walled semicircular reactor are analyzed for the CVD of boron from BCl₃ and H₂. The mixed problem of energy, momentum, and mass conservations is solved by a simple finite difference method. The concentration of the B-reactant on the deposition surface is substituted by the sum of equilibrium mole fractions of the B-containing gas species. The profiles of temperature, velocity, and reactant concentrations in the CVD reactor are illustrated, and the boron deposition rate profile along the substrate is predicted. The effect of the reactant input composition on the deposition rate is calculated, and compared with the experimental data.     

Structural properties of silica surface: a classical molecular dynamics study

The structural properties of silica's free surface affect a number of phenomena, such as surface catalysis or the deposition of metallic films. In this work we present a study on the structure of the silica surface based on molecular dynamics simulations. We have computed the bond-angle and bond-length distribution functions at different surface penetrations, as well as surface defect properties. All these features are affected by the Si/O ratio in the surface region which differs from the interior.     

A speculation concerning the origin of long-range crystallographic order in polytypic and related crystals

It is suggested that long-range crystallographic order may be mediated by acoustic vibrations which have their origin in thermoacoustic phenomena and on which structural details exert a filter effect.     

Dielectric and mechanical relaxation behavior in poly(butyl methacrylate) isomers

Dielectric and mechanical spectroscopies have been used to study the dynamics in poly(butyl methacrylate) isomers (namely PnBMA, PiBMA and PtBMA). This analysis has revealed four relaxation processes: δ, γ, β and α and has allowed the observation of the evolution of molecular relaxation phenomena with the lateral chain steric hindrance. The α relaxation is associated with the glass transition of the isomers and depends strongly on the lateral chain structure. The secondary relaxation phenomena are very similar for the three isomers. Arrhenius diagrams have been plotted for the three isomers. The activation parameters have been calculated from Arrhenius equation for the sub-glass processes δ and γ whereas the dynamics are characterized by a Vogel–Fulcher–Tamman law for the α relaxations. With a deconvolution procedure for the α and β processes, a departure from the Arrhenius law of the β process in the vicinity of the merging between the α and β phenomena is observed for each isomer.     

Mehrphotonen-Absorption in Kristallen und ihre Anwendungen. Will Kleber zum Gedenken

The paper summarily reports on absorption phenomena occurring in crystalline matter, whereby excitation states are obtained with more than one photon participating in the elementary excitation act. This is possible both by simultaneous multiphoton absorption and by a consecutive, step-by-step absorption of a number of photons (2 photons in most reported cases). Among possible applications of these phenomena, laser or 2-photon spectroscopy, infrared quantum counters (IRQC) and infrared frequency converters (frequency up conversion) have raised particular interest recently.     

Simplified Treatment of Transient Doping Behaviour in CVD(I)

Physiochemical reasons are discussed for the delayed response of doping concentrations within epitaxial semiconductors (Si and III-V compounds) to changes of the input partial pressure of dopant species for CVD processes. A simplified circuit representation for doping is used that takes care of five serial process steps, the first three of which are the topic of this work (Part I). Among the corresponding storage phenomena in which the gas phase is involved, those with adsorptional influences are to be expected as most important for transient behaviour. Storage of dopant species at the semiconductor surface is included into the circuit representation, as it has been done by Reif et al. for silicon doping. Moreover, adsorption at the reactor wall is represented approximately, assuming equilibrium with the gas phase.     

Use of a small-voltage electrical response to measure sodium motion in rf sputtered SiO2 films

Low voltage transient and ac responses of rf sputtered SiO₂ films are studied in the temperature range 473–593 K. Experimental results can be explained in terms of a model with trapped carriers and with only one type of recombining mobile charge carriers. Two distinct phenomena clearly appear in transient current curves; the rapid one is attributed to the space charge effect, the other to generation recombination. Theoretical and experimental curves are in good agreement. The concentrations and mobilities are deducted of carriers identified as Na⁺ ions. Concentrations values are compared (for glass and silica substrates) with ion microprobe analysis results.     

Stable Layer Systems with Diffusion Barrier Arrangements in Thin Film Technology

The physical and chemical interaction processes in thin film arrangements are followed by different ageing phenomena which influence the stability of their physical parameters. These determine the reliability of the electronic components existing of thin films. On the base of own experimental investigations on tantalum and its oxides, beryllium oxide and tantalum-rhenium alloys technological aspects and the application of new materials for lowering the ageing intensity are considered.     

Solute segregation in a lid driven cavity: Effect of the flow on the boundary layer thickness and solute segregation

Our objective in the present work is to study the effect of convective flows, ranging from laminar to fully turbulent, on solute segregation in directional solidification configurations. To do so, numerical simulations performed in a model 2D lid driven cavity; the problem parameters, apart from the species molecular diffusion coefficient, are the lid and growth velocities. Purely diffusive to fully convective mass transport conditions are modelled in our parametric study. In parallel, a scaling analysis aiming at the determination of the solute boundary layer thickness is proposed. The results show that a single non-dimensional number, based on the interface stress, is able to capture the physics of the solute transport phenomena.     

Space-resolved dynamics of a tracer in a disordered solid

The dynamics of a tracer particle in a glassy matrix of obstacles displays slow complex transport as the free volume approaches a critical value and the void space falls apart. We investigate the emerging subdiffusive motion of the test particle by extensive molecular dynamics simulations and characterize the spatio-temporal transport in terms of two-time correlation functions, including the time-dependent diffusion coefficient, the frequency-dependent conductivity, as well as the wavenumber-dependent intermediate scattering function. We rationalize our findings within the framework of critical phenomena and compare our data to a dynamic scaling theory.     

Kerr Effect Studies in Liquid Crystalline Substances

The static and dynamic pretransitional behaviour was investigated by the electric Kerr effect in three nematic substances above the clearing point. The measured Kerr constants exceed that of nitrobenzene by more than a factor of 50…︁ 80 which are due mainly to pretransition phenomena and the strong dipole moments of the compounds. A formula is given for the calculation of the Kerr constant. The latent heat at the nematic-isotropic phase transition calculated from the temperature dependence of the Kerr constant by means of the Landau theory is in good agreement with the experimental values. Size and relaxation behaviour of pseudonematic domains are determined by Kerr effect measurements.     

The strain relaxation in a lattice-mismatched heterostructure

Strain relaxation phenomena of the heteroepitaxial lattice-mismatched semiconductors have been investigated. The relationship between the residual in-plane strain and the width of the misfit cell was obtained geometrically. The residual in-plane strain was calculated for various film thicknesses by using the energy minimization theory on the misfit cell in the In_xGa_1−xAs/GaAs(1 0 0) heterostructure system. A generalized strain relaxation model is presented on the basis of the energy minimization theory.     

Macroscopic Phenomena in Polymer Liquid Crystals

Rigid and semirigid backbone polymers based on either helical structures or conjugated aromatic bonding often exhibit nematic ordering in solution or as melts. Because of the large axial ratio of these molecules, the resulting nematic phases exhibit hiahly anisotropic elastic and viscous properties. The study of macroscopic phenomena in these liquid crystals serves two purposes. First is the elucidation of the relationship between macroscopic material parameters and molecular properties. Second is the understanding of the consequence of the highly anisotropic nature of these materials, namely new phenomena not observed in low molecular weight liquid crystals. Several new phenomena will be described related to the Frederiks transition and flow instabilities.     

Nanofabrication in transparent materials with a femtosecond pulse laser

Femtosecond lasers have been applied for materials processing when high accuracy and small structure size are required. Various induced structures have been observed inside glasses after the femtosecond laser irradiation. We report the femtosecond laser induced refractive-index change, space-selective valence state change of active ions, formation of nanograting, and precipitation and distribution of nanoparticles. We systematically studied the morphology of structures that are induced in the bulk of transparent materials by the tightly focused femtosecond laser radiation. Rugby-ball-like asymmetric induced structures were observed inside Ag⁺-doped silicate glass. These structures are due to the aggregation of Ag nanoparticles at the depth of the focal point. The size of the induced structure depended on the time interval between successive femtosecond laser pulses. In the case of zinc-tellurite glass, TeO₂ rich parts were formed in the center of the focal spot, while zinc migrated to the outside. The mechanisms of the observed phenomena are discussed.     

Change of the X‐Ray Polarisation State by Diffraction

An introduction to polarisation phenomena observed at X‐ray diffraction is given. Using an arrangement being analogous to optics of visible light, the polarisation state of the diffracted beam has been investigated using quarter wave plates. Depolarisation phenomena at the excitation of a noncoplanar many‐beam geometry are shown for lithium fluoride samples. The results are explained in terms of incoherent diffraction, as known from light optics.