Table of contents

Charge distributions in maleic anhydride (MAH) grafted polyethylene (g-PE)/ethylene - vinyl - acetate (EVA) copolymer laminates have been measured with materials of different composition. All laminates showed interfacial charge, the polarity and the magnitude of which are explained by interfacial polarization. It was found that the interfacial charge increased with the increase of MAH content in the g-PE, whereas it decreased with the increase of vinyl - acetate content in the EVA. This feature was attributed to the differences in electrical conductivity of the materials. Details of the experimental results are described.

TiN films with different preferred crystalline orientations have been prepared by a new cathodic arc evaporation technique - filtered arc deposition (FAD). The evolution of the preferred orientation in the TiN films was investigated systematically. Three kinds of preferred orientation, i.e. the (200), (111), and (220) preferred orientation, were achieved continuously in one deposition procedure by varying the film thickness and substrate bias which determines the bombarding energy of the deposited energetic particles. At the initial stage of film growth, the (200) orientation is dominant at a lower substrate bias. When the film becomes thicker and/or substrate bias increases, the preferred orientation will be (111) instead of (200). If the substrate bias increases further, then the preferred (220) growth occurs at any film thickness. The evolution of the preferred orientation from (200) to (111) and then to (220) is discussed on the basis of a new concept, the so-called overall energy which consists of the surface energy, the strain energy, and the stopping energy. The preferred orientation of TiN films is determined by the competition between the surface energy, the strain energy and the stopping energy.

The reflection electron energy loss spectra in gold have been calculated using a Monte Carlo approach. A description of Monte Carlo simulations based on the dielectric response theory for inelastic volume and surface excitations and the partial wave expansion method for elastic scattering was presented. The influence of surface excitations on the angular and energy spectra of reflected electrons was analysed. These excitations contributed to the energy spectra by single and plural inelastic loss peaks and by the multiple inelastic loss background. Surface plasmons were particularly important for glancing incident or escape electrons. The contribution from surface excitations to the angular spectra was significant for energy losses of a few tenths of an electronvolt but less significant for lower and higher energy losses. The angular spectra revealed single elastic scattering peaks for zero energy loss but flatter multiple elastic scattering curves for large energy losses. In all cases, Monte Carlo simulation results, including surface excitations, agreed very well with experimental data.

The sol - gel technique was used to fabricate second-order nonlinear optical active hemicyanine-doped silica film. It was found that self-alignment of hemicyanine molecules in the above film existed in the interfacial area. During the drying of the film, enhancement of second-order nonlinearity of the film was observed; this was concluded to have resulted from the transformation of protonated hemicyanine to monomeric hemicyanine. Shrinkage of the film during its drying also resulted in a blue shift of the absorption peak of hemicyanine H-aggregates. The shift was concluded to be due to dipole - dipole molecular interaction.

Experimental results for the DC magnetic field influence on the anisotropy of attenuation of ultrasound in ferrofluids are presented. The measurements were performed for the frequency 1.18 MHz, at the temperatures 10 and , with magnetic field strengths H = 39.8, 79.58 and . Comparison of the experimental results with the Taketomi theory allowed the determination of the cluster radius and the number density of the colloidal particles.

As speckles carry information about polarization, we have perfected a polarimeter using the Stokes - Mueller formalism from which we exploit the matrix to analyse speckle polarization. The noise effects on the Mueller matrix are minimized to separate experimental noise from the depolarization phenomenon. In order to simplify this depolarization phenomenon, we used a polished aluminium sample. We describe a statistical polarization analysis of the speckle grains which show the depolarization evolution of the speckle field. A global polarization analysis of the clipped speckle is then performed. The experimental results show that it remains polarized, independently of the observation direction, and only shows a slight polarization dispersion.

Bragg grating inscriptions have been performed within strained, high numerical aperture (NA), germania-doped, monomode fibres. It is shown that the complex dynamics of Bragg grating spectrum formation recorded in these fibres depend strongly on the strain applied to the fibre at the time of photoimprinting. Thermal stability studies of gratings written in strained fibres have been carried out through 30 min isochronal bleaching experiments. It is shown that the stretching of the fibre during the grating fabrication is an important parameter governing the decay of the grating. The implications of these observations are discussed from a practical point of view.

A new method for solving the electron Boltzmann equation in spatially inhomogeneous, steady state plasmas by using a multi-term approximation of the expansion of the electron velocity distribution function is presented. This method is a generalization of that approach which has been recently developed to solve the inhomogeneous kinetic equation using the conventional two-term approximation. The objective of using the multi-term approximation is to improve the accuracy of the spatial relaxation treatment of the electrons and to analyse the impact of higher order terms on the relaxation behaviour of both the electron velocity distribution function and the relevant macroscopic electron quantities. In this paper the higher order approximation is used to study the spatial relaxation of plasma electrons in a constant electric field. The investigations are performed for a model plasma, varying in particular some atomic data of the electron collision processes in this model, and for real plasmas. A detailed comparison of the results relevant to the isotropic and the first anisotropic component of the electron velocity distribution function which have been obtained in the multi-term approximation and in the conventional two-term approximation is made. Based on such studies the accuracy already reached concerning the spatial relaxation process by the simpler two-term approximation is critically evaluated.

A theoretical and experimental study of a Penning recombination laser operating in the negative glow plasma of a pulsed high-voltage hollow cathode discharge at intermediate pressures is presented. A detailed kinetic model of the plasma - chemical reactions and radiative processes determining the inversion population on the transition is developed and the time-dependent behaviour of both the plasma and laser parameters (excited states populations, electron and ion densities, electron and gas temperatures, output power and gain) is numerically calculated. An extended experimental investigation of the main plasma and laser parameters is made and a comparison with theoretical results is presented.

A variational evaluation of the electrostatic capacitance of an array of thick metal rods parallel to the ground is presented. A straightforward procedure allowing unlimited numerical accuracy is given, as well as a simple analytical approximation sufficient for all practical purposes. The method is applied to the Faraday shield of the JET ICRF antenna, where it yields a correction of order 40% to the classical thin wire formula.

The first part of this paper is devoted to the electrical characteristics of the air below the canopy of a pine and spruce forest. In fair weather conditions, the site influence, i.e. the filtering effect of the trees on air conductivity and electric field, is evidenced. Under disturbed weather conditions, the meteorological influence is depicted to show: (i) that electric fields sufficiently high to produce `point discharges' occur not only during thunderstorms but also during mist; (ii) that, by taking into account the gaseous ions produced by the point discharges, it becomes possible to understand on the one hand the field divergence with height observed in the mist, and on the other hand the detection of alternatively positive and negative gaseous clouds of charges during the thunderstorm.

The second part presents the results of chemical analysis performed below and just above the canopy on the same site and for the same period. Increased ozone and hydrogen peroxide concentrations were measured during the thunderstorm. It is shown that these chemical species were not only locally produced by photochemistry and/or transported from different (industrial and traffic) sources, but also arose from transient electrical point discharges in the forest under high electric field conditions. Their local concentration is shown to be influenced by the electrical discharge current density on the one hand, and by the local conditions of atmospheric stability and of water content, determining the evolution of the chemical products, on the other hand. Actually, after their production, the initially gaseous chemical products were shown to be involved in the local droplet chemistry.

Under specific weather conditions, ionic densities as well as chemical by-products of a forest therefore depend both on the electrodynamical characteristics of the lower atmosphere and on the local environmental conditions (liquid water content of the air and atmospheric stability) associated with the two different situations investigated, a mist and a thunderstorm.

A two-dimensional transient model is introduced to describe the heat transfer and fluid flow in pulsed gas tungsten arc (GTA) welding. The current continuity equation has been solved with the combined arc plasma - cathode system, independent of the assumption of the current density distribution on the cathode surface which was essential in previous studies of the arc plasma. The temperature distribution in pulsed GTA welding has been described, and the transition processes of temperature contours and current densities at the anode centre have been studied. Moreover, the effects of pulsed welding parameters on the dynamic process of current density at the anode centre are studied using the developed model. The results have been compared with experimental data measured by the probe method.

The transport and thermodynamic properties of gas under contaminated conditions with Cu and PTFE vapours have been determined taking into account the new introduction of molecular particles, produced by chemical interactions between gas and impurities like CuF, , and , making in total 25 species. The main concern of this work is to predict, from the obtained material properties data, the transient behaviour of gas wall-stabilized arcs with these types of contamination that inevitably happen in gas circuit breakers during arc interruption. The results indicate that the electron density and the electrical conductivity increase with Cu vapour contamination, especially below 9000 K, due to the lower ionization potential of Cu atoms, but are almost invariant with PTFE contamination. The thermal conductivity changes only at higher admixture ratios above around 10% for both impurities. Typical increases in due to molecular dissociation have been found at temperatures around 4000 K for Cu vapour and at 3000 - 8000 K for PTFE vapour contamination. The transient behaviours of contaminated gas arcs have been analysed for step-current modulation in the wall-stabilized arcs under the condition of no gas flow. The greater value of arc conductance with Cu vapour contamination broadens the arc current channel, exposing possible disturbance of the current interruption function in gas circuit breakers. PTFE vapour contamination does not affect the arc decay process in wall-stabilized arcs significantly.

A kinetic model for low-pressure dusty plasmas is developed. The Boltzmann and the dust charging balance equations are solved self-consistently. The dependence of the dust particle surface potential on plasma parameters and the effects of particulate contamination on the electron energy distribution are investigated for direct-current argon glow discharges. It is shown that the dust particle surface potential obtained from this model is higher than that obtained for a Maxwellian electron distribution, and that the higher energy portion of the electron distribution is reduced in the presence of dust particles. Electron-dust collection and electron - atom inelastic collisions are the main electron energy loss processes, and the electron energy loss due to electron-dust elastic collision is negligibly small for under the discharge conditions considered in this work, where E is the externally applied electric field and N is the argon atom density.

Experiments are reported on the number and displacement velocity of arc spots on CuCr and Cu cathodes in the current range 40 - 1500 A. The spot number was found to increase linearly with current. The average current per resolvable spot amounted to for CuCr and for Cu. For times after ignition random spot displacement R was observed, having mean square values of for Cu and for CuCr. The Cu spots showed brightness fluctuations with intervals of . Because of this obvious dynamics, the theoretical models of the spot plasma must be time-dependent. A self-consistent theoretical description of Cu and Cr plasmas is given, yielding the cathode temperature, plasma density, electric field strength, current density and plasma velocity in the time range 10 ns to 3 ms.

A method for determining both the thickness and the average stoichiometry of thin films is presented. The method is based on implanting radioactive -sources in the substrate prior to layer growth and measuring the energy loss of the -particles as they traverse the layer. Information about the stoichiometry is obtained through the comparison of the energy loss of -particles of different initial energies. Experimental examples for the utilization of this method are presented, in which Sb was grown on Si substrates, GaAs, InAs and AlAs on GaAs and YBCO on YSZ. The experimental precision which can be expected using the method is discussed, together with specific scenarios in which it could be advantageously applied.

A method of estimating the electron affinity value of an insulator has been developed. The measurement was carried out from the simultaneous detection of thermoluminescence and thermostimulated exoelectronic emission (TSEE) curves presented by the material. This is possible when the TSEE phenomenon is governed by the thermoionic model and when the electron concentration of the considered trap becomes weaker than that of thermally disconnected traps. The application to an -alumina single crystal shows that the electron affinity can be evaluated as from the thermostimulated peak at 275 K and at from the thermostimulated peak at 440 K. The validity of the model and the signification of the results are discussed.

Direct measurements of the bulk photovoltaic current density in photorefractive and crystals were performed at high light intensities. Illumination of the crystals with light pulses of a Q-switched frequency-doubled Nd:YAG laser (pulse duration 20 ns; light wavelength 532 nm) yielded a photovoltaic current through the crystals which charged a capacitor. Afterwards an electrometer measured the voltage of the charged capacitor. From this voltage and from capacity and exposure time the current density was deduced. For intensities above a contribution to which increased quadratically with light intensity I appeared for crystals. Co-doping with Mg and Zn lowered the quadratic component. Our results are in good qualitative and quantitative agreement with previous holographic measurements and support the claim that the intrinsic defect acts as a secondary photorefractive centre in at high light intensities.