Table of contents

The interaction of CO₂, Nd:YAG, excimer and high-power diode laser (HPDL) radiation with the surface of an Al₂O₃/SiO₂ based ceramic was found to effect significant changes in the wettability characteristics of the material. It was observed that interaction with CO₂, Nd:YAG and HPDL radiation reduced the enamel contact angle from 118° to 31°, 34° and 33° respectively. In contrast, interaction with excimer laser radiation resulted an increase in the contact angle to 121°. Such changes were identified as being due to (i) the melting and partial vitrification of the Al₂O₃/SiO₂-based ceramic surface as a result of interaction with CO₂, Nd:YAG and HPDL radiation; (ii) the surface roughness of the Al₂O₃/SiO₂-based ceramic increasing after interaction with excimer laser radiation; and (iii) the surface oxygen content of the Al₂O₃/SiO₂-based ceramic increasing after interaction with CO₂, Nd:YAG and HPDL radiation. The work has shown that the wettability characteristics of the Al₂O₃/SiO₂-based ceramic could be controlled and/or modified by laser surface treatment, in particular, whether the laser radiation had the propensity to cause surface melting. However, a wavelength dependence of the change of the wetting properties could not be deduced from the findings of this work.

We have studied the photoresponse of diamond thin film/C₆₀-doped poly-(3-dodecylthiophene) heterostructure. The fine grain diamond thin film in the heterostructure was used as a protective photoactive window and also as an anti-reflecting and light-trapping layer due to its chaotically-oriented and well-faceted nano-sized polycrystalline structure. We have obtained a quantum efficiency of 1.8% in the UV region.

Transmission electron microscopy has been used to investigate the `free' layer reversal mechanism of a range of FeMn-biased spin-valves with parallel anisotropy. Fresnel imaging enabled three modes of reversal to be directly observed for different in-plane applied field orientations and interlayer coupling strengths. Low-angle diffraction has provided some quantitative information on the level of dispersion involved in the reversals. Comparison with a modified Stoner-Wohlfarth coherent rotation model is made and magnetic modelling of the free layer energy variation as a function of magnetization orientation is presented. This has helped provide a deeper understanding of the observed discrepancies between the model and experimental data. Finally, a qualitative description of the observed domain processes is given in relation to the free layer energy for the corresponding experimental conditions.

A theory of capture of magnetic particle carried by laminar flow of viscous non-Newtonian (power law) fluid in axially ordered filters is presented. The velocity profile of the fluid flow is determined by the Kuwabara-Happel cell model. For the trajectory of the particle, the capture area and the filter performance simple analytical expressions are obtained. These expressions are valid for particle capture processes from both Newtonian and non-Newtonian fluids. For this reason the obtained theoretical results make it possible to widen the application of high-gradient magnetic filtration (HGMF) to other industrial areas. For Newtonian fluids the theoretical results are shown to be in good agreement with the experimental ones reported in the literature.

An analytical solution is presented for the electrical conductivity of a material composed of spheroidal particles embedded in a matrix. The particles are arranged on a simple-cubic lattice with their axes of rotation aligned with one of the lattice vectors. In this arrangement, there are two independent components of the conductivity tensor; one for the electric field applied parallel to the rotation axis of the spheroids and one for the electric field applied perpendicular to this axis. Both components are calculated using a method in which each particle is replaced by a singular multipole source which gives rise to the electric potential in the interstitial domain. This potential can readily be written as a sum of spherical harmonics but, in order to treat spheroidal particles, it is necessary to transform the solution into one in terms of spheroidal harmonics. The calculation of the matrix elements required for this transformation is described and the solution for each component of the conductivity tensor is given in analytic form. Results are presented for various values of particle aspect ratio, volume fraction and conductivity ratio between the two phases. Very good agreement is observed with experimental data and the results of an independent calculation.

The scattering of s-polarized electromagnetic waves from an open circular cavity ruled on a planar, perfectly conducting surface is analysed by means of an integral method based on Green's theorem. We show novel effects in which s resonances, manifested by the appearance of sharp dips in the curves of scattered intensity versus incident wavelength, give strong enhancement of the local field intensity inside the cavity and near the surface. We show that the position of the dips can be estimated from the knowledge of the resonant wavelengths obtained for a closed resonant cavity.

A modified Allen-Cahn equation is combined with the compressible Navier-Stokes system. We show that, after a modification of the stress tensor, the second law of thermodynamics is valid for the resulting equations. We give a physical motivation of this alteration of the stress tensor and compare the new equations with the well known phase-field approach. The model can be used to describe cavitation in a flowing liquid.

An analytical model is developed and used to analyse the evolution in the refractive index profiles resulting from the annealing of electric-field-assisted 2-Na⁺ ion exchanged planar optical guides formed in soda-lime glass. The model takes into consideration diffusion effects and a relaxation effect that is observed to occur within the region of the glass into which the K⁺ ions are injected. Analyses of experimental results using the model show that the time constant for the relaxation mechanism depends on the annealing temperature and on the rate at which the K⁺ ions are injected into the glass. However, the degree of relaxation is relatively independent of these variables.

By analysing the magnetic induction created by the arc motion from the outside of a breaking system at numerous points, it is possible to determine the position of the average line of current that magnetically represents the arc. This method is called the `magnetic camera' method. It had to be adapted to the circuit breaker studied here. Thanks to the method three phases of the course of the electrical arc are highlighted for a typical experiment: expansion of the arc, commutation from the mobile contact onto the lower rail and displacement through the splitter plates. In order to be more precise about the duration of the commutation phase, during which more than a single line of current must exist, an improved model of the arc motion has been developed.

It has been demonstrated that a dielectric packed pellet-bed plasma reactor operating on a mixture of NO₂ in air at atmospheric pressure can be used as an efficient method for the synthesis of dinitrogen pentoxide, N₂O₅. The reactor is packed with glass beads and operates at high frequency (10-13 kHz) and high voltage (V_pk-pk<30 kV). Typically, the energy density is 38 J l^-1 and 45 ppm of NO₂ is converted into 53 ppm of N₂O₅. The synthesis of N₂O₅ is found to be plasma-assisted in the sense that sources of nitrogen in addition to the initial NO₂ are converted into N₂O₅ by the plasma. There is an energy cost of ~180 eV for every molecule of N₂O₅ produced. The possible role played by surface and heterogeneous effects in the pellet bed reactor is considered.

The structure of axisymmetrical dc planar magnetron discharge is clarified by the use of the particle-in-cell/Monte Carlo method. The magnetron has two concentric cylindrical magnets behind the cathode. Here the effects of magnetization in the magnets, M, and the emission coefficient of secondary electrons, , on the discharge structure are examined. Four discharge conditions are considered: (i) M = 0.50 T and = 0.12, (ii) M = 0.75 T and = 0.12, (iii) M = 1.00 T, = 0.12 and (iv) M = 0.50 T and = 0.15. The complete steady states are obtained for the four cases; no oscillations or waves are found in the plasma. The electrical field component normal to the electrode varies greatly in the axial and radial directions near the cathode. The plasma-density profile exhibits a peak near the edge of the cathode sheath. As M or increases, the sheath thickness decreases. Also, the spatial distributions of the space charge, ion flux onto the cathode, ion mean kinetic energy and rates of inelastic collision of electrons are examined in detail.

In order to make clear the physical grounds of deviations from local thermodynamic equilibrium (LTE) in atmospheric free-burning argon arcs, the heavy particle temperature, electron temperature and LTE temperature obtained from electron number density were measured by use of line-profile analysis of the laser scattering method without an assumption of LTE. The experimental results showed that the core region of the arc significantly deviated from LTE under both conditions of 50 and 150 A in arc current. As a result, it is suggested that the deviations from LTE in the arc core should be affected strongly by the cathode jet and that aspects of the anode heat transfer were greatly changed by the plasma state in the arc core.

This study is devoted to an investigation of the energy consumption and byproduct generation of the nonthermal plasma-chemical NO-reduction process. Nitrogen gas with a 200 ppm NO impurity has been processed at a pressure of 1.3 atm in a silent discharge reactor with a gap spacing of 50 µm. Detailed measurements of NO, NO₂ and N₂O concentrations at the reactor outlet were carried out and analysed by means of the created model. On the basis of the proposed three-collision reaction mechanism of N₂O generation the byproduct-suppression effect has been predicted and experimentally confirmed. An extremely low energy consumption (less than 150 eV per molecule) for NO reduction by the discharge nonthermal plasma has been attained.

Equivalent spin-valves grown on silicon oxide (SiO_x) substrates produced either by thermal oxidation of Si(100) wafers or low-pressure chemical vapour deposition (LPCVD) of the oxide have been studied by x-ray scattering, atomic force microscopy (AFM) and magnetotransport measurements. Grazing incidence x-ray scattering (GIXS) measurements have also been made on the bare substrates. The x-ray measurements, supported by AFM images, show a large difference not only between the roughness of the two substrate types but also of the spin-valves deposited on them. A high degree of conformality is observed in the roughness of the spin-valves. Magnetoresistance (MR) measurements made on the spin-valves show that the switching point of the sample grown on the LPCVD substrate is shifted away from the ideal zero point due to increased coupling and both the giant magnetoresistance (GMR) and exchange field are seen to fall with increasing roughness.

The initial energy deposition stage of the thermoluminescent (TL) process is investigated. A coupled ion-electron Monte Carlo (MC) transport code developed for LiF considering its solid-state nature is used to obtain radial dose distributions for incident proton and helium ions at several energies. Models which relate the initial energy deposition to the final TL light emission are used to predict TL efficiencies. Track structure theory (TST) efficiency calculations using the MC radial dose distributions and target sizes of 50, 100 and 150 Å were performed for the total signal of LiF. Comparison with recent high linear energy transfer (LET) efficiency measurements suggests a value for the target size within the interval 50-100 Å. Modified TST (MTST) proton-to-gamma and helium-to-gamma relative TL efficiency calculations were performed with the MC radial dose distributions and 8.1 keV x-rays as test radiation. It is found that both theories show good agreement with the data, though both predict an energy dependence stronger than observed. A `core radius' for a given ion may be found by applying MTST. The importance of the cut-off energy for secondary electron generation in the MC code is discussed. The fraction of ion energy deposited by the secondary electrons around the heavy charged particle (HCP) path obtained from the MC simulation is in accordance with known values. This work includes solid-state effects in the calculated radial dose distributions in LiF providing dose profiles which are necessary for the calculation of efficiency values and may prove to be essential for further understanding of HCP induced thermoluminescence in LiF.

The problem of structure formation in colloidal systems composed of polarizable and conducting particles is considered. It is demonstrated that, in certain frequency ranges of the applied field, the dipole interaction leads to patterns whereby particles of different types are connected across field lines. By applying a Monte Carlo simulation, the main characteristics of the chaining process in a mixture of polystyrene beads and yeast cells are analysed. A good correlation between the theoretical model applied and experimental data is achieved. The data show that different aggregation patterns occur as a function of frequency.

The vertical axis label for figure 1 should have Angström units as shown below.

Figure 1: Maximum thicknesses of strained SiGe alloys grown on Si(001) substrates. The upper curve is the metastable critical thickness t_m for growth at 500 °C, the lower curve is the equilibrium critical thickness t_e. After Houghton [5].