Table of contents

The electron energy distribution is determined to be anisotropic in a low-temperature plasma, when it is far from equilibrium. This leads to a kinetic instability of the highly concentrated beam in rarefied and dense plasmas over a wide range of the Knudsen parameter. The experimental criterion of threshold is true over a wide range of the Knudsen parameter. The beam isotropisation in plasma oscillations is shown to be realised simultaneously with the energy relaxation.

Bright centres were observed on dielectric layers (100 mu m) in vacuum as a pre-breakdown phenomenon at high-voltage pulses. They are origins of Lichtenberg figures on the insulator surface. The properties of this phenomenon are described and explained by a qualitative model which accentuates the importance of the insulator surface charge.

The well known two carrier transverse magnetoresistance in semiconductors is analysed in order to show that a high magnetoresistance coefficient can be reached for an impurity concentration which closely depends on the electron-hole mobility ratio and the magnetic field intensity. The condition for a strong magnetoresistance is shown to be quite different from that leading to a null Hall field. Experiments in InSb crystals fully confirm the analysis and outline the possibility to use this effect for magnetic or temperature sensors.

The p-n heterojunction with p-CuInSe₂/n-CdS has been fabricated by vacuum evaporation of n-CdS thin films on a sintered p-CuInSe₂ base. It has been found that the PV activity of such heterojunctions crucially depends on the grain size of CuInSe₂. The large grain polycrystalline material was easily obtained by an inexpensive sintering process, whereas it was impossible to obtain large grain (>1 mu m) when CuInSe₂ was prepared in the form of a thin film. The PV activity of the p-n junction employing sintered CuInSe₂ has been investigated for the first time in the present investigation and it shows improved response over the other known PV systems employing sintered CuInSe₂.

Simultaneous lasing of two or more ultraviolet rare-gas-halide transitions is reported. The kinetics and chemical stability of different mixtures is considered. Efficient and long-lived operation is demonstrated in XeCl with XeF and of KrF with XeF.

Stub transmission lines can easily be introduced into existing TLM models for heat flow in semiconductor devices. They provide a convenient means of eliminating inter-nodal reflections that arise as a result of either geometric factors or the temperature dependence of the specific heat and thermal conductivity. Stub lines have been used to identify a minor error in a previously published TLM formulation.

The transient hot-strip (THS) method has been used for thermal conductivity and thermal diffusivity studies of electrically conducting materials by introducing a thin electrically insulating layer between the hot strip and the metallic material under study. The insulating layer introduces a certain thermal contact resistance between the hot strip (heat source cum temperature sensor) and the surface of the sample to be studied. To account for this thermal resistance a theory has been developed which indicates how measurements on these kind of materials should be performed and how the reduction of data from transient recordings should be carried out to give reliable results. The new experimental approach, which should be applied whenever a thermal contact resistance is suspected, has been demonstrated by two series of measurements on a stainless steel at room temperature.

Numerical studies of beam filamentation in laser-produced plasma are presented. This involves the numerical solution of the parabolic wave equation, known as the Schrodinger equation, coupled with the thermal transport equations for both ions and electrons, in two dimensions. The solution of the resulting equation with non-linear refractive index due to thermal and pondermotive forces, shows self-focusing and a variety of strong aberration effects. Intensity amplification at the final focus is found to be between one and two orders of magnitude greater than the initial beam intensity, governed in general by diffraction and aberration effects within the beam.

The author's earlier work on the edge velocity and edge slope relation for silicone oil films is extended to cover the whole range of edge angles from zero to near 180 degrees . This is achieved theoretically by use of the two-dimensional wedge flow as the basis for approximation, in place of the one-dimensional parallel flow over a plate. Experimental methods are developed for measuring the inflexion height and angle and edge velocity, over the required range. The earlier results are found to be applicable with little modification. For angles up to 90 degrees , the radian angle replaces the slope. For greater angles a suitable function of the angle is required, tending to infinity as the angle approaches 180 degrees .

The generalised oscillator strength formalism is used to calculate a complete and self-consistent set of collision cross sections for incident electron energies ranging from thresholds up to 10 MeV. Results are reported for about 40 states with an emphasis given on the ionisation processes. The study of the loss function points out the importance of the inner-shell ionisation, which consumes nearly as much energy as the excitation and the ionisation of the outer shell. Moreover, the authors show that the mean energy of the secondaries ejected from a given shell is about twice the ionisation potential of this shell. As a result, many energetic secondary electrons coming from inner-shell ionisation are present in the plasmas produced by relativistic electron beams.

For pt.I see ibid., vol.19, p.761 (1986). The apportionment of the energy deposited in argon by a relativistic electron beam (REB) is studied in the context of the Continuous Slowing Down Approximation (CSDA). The deposition efficiencies of many argon states are presented, with special attention being paid to forbidden states excitations and inner-shell ionisations. Study of the processes leading to plasma formation shows the existence of two separated energy domains. For primary energies lower than 10 keV, the ionisation of argon is mainly due to direct pumping by the beam, while for higher energies the plasma is essentially produced via secondary and high-order generation cascades of electrons. Their contributions to the ionisation of the M-shell or to the excitation of the allowed states amount to about 70% and constitute the totality of the forbidden states production. The authors emphasis the fact that the cascade electrons arising from inner-shell ionisations are responsible for about 40% of the population of the various argon states.

The fulfilment of the increasingly stringent requirements for selectivity and anisotropy in etching relies on absolute control of the interaction between a plasma and the substrate being processed. In the present study, the way in which the working point of radiofrequency capacitive discharges determines this interaction is shown and the definition of etching processes is seen to be the result of necessary compromises. Improved etching control can be obtained using multipolar magnetic field confinement discharges, which produce large volumes of low-pressure homogeneous isotropic quiescent DC plasma. So far, the field of application of these hot-cathode-generated plasmas has been limited to non-corrosive gases. A microwave discharge used in association with multipolar magnetic field confinement produces plasmas exhibiting the characteristics required for accurate etching control.

Measurements of population densities and temperature distributions have been performed in a double-flux tungsten inert gas (TIG) arc plasma column using high-resolution spectroscopy. The experimental conditions have been chosen to mimic typical welding conditions with argon gas. The results show that the plasma is dominated by metallic vapour species in the vicinity of the molten anode, while a nearly pure argon plasma is observed in the cathodic region.

The energy distributions of electrons and ions which are carriers of the pre-breakdown current, are measured for Cu and Al electrodes under a steady-state prebreakdown condition (applied voltage: DC 3 kV maximum). These profiles of energy distributions of electrons irradiating the anode are broad for both electrode materials. The spread extends across the upper half of the applied voltage, and includes two sharp peaks: the upper one due to high-energy electrons, equivalent to the applied voltage, and the lower one due to low-energy electrons (1-10 eV). The ion energy distributions measured at the cathode have peaks at high energies (corresponding to the applied voltage) and sometimes at low-energy positions (1-20 eV) as well. The implications for the carrier energy distribution and the carrier-forming mechanisms are discussed.

Spectral analysis of Johnson noise has been used to determine the ionic conductivity of the super-ionic polycrystalline material rubidium silver iodide. The paper demonstrates the direct accessibility of conductivity data, eliminating the need for an often complex model of the electrode-electrolyte interface.

This paper describes the use of the blister test to examine the efficiency of a homologous series of aliphatic ester films in reducing the strength of adhesion of the interface between polyurethane and a smooth stainless steel plate. The measured works of adhesion indicate that low values are only produced when the interface comprises of a rather friable solid particle array. These arrays may be produced by the deposition from suspensions in suitable solvents. If the solid coating is created by heterogeneous nucleation on the steel surface from a homogeneous solution, the work of adhesion is relatively large-comparable with that found with liquid interlayers. The especially low adhesion produced by particle arrays is readily destroyed by protracted aging or by the melting and cooling of the deposited layer. These treatments appear to produce secondary surface reordering or crystallisation of the coating and hence a rather strong interface. In its simplest form the blister test measures the force or pressure required to rupture the interface. However, the weaker the interface, the faster the initial crack propagation rate. For these systems the rupture work is an increasing function of this crack velocity. The efficiency of the coatings may be ranked according to the force to rupture the interface or the calculated work to rupture the interface at a constant initial crack velocity. In either case the relative performance is the same although the latter criterion provides a greater scale for the relative evaluation.

The electrical conductivity of solution-grown PVF₂ films has been studied as a function of iodine concentration (0.2 to 1.0%, by weight). It has been found that doping of iodine enhances the conductivity and lowers the activation energy of the charge carriers. These effects have been attributed to the formation of charge-transfer complexes.

Hall coefficient, photoconductivity and photoconductive relaxation measurements have been carried out on vacuum-evaporated air-exposed SnSe films in the temperature range 300-130K to probe into the mechanism of photoconduction in these films. The results have been explained by the trapping of majority carriers in the grain boundary region. The barrier height estimated from the temperature variation of the photorelaxation time is of the order of 0.16 eV, which agrees well with the values obtained from the temperature variation mobility as well as from the temperature variation of steady-state excess photoconductivity. The value of the trap density obtained from this analysis is of the order of 2*10²⁵ m^-3.

Measurements are reported of the real part of the magnetic susceptibility, chi ', of polycrystalline YIG at 6 GHz and at room temperature, in magnetic fields outside the spin wave manifold. Above applied fields of about 4000 Oe the simple theory that gives chi '/4 pi M=H mod (H²-H_R³) holds accurately, while at lower fields a small shift S of the resonance field H_R is found. The dependence of S on the porosity of the sample is quantitatively in agreement with the theory of Motizuki and co-workers (1965) while the small anisotropy-dependent shift is comparable with that calculated by Vrehen and co-workers (1970) for ferrite samples. Measurements on samples containing Gd and Al confirm that chi ' is directly proportional to 4 pi M.

Compositionally modulated (Gd+Co) films were prepared by an RF magnetron sputtering system with double targets and a revolving substrate. An X-ray small angle scattering, composition profile, temperature dependence of electrical resistivity and magnetisation curve were measured. One theoretical method assuming a compositionally modulated waveform using the angle and intensity of X-ray small angle scattering is shown. The relation between modulation wavelength and magnetic properties of (Gd+Co) films is studied.

Data are presented on the variation of the dielectric constant and the tribo-electric coefficient for a series of pigmented, melt mixed, polymer materials. Dielectric spectra are also presented for other pigmented polymeric materials. On the basis of these data it is shown that in certain situations a correlation may exist between the dielectric constant and the observed tribo-electric coefficient. A comparison of the values obtained with those predicted on the basis of the simple Wagner Model indicates that the dielectric increment can only be explained if a significant proportion of the material is present in a chained form. Model studies of carbon fibres are presented and a model for the prediction of the dielectric properties of chained carbon particles is also described.

Interfacial gaps between fibre and matrix materials in glass-fibre-reinforced composites influence both the distribution and phase properties of the reflected light. For small interfacial gaps, an ultrasound Schlieren system can be used to model the optical reflection properties and visualise the wavefront trajectories. Quantitative estimates of the intensities of the reflected light for TE and TM modes, and the nature of the reflected phase properties, can be obtained from the 'characteristic matrices' of tunnel and dielectric films. It is demonstrated that complete information about interface geometry can be derived from the study of the distribution of transmitted and reflected light.

The optical absorption spectra of facet-core-free and facet-core parts in Bi₁₂SiO₂₀ have been measured precisely at various temperatures between 30 and 300K and analysed in the region of the absorption coefficient from 50 to 1600 cm^-1. The data are interpreted as indicating there are indirect allowed transitions with energy gaps of 3.380 eV (facet-core-free) and 3.353 eV (with facet core) at 0K. The temperature dependence of the energy gaps in facet-core-free and facet-core parts are different from each other within experimental accuracy.

An electrodeposition process to grow high-purity CdSe films from low-purity materials is described. Purity control was achieved by optimising the deposition potential and impurity masking with EDTA. Auger depth profiles of CdSe films were used to examine their stoichiometry and impurity content. The photo-anodic performance of CdSe film depends on annealing history and etching conditions. Optimum annealing and etching conditions are reported to achieve the best efficiency. A typical n-CdSe/ Ni/(S₂^2-,S^2-)/Ni solar cell yielded an open-circuit voltage of 500 mV, short-circuit current of 10 mA cm^-2 and 3.6% efficiency under 50 mW cm^-2 illumination from a tungsten-halogen lamp.