Table of contents

X-ray photoelectron spectra are reported for the spinels CuMnCoO₄, CoMn₂O₄, Co₂MnO₄ and CoZnMnO₄, from which the following ionic configurations can be induced: Cu_0.65⁺Mn_0.35³⁺(Cu_0.35²⁺Co³⁺Mn_0.65)O₄, Co²⁺(Mn₂³⁺)O₄, Co²⁺(Co³⁺Mn³⁺)O₄ and Zn(Co³⁺Mn³⁺)O₄.

The theoretical basis of the random walk movement of cathode arc spots is reconsidered, and the probable causes of some discrepancies in measured spot movement parameters and in their interpretation are discussed.

Measured Hall mobility in polycrystalline silicon layers shows a minimum at a certain doping concentration. This is interpreted in terms of the decrease in conductivity rather than a decrease in inherent mobility in the grain boundary space charge-region. The inherent mobility is suggested to be about the same as in the surrounding neutral region.

The depolarisation behaviour of PVF films doped with iodine (0-2.0% by weight) has been studied using the TSD technique. The TSD spectra of these films reveal two relaxation peaks. The peak positions, peak currents, charges and activation energies associated with the two peaks are strongly affected by the concentration of iodine and have been explained in terms of formation of charge transfer complexes and molecular aggregates.

Temperature measurements in an automobile engine running in normal operating conditions have been obtained by observing the CARS spectra of molecular nitrogen. Pulsed lasers and a broad-band technique have been used to allow the single-pulse measurements necessary for studying combustion behaviour and cycle-to-cycle fluctuations. A fitting technique has been used to determine temperatures from the experimental data, with an uncertainty of about 50 to 100K. The authors discuss the problems that are still unresolved in order to achieve better accuracy: beside experimental refinements a further knowledge of molecular parameters seems to be required.

Measurements of the ratio of diffusion coefficient to mobility (D/ mu ) of electrons in SF₆-N₂ and CCl₂F₂-N₂ mixtures over the range 80<E/p<200 (where E is the electric field in V cm^-1 and p is the pressure in Torr reduced to 20 degrees C) are reported. Values of (E/p)_c.mix (the critical E/p of the mixture, where alpha = eta ), and the electron mean energies epsilon _c.mix corresponding to (E/p)_c.mix, are found to vary with the percentage of the electronegative gas in the mixture (F) according to the following relationship: (E/p)_c.mix=(E/p)_c.N(2)+((E/p)_c.A-(E/p)_c.N(2)) (1-exp(- beta F/100-F)) and epsilon _c.mix= epsilon _c.N(2)+( epsilon _c.A- epsilon _c.N(2)) (1-exp(- beta F/100-F)) where A refers to the attaching gas, either SF₆ or CCl₂F₂ and beta is a constant, equal to 2.43 for SF₆ mixtures and 5.12 for CCl₂F₂ mixtures. In the present study, it has been possible to show that beta is indeed to a factor of synergism. Estimated gamma values (secondary ionisation coefficients) did not show any significant variation with F for F<50.

Using a time-resolved technique (uniform field), ion transients in SF₆ at low E/p₂₀ (2.5-80 V cm^-1Torr^-1) and a high gas pressures (70.1, 192.8 Torr) have been analysed by curve fitting to an expression derived from a simplified discharge scheme which considers complete stabilisation of unstable (SF₆^-)*, followed by a saturated reaction leading to the formation of predominantly SF₆^-(SF₆) clusters. Reduced mobilities for this ion are reported, together with an 'apparent' stabilisation rate constant.

A self-consistent set of electron impact cross-section and of excitation and ionisation rates was obtained for argon by making some adjustments in the experimental cross-section data available from the literature and requiring that calculated and measured electron transport quantities be in agreement. The calculations were made by numerically solving the Boltzmann transport equation. Values of the ratio of the electric field to the gas number density of interest in this work are in the range from 10 to 100 Td (Townsend). The resulting final set of cross-sections obtained here is not unique but represents one of the best possible combinations which can be sought for on the basis of presently available data. Therefore, the present results are relevant for the modelling of discharges in argon and in various visible and UV laser mixtures containing high concentrations of argon atoms.

A novel method for the investigation of electron detachment from negative ions has been developed. It allows the study of the influence of the age of the ions on the detachment process. Measurements were performed on sulphur hexafluoride at 73.3 and 110 mbar. The reduced detachment coefficient delta /n was obtained for a narrow range of E/n values around 3.8*10^-15 V cm². A significant influence of the age of the ions on delta /n was found, which is interpreted as being due to excited states of SF₆^-.

Axial magnetic fields are measured in the vacuum region surrounding a vacuum spark plasma providing information on the stability of the plasma column. The measurements are correlated to the amount and times of X-ray emission showing that X-ray bursts are produced only in linear discharges.

A theoretical model of the cathode of a thermionic arc is presented. Attention is focused on the energy balance of the electrode, with the interplay between the cathode and the arc plasma being described by boundary conditions specified on the electrode surface. Physical processes included in the model are thermal conduction and Joule heating in the electrode, radiative energy exchange between the electrode and the arc plasma, thermionic emission, and ion flow in the cathode sheath. A model of the cathode of a 100 A arc burning on tungsten in argon at atmospheric pressure is described in detail. It is shown that the flow of electric current and heat close to the tip of the electrode is controlled by thermionic emission and arc radiation, while the ion current plays a dominant role in the outer parts of cathode spot.

Several material functions of SF₆ were calculated for temperatures between 1000K and 20000K and for pressures of 0.1, 0.5, 1, 2.5, 5 and 10 MPa. In the basic equations for the computation of SF₆ material functions, the authors have also taken into account plasma nonideality effects. They have analysed the SF₆ plasma radiation in high current discharges using an Optical Multichannel Analyser, to determine the dependence on the current and the discharge pressure.

A complete theoretical description of a low-pressure, cylindrical plasma column sustained by a weakly damped surface wave is derived in which the equations describing the steady-state plasma maintenance conditions are coupled with the surface wave propagation and attenuation characteristics. The present formulation extends a radial theory of the maintenance of the plasma column previously reported to include the axial variation in the radially averaged plasma properties. Simple similarity laws for this type of discharge are proved to exist under quite general conditions. Analytic expressions are derived for the variation of the electron density along the discharge axis and for the length of the plasma column as a function of the operating parameters. The calculation are shown to agree well with available experimental data.

Ionisation processes in the He-CO and He-CO-O₂ glow discharges are studied. Various models are critically reviewed and an alternative ionisation mechanism is proposed. The populations of the CO and O₂ metastable levels and the rates of direct and step ionisation processes are calculated. It is argued that the metastable level of CO can be efficiently populated by energy transfer due to collisions between vibrationally excited molecules. It is shown that the direct ionisation of CO in the H-CO discharge is replaced by step ionisation of O₂ in the He-CO-O₂ discharge. This explains both the reduced axial electric field and the fact that O₂⁺ is the dominant ion in the He-CO-O₂ discharge.

The process of beam spreading of field-emission electrons under the action of space charges, suggested by Maitland (1961) as an explanation of vacuum breakdown initiation, is analysed. This type of space charge effect is shown to be negligible. A plausible model of breakdown initiation as a result of ions focusing within the electron beam is discussed and shown to be unreal. The effects of space charges on the initiation of vacuum breakdown are thus concluded to be very small.

In the cathode fall region of a glow discharge, where the electric field decreases rapidly with distance from the cathode, parameters for electrons obtained in an equilibrium state can not be correctly used in a theoretical study. In this paper, the cathode region in a normal glow discharge has been analysed by a Monte Carlo simulation. Four types of inelastic collisions together with an elastic collision, the reflection of electrons from electrodes and the back-scattering of electrons to the cathode, were taken into account considering the three-dimensional motions of electrons. Results show that alpha /p (where alpha is the ionisation coefficient and p is the gas pressure) is in good agreement with Friedland's result. Also, the mean energy of electrons in the negative glow region was found to be about 11 eV, which is much smaller than previous values. The difference in spatial distribution of optical emission between singlet terms and triplets was also indicated.

The dynamic friction between polyethylene and a mixture of crushed ice and small amounts of a very dilute solution of H₂SO₄ in water was measured at temperature from 0 degrees C to -20 degrees C. The liquid has only a moderate 'lubricating' effect which indicates that the generally low friction between polyethylene and ice and snow cannot be explained simply by a liquid or liquid-like layer on the ice. Larger amounts of liquid (>or=1%) lead to an increase in friction, due probably to viscous drag. Contrary to what is commonly stated, the increase in friction, which is observed as the temperature approaches 0 degrees C, is not caused by viscous drag.

The paper describes a large number of experiments in which radiotracer silver was diffused into the III-V semiconductor InP over a wide range of experimental conditions. Diffusion profiles were plotted. The diffusions were performed over the temperature range 550-900 degrees C for diffusion times between 2 min and 97 h. The ambient phosphorus vapour pressure was also varied over a wide range. Most of the experiments were carried out on undoped material, but doped n-type, p-type and semi-insulating materials were also used. The results cannot be explained by any simple diffusion theory and it would appear that a rather complex set of phenomena is in operation during the diffusions. The variation of surface concentration with phosphorus vapour pressure implies either that the silver atoms occupy phosphorus sites or that they are involved in some complex when occupying lattice sites. The latter explanation is considered the more likely and the complex (V_pAg_InV_p) is proposed as a possibility. The very fast diffusion which is observed strongly suggests that the silver atoms diffuse in the interstitial state and the ion Ag₁⁺ is proposed as the most likely. At lower diffusion temperatures most of the atoms in the bulk of the semiconductor probably remain interstitial, but at higher temperature, some of them join the lattice.

A method of obtaining polymeric materials showing high anisotropy of electrical conductivity (up to 10⁸) is reported. Electrical properties of polycarbonate films doped with TTT-TCNQ crystalline CT complex obtained using this method are discussed.

A theory of open-circuit photovoltage decay in a pn junction solar cell is presented which accounts for the pn coupling, i.e. the coupling between the diffused layer and the base of the solar cell. The results have been analysed in some detail which show how the voltage decay is influenced by the various parameters of the diffused layer. It is found that the decay is sensitive to pn coupling in the initial stages, particularly in those solar cells in which a heavy doping of the diffused layer may have caused sufficient band-gap narrowing. A measurement of the voltage decay in the initial stages can therefore yield the parameters of the diffused layer in a solar cell.

Single carrier space-charge-influenced effects (for non-zero injection fields) are considered. Initial, transient, and DC currents are derived analytically. The transient problem is solved only for planar samples. The transient current shows the normal space-charge-limited (SCL) form even for space-charge-free conditions. For fixed non-zero injection fields a sharp rise of current with voltage above the 'switch-on' voltage (V_I) gives way to the normal SCL square-law for V>or approximately=5 V_I. The 'zero-time' current-voltage curve is universal in form for the simple geometries. For Schottky injection, the initial rise with voltage is less rapid; both cases could readily be misinterpreted as due to a trap-filled limit.

Changes in the electrical characteristics of polycrystalline Cu_xS-CdS solar cells have been studied following annealing treatments in air, vacuum and hydrogen, together with corresponding changes in the stoichiometry of the Cu_xS layer. Vacuum and hydrogen treatments have been found to produce very similar effects markedly different to the effects of air annealing. The results are consistent with previously reported Auger spectroscopy measurements which showed the Cu_xS layer and the Cu_xS-CdS interface structure to be very unstable when heated in air in comparison with the effect of annealing in either vacuum or hydrogen.

Critical current and flux pinning measurements of a variety of Zr-based metallic glasses are reported. The measurements were performed as a function of temperature and applied magnetic field on as-quenched samples. A universal behaviour of the critical current density of flux pinning force density is observed for glasses of the form Zr₇₀X₃₀(X=Cu, Ni, Co and Ni_0.5Fe_0.5). This result is attributed to pinning due to quenched-in stress fields and edge pinning.

The results of a detailed study into the nature and concentration of magnetic components as a function of particle size in five flyash samples of bituminous coals are reported. Samples were size-fractioned into ten fractions each using sieves and temperature-dependent magnetisation studies were used to determine the magnetic components. Observation of the Verwey transition near 120K and an anomaly near 250K in the magnetisation indicate the presence of Fe₃O₄ and alpha -Fe₂O₃ respectively. Confirmatory evidence for the presence of these minerals was obtained from X-ray diffraction studies of the samples. Magnetic components and mass distribution were determined as a function of particle size and it is found that about half the mass and magnetic components are contained in the fraction with the smallest particles (diameter <or=38 mu m). Based on the variation of the saturation magnetisation M_s with particle size, the five samples can be classified into two groups: group I of three samples for which M_s falls off with increasing particle size and group II of two samples for which M_s is nearly constant with particle size. Other similarities within each group are: (i) nearly equal levels of Fe₃O₄ and alpha -Fe₂O₃ in group I whereas in group II, alpha -Fe₂O₃ has nearly four times the concentration of Fe₃O₄ and (ii) group II has a much higher level of unburnt carbon than group I. Correlations between these observations and combustion conditions of flyash are discussed and their possible applications are outlined.

Complex permittivity equations have been derived using the Bruggeman method at high volume fractions for a random distribution of ellipsoids dispersed in a continuous medium.

A stochastic mixture model is proposed for the dielectric formed by the powder of an isotropic polycrystalline material included in an embedding medium of air or a non-polar substance. The relevant expression of the complex dielectric constant of the mixture is obtained in terms of the dielectric parameters of the mixture constituents and the volume fraction of the crystalline material. Hence the possibility of deducing the dynamic state dielectric characteristics of the solid (compact) crystal from the measured data on the powder is indicated. Theoretical results obtained for 1-cyanoadamantane using the present model over a wide spectral range (1 kHz to 1 GHz) are compared with corresponding experimental data available elsewhere. Results due to the present method agree more closely with the measured values for both low and high volume fractions, when compared with the results based on other existing models due to Bottcher and Looyenga.

Optical constants of amorphous hydrogenated Si_1-xGe_x(H) films fabricated by radio frequency sputtering have been measured for 0<or=x<or=1 at wavelengths from 0.35 mu m to 2.65 mu m using both spectrally-resolved ellipsometry and spectrophotometry. The data include measurements on the refractive index in the high absorption region. The results show that the refractive index, the extinction coefficient, the loss factor and the optical band gap vary approximately linearly with x (the content of Ge). The refractive index and the extinction coefficient are dispersive and exhibit two peaks in their spectra, one above and the other below the optical absorption edge. The first peak is attributed to interband transitions and the second peak to transitions involving localised states in the mobility gap.

The trap distribution analysis of CaSO₄:Dy has been carried out using a fractional-glow technique. It shows that the TL process in CaSO₄:Dy involves quasi-continuous distribution of traps with activation energies ranging from 1.15 to 2.39 eV in the 340-370K glow-temperature range. The trap spectrum of CaSO₄:Dy reveals that the activation energies are distributed in a number of groups, with a prominent group, linked with the 495K dosimetric peak, peaking at around 1.40 eV.

LiYF₄ doped with 1% Ce, and manufactured using fully enriched 99.6% ₃⁶Li, has been evaluated as a neutron detector in a comparison with an optimum form of Ce-doped lithium aluminosilicate glass. Room temperature absorption and excitation spectra are presented and discussed. The pulse height of the ₃⁶Li (n, alpha ) reaction using moderated Am/Be neutrons is shown to be a factor of approximately six times poorer than that of the glass.