Table of contents

Using the framework of the Mayadas-Shatzkes and the effective Fuchs-Sondheimer conduction models an approximate relation for the product of the film resistivity with its TCR is obtained. As a consequence, the film resistivity may be represented by the sum of the bulk resistivity and an additional resistivity which is temperature-independent.

Microparticles with radii greater than 2 mu m have been observed in a high-voltage vacuum accelerator tube. The charge acquired by most of the particles is similar to the contact charging of a conducting sphere on a plane.

A transient hot-strip method has been developed for use with solids and fluids with low electrical conductivity. The hot strip (thin metal foil) is used both as a constant plane heat source and a sensor of the temperature increase. The accuracy of the method is so good that it might even be used for the measurement of the specific heat especially under difficult experimental conditions when the standard methods cannot be used or would be very inconvenient. This method has been tested in measurements on fused quartz, glycerine and Araldite at room temperature. The experimental conditions that cause deviations from the mathematical solution of the thermal conductivity equation are discussed and estimates for their maximum influence on the measured quantities are given.

The performance of three designs of electromagnetic flowmeter having large-area electrodes is analysed using the weight function concept for rectilinear flows. The problem of electrode fouling and the consequent change in performance is examined for certain extreme cases. It is shown that the resulting errors may be as high as 12%.

Anti-Stokes rotational Raman scattering from nitrogen gas at near atmospheric pressure and room temperature has been used to calibrate the intensity of ruby laser light Thomson scattered from a plasma in a transverse magnetohydrodynamic shock tube. The main limit to the accuracy of this calibration method is the uncertainty in the available Raman cross section for nitrogen.

An equation is developed for calculating the X-ray fluorescence produced in a coating by characteristic X-rays generated in the substrate material. The correction is applied to experimental microanalysis data obtained for thin coatings deposited on a range of substrate materials and is shown to give satisfactory results. An extension of the method to include multicomponent systems is then described.

A computational study is made of the effects on various blanket parameters of the neutron moderation produced in the highly compressed deuterium-tritium pellet of an inertially confined thermonuclear reactor based on the Wisconsin SOLASE design. For a pellet in a compressed state of rho R=1.2 g cm^-2, studies are made of the blanket neutron heating, gas production and tritium production. Compared with a monoenergetic 14.1 MeV neutron source, the values of these parameters can change by as much as 15%.

The strain-energy function of a rubber-like solid may be characterised by stress-deformation data from experimental tests in which two principal stretches of a homogeneously deformed specimen are varied independently. In the context of the continuum theory of finite elastic deformations, a framework is described within which such experimental results can be assessed. It is based on the separability of the strain-energy function according to the Valanis-Landel hypothesis (1967). This hypothesis is supported by experimental data for a variety of rubber-like solids up to quite large biaxial stretches, and for this reason the strain-energy function is best expressed in terms of principal stretches rather than a pair of independent deformation invariants.

A study of the spreading of silicone oil drops is presented, with particular attention to the dominant effect of the conditions near the edge and the surface tension forces acting there. It is shown that the drop profiles can be predicted and that this leads to a relation between the edge velocity and the maximum slope, which occurs at an inflection point close to the edge. This relation leads to others governing the variation of drop size and slope with time. The predictions are compared with experiment, using silicone oils, and good agreement obtained. The lubrication approximation theory gives no solution for thicknesses below a value varying from 2 to 9*10^-8 m at the drop edge. At thicknesses of this order, or possibly even larger, other effects become important, and some observations on edge behaviour are included.

An experiment has been constructed for studying thermal diffusion in the binary mixture ²²²Rn-CO₂ by means of the two-bulb method. A smaller thermodiffusional chamber has been constructed as a proportional counter to facilitate the continuous monitoring of the ²²²Rn concentration during the whole measurement. A difference method has been used for determining the steady-state separation factor in order to eliminate the effects of the adsorption of radon on the walls of the apparatus. The thermal diffusion factor alpha _T has been measured at the temperature T=338.8K.

The motion of metal introduced from an arc into a rotating plasma has been followed spectroscopically. The experimental observations agree well with a theory in which the metal is evaporated from the cathode in aggregate of about 100 particles.

A new design of TEA N₂ laser for producing high-density excitation by combined use of a modified Marx generator and a pair of high-speed capacitors is described. Laser output of 1.5 MW (1.2 mJ, 0.8 ns) is obtained from a 12 cm long uniform discharge at a charging voltage of 25 kV.

The mechanism of ozone generation in the silent discharge of air-fed ozonisers is studied theoretically and experimentally. The nitrogen oxides (NO_x) formed in the silent discharge have been found to play an important role in the process of ozone generation due to the catalytic cycle for O₃ destruction: NO+O₃ to NO₂+O₂ and NO₂+O to NO+O₂. Taking this catalytic cycle into account, a mechanism is proposed to explain the characteristics of ozone generation in air-fed ozonisers. The electron impact dissociation coefficients of O₂, N₂ and O₃ and the gas temperature in the silent discharge are estimated by the computer matching of the theoretical calculations to experimental results.

When a well-collimated beam of high-energy electrons traverses a thin single-crystal specimen (as in transmission electron microscopy), an inelastic event may induce an angular spread in the inelastic beam, effectively reducing collimation. Calculation of the 'smeared out' diffraction contrast preserved in the inelastic beam indicates that measured mean free paths for discrete excitations may alter with diffraction conditions. Theory is correlated with experimental observations for plasmon and nitrogen K-loss signals from single-crystal aluminium nitride platelets. These results enable favourable diffraction conditions for quantitative microanalysis of single crystals by electron energy-loss spectrometry to be defined.

A nonlinear current-voltage characteristic is observed in hexatriacontane (C₃₆H₇₄) single crystals and a Schottky effect or Poole-Frenkel effect mechanism is suggested as the cause. It is shown that the breakdown strength (1.5 MV cm^-1) of the crystal at room temperature: (i) is much smaller than that of polyethylene (6 MV cm^-1), (ii) decreases with increasing electrode distance and (iii) is temperature insensitive until the temperature nears boiling point. These results can be explained by taking into account the large electron mobility in hexatriacontane single crystal compared with that in polyethylene. The important role of the amorphous part of the electrical conduction and breakdown characteristics in polyethylene are indicated from these discussions.

Tunnelling of electrons between a metal and localised states in an insulator is considered, with a view to determining the charge that an insulator can acquire by this mechanism when it is contacted to a metal, and also the extent to which it can lose charge by back-tunnelling during separation. Traps at a single energy are considered primarily, but some attention is given to traps distributed over a range of energy. Back-tunnelling is likely to be significant only at the very highest observed charge densities.

The polarity effect of the dielectric breakdown voltage in liquid He is studied. The breakdown voltage for a positive needle is higher than that for a negative needle and even than that for uniform field. The field strength on the cathode surface at breakdown threshold for a positive needle is calculated with a simple hyperboloid approximation of field distribution, and agrees approximately with the breakdown field in the uniform field condition. The breakdown strength also depends on the work function of the cathode metal but not that of the anode metal. Therefore, breakdown threshold in liquid He seems to be determined by the field strength at the cathode.

The influence of internal potential relief, formed by the inhomogeneous distribution of impurities in doped piezosemiconductors, upon their acoustic properties was studied. The analysis of the obtained equations was conducted for the limiting cases of weak and high inhomogeneities. It was predicted that weak inhomogeneities suppress the manifestation of electron-phonon interaction in sound attenuation. In high-doped compensated crystals specific sound attenuation is predicted, which may be used for experimental determination of electron concentration in drops.

Thermoluminescence was studied above room temperature for polyoxymethylene samples with various morphologies. As expected, the appearance of the luminescence glow curve was different between samples in both shape and intensity, reflecting the difference in crystalline perfection: needle-like and fibrillar crystals, with extended-chain structures, showed a sharp and strong glow peak around their melting temperatures whereas a broad glow maximum appearing above crystalline dispersion temperature was predominant for folded-chain crystals. The results are discussed in comparison with those of differential scanning calorimetry/thermograviometry and other physical measurements.

The authors demonstrate that the order of kinetics of the TL process can change with the dose received by a sample. In LiF the order of kinetics becomes constant only when the dose given to the sample is smaller than the saturation dose by at least an order of magnitude. The order of kinetics followed by glow peaks V (190 degrees C) and XII (385 degrees C) of LiF TLD-100 is determined using two methods: (i) peak shape, and (ii) isothermal decay. The former gives the values as 1.4 for peak V and 1.35 for peak XII and the latter 1.6 for peak V and 1.5 for peak XII. For the saturation exposure of 10⁵ R when no empty traps are available, peak V decays exponentially in the beginning (first-order kinetics) and as the decay progresses the order of kinetics continuously increases. After 3 min of decay at 165 degrees C, when the intensity has fallen to less than 20% of initial value, the order of kinetics stabilises at 1.6. The activation energies E of the two peaks are determined using (i) peak shape, and (ii) initial rise methods. The initial rise method is found to give lower values of E than the peak shape method. This is explained on the basis of a thermal effect on luminescence efficiency.

The determination of the precise geometry of the field-ion emitter from its field-ion image has been a long-standing problem. An analytical method is given which allows the cartesian coordinates (x,y,z) of each imaging site to be determined using data extracted from the micrograph by ring counting techniques. The coordinate data extracted in this way are used to produce profiles of the shape of symmetric and asymmetric iridium and tungsten emitters.

Sequential RF sputtering has been utilised to produce Au/TiC multilayer structures up to 100 layers. Auger electron spectroscopy (AES) combined with an ion etching technique has been utilised to analyse these multilayer structures. The studies indicate no interfacial alloying. Microhardness and electrical resistivity measurements show that, whereas the microhardness is increased by a factor of 2.5-3, the electrical conductivity of the multilayer structures is very close to that expected from stacks of individual (30 nm) pure gold films.

A study of the electrical properties of InAs heteroepitaxial layers grown on (100) GaAs and their dependence upon growth parameters has been undertaken. InAs films 1 mu m thick were grown by molecular beam deposition at a substrate temperature of 370 degrees C. Layers with residual n-type carrier concentrations in the range 5*10¹⁶-2*10¹⁸ cm^-3 at room temperature were obtained. These mobile carriers in arise from both bulk dopants and interface effects. It has been observed that the electrical properties of the InAs epilayers are critically dependent upon the incident indium and arsenic fluxes. High values of In and As₄ fluxes produced residual bulk n-type doping levels in the 10¹⁸ cm^-3 range and caused additional scattering. The lowest carrier concentrations and highest mobilities were obtained for the lowest value of indium flux used (1*10¹⁴ atoms cm^-2 s^-1) and with the smallest arsenic flux consistent with the deposition of stoichiometric layers. Depth profile measurements on the best films indicated that the residual carriers primarily arose from donor centres situated at the film-substrate interface. The material remote from this interface had bulk-like mobilities and near-intrinsic carrier concentrations. The use of a 0.1 mu m GaAs buffer layer isolated the films from a further source of donor centres. The presence of gaseous oxygen during film growth has been found to degrade film electrical properties. No effects were observed when hydrogen was present.

Preliminary results of an investigation into the reversible nature of precipitation effects in doped silicon-germanium alloys are reported. Alloy specimens were initially annealed at 1300K and then subjected to various heat treatments and the change in their thermoelectric properties with time and temperature measured. Precipitation effects on the thermoelectric properties of these materials are to all intents reversible and this phenomenon offers a possibility of rejuvenating silicon-germanium thermo-elements by judicious heat treatment.

Experiments show that argon ion bombardment of many substances results in the chemical sensitisation of the irradiated surface. As a consequence, subsequent exposure to atmospheric water vapour causes evolution of hydrogen, and in certain cases leads to severe surface corrosion. The effect occurs on targets containing elements from the first and second column of the periodic table, and therefore includes some widely used electro-optical materials. A mechanism is proposed to explain the observed phenomena and the possibility of ion-polishing sensitive materials is discussed.