Table of contents

Small hollow glass shells have been filled with gases by in-permeating the gases through their thin walls. The resulting internal gas pressures have been determined by analyzing the gases released from the rupture of individual shells. Shells have been fabricated which when filled at elevated temperatures have been stored at room temperature and atmospheric pressure for 18 months with no measurable decrease in pressure.

A technique for stabilizing crystal surfaces of III-V compounds against thermal decomposition by impinging molecular beams of group V dimers or tetramers on the surfaces is presented. The technique has been successfully applied to InP (100) surfaces. Other areas where it would find application are suggested.

Compensation effects for a series of polyacrylonitrile polymers are discussed. It is shown that a proposed empirical equation does not lead to a physical insight into the phenomena.

The emission of hot electrons through the surface of electro-formed vacuum-deposited thin-film cathodes of Au-SiO_x-Au has been studied. In the lower voltage range (<20 V) coherent scattering from pinhole edges in the Au counter-electrode was observed. For higher voltages (20-70 V) multilayer structures were necessary to avoid dielectric breakdown and in such samples coherent scattering through the top surface of the Au film from the (111), (200) and (220) planes was observed. The radii of emission patterns and the threshold voltages for the observation of diffraction from a particular set of planes, were in agreement with existing theory.

Magneto-microwave Kerr effect in terms of Rg, the amplitude ratio of the two orthogonal components of the linearly polarized reflected wave, has been studied as a function of magnetic field and temperature on an n-type single crystal of indium antimonide. The experimental measurements have been done using a double microwave bridge. A good agreement between theoretical and experimental results has been found.

Decreases in crack propagation rates of several orders of magnitude are observed.

An X-ray diffraction profile resulting from microstructural changes in materials is a convolution of the instrumental and the true diffraction profile. The simultaneous convolutions of the functional forms representing the respective profiles are dealt with. The convolution of schoening's true diffraction profile, originating from the cauchy particle-size profile and the guassian strain profile with the instrumental profile having several functional forms (namely, gaussian, cauchy and an intermediate exponential one), has been examined and applied to profiles of several cold-worked alloys and vapour-deposited silver films. A fairly good agreement for the calculated and experimental integral breadths of the profiles has been observed for a gaussian instrumental function. The analysis gives a confirmation of the functional forms assumed and also of the schoening's particle size and strain parameters.

Results are presented of torsion pendulum measurements of the longitudinal shear modulus G_LT and damping Psi _LT of single carbon fibres in the frequency range 0.01-0.1 Hz. Cyclic surface shear strains up to 10^-3 had no noticeable effect on either G_LT or Psi _LT. Both G_LT and Psi _LT increase in the presence of an axial tensile stress. A detailed investigation was made of the effects of heat treatment temperature on a range of fibres from polyacrylonitrile to those graphitized at 2800 degrees C. There was a rapid increase in G_LT and a corresponding decrease in Psi _LT up to 1000 degrees C, this being associated with cross-linking. Above 1000 degrees C, neither property changed appreciably except for a slight, but significant, reduction in G_LT for 2800 degrees C fibres.

Structural parameters derived from absolute intensity small-angle X-ray scattering experiments have been combined with strength and failure strain data for pan carbon fibres in an elastic/plastic theory of fracture. Good quantitative agreement with the theory is obtained throughout the heat treatment temperature range of 1000-2800 degrees C. The application of a modified griffiths theory, including a plastic work term, gives more qualitative agreement. The influence of the microstructure, in the form of crystalline ribbons, elongated micropores, and non-organized carbon and nitrogen, is discussed in relation to the fibre failure strain. The influence of grosser internal flaws on mechanical properties is also considered.

The deformation of undrawn polyester fibre has been studied using apparatus which simulates the conditions existing on a high-speed drawing machine. This apparatus was designed to apply a sudden tension to a fibre sample held in a controlled environment and then measure the extension produced as a function of time. When the load was applied there was an instantaneous small extension of a few percent only, followed by a relatively slow creep to 10% extension. At this point the fibre extended rapidly to between 200% and 300% at which level the rate of extension reduced again. The time to reach 10% extension ranged from a few milliseconds to several seconds, depending on the temperature and the applied tension. The effect of water in the sample and other fibre properties such as molecular weight, pre-orientation, and filament diameter were studied.

A pulsed CO₂ laser was used to irradiate aluminium alloy in a vacuum with powers of up to approximately 10⁶W mm^-2. The pressure generated was recorded by a quartz gauge. Sample reflectivity and plasma attenuation for 10.6 mu m radiation were measured in separate experiments. A computer program was developed to model the interaction of laser radiation with aluminium. This yielded pressure values in good agreement with the experimental results.

Range-energy relationships for 8.78 MeV alpha particles in polystyrene, polypropylene and ethyl cellulose have been determined. The stopping powers of CH and CH₂ groups are compared in the solid, liquid and vapour phases and significant differences are noted. The experimental results are also compared with theoretical results. The differences indicate that the mechanism of charge-changing in different phases is incompletely understood.

When Hall measurements are made on samples having a length-to-width ratio that is not much greater than unity, the transverse potential difference usually differs appreciably from the Hall voltage. However, it has been found experimentally that this difference can be substantially reduced if the commonly used metal contacts are replaced by contacts having a high electrical resistivity. This observation is explained by a theoretical calculation of the variation of transverse voltage with distance from the contact for a long Hall specimen connected to a long sample of another material having a different resistivity and zero Hall coefficient. The calculation, which has been carried out for various resistivity ratios, allows one to specify conditions under which the Hall coefficient can be determined for very short samples without the need for end corrections.

Measurements have been made of secondary electron currents resulting from positive ion bombardment of clean (100) crystal targets of tungsten, molybdenum and vanadium, as well as polycrystalline tungsten, by a range of ions. Data from a relatively large number of bombarding ion species give support to Parilis and Kishinevskii's theory of kinetic electron ejection from metals (1960) and indicate the isotopic dependence of kinetic electron ejection, and that of the ejection coefficient and threshold velocities, on ion and target atom numbers.

A crude energy analysis of positive secondary currents (measured on the collecting surfaces) from clean single-crystal targets of tungsten, molybdenum and vanadium, as well as polycrystalline tungsten, indicates that significant proportions of the currents measured result not only from sputtered target ions but also from kinetic electron ejection from the collecting surfaces by scattered incident particles. Some correlation has been achieved with kinetic ejection thresholds calculated according to simple hard-shape collision theory.

Energy distributions of kilovolt electrons transmitted through thin films of aluminium were measured with a spherical gridmesh retarding analyser mounted in a commercial-type electron probe microanalyser JXA-3. Some modifications to the Monte Carlo calculation based on continuous slowing down approximations have been made to obtain a more realistic model for electron penetration and energy loss. These calculations are compared with experimental measurements of the total energy distribution of 15 keV electrons transmitted through aluminium films of various thicknesses. Analysis and experiment are in satisfactory agreement.

Magnetoresistance is reported in thin films of single-crystal Ge prepared by vacuum evaporation at different temperatures. The paper also describes the variation of Hall constant and mobility with magnetic field. It is observed that the results obtained when Ge films have been prepared at a substrate temperature of approximately=940 degrees C are comparable with those of a bulk Ge single crystal.

The magnetoelastic anisotropy introduced by torsional twist in ferromagnetic wires allows the measurements of the circular magnetization M_phi as a function of the longitudinal magnetic field H_z and the longitudinal magnetization M_z as a function of the circular magnetic field H_phi . For two types of samples, twisted to saturation the M_phi -H_z and M_z-H_phi curves were obtained. These curves show two different types of behaviour.

The magnetic field of a complicated magnetic circuit consisting of both electromagnets and permanent magnets situated in air can be derived from the solution of a boundary value problem. Such a problem can be formulated so as to find a potential function giving a stationary value to an appropriate functional. A numerical solution can then be found by applying the finite-element method. Expressions of the functional for materials with different magnetic properties and the derivation of the numerical solution of the boundary value problem by the finite-element method are given with special emphasis on systems with permanent magnets. In one of the two examples illustrating the application of the method, design considerations of the magnetic device are related to the solution.

The use of photon-stimulated current spectroscopy (PSC) for the examination of defect levels in insulators and semiconductors is described and a quantitative analysis presented. The mathematical treatment is developed separately for the monomolecular (no retrapping) and bimolecular (retrapping) cases. The analysis describes how the trap depth (E_t), the capture cross section of the traps (S_t) and the trap density (N_t) can be evaluated for each case.

Infrared and Raman spectra have been recorded in the region below 420 cm^-1 for the two simplest polystyrene model molecules. Attempts to assign the vibrational absorptions are presented. There are marked changes in the spectra with variations in the conformational structure of the alkyl chain. These changes are discussed in terms of coupling between the out-of-plane 10b mode of the benzene ring and deformation vibrations of trans conformation alkyl chain segments of different lengths.

A modified ZAF method was chosen. For the atomic-number correction, the classical form is maintained by using the mean ionization energy of Zeller. For the absorption correction, the use of the complete expression of the function f( chi ), including the surface ionization phi (O), is required. A few examples of quantitative analysis are given, based on this method. A new semi-empirical table of absorption coefficients, with regard to these elements, is presented. The experimental difficulties which were encountered are examined. This method does not apply to all the elements, only to the low-atomic-number ones. In fact, for each element, a particular value for sigma and h must be chosen.