Table of contents

For the two main faces of a Néel-cut crystal of silicon iron a detailed study is made of the changes in domain patterns occurring when the crystal dimensions are changed. The contribution of closure domain systems to bulk magnetization along a [110] direction is treated experimentally and theoretically; the results explain differences between the ideal (Akulov) magnetization curve and curves obtained experimentally, and prove that a substantial hysteresis loss occurs in high fields with crystals of finite size.

Measurements have been made of the absorption coefficient of amorphous selenium in the region from 0.58 to 0.66 microns. The effect of temperature on the absorption edge has also been determined, and the edge is shown to shift by 2.7 Å deg^-1, equivalent to a change in the energy gap of 9.7 × 10^-4 eV deg^-1.

The voltage-current and capacity-current characteristics for current flow across a surface of discontinuity between two semiconductors have been derived. Both the diode and diffusion theories are dealt with, the former being treated in detail for Mott barriers and the latter for Schottky barriers. The results are applied to measurements on silicon carbide point contacts and a grain boundary in germanium respectively.

The resistance is shown to be consistent with a barrier which is caused by donor and acceptor surface states. On S₁C the density of these states is about 10¹³ cm^-2 and on Ge about 5×10¹¹cm^-2.

The theory of the electrical conductivity in alternating fields is developed for non-degenerate semiconductors with spherical energy surfaces As in the Drude-Zener theory, the conductivity is a complex quantity and the real and imaginary parts are derived as functions of frequency and of temperature.

The cases of lattice scattering and impurity scattering are investigated separately for single-band models and the results are applied to intrinsic semiconductors by considering the two-band model with lattice scattering, and to imputiyy semiconductors by combining the scattering mechanisms. The loss tangent is also calculated and a comparison is made with the available experimental data

The excess current induced in a germanium p-n junction by water vapour was found to be time dependent, and three separate relaxation times were observed. By taking the time of growth into account the excess current was resolved experimentally into two components having linear and saturation relationships with the applied voltage. The surface structure assumed to be responsible for the saturation component does not develop until after a reverse voltage has been applied to the junction, and when the applied voltage is removed this surface structure disappears rapidly compared with the time of growth.

The possibility that these components correspond to channel and surface leakage currents is discussed.

The powder striations which may be produced, on either flat surfaces or in tubes, by means of electric sparks are shown to be similar to those obtained in a sound field due to a mechanical vibrator; that is to say they depend upon the presence of aerial vortices. Comparisons of published records show that the frequencies of vibration involved lie in the lower ultrasonic range, and must derive from the shock wave which is associated with the spark. There is no direct relation between the inter-striation distances and the frequencies of the electric circuit.

The scattering of electrons whose energy is a function only of the magnitude of their wave number vector is considered for an elastic and an in-elastic process. The elastic process is scattering by ionized impurities, the in-elastic is scattering by the non-acoustical modes of the lattice vibrations in a homopolar crystal. The times of relaxation for these two processes are calculated.

In optical systems the pencils forming images of extra-axial object points are generally oblique to both the object and image planes. The diffraction image of a point source observed in an oblique image plane differs significantly from that obtained in a plane normal to the image-forming pencil. The theory of the frequency response of optical systems is formulated for this more general case. The resulting formulae are used to relate the response obtained between object and image planes perpendicular to the optical axis to that obtained between planes perpendicular to the principal rays. It is shown that no loss of generality is introduced by the restriction to unidimensional objects. Some general properties of the response function for optical systems having aberration are derived.

Approximate expressions are obtained for the total intensity in a spherically or cylindrically symmetric diffuser containing respectively a point or a line source centrally placed, the source emitting with an arbitrary directional dependence. Results are given for homogeneous media and for simple cases of composite media.

Corrections to 1956 Proc. Phys. Soc. B 69 396.