Table of contents

An experimental study was made of the damage to p-type Si crystals whose carrier lifetime has been reduced by neutron and gamma irradiation. No correlation between the carrier lifetime and the damage threshold was found in our experiment.

It has recently been stated that the direct emission of X electrons out of the (110) face of GaAs activated to negative electron affinity is blocked by conservation laws. It is shown that proper application of the conservation laws contradicts this conclusion and that there exists firm experimental evidence for the emission of such electrons. Similar considerations apply to (110) Si. Hence the reason emission is not observed in this case is because negative electron affinity has not been achieved on this face to any significant degree rather than the emission being blocked by conservation laws.

Diodes with a buffer on the substrate are reported. The buffer layer is effective in eliminating the undesirable influences from the substrate. The variation among the samples with the buffer layer is far less than those without the buffer layer.

The implications of a scaling argument employed by Bishop (see abstr. A10294 of 1974) are extended to consider the effects of external and demagnetizing fields on the stability of cylindrical domain wall configurations. It is found that the magnetostatic energy must be included to ensure stability at finite radius.

It has been shown that the effects of demagnetizing fields upon the stability of thick-walled bubble domains can be approximately incorporated into Thiele's (1969) stability equation through an effective wall energy gamma '. External and demagnetizing fields have also been shown to increase the domain wall width.

The authors are engaged in a study of water treeing in polythene. In the course of these studies, cups moulded from cable-grade polythene were suspended in sodium chloride solution at 60 degrees C. The gain in weight by the cups was measured. The infrared absorption spectra of these cups was compared with those of untreated cups. The effect on the oxidation of polythene, of the presence of sodium chloride in solution is discussed.

The imaging gas in a field ion microscope to some extent changes the surface temperature of the sample. This temperature change can be evaluated from the nonlinear dependence of the image brightness on the pressure of the imaging gas. It is found that the impact of polarized gas atoms on the surface is of minor importance. The largest fraction of the temperature change is caused by normal heat conduction through the gas.

Photostimulated exoelectrons resulting from plastic deformation are emitted from slip steps. This was recently demonstrated and described in terms of photoemission from the freshly generated bare metal steps. An alternative explanation has been proposed in terms of emission from hypothetical electron traps in a 'transitional metal oxide layer'. This concept was developed on the basis of earlier observations of photostimulated emission from abraded metal surfaces. The emission from abraded aluminium is shown to behave quite differently to that resulting from plastic deformation. However, in neither case is it necessary to invoke electron trapping. In fact, the emission after deformation is not consistent with the electron trap concept. The model of photoemission from the freshly revealed metal better describes the observations.

The elastic constants c₁₁,c₁₂ and c₄₄ of sodium bromate have been calculated from measurements of the velocities of 10 MHz ultrasonic waves transmitted through a single crystal specimen in the following directions: longitudinal waves transmitted in the (100) and (111) directions, and shear waves transmitted in the (111) direction. The measurements have been made over the range 150-300K. The results have been extrapolated to 0K to permit the calculation of the Debye characteristic temperature which at 0K was found to be 238K.

In a study of solid particle erosion mild steel targets have been impacted obliquely by steel spheres at velocities up to 356 m s^-1. It is shown that metal can be removed from the surface by a process involving the shearing of surface material in the direction of motion of the projectile. In this way an overhanging lip may be formed and detached. It was found that adhesion between the sphere and the surface and localized thermoplastic shear in the target both played important roles in this process. The weight of material lost in individual impacts has been measured as a function of both impact velocity and angle. Good agreement is found between these results and those of multiple impact experiments reported by Kleis (1969).

Studies have been made of crack propagation in fibre-reinforced metal sheets. The reinforcing fibres were arranged not to fracture, whatever the tensile extension of the composite structure by use of a controlled decoupling mechanism, acting at the fibre/sheet interface. The fibres carry loads across the entire length of a crack in the sheet and energy is absorbed by interactions between the components of the composite structure as the crack extends. Two conditions for crack growth have been investigated: (a) an edge crack with non-uniform loading conditions, and (b) a central crack with uniform tensile loading of sheet under fixed-grip conditions.

A lamellar composite is approximated by a stack of very long longitudinal strips, of rectangular cross section, of elastic material bonded to rigid strips on their upper and lower faces and extended in a direction perpendicular to these faces. The lateral faces of the strips are assumed stress-free. The stresses and displacements in the cross section are calculated using two-dimensional stress analysis giving solutions in Fourier series. The effective modulus of the material is calculated for a range of thickness/width ratios and compared wth literature values. The analysis has relevance for the deformation of lamellar composites in polymeric and other materials.

The author has measured the electrostatic charging of two metal bodies which have been brought into contact and then separated. The charge Q is found to be given by Q=C₀V_c, where V_c is the contact potential difference and C₀ is the 'contact capacitance'. A technique for measuring C₀ is described, and it is shown that C₀ is simply related to the height of surface asperities. The charge is not affected by the velocity of separation or by sliding during separation in contrast to the findings of previous investigations. Tunnelling of electrons during the initial stages of separation does not appreciably reduce the final charge.

It was found that at low currents and low fields the steady-state forward postswitching curve of a silicon diode at low temperatures (below 15K) could be represented approximately by logI approximately=A+CV-B²( alpha sin² theta + beta sin⁴ theta ) where I is the current, V the voltage, theta is the angle between the direction of current flow and the magnetic field B, and A, C, alpha and beta are constants. A simple filament model with enhanced surface recombination is used to explain the results.

The authors present further results on the crystal structures of alkali antimonide photocathodes obtained from the scanning electron diffraction system reported previously (see abstr. A75195 of 1972 and abstr. A53166 1973). The first part describes investigations that have been carried out on the correlation between the crystal structures and photosensitivities of the following antimonide cathodes: caesium, rubidium, potassium, potassium-caesium, and sodium-potassium. The second part presents a review of previous work on the multi-alkali S20 photocathode, the initial SEDS results, and a possible model for the S20 photosurface.

Experimental measurements of backscattering as a function of incident electron beam energy, angle of beam incidence and atomic number of scatterer, together with energy spectra of backscattered electrons, are discussed within the framework of a simple, qualitative theory. A semi-empirical expression for the variation of backscattering coefficient with angle of beam incidence is derived. Spectra integrated over energy and angle of take off also tabulated from experimental measurements for several elements. The use of the experimental data to derive backscattering corrections for X-ray elemental analysis, particularly at non-normal incidence, is briefly described.

A method of measuring the magnetic easy axis misorientation relative to the substrate misorientation is described. A simple phenomenological theory of growth induced anisotropy is used to describe the observed effect. Results for six garnet compositions are given which show a variation in the ratio of the magnetic easy axis misorientation relative to the substrate misorientation. The effect of a substrate misorientation on the operating margins of a simple shift register is described.

Measurements of the phase of oscillating domain walls made by the Faraday method reveal nonlinearities in the motion which are affected by in-plane applied fields. These occur at velocities corresponding to theories by Sloncewski (see abstr. A36754 of 1973 and abstr. A57325 of 1974) concerning interactions of the moving wall with surface stray fields. Driving the walls at these velocities gives rise to additional hysteresis in the subsequently measured loops, which is associated with the dynamic formation of the Bloch lines. For ion-implanted specimens it is indicated that Bloch lines are still formed dynamically but do not persist after the drive fields are removed.

SnO₂ single crystals have been doped with varying amounts of Eu. The cathodoluminescence and photoluminescence spectra have been measured Thermoluminescence has been investigated in as-grown and doped crystals over the temperature range 100-400K. New traps appear, which are associated with the addition of Eu. When Li is added as well, these traps are not created to any significant extent because charge compensation by interstitial Li⁺ ions occurs preferentially.