Table of contents

A high voltage scanning electron microscope was used to observe the magnetic domains of an iron-3% silicon polycrystal sheet. The increased accelerating voltage results in the enhancement of magnetic contrast, the moderation of topographical contrast caused by the surface projections and the reduction of electron channelling contrast, thereby making it possible to observe the domain structure with great ease.

New developments of the electro-optic light deflector using total internal reflection of the light are given. By arranging the electrodes in the manner described it has been possible to deflect over 80% of the transmitted light from the zero to either of the first orders. The arrangement is ideally suited for further miniaturization and it is anticipated that switching between the orders will eventually be possible with an applied voltage of only a few volts. Suitable applications include beam steering, multi-stage deflectors and information processing.

An error in an earlier publication (Bell 1973) has been pointed out by Burt and Inkson (see abstr. A22442 of 1975). The corrected treatment still implies appreciable hindrance by momentum conservation of negative affinity emission from silicon (110) and (111) surfaces.

Observations of very low values of the holding current of amorphous chalcogenide memory devices, which have nearly complete crystalline filaments, are attributed to microfilaments which connect neighbouring crystallites. The effect of the trailing edge of the set pulse when switching memory devices is described, and the observations are attributed to the occasional occurrence of microfilaments which do not crystallize unless cooled slowly. Microfilaments may also explain the effect of polarity when additional short set pulses are applied to a fully set switch. Distinctive changes in resistivity occur, which may be due to electromigration.

A system of first-order coloured fringes is described. Microtopographical survey of features lying within the spectral spread of the first order is rendered possible. Measurements can also be made within the spread of the second order.

An analysis, by nuclear methods, of AF₃ and MgF₂ thin films has been made using 2.5 MeV He⁺; backscattered alpha -particles and K X-rays emitted in ( alpha ,X) reactions are observed. The impurity concentrations are strongly dependent on the conditions of preparation and can reach high values. Electrical properties of such thin films appear to be nearly independent of the impurity concentrations and are discussed in the framework of the Mott-Davis model.

A study has been made of the growth behaviour of zinc selenide deposited from the vapour phase on to (100) germanium surfaces. The deposition has been performed upon clean, restructured Ge (100) 2*2 and ordered, oxygen covered Ge (100) 1*1 surface structures in conditions of ultra-high vacuum (10^-9-10^-10 Torr). Prior to deposition the germanium surfaces were assessed with low-energy-electron diffraction and Auger electron spectroscopy. An investigation has then been made of the influences that substrate temperature, substrate contamination (specifically oxygen) and degree of vapour saturation have in controlling the growth behaviour of zinc selenide deposited on to these structurally ordered germanium surfaces.

The adhesion of small gold particles and evaporated gold films to air-cleaved and ultra-high-vacuum-cleaved mica surfaces has been investigated. A vacuum microbalance revealed large variations of particle adhesion for different regions of a vacuum-cleaved surface. A potential probe available in the same system similarly showed large variations in the surface charge. The potential variation and large adhesion disappear on exposure of the surface to contaminants or upon irradiation by an electron beam. These regional variations are believed to be due to local excess and deficiency of potassium ions, created during cleavage. For evaporated gold films on mica, adhesive strengths were compared using a simple cantilever method. Films deposited on vacuum-cleaved faces adhere much more strongly than those on air-cleaved surfaces.

The characteristic parameters of a solid-to-solid diffusion system are investigated. The net boron concentration of the pyrolytically deposited SiO₂ films used as diffusion sources is determined by infrared spectrophotometry. The data of the diffused layer in Si are used to correlate the infrared absorption spectrum with the composition of the SiO₂ films. The absorption cross section of the B-O oscillator is determined. The surface concentration and junction depth of the diffused layer in the Si are determined from the infrared absorption of the SiO₂ film and by the four-point probe and bevelled-edge methods.

Torsion pendulum measurements of the longitudinal shear modulus in 'single-crystal' samples of an S-B-S block copolymer are reported. These samples consisted of a hexagonal array of polystyrene cylinders embedded in a matrix of polybutadiene, with the cylinder axes uniaxially aligned. Sample morphology and associated anisotropic physical properties resemble those of a miniature fibre-reinforced system. The shear modulus calculated from the torsional stiffness by conventional means, assuming St Venant's principle, is found to depend upon the sample length/width ratio, the results for short specimens being double those for very long specimens. It appears that St Venant's principle expressed in its usual form is not applicable to materials possessing a large mechanical anisotropy. An alternative interpretation of experimental results is given by invoking the shear-lag theory of fibre reinforcement.

Studies have been made of the behaviour of metal tubular reinforcing elements having a high yield strength and limited ductility. When incorporated in a brittle resin matrix, these elements normally fail with the occurrence of very limited ductile deformation on each side of a matrix crack. It has been observed that immediate failure can be prevented by the presence of a loosely fitting cylindrical core of suitable dimensions. In these circumstances the initially necked-down region propagates progressively along the length of the tube allowing the reinforcing member to extend by a considerable amount.

Fracture of a reinforcing element of any length can be prevented by progressively decoupling the element from the rest of the composite structure as the tensile load carried by the element increases. The design and fabrication of one type of reinforcing element possessing such stress-controlled decoupling characteristics is described and its behaviour is compared with that predicted from simple theory over a wide range of conditions.

A method is proposed which allows for the reinforcing effect of a birefringent plastic coating used in assessing strains in a loaded metal structure by photoelastic techniques. Existing equations are only valid for elastic deformation, but the new equations, which make use of the strain-hardening characteristics of the metal structure and the properties of the plastic and adhesive employed, are applicable to strains beyond the yield point of the metal. Test results show that, for a strain of 0.02 in the coated metal, failure to allow for the reinforcing effect of the plastic would introduce an error of approximately 25% when strains are measured. The new equations can be used to allow for the stiffening effect of the birefringent coating if the stress-strain characteristics of the coating and the metal are known.

Room-temperature electrical resistivity, Hall mobility and Seebeck coefficient measurements on relatively-low-density, hot-pressed, boron-doped Ge₂₀Si₈₀ alloys are reported as functions of 1/R_He in the range 2*10¹⁹-3.4*10²⁰ cm^-3. The temperature variations of resistivity and Seebeck coefficient are reported over the temperature range 300-1200K and of 1/R_He and the Hall mobility over the range 300-950K. Within experimental error the absolute values and 1/R_He dependence of the Seebeck coefficients are indistinguishable from single-crystal values. Substantial reductions in carrier mobility accompany the hot-pressing method of preparation, although the reduction is not solely due to porosity effects. A simple mixed scattering model is employed in analysing the electrical data and the conclusion reached that assigning a Hall factor of unity leads to an overestimation in carrier concentration by between 30 and 40%.

Detailed electrical measurements on silicon solar cells before and after electron irradiation show that the degradation in performance is due entirely to a reduction in minority carrier lifetime in the bulk material. The measurements also reveal a systematic difference between cells made from pulled and floating zoned crystals.

Several works on punch-through diodes have shown the capability of the device when used as a low-noise local oscillator or amplifier. Similar noise performances are thus expected in self-mixing systems. Some experimental and theoretical results concerning punch-through diodes used as self-oscillating X-band mixers are presented. The noise figure and conversion gain have been measured against bias current, self oscillator (LO) power level and input power, for IF frequencies ranging from 100 KHz to 100 MHz. A noise figure of 8.5 dB was obtained with N+P pi N⁺ diodes. An analytical treatment is given for frequency conversion effects in terms of a quasilinear network theory. Theoretical results on conversion gain are presented which indicate substantial qualitative agreement with experimental results.

Differences in the polar dielectric constant and loss of the 'tungsten-bronze', KSr₂Nb₅O₁₅ have been observed between the poled and unpoled states. Dielectric dispersion occurs in the multi-domain state at frequencies four orders of magnitude lower than in BaTiO₃ crystals. An explanation of this behaviour is presented in which unsaturated material in the 180 degrees domain walls makes a large contribution to the dielectric constant and loss. Analogy is made between the behaviour of domain-wall material and the dielectric softening of bulk material at the ferroelectric-paraelectric phase transition.

The electrically excited thermally stimulated current (ETSC) in evaporated silicon oxide films was studied below room temperature. The experimental results had only one peak at a temperature T_m, which varied with the exciting field. The peak temperature T_m became lower and the half-width Delta T of the peak extended to the lower-temperature side as the exciting field increased. It is reasonable to adopt the two-site hopping model to analyse the ETSC results; however, it is shown that the features of the ETSC results could not be explained on the symmetric model but on the asymmetric one proposed by Pollak (1972), i.e. the depths of potential wells of the two-site pair have a difference Delta phi . The relaxation current also depended on temperature, which was distinctly observed below the temperature range where the ETSC was observed.

The extrinsic electrical conductivity of sodium chloride may be reduced or even eliminated by the association of anion and cation impurities. One of these impurity associations (Ca...PO₃) takes place when the melts from which the crystals are grown contain added boric oxide. The Ca...PO₃ association gives rise to absorption bands in the infrared and the decrease in the electrical conductivity is associated with an increase in the measured absorption of the bands. Measurements permit a calculation for the formation enthalpy of a Schottky defect (2.30+or-0.01 eV), anion vacancy migration enthalpy (1.11+or-0.04) eV) and the binding energy for the anion impurity-anion vacancy association (0.44+or-0.16 eV).

The piezoelectric, dielectric and elastic moduli of poled BaTiO ceramics are shown to deteriorate after the temporary application of a high compressive stress applied parallel to the polar axis. The degree of deterioration, or change, is shown to be a function of previous ageing time. The samples were aged at 70 degrees C. This change is greatest for the Least aged samples and is shown to diminish markedly as ageing time is increased. The permanent loss in ceramic remanent polarization after application of the stress, as calculated from the measured moduli, diminishes with ageing time. The calculated permanent transverse strain associated with this loss in polarization is compared with experimental measurements. A good agreement, within the bounds of experimental error, is shown for all but the least aged specimens.

The topological switching of a bubble array into one of the opposite polarity by a bias field pulse is studied in a garnet film by high-speed photography. The key requirement for regular switching is found to be an anisotropic wall velocity which causes the expanding bubbles to make contact with only four out of six of the nearest neighbours. The same anisotropy of almost 2:1 in the saturation velocity is also observed in isolated bubbles pulsed to expand. The velocity anisotropy and the static bubble ellipticity are related to a 2.2 degrees misorientation of the film's (111)-axis from the surface normal, which gives rise to an in-plane magnetic anisotropy.

The spontaneous polarization of the triglycine sulphate in the form of compressed powders with varying particle size has been measured from 0 to 55 degrees C, and it is very much lower than that expected for a polycrystalline sample. This, along with the evidence that spontaneous polarization decreases with the decreasing particle size, indicates that the surface layers may have lower values of spontaneous polarization than bulk material.

A study is made of electro-optic total-internal-reflection diffraction device modulator electroding. This can cause reflection phase inequalities which can reduce transmission (zero order) and degrade the extinction ratio. Al, Cu, Au, and Cr electrodes are considered and Al/Cr appears the optimum choice for LiNbO₃ devices. A practical LiNbO₃/Cr device realization is shown to exhibit a 0.6% insertion loss contribution due to this effect and agrees with theory. Analysis shows that a reflection phase mismatch of 16 degrees adds to insertion loss by 2%, but at 28 degrees (mismatch) this addition rises to 6%. An extinction ratio >100:1 was noted.