Table of contents

The MESFET-gate-conductor interruption, often representing a device lifetime limitation, has been characterised by measuring the activation energy E_a and material drift velocity nu _B for several types of narrow Al conductors regarding electron wind voiding. The Arrhenius temperature dependence law for current-guided diffusion has been found to hold good and E_a has been measured to be 0.16 eV and 0.14 eV for Al directly on GaAs and for Al on GaAs with a thin intermediate Cr layer, respectively. This result indicates that the presence of a chromium interface is detrimental to the stability and lifetime of Al gate structures.

An isotope effect on boron ions emitted from a liquid-metal-ion source utilising Ni-B base alloy is described. The B⁺⁺ ion intensity is as weak as 1/30 approximately 1/50 that of B^-, but the proportion of ¹⁰B⁺⁺ in (¹⁰B⁺¹⁰B⁺⁺) is smaller by 13 approximately 17% than for ¹¹B⁺⁺. This effect is predicted by the post-ionisation model of field evaporation, although there are certain discrepancies between experimental results and theory.

³He⁺(2S) production by a RF ion source has been measured by detecting the 30.4 nm radiation emitted when the 2S state is quenched in a high electric field. The production was maximum when extraction voltages and gas pressures in the source were low. The highest fraction He⁺(2S)/He⁺(1S) observed was 0.08%. This fraction is estimated to be accurate to within a factor of two.

In order to examine the lasing characteristics of the N₂ ion laser excited by a fast discharge, time-resolved measurements of the gain for the 391.4 nm and 427.8 nm transitions were carried out. The temporal behaviour of the population densities of the laser lower levels were measured by means of the interferometric method. The time histories of the sidelight at the laser transitions, which reflects the relative upper level population, were also measured. On the basis of these experimental results, a fairly good explanation of the lasing characteristics of the two laser oscillations is given.

A hybrid TEA CO₂ laser with intracavity CdTe electro-optic modulator has been constructed. Heterodyne experiments demonstrate that the laser induced chirp of 0.88 MHz mu s^-2 could be eliminated by application of the appropriate voltage waveform to the electro-optic modulator.

A high energy optically pumped laser system comprising a multipass cryogenic gas cell pumped with a frequency locked CO₂ TEA laser is described. Mid-infrared output energies for a number of lines in CF₄, FClO₃, NOCl and CH₃CCH are up to two orders of magnitude larger than those previously reported. Strong far-infrared emission is observed from CH₃CCH, and competition from the far-infrared transitions limits the output energies achieved from this gas.

Plane-strain wedge indentation of a rigid-perfectly plastic semi-infinite bi-layer is studied. A kinematic solution using rigid blocks is given. It is compared with well known solutions in two particular cases: wedge indentation of an homogeneous material and indentation of a bi-layer by a flat punch. The existence is shown of a critical ratio of layer thickness to wedge indentation width at which plastic flow is influenced by the substrate. The dependence of this critical ratio on the relative flow stress of the two materials is described. Close agreement is obtained from experimentally Vickers indentations performed on metallic bi-layers.

Cells previously used to study the streaming potential evident in fluid flow are modified to allow the insertion of test piece to study corrosion phenomena. The effects on metallic corrosion of induced streaming potential, charge transport mechanisms and mechanical aspects of the flow are evident in several experiments with a variety of cell configurations.

Low current, low pressure steady electrical discharges in pure helium, neon and argon have been investigated using the photon flux technique. Such discharges have been found to form layers of luminosity throughout the inter-electrode space which indicate a spatial variation of the electron transport parameters. The layers can be quenched by adding a few per cent of nitrogen to the rare gas.

The qualitative features of the gas motion in a convergent gas-blast circuit-breaker nozzle with an electric arc burning along its axis are studied by assuming that the gas is inviscid and incompressible. It has been found that when the current is sufficiently high the Lorentz force accelerates the flow strongly within the arc, thus increasing the flow entrainment into the arc. A region in which the flow is rather stagnant is also formed. The flow characteristic time is in the order of 150 mu s.

The depolarised Rayleigh scattering temperature dependence of the seventh, eighth, ninth and tenth homologues of 4,n-alkyloxybenzoic acid was investigated. A sharp increase of the scattered light intensity upon cooling was observed in the middle of the nematic phase. Polarised microscopic investigations confirmed the textural difference between the high- and low-temperature nematic regions (N₁ and N₂). The observed anomaly as well as the transition between classical (N₁) and smectic C-like (N₂) regions are discussed.

The effect of prior plastic deformation on the precipitation kinetics of europium-doped NaCl, KCl and KBr has been analysed using optical absorption, photoluminescence and electron paramagnetic resonance techniques. In the host NaCl, plastic deformation produces a considerable influence on the Eu precipitation processes into the metastable and stable phases. The introduction of defects by mechanical treatment strongly favours the formation of a second phase precipitate which does not nucleate in the undeformed samples and which can be tentatively identified as either NaEuCl₃ or Na₂EuCl₄. In contrast, in the hosts KCl and KBr, plastic deformation does not influence Eu precipitation into the metastable phase which nucleates at low temperatures (<100 degrees C) and was previously related with the Suzuki phase, indicating that the nucleation of this phase is homogeneous. However, the rate of Eu precipitation into metastable and stable phases with EuX₂ structure (X=Cl, Br) which nucleate at high temperatures ( approximately 200 degrees C) is enhanced in the plastically deformed samples, suggesting that the nucleation of these phases is heterogeneous. The effect of dislocation on pre-existing Eu second phase precipitates in both KCl and KBr has also been investigated. The results suggest that moving dislocations cause the re-solution of the preexisting Suzuki precipitates, creating complexes of a much simpler nature, while they create plate-like zones when acting on pre-existing stable dihalide EuX₂ second phase precipitates.

This paper reports the use of the nuclear transmutation back doping technique for studying the deep Cr and Fe acceptors in InP. The authors have demonstrated the changes in the electrical characteristics and the photoconductivity spectra for the InP materials studied brought about by this shallow donor compensation technique. In InP:Cr, it has been shown that the E_vb+0.95 eV level belongs to the Cr^2- lower charge state. In InP:Fe, it has been possible to confirm some of the optical transitions involving both Fe^3- and Fe^2-. In particular, this work has confirmed that the deep level E_cb-0.66 eV is the ground state of Fe^2-. This investigation has also allowed the authors to estimate the Fe doping concentration in a heavily doped sample and this has been found to be approximately 4.8*10¹⁶ cm^-3.

The magneto-optic polar Kerr rotation is calculated for films of Gd-Co (20/80) and shown to be thickness dependent for films <40 nm thick. The theoretical analysis is extended to search for the optimum overlayer material for rotation enhancement. Results indicate that careful matching of the overlayer and film thicknesses can lead to significant enhancement of the rotation developed.

Thin films of polyvinylidene fluoride in crystal form II have been subjected to detailed thermally stimulated discharge (TSD) studies. The poling parameters were varied systematically up to a poling field of 600 kV cm^-1, a poling temperature of 130 degrees C and a poling time of 30 min. Five TSD peaks were observed in the temperature range from -60 degrees C to 165 degrees C. Two of these peaks seem to be of dipolar origin, while two are probably caused by space charge. The fifth peak is attributed to premelting of the sample. It is suggested that the folds in the molecular chains are of importance to both the dipolar and the space charge relaxation.

A technique has been developed whereby a single glow curve measurement may lead to the determination of the trapping parameters E and S (the trap depth and frequency factor respectively) and the order of kinetics, without need of mathematical approximations, for first and second-order glow curves. This has been facilitated by using a hyperbolic heating profile. The technique measures t_m (time to maximum intensity of glow curve). and t_i (points of inflection on the rising and falling slopes). For first-order kinetics E gamma /k=1.925/D where D=t₂-t₁, gamma is the heating constant and k is the Boltzman constant, whilst for second-order kinetics E gamma /k=2.643/D. This analysis is developed further to include non-integer orders of kinetics, from which a technique is derived to uniquely determine the order of kinetics.

The study of the accuracy of methods for measuring the optical constants of thin films has been extended to combinations of transmittance and phase changes on transmission and also to transmission ellipsometry. All combinations of (T, phi _T) and also the ellipsometric functions generally produced regions of accuracy on an n-k diagram in the form of a concentric quadrants whose size decreased with d/ lambda ; for (T_s, phi _(Ts)) and (T_s, phi _(Tp)) the size of the quadrant decreased with angle of incidence, but the reverse was the case for (T_p, phi _(Tp)) and (T_p, phi _(Ts)). The combination ( phi _(Ts), phi _(Tp)) produced a double lobe pattern which showed only small regions of accuracy.

A simple scattering model-providing analytical expressions of electron inverse mean free path, stopping power and straggling parameter-is proposed. Such a model can be used in Monte Carlo simulations of electron transport problems. Cross-sections are derived from a schematic Bethe surface based on the single-mode approximation for the free electron gas. Fairly good agreement with experiment results and with other theoretical calculations is found for electron energies in the range between 50 eV and 50 keV for free-electron-like materials. An easy empirical correction to the conduction band cross-section allows one to use the model for transition and noble metals.

Photo-transfer thermoluminescence (PTTL) has been found to be highly dependent on gamma ray dose. The PTTL and the reduction in residual thermoluminescence intensity ( Delta RTL) suggest that transfer originates not only from the residual thermoluminescent (RTL) traps but also from other radiation-induced nonluminescent centres.