Table of contents

The electron-beam-induced conductivity of thin sputtered films of Al₂O₃ has been investigated. Measurements have been made of the variation of the coefficient of induced conductivity γ with primary beam voltage, primary beam current and bias voltage. The maximum value of γ observed in the films was 5, being mainly limited by the low (8 × 10⁷ V m⁻¹) breakdown strength of the films.

The change from high to low impedance of an amorphous semiconductor switch takes place at a critical field identified by the threshold voltage. The presence of conductive regions in the switching path reduces this threshold voltage. This change has been modelled by calculating the minimum resistive path length obtained when randomly placed uniform conductive spheres grow in a resistive matrix. The computed results are rather similar to those given by simply placing the spheres on a square or cubic lattice and are consistent with electrical observations in switching experiments.

An error in the usual analysis of thermally stimulated depolarization (TSD) phenomena is corrected.

It has been found that the FWHM of energy spectra of secondary electrons from a Be layer evaporated on Cu becomes smaller initially with increase of the Be film thickness, and then becomes broader as the thickness increases beyond a certain level. This feature has been simulated by a Monte Carlo calculation of secondary electron emission with satisfactory agreement.

In this paper the compressibility equation of Tait is generalized in a basic form with three arbitrary parameters. Data-fitting of these parameters can be made correct to the third order. Thus, the generalized Tait yields a more flexible equation of state that is also related simply to several other well-known equations of high pressure, all accurate only to the second order.

Optical and electron microscopy are employed to find the best deposition conditions for the growth of electrolytic amorphous germanium films. The polishing treatment of the substrate and the electrodeposition time are found to influence the homogeneity of the films, while the method of cleaning the substrate affects their structure. Chemical etching behaviour is also studied: it is characterized by a much higher etching rate than in crystalline germanium samples and by various etching figures. A brief discussion of the causes that may produce the observed patterns is given.

Some results concerning the effects of annealing galena in air atmosphere on its dislocation density and microhardness are presented. It is shown that the decreases in the dislocation distribution and hardness are related to the temperature and duration of annealing, and that the results are substantially similar to those of Stanton on naturally deformed crystals.

Measurements of the critical strain energy release rate G_c and the critical crack tip stress intensity factor K_c have been made on chopped-strand-mat/polyester-resin laminates using centre-notched specimens of constant width and varying initial crack length. In the determination of G_c allowance was made for irrecoverable energy due to progressive damage. The G_c values were converted to K_c values using the relationship K_c²=EG_c, where E is the initial modulus of the material. The direct determination of K_c gave lower values. However, when Irwin's plastic-zone correction factor for metals was applied, using the resin cracking stress as an equivalent yield stress, the corrected values compared well with those obtained from the G_c values. All the results showed a variation of K_c with initial crack length.

An analysis is given of the problems associated with measuring thermal conductivity in poor conductors at low temperatures, and a new sample design is described. This design, which employs inward radial flow in a disc, has been used for obtaining measurements in a number of two-phase polymers between 1·3 and 100 K. The samples consisted of varying percentages of polymethylmethacrylate dispersed in a continuous phase of polyoxypropylated glycerol. In spite of the very small size of the dispersed phase (similar 50 Å and upwards), it was found that anomalous behaviour only occurred below similar 10 K. It is suggested that at these temperatures the important phonon wave-lengths have become greater than the scale of the disorder introduced by the dispersed phase and that the phonons are therefore subject to additional scattering.

Solid solutions of tetragonal MgMn₂O₄ and cubic MgAl₂O₄ have been synthesized and characterized using the x-ray diffraction technique. Electrical conductivity (σ) and magnetic susceptibility (χ) have been measured over the temperature ranges 25-1000 °C and - 195-60 °C respectively.

All the compounds were found to be monophasic and crystallize, with either tetragonal (c/a> 1) or cubic symmetry. The critical concentration of MgAl₂O₄, required to stabilize the cubic structure, was found to be only 12·5%. This may be explained as due to migration of a considerable amount of Mn³⁺ to A sites. The values of energy of activation and free energy of activation obtained from ln σ-1/T and ln (σT)-1/T plots were found to be almost identical. All the samples exhibited paramagnetism at T> - 195 °C and indications of antiferromagnetic ordering at lower temperatures. Further, an increase in χ values with increasing concentration of MgAl₂O₄ was observed. An explanation is offered for this behaviour.

The optimum operating conditions for an 8-bit three-phase p-channel CCD were established. This was done by studying the electrical output and the transfer efficiency as a function of six variables: the input and output gate voltage and the clock voltage, overlap, offset and frequency. A transfer efficiency of 99·9±0·1% was recorded for the best devices using a scanning light spot efficiency measurement technique.

The heat capacities of the compounds Pb(Fe_0·5Nb_0·5)O₃, Bi_0·2Pb_0·8- (Fe_0·6Nb_0·4)O₃, Bi_0·4Pb_0·6(Fe_0·7Nb_0·3)O₃ and Bi_0·6Pb_0·4(Fe_0·8Nb_0·2)O₃ were determined in the temperature range 300-670 K with an adiabatic calorimeter that permitted a precision of about 1·5% in the measurements. Experiments were performed using an intermittent heating technique in order that equilibrium heat capacities might be obtained.

The curves of specific heat against temperature revealed anomalous behaviour at 374, 365, 424 and 492 K in Pb(Fe_0·5Nb_0·5)O₃, Bi_0·2Pb_0·8(Fe_0·6Nb_0·4)O₃, Bi_0·4Pb_0·6- (Fe_0.7Nb_0.3)O₃ and Bi_0.6Pb_0.4(Fe_0.8Nb_0.2)O₃ respectively. The transition enthalpies were estimated to be 82·8, 60·8, 75·6 and 54·0 cal mol⁻¹ respectively. The anomalous peaks in Pb(Fe_0·5Nb_0·5)O₃ and Bi_0·2Pb_0·8(Fe_0·6Nb_0·4)O₃ have been correlated with their ferroelectric Curie points, and those in Bi_0·4Pb_0·6(Fe_0·7Nb_0·3)O₃ and Bi_0·6Pb_0·4(Fe_0·8Nb_0·2)O₃ with their Néel points. Probable reasons for the low values of the enthalpies of transition have been suggested.

Thermodynamic functions such as enthalpy and entropy have been evaluated over the temperature range 300-670 K.

High-field electrical conduction over a temperature range of 303-363 K has been studied in sandwich structures of Al/Ta₂O₅/Al and Al/Ta₂O₅/Ta in the thickness range 400-900 nm. The oxide film was produced by reactively sputtering a tantalum target in a mixture of argon and oxygen. No marked rectification was observed in the samples and it was observed that the conduction process bore strong resemblance to either a Poole-Frenkel or a Schottky mechanism, the results showing a definite lowering of the activation energy for the conduction process with field. Detailed analysis of the data suggest an electrode-limited mechanism such as that suggested by Schottky.

The dielectric constant of triglycine sulphate in the form of compressed powders of varying particle sizes ranging from 55 to 500 μm has been measured at 100 KHz from 0 to 90 °C. Dielectric anomalies indicating the existence of ferro-electricity were observed for particle sizes up to 55 μm. The dielectric constant decreases with decreasing particle size and is much lower than that expected theoretically. These results have been qualitatively explained by postulating the formation of a defective surface layer of low dielectric constant.

The applications of and the problems encountered in the use of field electron emitters as cold cathode sources for electron beam devices have been reviewed. The possibility of using an etched carbon fibre as a cold electron source in such devices has been examined. A simple scanning electron microscope using a carbon-fibre field emitter has been constructed and produced stable pictures with a resolution of approximately 0·2 μm at a system pressure of 10⁻⁵ Pa. Unlike tungsten, the fibres will emit electrons for many thousands of hours at estimated current densities of the order of 10⁵ A cm⁻². Recently emission currents as high as 1 mA at applied voltages of approximately 3·5 kV have been obtained without any sign of breakdown after running continuously for 100 h.

A general technique is described for the inversion of formulae relating the optical constants n and k of a component of a thin-film system to observable functions of the system such as reflectance, transmittance and phase changes. The program may be applied to systems having complex refractive indices on both sides of the system interfaces, and the method is illustrated by reference to metals in the region of high reflectivity when reflectance and transmission ratios are measured.

Mössbauer spectroscopy has been used for the study of Egyptian goethite from different deposits of the Bahariya Oasis, in order to identify the different iron forms in the ore, and to investigate the physical properties of the mineral and its changes according to the geochemical conditions under which the ore was formed. Four representative samples were selected: the first one showed the existence of haematite with goethite, which is the normal final form to which goethite is transformed under high temperatures; the second gave two internal magnetic fields which could be due to water excess; the third one showed a relaxation effect due to small particle size; the fourth gave an extra hyperfine pattern with negative isomer shift which is still under investigation. The results obtained were confirmed by the x-ray diffraction and thermal analysis. A synthetic sample of α-FeOOH has been measured for comparison, in the temperature range from 77 to 392 K (the Néel point).

Electron probe microanalysis of oxygen in a range of binary and ternary oxides is described. Experimental data are presented for a range of electron accelerating voltages and for two different take-off angle instruments. The ratio of oxygen K emission from specimen and standard is found to reach a limiting value, the same for each instrument, as the applied voltage is increased. The observations are shown to support the thin-film model (Duncumb and Melford 1966) proposed for quantitative analysis of light elements and also to enable its range of applicability to be established in terms of specimen characteristics and experimental conditions. The model is used together with chemical composition data for the oxides, and a consistent set of mass absorption coefficients are calculated which are considered to be accurate within 10%. These new data are discussed and compared with previously published values.

Proposed absorption correction methods for quantitative electron probe microanalysis are evaluated with reference to oxygen analysis of oxides. Three established absorption correction procedures, the Andersen-Wittry, simple Philibert and full Philibert models, are considered and their predictions compared with experimental measurements. The findings are discussed in relation to the x-ray distribution with depth in the target as given by the different models. It is shown that the full Philibert treatment gives best agreement, although none of the models provides a satisfactory absorption correction for practical light-element microanalysis.