Table of contents

Evidence from X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) is presented for a solid state reaction between aluminium and oxidised silicon, which results in the formation of a crystalline oxide phase of aluminium and elemental silicon. The oxide phase has been identified as a mixture of eta and gamma phases which are less dense and have more 'open' structures than the most stable alpha -Al₂O₃ phase. The authors suggest that this reaction which can occur under the conditions used for the manufacture of integrated circuits may be significant for electromigration failure mechanisms.

The photoconductivity transient following a short illumination pulse close to a surface is calculated as a function of surface recombination velocity, bulk minority carrier recombination time tau , diffusion constant, absorption length of the incident light and the strength of an electric field applied to drive carriers into or away from the surface. The shape of the decay is sufficiently sensitive to the competition between field and surface recombination velocity S to allow a unique determination of S and tau from a proposed experiment.

The semiconductor properties of Li-doped CoO crystals were investigated electrochemically. Depending on the doping conditions, the observed photoelectrochemical effects either corresponded to n-type behaviour or to the presence of a buried p-n junction. The predominant electronic defect type appears to be determined by the lithium concentration.

Visible electroluminescence has been observed in a suitably double-diffused silicon p-n junction under reverse-bias conditions. The threshold voltage for light emission can be made very stable by introducing a thin n⁺ layer between the p and n regions of the structure. When the bias across the structure is increased above this voltage a sharp rise in current due to avalanching is followed by emission of reasonably strong visible light from the diode surface. The current-voltage characteristics and the spectrum of the emitted light are reported, together with a physical interpretation based on intraband and interband transitions, and in good agreement with the observed spectral distribution.

Time integrated photographs have been obtained of the ³/₂ omega ₀ harmonic emission from spherical targets irradiated uniformly with a six-beam Nd glass laser system in the ablative mode. Extended filamentary structures are observed which indicate that self-focusing of the incident laser beams in the subcritical density plasma corona is occurring.

All types of polygranular carbon and graphite materials take advantage of the extremely high strength of sigma -bonds in elemental carbon. Manufacturing processes have been developed during the last century which allow the control and distribution of domains with anisotropic microstructure within the bulk material. Such polygranular graphite materials may be considered composites, consisting of the filler grain as skeleton and the binder carbon as matrix. However, the strength of sigma -bonds of elemental carbon is only partially utilised, because the fracture behaviour is controlled by crack propagation through the brittle and porous binder matrix. The basic problems encountered in manufacturing common polygranular carbon and graphite materials are also present in the fabrication of C/C composites. The carbon binder between the structural skeleton-now made of fibres instead of filler grains-remains the weakest part. Problems in manufacturing C/C composites and problems concerning fibre/matrix interactions are discussed. The possibilities and limitations in 'tailoring' carbon and graphite composites are considered.

A description is given of a method which may be used to predict the performance of a flowmeter subject to certain constraints. The flow channel is an insulating cylinder of circular cross-section, the contact electrodes are assumed to be mathematical points and the flow is restricted to the rectilinear axisymmetric case. The analysis includes the effect of a concentric annular stationary medium surrounding the liquid, but of different conductivity. The magnetic field may have any form, and this is found experimentally by measuring its normal component at a number of points on the cylindrical surface bounding the flow channel. The mathematical basis of the method is given, together with an outline of the computation and a description of the apparatus used to measure the magnetic field. The method can be used both as a means of 'dry calibrating' a given flowmeter and as an aid to flowmeter design.

Reports work which was carried out with the intention of making a semiconductor particle radiation detector with a small active volume. A study of the detector was made using a narrow collimated beam of alpha particles. The results, which showed that the authors' expectations were not fulfilled, can be explained qualitatively in terms of the electric field in the device.

A slice of silicon with specially patterned electrodes on each side was fabricated in an effort to make a particle radiation detector with a small active area. The active area was mapped out with the aid of a narrow collimated beam of van de Graaff generated protons and the area thus found is compared with the shapes of the electrodes on the faces of the slice. An attempt was made, by altering the bias condition on the electrodes, to improve the coincidence between the active area and the electrodes.

Silicon carbide may be an ideal mirror material for synchrotron radiation applications. Measurement of reflectance at 45 degrees angle of incidence, with two orientations of the reflector about the optic axis, allowed direct comparison of the reflectivities of various polycrystalline forms of silicon carbide with that of gold. Scanning electron microscopy revealed the surface characteristics of the silicon carbide samples.

The use of a tubular glass-fibre structure, cladded inside and outside with a material of rather lower refractive index, is proposed as a means of transmitting optical waves in a single mode, without restriction of diameter. The thickness of the wall of the tube becomes the critical dimension and this can easily be limited to 1-2 mu m to ensure cut-off of unwanted modes. Application of the usual HE₁₁ wave to transmission along a solid-core fibre can easily be adapted to a tubular fibre structure, offering the advantage of operation in a single mode even when the overall diameter is as much as 100 mu m.

An analytic expression for the ultrasonic dispersion in porous materials is obtained. It is shown that size determination of pores of a few microns radius using ultrasonic dispersion should be possible with available techniques. For pores with radius 0.1-1 mu m higher frequencies, such as those characteristic of vapour-deposited transducers, will be necessary. The velocity dispersion and ultrasonic attenuation depend on averages of different powers of the pore radius. A measurement of both will give information on the mean square deviation in pore sizes as well as the average pore size.

For application to aeronomy and space physics problems involving strongly magnetised plasma flows, the authors derived momentum and energy exchange collision terms for interpenetrating bi-Maxwellian gases. Collision terms were derived for Coulomb, Maxwell molecule, and constant collision cross-section interaction potentials. The collision terms are valid for arbitrary flow velocity differences and temperature differences between the interacting gases as well as for arbitrary temperature anisotropies. The collision terms had to be evaluated numerically and the appropriate coefficients are presented in tables. However, the collision terms were also fitted with simplified expressions, the accuracy of which depends on both the interaction potential and the temperature anisotropy. In addition, the authors derived the closed set of transport equations that are associated with the momentum and energy collision terms.

For an aluminium plasma produced by laser irradiation of 1.06 mu m, 0.15 ns and 3*10¹⁴ W cm^-2, hydrogen-, helium- and lithium-like emission-line intensities have been measured. Population equations of the helium-like ion have been solved for as many as 60 excited levels, where the escape factor has been incorporated to take account of the effect of radiation trapping for optically thick lines. The dominant broadening has been assumed to be due to the expanding streaming motion of the plasma. Fitting the calculation to the experimental data leads to this conclusion: the plasma is predominantly recombining while the lines are emitted, T_e approximately=1.3*10⁶K, n_e approximately=3*10²¹ cm^-3, N(Al¹¹⁺)R/v₀ approximately=2*10¹⁰ cm^-3 s (R is the radius of the plasma and v₀ is the typical expansion velocity), and the ion abundance ratio is N(Al¹³⁺):N(Al¹²⁺):N(Al¹¹⁺)=1:10²:3*10⁵.

Unit-cell parameters for the chalcopyrite type ternary semiconducting compound copper gallium selenide (CuGaSe₂) have been determined accurately, using the least-squares method, for reflections in the range of Bragg angles 64-82 degrees , by the X-ray powder diffraction method. A study of the thermal expansion of the chalcopyrite structure unit-cell of the compound, determined over the temperature range 28-685 degrees C, has revealed the anisotropy between the axial expansion coefficients; that for the c axis (24.93*10^-6 degrees C^-1) is about four times that for the a axis (5.91*10^-6 degrees C^-1) at 50 degrees C. Anomalous behaviour of the expansion coefficients, similar to that for AgInSe₂, AgGaSe₂ and AgGaS₂, has not been observed for this compound.

Studies the effects of adding Zn to CdS films and solar cells. It was observed that the film surface structures were quite similar to CdS films although the electronic properties showed a marked difference as the film resistivity increased considerably with increasing Zn concentration. Measurements on uniformly doped Cu_xS/Cd_yZn_1-yS solar cells showed no significant improvements in the photovoltaic response for concentrations up to 10% of Zn. Similar measurements on a Cu_xS/Cd_0.9Zn_0.1S, CdS solar cell, however, showed a significant increase in the open-circuit voltage, suggesting that the high series resistance in Zn-added films could be a cause for the observed low photovoltage.

Excess and 1/f noise intensity has been measured between 80K and 380K in uniform cross-section silicon resistors with various geometries and surface conditions. It can be analysed as a fluctuating conductance proportional to (mobility)², that is a carrier number fluctuation independent of temperature.

A detailed study has been made of the surface state of (100) orientated epitaxial layers of indium phosphide produced by the closed-tube-vapour-transport growth process. Particular attention has been paid to investigating the composition and chemical state of the first few atomic layers of the semiconductor surface. A well defined oxidation state has been found to be present. This also results in a surface that is heavily depleted of phosphorus and which is rich in indium. The study has been performed with Auger spectroscopy and Auger profiling. A fine structure was found to be present in the low energy Auger spectra obtained from these surfaces. The most consistent interpretation of this structure is in terms of cross-transitions originating from In-O and P-O complexes resident upon the semiconductor surface.

SiO₂ thin films (3000 AA) are chemically deposited on a silicon substrate at room temperature. Once densified the films exhibit physical and electrical properties comparable to thermal oxides, C-V studies indicate the presence of mobile positive ions inside the oxide layer.

The piezoelectric effect in stretched and polarised PVDF film is found to show strong dispersion in the audio frequency band in fact showing a reversal of sign between high and low frequencies. A possible mechanism is suggested.

Neutron flipping ratio measurements have been made on the intermetallic compound series Pd_2-xMnSb in order to determine the suitability of the series for future use as improved neutron polarisers. High polarising efficiencies were observed at several compositions and temperatures for the (111), (002), (220) and (222) reflections. The suitability of the series for use as polarisers is discussed in terms of polarising efficiency, reflectivity, resolution, absorption and residual radioactivity, and lambda /2 contamination, and comparisons are made with the currently used polarisers Co/Fe and Cu₂MnAl.