Table of contents

A physical system capable of using low temperature differences is investigated. The results of the experimental study are in good agreement with those obtained from a simple theoretical model reported earlier (see Rup et al., J. Appl. Phys., vol.49, p.3521 (1978)). The system makes use of the regenerative oscillations set up in water columns in a three-limb arrangement consisting of a U-tube enclosed at the top and an output tube which is open to the atmosphere. Air is used as the working fluid.

Crystals of semiconducting CdF₂:Mn:Y have been heated under a dynamic vacuum of 1*10^-4 Pa at temperatures ranging between 120 degrees C and 700 degrees C for 1-6 h. The results of van der Pauw measurements indicate that the deconversion does not make any difference as far as the initial resistivity of the crystal is concerned if the heating temperature is kept below 250 degrees C. However, above 250 degrees C the resistivity increases in an irreversible manner due to heat treatment, the total rise depending on the duration and temperature of such treatment. Deconversion is favoured by a set of the atomic concentrations of Cd, Mn, and F which have been computed on the basis of microprobe analysis data.

Measurements of the energies of electrons emitted from the surface of a silicon dioxide film thermally grown on a silicon substrate are reported. The results indicate that significant charging of the oxide surface occurs at low beam energy but when the beam completely penetrates the oxide layer little or no charging occurs following the predictions of a recently developed theory of electron-beam-induced conductivity. Further measurements showing the effect of substrate potential on the energies of the back-scattered electrons suggest that voltage measurements and the observation of voltage contrast in the scanning electron microscope should both be possible on passivated devices if the beam completely penetrates the insulating passivation layer. At lower beam energies these measurements are only possible for short periods of time after the commencement of irradiation.

The author considers a point source emitting particles in an infinite, absorbing medium. The subsequent history of these particles is governed by the one-speed Boltzmann transport equation which is solved with a new synthetic scattering law. The modelled scattering law allows a combination of forward scattering, backward scattering and isotropic scattering and it enables an exact, closed form solution to be obtained by the method of Fourier transforms. The solution of the transport equation is evaluated numerically for a range of parameters and compared with some essentially exact results obtained by Vanmassenhove and Grosjean (1967) who employed the Henyey-Greenstein scattering law.

The time evolution for the populations of the ground state hyperfine Zeeman levels of caesium atoms are analysed for the case where a caesium beam is optically pumped, under different conditions of polarisation, either with a weak monochromatic laser light or with the resonance light from a spectral lamp filtered by a caesium cell. The optical detection of the 0-0 'clock' transition in the atomic beam is also discussed for applications to frequency standards.

The mechanism responsible for the effectiveness of xenon addition on the room temperature operation of sealed CO-He CW gas lasers is investigated with electron density, discharge potential and small-signal gain measurements. It is established that the discharge impedance is lowered, the electron density increased and the gas heating decreased, but there is no need to postulate a change in the electron distribution function. One causal sequence explains all the xenon addition results and also the effects of the addition of argon and krypton.

A new model is presented for a reflector producing a shaped narrow beam when illuminated by a point feed. The deviation from an idealised (Dunbar) model which has zero beam width in the geometrical optics approximation is regulated by a single arbitrary function tau , introduced to enhance the physical optics performance. In terms of tau , the phase distribution on a plane aperture is readily computed. Reflector profiles are then calculated by integration along the characteristics of a first order non-linear partial differential equation, leading to explicit formulae involving only ordinary quadratures. Initial data arises naturally on the central-section curve. It is shown that for continuous reflectors a well-known design due to Brunner (1971), frequently used in surveillance radar, is mathematically inconsistent.

The author presents a theoretical discussion with experimental comparison of the factors limiting the performance of a surface acoustic wave spectrum analyser plus digital integrator when used with photodetection pulses at the input. It is shown that photodetection-noise-limited operation can normally be achieved in which case the performance is expected to be similar to that attained with a digital autocorrelator. A discussion of the factors which ultimately limit the performance of such a system is included. Finally, examples of actual optical measurements are given demonstrating that the expected performance can indeed be achieved.

The thermal conductivity of O₂, N₂ and CO₂ has been calculated as a sum of translational, rotational, and vibrational components. The rotational component is a fixed fraction of the translational component of the thermal conductivity. The vibrational component is calculated explicitly and estimated or experimentally determined values of relaxation times and diffusion coefficients are not required. The results of the calculations compare favourably with experiment over a temperature range 400-1500K.

The authors present an account of experiments to determine the effect of polyacrylamide additives on the breaking tension of water. Firstly, a new strain-gauge method for measuring the static breaking tension of a liquid enclosed in a stainless steel Berthelot tube is described. Secondly, the results obtained for the static breaking tensions of dilute polyacrylamide solutions are reported. Thirdly, the results found for the dynamic breaking tensions of these solutions are also given. It is found that the presence of the polymer additive in the water makes no different to the values of the static breaking tension but leads to a reduction in the values of the dynamic breaking tension.

The author discusses the problem of relating the fundamental elastic properties of anisotropic single crystals to those of polycrystalline bulk materials. It is shown that the orientation-independent relationships are not in fact independent of each other and are insufficient to enable the constants to be found. Some useful results do, however, follow. Thus, the methods of Reuss (1929), Voigt (1928), and Hill (1952), lead to the same calculation of bulk modulus for polycrystalline materials and show that it should be identical with the single-crystal value. It is also shown why polycrystalline cubic metals behave in an isotropic manner when the grains are completely randomly oriented. Departures from randomness (development of an orientation texture) render increasingly invalid the widely accepted relationship between the moduli, E and G, and v (Poisson's ratio), viz. E=2G(1+v).

The structural change from wurtzite to rock salt in solid CdS has been observed both under static and dynamic conditions. A static change was reported also for powder samples. The phase transition is accompanied by a decrease in the specific volume and a drop of several orders of magnitude in electrical resistance. Using a powder gun, a manganin pressure gauge and measurements of electric resistance, the phase transition of porous CdS was found to begin at 24 kbar. The resistance drop obtained was about ten orders of magnitude. A single loading wave results in a two-wave structure in the porous material. It indicates that the compaction of pores is done along an incomplete compaction Hugoniot. Hence the volume change is less than that obtained by assuming a complete compaction at zero pressure.

A series of experiments is described in which radioactive tin was diffused into GaAs for a wide range of conditions. Radio-tracer profiles were plotted and diffusion coefficients were calculated. It was found that at the lowest temperatures used ( approximately 850 degrees C), the measured diffusion coefficients depended on the doping of the original GaAs slice used in the experiment. At higher temperatures ( approximately 1100 degrees C), however, the diffusion coefficient was independent of the substrate material. Electrical measurements were also carried out on the diffused specimens so that direct comparison could be made between tin concentration and free carrier density. It was found that at high doping concentrations there were many more tin atoms than electrons in the samples. The results are interpreted in terms of a model in which the tin diffuses by way of charged gallium vacancies.

Polycrystalline films of PbSe and PbTe up to 10⁴ AA thick were condensed at 15 to 300 AA s^-1 in residual air at 10^-3 to 10^-8 Torr pressure on to glass and polished stainless steel substrates, initially at room temperature, at normal and oblique vapour incidence. Surface structures were determined by high-energy electron diffraction at a series of film thicknesses. Distinct regions of different crystal orientation are identified dependent on film thickness, residual gas pressure and composition, deposition rate and the nature of the source material. The relationship between the angle of vapour incidence and the tilt of the orientation axis is also established. The influence of the experimental parameters on the development of the different orientation regions is discussed and the results are compared with similar results from PbS films.

Barium borate glasses containing 0-35 mole% V₂O₅ were found to be homogeneous. Optical absorption spectra indicated that only V⁴⁺ of the lower valence states of vanadium was present. The molar volume data suggested that a change in the structure associated with vanadium ions occurred at around 22% V₂O₅. ESR spectra showed that a more continuous change occurred in the electron structure associated with the V⁴⁺ ions as the V₂O₅ content was varied. Resistivity and activation energy decreased rapidly with decreasing vanadium-vanadium separation, while, at constant % V₂O₅, they showed a minimum at V⁴⁺/(V⁴⁺+V⁵⁺)=0.45. Thermoelectric power of glasses with 25-30% V₂O₅ showed very low activation energies, in agreement with a polaron hopping mechanism.

A measuring method is presented that allows the determination of the electric charge transferred during a metal-polymer contact in the presence of an external or internal field, the latter being produced by the charges that are transferred to the polymer. The polymer is used in the form of grains of about 1 mm diameter which oscillate in an electric field between two metal electrodes. Each time the grains collide with these electrodes a transfer of electric charge takes place which causes a change in the mobility of the grains. This change in mobility shows a pronounced dependence on the work-function of the metal electrode, when the electric field produced by the charges deposited on the polymer grains is properly taken into account.

The effect of interfacial conditions upon the opto-electronic properties of p-Ge/n-ZnSe heterojunctions has been studied by engineering the interface of such junctions into two quite distinct and different forms. The first of these has been produced by the evaporation of zinc selenide on to an ordered and oxygen-stabilised (100) germanium surface. The second has been a consequence of the post-growth annealing of junctions formed from the evaporation of zinc selenide on to clean, restructured (100) germanium surfaces; a treatment that has resulted in the development of an interfacial compound phase. The current-voltage and photoresponse characteristics of the junctions have then been determined and models have been proposed that relate to the various conditions existing within the junctions.

Electron cyclotron resonance in alloys of mercury cadmium telluride having a mole fraction x of CdTe equal to 0.20 and 0.215 has been observed in transmission at 337 mu m using an HCN laser. Semiclassical interpretation of the lineshapes leads to values of the band edge effective mass and estimates of the relaxation time between 77 and 136K. For x=0.215 the effective mass ratio is 9.7+or-0.3*10^-3 at 77K. The temperature dependence of the effective mass is compared with Kane's theory (1957) and is found to be stronger by a factor of two than that predicted, with an experimental temperature coefficient of 5*10^-5m₀K^-1.

Charge transport phenomena in complex dielectric media are frequently characterised by distributed relaxation times and associated activation energy spectra. The population distribution of such relaxation phenomena may be determined via isothermal observations of associated rate processes or by variable temperature (tempering) observations. The author shows how power law and logarithmic power law initial relaxation time population distributions lead to analytically simple forms for reaction rates under both isothermal and tempering conditions. It is thus indicated how measured relaxation rate data can be used to deduce arbitrary population distributions.

The sixth-rank tensor K describing the nonlinear electro-optical fourth-order effect has been calculated. A relationship between the non-zero components of the above tensor for all 32 crystallographic classes is shown. The calculations were executed with the aid of a tensor function describing the dependence of the dielectrical impermeability tensor on the electrical field tensor. It has been shown that changes in the optical properties of crystals due to the fourth-order electro-optical effect are similar to those brought about by the Kerr effect.

A modified equation is proposed for the X-ray production range of 2-15 keV electrons in solids. The modification is obtained by an experimental procedure which compares the difference in X-ray intensities between pure element thin films and 'bulk' standards. The elements evaluated were Al, Ti, Ni, Zr, Nb, Mo, Pd, Ta and Pt. Monte Carlo simulations were made for several of the elements and agree with experimental results to within 5%. There was one exception, in the case of a high-atomic-number film (Pt on Si) at low keVs. Here the deviation increases to 10-20%. The modified equation is also compared to other range equations in the literature.