Table of contents

The method of elementary solutions is used to deduce numerical results for the critical thickness of a multiplying slab in neutron-transport theory.

Presents a detailed calculation using the method of finite differences to study the dynamics of pulsed CO₂ laser annealing of ion-implanted Si. The calculations are based on a thermal melting model, taking into account the temperature dependences of all pertinent material parameters, including the absorption coefficient. The authors investigate the 'thermal runaway' behaviour and calculate the threshold power density to cause thermal runaway and surface melting of Si during CO₂ laser annealing.

A model is developed for plasma in the 'vacuum' region outside a compressed Z-pinch. Currents induced at the wall are shown to remove the outward bounce after compression observed in numerical simulations of pinch formation.

The conductivity of phosphate glasses containing two transition metal oxides, vanadium and iron oxides, has been investigated. Mossbauer spectroscopy studies of the valency state of iron ions excluded the influence of the electron transition Fe²⁺ to Fe³⁺ on the conductivity for the case in which the content of V₂O₅ exceeds X=10 mol% in a glass of 50 P₂O₅+(50-X)FeO+XV₂O₅ composition.

Reports on the effect of DC electric field on the sheet resistance of thin tin and chromium films in the thickness ranges 200 to 800 AA and 50 to 500 AA respectively. The sheet resistance increases in chromium films and decreases in tin films, with the increase in DC electric field during film growth.

The dependence of the dielectric properties (permittivity and phase transition temperatures) on the DC bias field (0-0.9 MV m^-1) for the paraelectric to ferroelectric (I to II) and the paraelectric to pressure-induced phase (I to III) transitions for trissarcosine calcium chloride (TSCC), was measured. The effect of the DC bias field on the dielectric properties is striking for the I to II transition, whereas it is less so for the I to III transition. The above facts support the theory that the pressure-induced phase III is antiferroelectric. The effect of the DC bias field on the dielectric properties for the I to II transition is explained in terms of the phenomenological theory.

Presents a method of measuring the thermal conductivity of very tiny and fragile samples, based on the differential thermal conductivity technique. To illustrate the possibilities of this method the authors have measured the thermal conductivity of filaments of NbSe₃ (10 mu m in diameter and 3 mm in length) in the temperature range 2 to 150K with good resolution.

The electron trajectories of the retarding field electron energy analyser proposed by van Oostrom (Philips Res. Suppl., vol.1, p.1, 1966) are simulated with a digital computer, as an aid to designing an energy analyser of high resolution. It is shown that the energy resolution is highly dependent on the anode-lens and lens-shield electrode distances; however, the collector electrode does not need to be hemispherical, and its shape is not critical as argued by van Oostrom in his original paper. It is also shown that it is theoretically possible to obtain much higher resolution than the experimentally obtained value of 10 meV.

Theoretical principles of a method for measuring the absorption cross-section for thermal neutrons are presented in a one-velocity approach. In consecutive measurements the sample investigated is enveloped in shells of a known moderator of varying thickness and irradiated with a pulsed beam of fast neutrons. The die-away rate of thermal neutrons escaping from such a system is measured. The absorption cross-section of the unknown sample is found as the intersection of the experimental curve (die-away rate versus thickness of the moderator) with the theoretical one, calculated for the case when material buckling of the sample is zero.

In the one-group model applying thermal neutron dynamic parameters, average dynamic parameters including the energy distribution of thermal neutrons are used instead of the one-velocity approximation for a two-component system. Next, the diffusion cooling correction is introduced into the thermal neutron average dynamic diffusion coefficient, into the dynamic material buckling, and into the Maxwellian distribution for thermal neutrons. An example is given for spherical geometry. The relation between the experimental pulsed parameters and the definitions for the average macroscopic cross-sections are given for hydrogenous media. Results of the measurements for the system of concentric spheres are presented.

Commonly used models for electron energy transport involve free parameters which must be tuned to experiment. Such models often give a poor representation of the effects of self-consistent electric fields. The author briefly discusses the various approaches that have been employed and outlines a novel method which attempts to model the expected effects of such fields. This is as a substitute for accurate solution of the relevant kinetic equations which is totally uneconomic in a two-dimensional simulation code. Simulated X-ray spectra are compared with experimental measurements to assess the performance of the model produced.

A laser Doppler technique has been used to measure the velocity of a 'falling-slug' in a high pressure viscometer. From this data the viscosity of two polyisobutenes, M_n approximately=400, M_n approximately=700 have been determined as a function of pressure. Viscosities in excess of 10⁷ Pa s have been determined by this method.

Cylindrical reactive blast waves were generated in a rectangular shock tube by the incidence of a detonation wave on a two-dimensional converging-diverging nozzle, with a narrow throat, placed in the tube. The observed trajectories of the shock front and reaction zone in the diverging section show that the blast wave behaves in a similar manner to that of the lead shock in a detonation cell. One particular similarity is the abrupt rate of decay that occurs in both types of waves following the decoupling of the exothermic reaction zone from the frontal shock. From the post-shock density field, obtained by a Mach-Zehnder interferometer, and the velocity profile, it is shown how the locus of the reaction zone may be calculated. A comparison is made of the predicted and observed reaction zone trajectories for oxyacetylene at an initial pressure of 15 Torr; these agree well for an assumed value of the activation energy of 71 kJ mol^-1 for this system. It is suggested that the nozzle technique could be used for induction-delay measurements in detonation waves.

A comprehensive theoretical analysis of the form of measurements obtained in the electron swarm experimental method due to Grunberg is presented. The analysis covers the general case of such experiments in which electron diffusion, electron collisional ionisation and electron attachment are present. The approach is based upon the scalar form of the Maxwell-Boltzmann continuity equation; the concept of energy supplied from a uniform drift field; and, the fact that typical experimental measurement information may be resolved into distinct electron and ion components. A generalised voltage ratio expression is derived in a form which is directly applicable to the characteristics of integrated voltage transient measurements. A special case of the analysis is shown to be consistent with the existing experimentally tested, simplified theory. The generality of the analysis provides the opportunity of designing new experimental situations in which drift velocities, diffusion coefficients, ionisation coefficients and attachment coefficients may be analysed from the same set of measurement data.

Ion line enhancement detected by the Arecibo 430 MHz radar is interpreted to be a result of nonlinear interaction of weak Langmuir waves via ponderomotive force. These weak Langmuir waves originate in the scattering of the O-mode heater wave and of the excited Langmuir waves from thermal ion acoustic waves. Theoretical analysis shows that those enhanced density irregularities associated with ion lines are forced ion acoustic modes; but their frequencies, determined by the beat frequencies of Langmuir waves, are not necessarily their characteristic frequencies. It is expected that much stronger ion line enhancement would be observed if back-scatter radar of lower frequencies (e.g. 50 MHz) was employed.

It is suggested that a very energetic (>10 MV) electron beam can be used for efficient compression, provided its energy is properly programmed. The optimal voltage shape was found numerically for boron spheres, and was compared with that derived from the theory of homogeneous isentropic compression. Shaping improves the compression ratio by a factor of 7 as compared to that attained by a constant voltage pulse.

The firing and delay characteristics of a simple coaxial type of triggered vacuum gap are described and compared with the planar type. The designs are new and differ from those reported earlier. By analogy with gaseous breakdown the statistical and formative time lags have been determined.

The kinetics of silicide growth are usually studied using the Rutherford ion back-scattering technique. The author employed a sheet resistance method to investigate the kinetics for Ni₂Si growth. The results confirm that the process is diffusion limited. The resistivity of the Ni₂Si layer appears to depend on the substrate type. Ni₂Si grown on n-type silicon wafer has a resistivity of 60+or-3 mu Omega cm while that formed on p-type substrate has a resistivity of 32+or-2 mu Omega cm. There is also a dependence of the activation energy for the diffusion on substrate type. A value E_a=1.0+or-0.1 eV is obtained for n-type substrate, and E_a=0.51+or-0.05 eV for p-type substrate. These results further highlight the dominant role played by the substrate in silicon-based technology.

Calorimetric measurements of the emissivity and absorptivity on Cu, Al and Ta samples of high purity are performed. The measurements are compared with other experimental results and theoretical predictions. The disagreement between the experimental results and theoretical predictions is considered.

The efficiency of solar energy conversion in a photovoltaic device consisting of an infinite number of solar cells is examined in detail. A mathematical analysis of the complicated functional dependence of the efficiency on temperature and light concentration ratio is presented. Although an infinite tandem seems, at first sight, only of academic interest, it is shown that the various approximate expressions obtained for the complicated efficiency function can give some more insight into the basic limits of the photovoltaic conversion, and can enable easy predictions of an upper limit of the efficiency of tandem structures with a finite number of solar cells.

A method is presented for determining the interface-state distribution in MOS structures by deep-level transient spectroscopy (DLTS) with a bipolar rectangular weighting function which has the better signal-to-noise ratio (S/N) than the ordinary DLTS using a dual-channel boxcar averager. Experimental results are given for electron traps at the Si-SiO₂ interface and compared with those obtained from the ordinary DLTS method. Experimental requirements for the present method to evaluate the interface-state distribution are also discussed.

Electrical conduction measurements were made at different temperatures on antimony trisulphide films prepared by the three-temperature method and by flash evaporation. In both cases, space-charge limited conduction was observed. The trap densities in the films were determined and the trap energy levels evaluated. The conductivity measurements indicate that the Sb₂S₃ films are non-extrinsic. The dominant electron and hole levels in the system were evaluated.

An investigation of the back-scattering process in a substrate-polymer film structure has been undertaken. The results of experiments have been correlated with theoretical diffusion models. The influence of some parameters of the substrate, the electron-sensitive polymer film and the electron beam on the size of structures produced with electron beam lithography has been shown.

The influence of temperature on the torsion magnetoelastic effects for polycrystalline tubular Ni samples has allowed the authors to find the dependence of the magnetostriction constant lambda _s on temperature in the range from room temperature to T_c. The experimental results are in good agreement with those evaluated from data for the variation of delta ₁₀₀(t) and lambda ₁₁₁(t). In the same way, the lambda _s behaviour with temperature is found to be like that of M_s,t³, as is experimentally shown.

Transparent electrically conducting SnO₂ films were prepared by the chemical vapour deposition technique. The films were deposited at substrate temperatures of 400, 450 and 500 degrees C by stannous chloride oxidation. The optical absorption studies, using unpolarised light, indicated that the deposition temperature is an important parameter influencing the optical properties of the films. The absorption edge for the films occurs at about 3.7 eV. The films also indicated direct transitions at about 3.95 eV and indirect transitions at about 3.27 eV.

Some experimental and theoretical limits are investigated for a technique of nondestructively locating shear cracks in carbon and glass fibre reinforced plastics (CFRP and GFRP). The technique is based on the phenomenon that when a cracked material is subjected to oscillating stresses of sufficient magnitude, heat is generated owing to friction between opposite sides of the crack. Theoretical predictions have been made of the expected temperature rises, and these have been checked experimentally by using an infrared scanner. It was shown that the technique is more sensitive with GFRP owing to the substantially higher thermal conductivity of the carbon fibres. The technique has the possibility of being used to detect defects in composite sub-structures without removing them from the main assembly.