Table of contents

The Rayleigh wave velocity for a polycrystalline aggregate of cubic crystals with orthorhombic symmetry is derived. Use is made of the formalism of Roe (1966) for treating the texture of polycrystalline aggregates. It is shown that surface wave velocity measurements can be combined with the normal shear wave birefringence technique to give a texture independent determination of the difference in principal stresses. The accuracy of the theory is demonstrated for rolled aluminium and steel plates.

The ultrasonic velocities in a highly oriented polycrystalline aggregate of cubic crystals with orthorhombic symmetry are derived using the first-order perturbation theory. The results appear to be suitable for austenitic weld materials. A comparison with some experimental data is presented.

The experimental method of reflected caustics has been used to study the influence of the geometry of an edge-cracked plate on stress intensity factors K_I and K_II. This influence was determined for various values of the ratio, alpha /w, of the crack length to the width of the specimen. The influence of the geometry of the specimens of the form and orientation of the caustic was studied in relation to the orientation of the edge crack. The complex stress intensity factor K=K_I-iK_II was evaluated in terms of the angle phi of the angular displacement of the caustic axis. The values of the stress intensity factors K_I and K_II were compared with the respective theoretical values of stress intensity factors. From this comparison, correction factors are derived and nomograms given in terms of the angle omega of inclination of the crack.

Outlines a method for the generation of realistic random, multi-directional waves in wide wave tanks. The theory of the method is briefly discussed and comparisons are made between theoretical statistical wave properties and the output of a computer program, written to implement the wave generation technique.

The authors describe a spectroscopic technique to investigate the transport processes of electrons and the quenching processes of excited metastable molecules under the condition of non-self-sustained Townsend discharges. The technique is applied to pure N₂, and N₂ including NO as an impurity at E/N=282.5 Td and currents less than 10^-9 A. The quenching factor of N₂(A³ Sigma _u⁺) metastable by NO, defined by (1-(density of N₂(A³ Sigma _u⁺) in N₂ with NO)/(density of N₂(A³ Sigma _u⁺) in pure N₂)), is measured as a function of total gas density from the emission spectrum both of the second positive bands of N₂ and of the gamma system of NO. The spatial profile of N₂(A³ Sigma _u⁺) is also monitored and estimated by the emission of the gamma system. It will be noted that half of the N₂(A³ Sigma _u⁺) metastables are deactivated with only 20 PPM of NO at N=1.94*10¹⁷ cm^-3 in the low pressure ionisation growth chamber. The results give a quantitative explanation for the rapid decrease of the secondary ionisation coefficient in N₂ in the presence of small amounts of the impurity. Also the radiative lifetime and the self-quenching rate coefficient are estimated in the present experimental conditions.

A closed system of equations was devised, enabling a model showing the behaviour of the cathode spot to be set up. The results obtained provide, for a given arc current I, the mean values of the following characteristic magnitudes: current total density, cathode spot area, density of the emitted current of electrons, electron fraction, electric field on surface temperature and erosion speed through vaporisation of the given material. The contacts along which the cathode spot moves were made of copper and silver. A comparison was made with results of other authors from a theoretical as well as experimental point of view.

Characteristics of striations-the onset current for the excitation of waves, the dispersion, the velocity, the waveform, nonlinearities and the gas temperature dependence-are studied in tubes with diameters 1.0 to 3.0 mm in He, Ne and their mixtures. Only hydrodynamic modes are excited. As the tube diameter is reduced, both the wave number and the angular frequency increase. For a given diameter, there is a critical pressure below which waves cannot be excited. Similarity rules hold for the onset current, but not for the frequency. Discreteness in frequency appears strongly for the excitation of striations. Also, an increase in gas temperature affects the striations, especially at lower pressure and higher currents: the wave frequency increases and its amplitude decreases. The observed characteristics are found to be consistent with the results derived from the macroscopic equations.

Measurements on the temperature dependence of the electrical and thermal conductivities and thermopower of several binary Fe-Mn and ternary Fe-Mn-Al alloys from 77 to 300K are reported. The effect of Mn and Al additions on the transport properties and some observed anomalies related to antiferromagnetic ordering are discussed. It is suggested that these alloys might be considered as substitutes for Fe-Ni-Cr austenitic steels in cryogenic applications.

Measurements have been made of the excess noise in silicon. The specimens were ohmic, uniform cross-section JFET channels with no active oxide interfaces. The gate voltage was used to deplete the channel and change one transverse linear dimension. The temperature was varied between 77K and 368K to change the dominant scattering mechanism. The carrier density and mobility profiles across the channel were measured. At low temperatures one excess noise component was identified as due to donor occupation fluctuation. The observed excess noise component with a 1/f spectrum has been compared with the predictions of various models. The magnitude of the noise and its dependence on the scattering mechanism do not agree with the mobility fluctuation model.

CuInSe₂ films with different compositions around stoichiometry have been deposited by coevaporation of Cu, In and Se. In p-type films the electrical conductivity is largely dependent on the Cu-In percentage ratio and increases from 10^-6 to 10² S cm^-1 when the ratio increases from 0.66 to 1.58. The thermal activation energy is also correlated to this ratio, and decreases from 0.36 to 0.009 eV. The results are analogous to those obtained in polycrystalline silicon and are qualitatively explained by the grain boundary carrier trapping theory.

Sputtering yield characteristics of Ar ion-beam etching on InP have been determined. Damage generated by ion-beam bombardment has also been investigated by using scanning electron microscopy, photoluminescence and Auger electron spectroscopy. A two-dimensionally non-uniform surface structure which consists, in the depth direction, of a non-stoichiometric surface layer followed by a region involving nonradiative recombination centres, has been revealed from these measurements.

The fractions of 15 to 60 keV electrons back-scattered from and absorbed in transparent polycrystalline films of Al and Au have been measured at angles of incidence from 0 degrees , i.e. normal incidence to 80 degrees . Subtracting the sum of both these fractions from unity, the fraction of electrons transmitted through a film is determined. The experimental data for back-scattering and transmission are fitted by empirical expressions as functions of film mass-thickness, incident electron energy, and angle of incidence. Results for back-scattering are compared with the predictions of Niedrig's (1981) and Werner's (1982) analytic model.

A Monte Carlo computer program which takes into account both elastic and inelastic scattering of electrons has been set up. In the present paper the latter is limited to valence electron losses. These are described through three models: a modified form of the Lindhard dielectric function to take into account the energy gap, the plasmon-pole approximation to the dielectric function and the cross-sections for plasmon and single electron excitation simply joined at their intersection point. Calculations were performed for 100 keV electrons in silicon, with thickness varying from 850 to 2550 AA, i.e. from 1 to 3 total mean free paths. The first two models give practically the same results while the third one is not good enough. The effect of the thickness on the transmitted energy spectrum is analysed for the purpose of thickness determination. This analysis is extended to the complete energy-angle spectrum to discriminate between the effects of plural elastic and inelastic scattering in order to reconstruct the single inelastic scattering spectrum.

Liquid metal ion sources usually employ a single point geometry for the anode either in the form of a wetted needle or a capillary. The realisation of high ion currents whilst, at the same time, maintaining a low neutral mass emission rate has necessitated a different approach. Here the authors report a Cs field ion source which is novel in that emissions issue from a multitude regularly spaced liquid cusps. These sites are anchored at the mouth of a micrometre-sized slit which forms a channel of high flow impedance through which liquid caesium is constrained to flow. The properties of this emitter have been investigated by electrical and mass-loss measurements, the latter having been performed on a sensitive dual-axis vacuum microbalance permitting independent real time measurements of the total mass emission rate and of the thrust. Some properties of the emitter may be understood from a consideration of the hydrodynamic stability where the applied electric field acts on the liquid surface at the mouth of the emitter slit. Following this, a simple viscous flow model of the emitter is given which agrees well with experiments.

The threshold fluences for combustion (at lambda =10.6 mu m) of cellulose nitrate are shown to be at least an order of magnitude greater than those for the volatile decomposition. It makes processing of this plastic feasible in air using a laser. Optimum processing parameters for a CW CO₂ laser are reported.