Table of contents

It is shown that an electrical sensor, plunged in water in which ultrasonic cavitation is produced, generates pulses whose amplitude may reach several hundred microvolts. By using this sensor jointly with a piezoelectric sensor, the author demonstrates the simultaneity of the electrical pulses and the pressure pulses produced by the collapses of the cavitation bubbles.

Analysis of the recent data of Henson (1978) indicates that the energy of vaporisation of the droplets is similar to that of bulk water. If the droplets had reached their equilibrium sizes, the electrostrictive effect of the ion reduced their vapour pressures by factors of 3-4.

Transmission electron diffraction patterns (Kikuchi lines) have been observed for the first time in very thick samples (a few tenths of a millimetre). The experimental apparatus, using a 'drift chamber' detector, which is new for electron diffraction studies, is described. Experimental results on a single-crystal silicon slab 0.14 mm thick are reported.

The parameters of a new type of thermionic converter, which has a number of concentric electrodes, are computed. The obtained theoretical efficiency of this new type of converter is close to the efficiency of the ideal thermionic diode converter. The results obtained are explained by the reduction of the radiation loss from the emitter due to the electrode configuration. Efficiencies as high as 20% are expected from this type of converter, which is now being constructed.

Presents theoretical calculations and experimental observations on electron scattering by gases in the specimen chamber of a scanning electron microscope. The observed scattering is in good agreement with theoretical calculations based on elastic and inelastic electron scattering. For normal surface inspection work, good resolution is retained in back-scattered imaging when gas is deliberately introduced into the specimen chamber. Experimental and calculated beam profiles are discussed for 25 keV electrons in nitrogen gas. Guidelines for choosing operating conditions for higher than normal gas pressures in the specimen chamber are also presented. Micrographs are provided to illustrate the image clarity attainable under high electron scattering conditions.

The low-temperature operation and performance of the 19 mu m OCS and 16 mu m CF₄ CO₂-laser-pumped lasers is reported. Both in terms of output energy and operating pressure the performance of these lasers is shown to improve greatly with decreasing temperature in agreement with the predictions of a simple theoretical model.

Theocaris's method of reflected caustics can be used for the experimental determination of the stress-optical constants of an isotropic or anisotropic elastic material using a single simple tension test with a specimen having a circular hole. The results show a significant improvement over an analogous method, based both on reflected and transmitted caustics and developed by Kartalopoulos and Raftopoulos (1976).

The friction and adhesion developed between nominally clean monofilaments of polyethylene-terephthalate in a crossed-cylinder configuration. The adhesion is determined by the free surface energy of the fibres and by the contact geometry. A single region of contact is assumed, this provides a means of estimating the effective geometry of the fibres in the contact zone. From the deduced contact geometry, the area of contact as a function of normal load may be calculated using classical elasticity equations. The friction as a function of normal load may be deduced assuming that it arises primarily from shear of polymer at the interface. The calculated values are in good agreement with friction measurements carried out over a wide range of positive and negative loads. However, the friction experiments at negative loads are best considered as a special case of adhesive failure.

An improved method of measuring the coefficient of sliding friction of floor products is described, whereby similar measurements are made on laboratory samples and floors. An average value over the surface and a trace showing the local variations in friction across the surface are obtained. The latter facilitates studies of the efficiency of geometric projections and other surface effects that are intended to provide resistance to slipping. Measurements on floors show that both organic and inorganic deposits contribute to a reduction of the coefficient of friction.

When a liquid jet at a ground potential is ejected from a capillary toward an opposing electrode at a certain voltage, the jet acquires corresponding charge and then splits into charged droplets. For this charging process, the model proposed is a cone-sphere to plane geometry. Laplace's equation is used to estimate the charge on the droplets, and the solution is expressed in terms of Legendre functions of non-integral order. Experiments were made to examine the theoretical results. A capillary nozzle, which was vibrated mechanically, was set normally to a plane electrode. Water was ejected from it under an electric field and formed a series of charged droplets. The charges were measured from the current carried by the droplets. The comparison showed the agreement to be quite reasonable so that one could apply this method to estimate charges on the droplets.

Criteria for replacing the real impact of a hypervelocity macroparticle by certain modelling effects have been considered. For direct modelling it has become possible to replace a high-velocity projectile by a slower one of another shape and made of material with a steeper shock adiabat (Huhoniot). The authors give calculated curves for the efficiency of the impact of various particles on different targets. Correct conditions for replacing the real particle impact by different processes are formulated in the general case of indirect modelling. They represent tentative experimental results on effects of an intensive Q-switched laser pulse upon a polycrystal target and demonstrate a possibility to achieve high shock load stresses, which are characteristic of hypervelocity impact, by laser cumulative compression of a pseudoprojectile placed on the target surface.

A weakly abnormal glow discharge, started at one end of a pair of long coaxial electrodes, spreads laterally over the whole length of anode and cathode. In helium and neon at 10 Torr and for short interelectrode distances, the lateral velocity is independent of position and gas pressure when the applied voltage is kept constant. When the voltage approaches the normal cathode fall, the speed tends to zero and it rises with voltage in excess of the normal cathode fall. The spreading mechanism is assumed due to positive ions emerging from the boundary between cathode fall or negative glow and the virgin gas. Discharge expansion rate calculations are based on a model representing the boundary by an edge normal to the cathode.

The equations describing gas flow surrounding an electric arc in a converging-diverging nozzle are derived for the case where the gas temperature changes as a function of distance along the nozzle. It is shown that analytic solutions can be obtained if the temperature varies exponentially with the local flow Mach number. Only small temperature increases are needed near the nozzle throat to substantially modify the flow conditions from the usual adiabatic expansion. Under heating conditions which produce a strong axial temperature rise the theory predicts that the sonic point will move a considerable distance down stream from the nozzle throat. For short nozzles containing high current arcs, such as those used in gas blast circuit-breakers, this effect may be sufficient to restrict the entire flow outside the arc core to subsonic values.

The phosphorus concentrations of P-doped SiO₂ films deposited on to Si wafers by pyrolysis have been determined by activation analysis and using the data of diffusion layer prepared by the doped SiO₂ film in the Si substrate. Using these P concentrations and the P=O infrared (IR) absorption bands of the films the constant K' of the IR P determination has been calculated. Inversely, measuring the IR absorption band corresponding to the P=O groups and knowing the constant K' can give estimates of the surface concentration of the diffusion layer prepared by the SiO₂ diffusion source and the p-n junction's depth. The values of the constant K'; for SiO₂ films doped by triethylphosphate and POCl₃ are significantly different, explained by the difference in the ratio of the concentration of P=O bonds to the concentration of P atoms for the two doping materials.

Results are presented for quasi-steady-state conduction in 12.7 mu m and in 25.4 mu m Mylar C film at temperatures in the range 100-180 degrees C and at field strengths extending to 2.4*10⁸ V m^-1. Further data are obtained using single voltage pulses at temperatures >or=150 degrees C for current densities >or=10^-2 A m^-2. Support is given for the hypothesis of two conduction mechanisms in polyethylene-terephthalate, and it is shown by combining data presented here with that obtained previously that certain features of the high-field, high-temperature transient conduction can be accounted for.

For pt.I see ibid., vol.12, no.4, p.579 (1979). Several conduction mechanisms are examined in an attempt to account for the steady-state current in Mylar C (as reported in pt.I) for the temperature range 120-180 degrees C at field strengths extending to 2.4*10⁸ V m^-1. The data are found to be well fitted by the expression J=KTⁿ F^1/2 exp (- phi kT) exp ( beta F^1/2/kT) where n=2 corresponds to electronic or hole Poole-Frenkel conduction and n=¹/₂ to ionic conduction resulting from field-assisted dissociation of protons. Several features of the analysis are of more general interest and attention is paid to some shortcomings of theory. Direct evidence for ionic conduction is also mentioned, but the extent to which this can account for the complete conduction is not known.

For pt.I see ibid., vol.11, p.L139 (1978). Photoinjection of holes into poly(2-chloro-p-xylylene) (PCPX) has been studied by using Au, Ag, Cu, Sn, Pb and Al electrodes. The threshold energy shifted to lower energies with the higher work-function of metals and also the applied field. It was estimated to be 2.24 eV for Au with no fields applied. The ionisation potential measured from the valence band top to the vacuum level was calculated to be 6.84+or-0.25 eV. The barrier height as well as the photocurrent in itself were affected by the presence of oxygen, which suggested that oxygen formed acceptor-like surface levels.

Crystals of lithium germanate (Li₂GeO₃) and of Li₂GeO₃ containing small amounts of silicon and magnesium were grown by the Czochralski method. The elastic, piezoelectric and dielectric tensor components were measured over the temperature range -40 to +100 degrees C. Crystal quality deteriorated drastically at SiO₂ contents (in the melt) greater than 2 wt.% and at MgO contents greater than 1 wt.%. There was some degradation in piezoelectric properties at impurity levels giving tolerable crystal quality. The evaluation of the crystals with regard to surface acoustic wave applications is discussed.

Based on the energy retardation power formula concerning the penetration and the energy loss of an electron probe into solid targets, the secondary electron emission yield delta due both to primary and back-scattered electrons is derived as functions of three parameters such as atomic number Z, first ionisation energy I and back-scattering coefficient r, which are found to be in good accordance with the results obtained experimentally. Notable in such theoretical procedures are the maximum yield delta _m and the primary energy E_m, giving delta _m=0.12Z^1/15I^4/5(1+1.26r) for E_m=57.9Z¹15/I^4/5(1+5r²)^4/5 (eV) which substantially agree with the miscellaneous experiments of many authors. The energy dependence of the yield-energy distributions, the yield of thin films and the lateral distribution of secondary yield at the distance from the centre of the beam are given as functions of the back-scattering coefficient and the primary energy.

The growth of fully deuterated D(3) TGS, both alanine-doped and undoped, is described. The rotating disc method of growth was used with modified apparatus to facilitate crystal handling and reduce loss of deuteration in solution. Some characteristic types of cracking occur when highly deuterated material grown on undoped crystal were subjected to extensive electrical measurements. A selection of comparative results is reported, and attention is drawn to the effect of thermal cycling on the doped material.

The nature of mechanical damage caused by grinding (100), (110), and (111) faces of MgO crystals is investigated using microindentation, scratch and etching techniques. Conclusive evidence in support of a plastically deformed layer containing dislocations is presented. It is shown that microcracks and dislocations introduced by the mechanical process affect microhardness and dissolution rate.

Using the technique of selected area Auger sampling, an examination has been made of the composition and contaminant state of (100) surfaces of indium phosphide. The chemical state of surfaces stored under various conditions and following cleaning with organic solvents or etching with hydrofluoric acid has also been investigated.