Table of contents

The doping of PcAlF polymer thin films by iodine implantation at 100-200 keV is reported. Depth profiles obtained by Rutherford back-scattering show that the iodine is quite mobile during implantation, stable at room temperatures, but driven out by a 300 degrees C anneal. Doses of 10¹⁶ atoms cm^-2 result in a slightly reduced DC conductivity showing that the material is not graphitised under the ion beam. This is confirmed by optical absorbance spectroscopy of the iodine implanted films which shows a Q-splitting at 630 nm similar to that observed by chemical doping.

Various carbon films which have been produced in plasma have been fluorinated so that their surface structures could be analysed. Every fluorinated carbon film shows a characteristic contact angle change which follows its surface structure. These samples can be classified into two groups: amorphous and crystal, from comparison of the ratios of the area due to fluorine in the C_1s peak to the total area of the C_1s peak in ESCA results.

Heterogeneous catalysis in the low-pressure (5 mbar) plasma phase is shown to result from mass and energy exchanges between the plasma and the solid surface. Perturbation of the plasma medium by the solid is interpreted as a catalytic action to the extent that it leads to an increase of chemical reactivity of the system. The chemical reactivity in non-equilibrium media is shown to be controlled by vibrational or translational energy when the determining step of the reaction is respectively endothermic or exothermic (Polanyi). For nitrous oxide synthesis (N₂+O₂ to 2NO) and ammonia decomposition (2 NH₃ to N₂+3 H₂), an increase in the N₂(C³ Pi _u) vibrational temperature increases the reaction rates. The reactions are thus controlled by an endothermic step. These theories applied to surface reaction dynamics (Wolken) added to the results concerning gas/solid energy transfer during catalytic atoms recombination (Halpern and Rosner) have established that the desorbed molecules leave the surface with a substantial vibrational energy which depends on the recombination-desorption mechanisms. These conclusions permit a new approach to non-equilibrium chemical reactivity in the heterogeneous plasma phase. The study of NO synthesis on WO₃ shows that the surface reaction necessarily involves a Rideal mechanism where vibrationally excited N₂ reacts with the mobile oxygen of WO₃. Study of catalytic NH₃ decomposition shows that the gaseous boundary layer with the transition metal is characterised by high exaltation of the vibrational temperature (T_vib increases from 3300 to 4200K) resulting in desorption of nitrogen molecules which carry off the major part of the released energy during the surface reaction.

The intensity measured in an absolute calibration, carried out with a tungsten ribbon lamp is theoretically computed as a function of the geometrical parameters involved in the experiment. The theoretical computations, confirmed by the experimental measurements, make it possible to place the lamp as close as possible to the detector and thereby improve the accuracy of the absolute calibration.

Measurements are reported of 10-100 A electron beam extraction from a vacuum diode and of high-power microwave emissions, of duration <or=1 mu s, from the interaction of the mildly relativistic pulsed electron beam 1< gamma <1.2, with a multimode cavity immersed in a 0.1-0.6 T magnetic field. The temporal behaviour of the diode indicates an interelectrode plasma expanding at 2-4*10⁴ m s^-1. Microwaves in the bands 8.2-12.4 GHz and 26.5-40 GHz have been detected, with a peak power approximately 100 kW near the relativistic electron gyro-resonance. Less than 1 W of incoherent electron cyclotron radiation would be expected. The much higher observed powers are considered to be electron cyclotron maser emissions.

Surface plasmon enhancement of second-harmonic generation has been investigated in a Langmuir-Blodgett monolayer of a hemicyanine dye deposited on a silver substrate. Measurements are reported for different thicknesses of silver. The signals obtained were 10³ times larger than the corresponding results without enhancement. The second-harmonic signal from the dye monolayer, which is 50 times larger than that from silver alone, is analysed in terms of an effective surface second-order susceptibility. This is compared with previous estimates. The results are discussed with references to film uniformity and to the general aspects of guided mode second-harmonic generation.

The advantages of producing images by scanning techniques are discussed. It is shown that scanning can result in improvements in resolution and signal-to-noise ratio, and can give a complete three-dimensional data set. Scanning can also result in true space-invariant imaging, and coherent imaging conditions can be achieved without the loss in spatial frequency band width normally associated with coherent imaging.

The author constructs a variational principle for the scattering coefficient of an acoustic wave incident onto a rough surface. The surface is taken to obey Dirichlet boundary conditions and has a roughness described statistically. Substitution of the acoustic Kirchhoff approximation into this variational principle, as a trial field, leads to a comparison of the results obtained using the Helmholtz scattering formula and the variational approach. They use the results obtained from this comparison to give an estimate of the accuracy of the former method. They conclude that the Helmholtz/Kirchhoff method gives a result equal to the 'optimum' available result, when using this form of trial field, for the special cases of specular and back-scattered signals from a smooth defect. The inclusion of roughness decreases the accuracy of the Helmholtz/Kirchhoff method and a better estimate of the true scattering coefficient is obtained using the variational principle.

The effect of temperature variations of both ionic mobility and dielectric constant on the stability of a horizontal layer of dielectric liquid subjected to a DC electric field with heating and an arbitrary injection of unipolar charge from below is analysed. The marginal stability boundaries for steady convection are determined by numerical solution of the linearised thermo-electrohydrodynamic perturbation equations.

Analytic velocity distribution functions of ions drifting through a buffer gas under the influence of an electric field are compared with experimentally obtained measurements of velocity and energy distribution functions. Good matches are found for particular examples, but in general the analytic functions relative to the experimental functions are shifted to lower velocities when the ratio of the electric field to the neutral number density is low and to higher velocities when the ratio is high. The effect of using experimentally determined values of the drift velocity and diffusion coefficients in the analytic expressions is also investigated.

Negative DC corona discharges in atmospheric air have been examined in a 20 mm point-plane gap using a polarisation interferometer and a chromel-alumel thermocouple. A fine thermocouple can be used to give sensible temperature data in a corona, provided that care is taken with respect to insulation and measurement technique, as well as to ranges of gap position and current over which the thermocouple is used. For an open-air corona, radial profiles of neutral density (N) obtained using the interferometer, and of temperature (T) obtained using the thermocouple, do not correlate according to p₀=NkT, where p₀ is the atmospheric pressure, because of pressure changes produced by the corona wind. Corona wind effects are minimised by containing the discharge gap within a cylindrical insulating chamber, and good p₀=NkT correlation of the radial profiles for N and T is then obtained. Several containing arrangements were used to provide further information on the effects of the corona wind. The results reveal that care must be exercised when inferring corona temperatures from interferometric measurements of neutral density.

A simple thermodynamic model has been developed to explain the incorporation of implanted impurities in GaAs. The model involves the interpretation of the electrical activity with annealing time and temperature and has been used to explain results obtained from 10¹⁴ cm^-2 of 300 keV selenium implanted into GaAs at room temperature. The electrical activity was found to increase with time at a given temperature below 950 degrees C, reaching a saturation value at long times. From the latter results of the time independent region an energy of 1.2 eV was deduced. This energy is suggested to be that required to split-up the selenium-gallium vacancy complexes that are responsible for the inactivity of selenium in GaAs, and to place the selenium atoms on nearby arsenic vacancies where they can act as donors. Analysis of the time dependent regime has produced an energy of about 4.5 eV which is thought to be the energy of diffusion of selenium in GaAs.

Experimental results for the response of Al and PMMA targets to shock loading are presented for peak pressures below 20 kbar. Uniaxial strain is produced by impacting a target plate with a flat projectile plate accelerated in a compressed gas gun. The free surface movement of the target is monitored interferometrically, the periodic signal structure being the result of a multireflected elastic longitudinal wave within the impacting flyer plate, the period itself allowing the determination of the speed of sound C in the flyer plate during dynamic loading. In case of target and flyer plate being of the same material (surface roughness about 0.3 mu m) they cannot be regarded as a continuum as postulated by the shock-wave model. Side-on Schlieren photographs of impacted PMMA targets prove the existence of a long lasting mutual action between target and flyer plate. This is not in accordance with the shock-wave model, which postulates a quasi-rectangular pressure against time profile within an impacted target.

The possibility of applying percolation theory to the sheet resistivity of thick-film resistors, noted for the segregation of conducting particles in grain boundaries between sufficiently large particles of glass, is investigated. The experiments, carried out on model resistor films, do not satisfy the models of Malliaris and Turner and R.P. Kusy. A new model, based on the distribution of threshold concentration for two-dimensional systems of finite size, was suggested. The theoretical values of conducting pigment critical concentration in the model films studied, which are in good agreement with the experimental results, are calculated on the basis of this model.

Both DC and AC resistivities of some silicate glass fibres containing 10 to 30 mol.% sodium and subjected to a sodium to or from silver ion-exchange treatment have been investigated. Ion-exchanged fibres exhibit resistivity and activation energy values lower than those of the untreated ones. A suitable combination of temperature and electric field brings about a further semi-permanent reduction in resistivity and activation energy values. Typical values of room temperature resistivity and activation energy in this high conducting state are approximately 50 Omega cm and 0.04 eV respectively. Such behaviour is explained on the basis of formation of an interconnected silver-rich phase under the combined influence of temperature and a suitable electric field. The properties exhibited by these materials are comparable to some of the conventional fast ion conducting glasses containing a higher silver concentration than those in the present system.

The authors attempt to characterise the electrical discharges initiated in hollow filaments of small diameter in low-density polyethylene. This study is related to electrical treeing, a pre-breakdown phenomenon in certain polymers submitted to high electrical stresses. A positive single pulse voltage was applied to a channel prepared in a polyethylene specimen. The channel diameter ranges from 1 mm to 13 mu m and the gap from 1 to 5 mm. The characteristics of the discharges growing in the channels were recorded and compared with free air discharges under the same conditions. It is shown that the channel walls disturb the discharge below a critical value of the ratio between the channel diameter ( Phi ) and the gap (d). A quicker heating of the gas is assumed to explain the behaviour of these confined volumes.

An effect of shot noise in the beam of a scanning electron lithography instrument is to introduce uncertainties in the measured positions of registration marks. The standard deviation in the measured position of the edge of a mark ( sigma ) is calculated for three types of registration scheme: a charge collection scheme, a correlation scheme, and a threshold detection scheme. In all cases it is found that sigma =( Delta X/ Delta I)(eI/ tau )¹2/: ( Delta I/ Delta X) is the rate at which the collected signal current changes with distance as the beam is scanned over the mark edge; e is the electronic charge; I is the mean collected signal current; and tau is the signal integration time associated with the collection scheme.

As a model for the mechanism of spacecraft discharging, the authors present numerical solutions for particle trajectories in two different electric fields. The first model considers two adjoining conducting infinite half-planes at different potentials. The second model considers two finite-width constant charge density dielectric plates. In both models they investigate the dependence of the particle trajectories on the origin, velocity, and direction of emission of the particles. Three conclusions emerge from this study: (i) shallow launch angles yield shorter trajectories; (ii) for a given launch angle there is an optimum energy which yields a minimum impact distance and (iii) dielectric plates generate much shorter impact distances than conducting ones.