Table of contents

Measurements of extended x-ray absorption fine structure (EXAFS) have been used in conjunction with glancing-angle x-ray diffraction (XRD) to study the structure of sputter-deposited nanocrystalline Ti - B - N thin films of various compositions. The chemical composition of the films was established by x-ray photoelectron spectroscopy and the equilibrium phase composition was calculated from an established phase diagram for the bulk Ti - B - N system. For the Ti - B - N layers low in nitrogen content a nanocrystalline -type structure in accordance with the predictions of the phase diagram was found. However, for a nitrogen-rich layer with the composition the expected Ti-containing phases, principally TiN, did not appear to be well formed. For this layer, the local structure around the central Ti atoms as deduced from EXAFS showed the Ti atoms mainly to be situated in disordered regions, possibly extremely small Ti - B or Ti - N clusters with no long-range crystalline order. The study has illustrated how the EXAFS technique can help one to understand the structure of poorly crystallized materials, especially in situations in which XRD measurements cannot be unambiguously interpreted.

The anodic oxidation of Al - Au alloys, containing 0.4, 3.8 and 11 at% Au, has been examined by high-resolution transmission electron microscopy and Rutherford backscattering spectroscopy. Oxidation proceeds initially by the formation of an anodic alumina film containing few, or no, gold species. The alloy layer just beneath the anodic film is then enriched progressively in gold as a consequence of the initial formation of relatively pure alumina. Upon sufficient enrichment of gold in the alloy, oxygen gas is produced at, or near, the alloy/film interface. At, or about, the same time, gold-rich clusters a few nanometres in size are incorporated into the film at the alloy/film interface. The necessary enrichment of the alloy for the production of oxygen gas is dependent upon the alloy composition: , and gold atoms for the 0.4, 3.8 and 11 at% Au alloys respectively. The extensive generation of oxygen within the film at, or near, the alloy/film interface, leads to the formation of oxygen-filled bubbles within the anodic alumina, which may subsequently rupture and release oxygen gas.

The giant magneto-impedance (MI) effect and magnetic permeability of alloy ribbons were measured as a function of the annealing temperature. When the ribbons had been annealed at the optimum temperature () they exhibited both a large MI and excellent soft magnetic properties. The MI was also calculated on the basis of classical electromagnetic theory. It was found that a large change in the effective magnetic permeability, caused by the application of an external magnetic field in an excellent soft magnetic sample, was crucial for the MI effect. Furthermore, the effect of the resistivity on the MI was also investigated. When the resistivity decreases, the eddy current losses increase and the frequency at which the variation in the complex impedance exhibits its maximum moves to a low value; thus the sample exhibts a large MI effect.

A method for the analysis of rotary permanent-magnet bias-field devices for magneto-optic recording applications is presented. The first part of the method entails a three-dimensional field analysis to determine the magnet dimensions that render a bias field of desired strength and uniformity across the medium. The second part of the method entails an analysis of the rotary dynamics of the magnet to determine the parameters that render a desired response time for field reversal. The theory is demonstrated via application to a practical device.

Transmission electron microscopy has been used to study the magnetic domain structure and its evolution under an external applied field in thin sections of Nd - Fe - B-type magnets produced by the solid-HDDR process. Grain sizes in the recombined material were typically 200 - 800 nm and the orientation of the c axis varied by about over distances in an aligned region. Mean relative orientations of adjacent aligned regions within the sample varied to a much greater extent. In samples with the c axis inclined with respect to the plane of a thin section, an irregular periodic domain structure was observed. Boundaries between oppositely magnetized domains tended to lie along grain boundaries of the smaller grains. Domain walls were observed within the larger grains when a substantial disturbance of the domain structure would be required to reach a grain boundary. In situ magnetizing experiments showed that domain walls in the centres of grains tended to move until they reached grain boundaries, where they remained pinned; with higher fields occasional jumps from one grain boundary to the next were observed until an applied field that appeared to remove all the domain walls in that region had been reached. Under the application of a reverse field, such that domain structures were observed, it was rare to find domain boundaries and grain boundaries which did not coincide. Restoration of the original state, with walls passing through the centres of grains, was only obtained by thermally demagnetizing the sample.

A table-top megagauss generator, employing the single-turn coil technique has successfully been applied in solid state physics. Magnetic fields up to 113 T are generated within a useful volume of about . A detailed description of techniques for high-quality field measurements under the conditions of a short time duration and the presence of strong transient electric disturbances during the field generation is given. Faraday rotation in CdS as well as cyclotron resonance experiments in n-type PbSe are presented as examples of the efficiency of the generator as a scientific instrument.

A forced convection heat transfer from an impulsively started translating, rotating and expanding circular cylinder is studied numerically. Use is made of a previously derived stability condition for the expanding cylinder surface. This condition assists in using the classical explicit forwards spatial scheme that is centred in time to solve the vorticity and the energy equation with a reasonable time step. The fast Fourier transform is used to solve the Poisson equation for the stream function. The time development of the temperature field is obtained and discussed. The progress of the local Nusselt number over the circular cylinder surface with time is explored. The effects of various parameters related to the flow field, surface expansion and rotation are investigated.

A method for simultaneous investigation of the diffusion of atoms and molecules in gas buffers and their reflection at the vessel walls is proposed. It is experimentally tested to obtain the diffusion coefficient of Mg atoms in neon and the coefficient of the reflection of these atoms from the metallic wall in the afterglow plasma of a pulsed hollow cathode at 320 K temperature. The diffusion coefficient value is compared with the theoretical calculation previously reported by Redko et al.

Analytical results concerning the heat transfer to a metallic wire exposed to a plasma flow for the extreme case of the free-molecule regime and a thin plasma sheath are presented. Expressions for the heat-flux components due to all the gas species (atoms, ions and electrons) and due to various different heat-transfer mechanisms including radiation and electron emission from the wire surface are derived. It is shown that the average heat flux per unit wire surface area is independent of the wire radius and increases with increasing gas temperature, pressure and speed ratio. At low wire temperatures, the contribution to the total heat flux due to radiation and thermionic emission from the wire surface can be ignored. However, the secondary electron emission due to ion bombardment may constitute a non-negligible heat-transfer mechanism. The predicted results of the heat flux are well consistent with corresponding experimental data for a fine tungsten wire exposed to an argon plasma flow of temperature about 9000 K at 500 Pa pressure.

In this work the broadening of the red wing of the 253.7 nm resonance mercury line is used to determine the radial distribution of the neutral atom density in a high-pressure mercury discharge. Abel inversion allows resolution of the integral relation between the wavelength at the maximum intensity of the red-wing resonance line and the square of the neutral atom density. This method, which does not require the assumption of local thermodynamic equilibrium, is applied to the pressure range 0.2 - 5 bar. Results are compared with those obtained from the broadening of the 491.6 nm mercury line.

Computational fluid dynamics calculations for high- and low-current arcs in an interrupter of the self-blast type have been performed. The mixing process of the hot PTFE cloud with the cold in the pressure chamber is strongly inhomogeneous. The existence of two different species has been taken into account by interpolation of the material functions according to their mass fraction in each grid cell. Depending on the arcing time, fault current and interrupter geometry, blow temperatures of up to 2000 K have been found. The simulation results for a decaying arc immediately before current zero yield a significantly reduced arc cooling at the stagnation point for high blow temperatures.

Rare-earth-doped thin films were made by plasma-enhanced chemical vapour deposition using a complex containing chelating ligands and tetraethoxysilane. By this means of deposition, the film was successfully doped with terbium or erbium and the luminescence properties were investigated. In the case of -doped films, strong luminescence peaks from the level were observed during excitation by a KrF excimer laser. Upon thermal treatment at 800 or , luminescence peaks from the level appear. Under DC voltages, electroluminescence from the level was also observed.

Ion drift in a single-source corona discharge occurs along trajectories which deviate relatively little from the Laplacian field direction. This allows the Deutsch approximation to be used with low errors as in the Popkov model. For coronas from more than one source, the interaction of the space-charge electric fields can cause significant trajectory distortion. Measurements of positive coronas from twin- wire systems make it possible to quantify the Deutsch error. A charge expansion model is used to calculate the ion trajectories at the corona boundaries. The Popkov model predicts, in agreement with measurements, that the normalization of the current density and electric field profiles with respect to the maximum values ( and ) yields unique curves independent of the magnitude of the applied voltage. However, the shapes of the profiles of current density and electric field for small wire displacements give poor simulations because of the effect of the proximity of the interacting coronas. In practice this would lead to failure of the Kaptsov condition at the wire surface. The charge expansion model avoids the difficulties of the Popkov model's assumptions. A finite-difference procedure of the charge-expansion model has been outlined and applied to the position of maximum current density where the ion path is known. This confirms the failure of the Kaptsov approximation of the field at the corona conductor. Application of the charge-expansion model to the position of minimum current density has been also possible in order to estimate the drift path length. This trajectory is non-Laplacian in shape and the results indicate that, along this path, a position of minimum field is encountered rather than the monotonic field found at .

Ion acceleration up to energy keV in a low-inductive vacuum discharge was investigated experimentally in detail. It was shown that the acceleration started at a distance about - 3 mm from the cathode and continued all the way to the anode. Negative potential `bursts' moving together with the plasma jet front were discovered. They apparently trapped ions and accelerated them to the observed high energies. A mechanism for the generation of the `bursts' and the plasma acceleration due to the jet constriction is proposed.

The gas temperature and the absolute density of the argon level in an 80 W inductively coupled low-pressure argon - mercury plasma are determined for three different argon filling pressures. This is done by measuring the line profile of the transition in argon, using a tuneable laser diode. Since the width of this argon line is found to depend on the kinetic heavy particle temperature only, radial profiles of the gas temperature can be obtained. It turns out that the maximum gas temperature in this discharge (550 - 810 K depending on the filling pressure) is significantly higher than that in a common tubular fluorescent lamp. From the radial distribution of the argon 4s density it can be concluded that the maxima of the electron density and of the electron temperature are situated close to the coil. It is also found that the position of these maxima depends on the argon filling pressure.

The photopyroelectric (PPE) technique is usually used as a contact photothermal method to characterize thin solid materials. We performed theoretical and experimental investigations of a non-contact PPE configuration to analyse the effects of an air gap between the thermal source and a PVDF sensor using a modulated laser beam as optical excitation. The detection of the thermal wave developed within the sample was possible across an air gap of up to 15 mm. The PPE signal was described well thanks to a two-dimensional (2D) model with axial symmetry, which could be reduced in some particular cases to a simpler 1D propagation model. Border effects can be artificially taken into account in the calculations by increasing the adiabatic lateral limits in the model, keeping the active sensor area constant. Despite there being strong attenuation with increasing modulation frequency, the PPE method can be used as well as can other non-contact photothermal techniques. New perspectives for the application of the PPE technique have been opened.

By incorporating the flow impedance into the space-charge model of Mair, the current - voltage curves of high impedance liquid-metal ion sources can be fitted to this modified model for an assumed liquid film thickness that decreases with voltage and/or for assumed values of the change in cone half-angle. The new model strongly suggests that what limits the current in high-impedance sources (and eventually in all sources) is a decrease in film thickness with voltage. Coupled to this effect is a self-shaping of the liquid emitter; the higher the flow impedance of an ion source the more pronounced is this self-shaping.

A two-dimensional, chemical kinetics and aerosol growth model is developed for the comprehensive simulation of the reactive synthesis of ultra-fine particles in a thermal plasma reactor. The model solves the velocity and temperature fields that are coupled to the equations describing the electromagnetic induction field. Conservation equations for the plasma species consider the multi-component diffusion and chemical reactions. For the condensable product, an additional term is introduced, due to the phase change. Particle growth occurs via homogeneous nucleation and surface condensation, and an evaporation term is considered for concentrations below saturation. The model is applied to the synthesis of silicon metal powders by the dissociation of . The effect of the input power and that of the radial quenching are investigated by comparison with a simulation base case.

R Bindi et al published recently a paper presenting a method of estimation of the electron affinity from the simultaneously measured thermostimulated luminescence and exoelectron emission graphs. The method is quite promising, but the results permit an alternative interpretation via field-assisted emission, suggested in the comment. Some conceivable ways of overcoming this ambiguity are also pointed out.

In recent work we described a method which allowed the estimation of the effective electron affinity of α-alumina. The interpretation of these results has given rise to the comment from Dr Käämbre. Here, we develop some arguments in response to this comment.