Table of contents

Accelerator-based nuclear techniques were used to study the ageing of as-prepared and aluminium-capped porous silicon samples with a porosity of 55% and with two different morphologies (microporous and mesoporous). Aluminium surface capping layers with thicknesses in the range 0.1-0.5 m were applied by rf sputtering. The uncapped microporous samples aged more rapidly in air than did mesoporous samples. The sputtered capping layers were found to be effective for stabilizing porous silicon against atmospheric oxidation, irrespective of the thickness of the capping layer.

The effect of electrical migration upon electrochemical deposition is investigated using a thin-layer electrodeposition method. The experiment is carried out by both methods of electrodeless and electrode reductions of silver ions from a solution. The silver metal is grown around the copper deposition plate within a Hele-Shaw cell under an electric field which is induced by the electrodes positioned outside the cell. It is shown that a locally electric migration has an important effect on the deposition profile. For comparing with the experiment, an extended DLA simulation is carried out to take into account the local electric field. It is found that the deposition profile obtained by the simulation is consistent with the experimental result.

High-quality organic multiple quantum well (MQW) structures based on tris(8-hydroxyquinoline) aluminium and 2-(4-biphenylyl)-5-(4-tert-butyl-phenyl)-1,3,4-oxadiazole (PBD) have been prepared by use of a multisource-type high-vacuum organic molecular beam deposition system. Small-angle x-ray diffraction measurements indicate that the MQW structures have a very uniform layered structure throughout the entire stack. Both optical absorption and photoluminescence (PL) measurements reveal the evidence for exciton confinement in the /PBD MQW structures. The thickness-dependent blue shift of the PL peak observed upon decreasing the well width is attributed to the change of exciton energy as a result of quantum confinement. Theoretical calculations have been performed and the results agree with the experimental results. Light-emitting diodes (LEDs) based on the /PBD MQW structure with greater efficiency, a narrower electroluminescence spectrum and less of a blue shift than the single heterostructure LEDs have also been fabricated.

The present study discusses the effect of iron doping in thin films deposited by rf sputtering. Iron doping induces a structural transformation from anatase to rutile and electrical measurements indicate that iron acts as an acceptor impurity. Thermoelectric power measurement shows a transition between n-type and p-type electrical conduction for an iron concentration around 0.13 at.%. The highest p-type conductivity at room temperature achieved by iron doping was .

Two-dimensional electrodeposition profiles around a single trench on a substrate are investigated using a thin-layer experiment and a Monte Carlo simulation. The thin-layer electrodeposition for the diffusion-limited aggregation is applied to the problem of the coverage of a small trench on a substrate. The metal deposit is grown on the thin deposition plate within a Hele-Shaw cell under an applied electric field. It is shown that a well-covered electrodeposit is formed when the concentration of electrolyte is high or/and the voltage is applied. The Monte Carlo simulation method is presented by extending the simulation method of the diffusion-limited aggregation fractal. The morphology of the electrodeposit obtained from the simulation is compared with the experimental result. It is shown that the experimental result is consistent with the simulation result.

The relationship between the fraction of material removed and the degree of penetration often observed in the literature during single-particle grooving tests on metals is examined in terms of low cycle fatigue. It is shown that the fraction of material removed is closely related to the low cycle fatigue behaviour of the material. On the basis of the argument presented in this paper, the single grooving test provides a very useful method for obtaining low cycle fatigue properties of metals in the study both of hard particle wear and of sliding wear.

Two highly sensitive and quantitative absorption techniques have been applied to the detection of in an argon-5% silane DC discharge, the new method of CW cavity ring-down spectroscopy (CWCRDS) and intracavity laser absorption spectroscopy (ICLAS). Doppler-limited absorption lines of the transition around 580 nm could be observed. By using the rotational constants and the electronic transition moment available in the literature, we have calculated the line intensity of some specific rovibronic transitions from which we deduced the concentration of in the discharge to be about . Taking into account the signal-to-noise ratio, concentrations as small as a few times can be detected by both methods. We also observed a weak broadband absorption of several due to the dust particles formed in the plasma volume, which for particles of 1 nm diameter would correspond to a few times . The performances of ICLAS and CWCRDS are compared.

The thermodynamic inequality has been considered and the heat conduction described by Fourier's law has been studied. An inequality between thermal conductivity and specific heat exponents has been found from the thermodynamical relationship. The inequality holds for temperature intervals for which phenomenological power laws can be fitted to the conductivity and the specific heat. We have checked our analytical result with data for some materials and the inequality is always satisfied.

We have studied the interference pattern produced under normal incidence by a system of two plane-parallel plates in sequence, one birefringent and one Faraday rotatory. The interference pattern of transmitted light consists of strong fringes at large phase intervals with a set of weak fringes between them. The ratio of intensities of the strong and the weak fringes is much larger than that of birefringent, optically active plates studied earlier and the system appears more suitable for interferometric applications.

Modelling results concerning the heat transfer and fluid flow in a radio-frequency plasma torch with argon and hydrogen as the working gas are presented. The diffusion of hydrogen in the gas mixture due to the presence of temperature and concentration gradients within the torch has been modelled by using the combined-diffusion-coefficient approach. Included in the modelling are also the effects of the induced currents appearing in the brass probe for central gas injection on the electromagnetic fields and thus on the plasma flow and heat transfer within the plasma torch. It has been shown that the electrical conductivity of the probe affects the modelling results of the flow field and the temperature distribution in the torch. The flow rate of the central argon flow has substantial effects on the temperature, velocity and concentration fields, especially in the region near the axis of the torch. Computed temperature profiles at a few cross sections of the torch are favourably compared with corresponding experimental data for a typical case.

A laser-induced fluorescence (LIF) technique has been applied to the measurement of population density in a pulsed parallel-plates rf discharge at 0.1 Torr pressure. The method is based on a single rotational line excitation-detection LIF scheme on the first positive band system of . This approach makes the correct application of a standard model of three-level rate equations to the description of the LIF process for the treatment of experimental results possible. Conditions for true single-line operation using a line-width pulsed tunable laser are discussed and applied to the measurement. The measured density value is then used for the absolute density calibration of a previous relative vibrational distribution of -9) obtained by a non-single-line excitation-detection LIF measurement.

The unusual and complex structures of the breakdown time-delay distributions in a neon-filled diode at 4 mbar pressure for lower overvoltages are reported in this paper. Each distribution was established on the basis of the 1000 successive and independent measurements of the electrical breakdown time delay. It is concluded that the expected one-stage Laue distribution cannot be applied successfully because of the complex structures of the measured distributions. For very low overvoltages, multiple breakdown mechanisms seem to appear with different (by two orders of magnitude) mean values of the statistical time delay and formative time. A multi-stage model for the Lauegrams is used in order to fit our data.

Rotational and vibrational temperatures are measured by optical emission spectroscopy in a discharge with liquid non-metallic electrodes (DLNME) in air at atmospheric pressure. We used the transition of the second positive system of to determine the two parameters of this discharge. In this paper we describe first the experimental set-up and then the method of determination of rotational and vibrational temperatures by comparison with calculated spectra. We present the results obtained along the discharge's axis.

During the decay of a circuit-breaker arc, the plasma is subjected to strong blowing which can lead to deviations from chemical equilibrium. The intense convection may therefore be responsible for the presence of cold gas in the hot parts of the plasma. The cold particles then rapidly recombine with electrons, modifying the resistivity of the plasma. In order to study this phenomenon as it appears in circuit-breakers, we made a modelling of the extinction of an arc for a simplified geometry. The two-dimensional model that was set up was followed by a study of the kinetics of which enabled us to identify the various reaction processes governing the disappearance of electrons.

The results show that convection acts on molecules which, at the edge of the discharge and for temperatures of between 4000 and 6000 K, are overpopulated with respect to equilibrium. Through charge exchange processes between and particles, the overpopulation of leads to an overpopulation of the ions. These ions mainly recombine with electrons, lowering the electron population and modifying the electrical conductivity of the plasma.

A dynamic two-dimensional arc model has been used to investigate the effects of the various forces acting on the droplet in gas metal arc welding (GMAW). The model is based on the equations of conservation of mass, energy, momentum and current, Ohm's law and a Maxwell equation. The model treats the welding wire, the plasma and the workpiece. For molten metal droplets at the tip of the welding wire, we account for effects of inertia, gravity, surface tension, magnetic force, viscous drag force and arc pressure. Calculations are presented for a 1.6 mm diameter wire of mild steel for arcs in argon to determine the separate effects of these forces on droplet formation. It is found that, for arcs in pure argon at currents around the transition from the globular transfer mode to the spray transfer mode, viscous drag and arc pressure effects are approximately self-cancelling. It is also found that forces have a much larger effect than do forces on the transition from globular to spray modes of metal transfer.

A study of the electronic properties of a polythiophene (poly(4,4-dipentoxy-2,2-bithiophene) as functions of the positive doping level has been carried out. The oxidative cyclic voltammogram and the electron spin resonance (ESR) spectrum show the consecutive formation of polaron and bipolaron states on increasing the doping level of the polymer. From the optical spectra it was found that the band undergoes a blue shift with the doping. The Fermi level of the polymer was derived from the diffusion potential of the heterojunction between n-doped silicon and poly(4,4-dipentoxy-2,2-bithiophene). As expected for p-type inorganic semiconductors, the Fermi level was found to be pushed towards the valence band by increasing the doping level. The trend of the experimental Fermi level is in good agreement with the one calculated for a p-type semiconductor with the same doping level and bandgap as those of poly(4,4-dipentoxy-2,2-bithiophene).

Modifications of the steady-state free-precession (SSFP) sequence are proposed for the effective detection of pure nuclear quadrupole resonance (NQR). These modifications enable the suppression of the effect of intensity anomalies observed under steady-state conditions. The steady-state signals in SSFP-type sequences strongly depend on the frequency offset from resonance and the pulse spacing. This dependence has some peculiarities which were taken into consideration. Experimental results of modified SSFP sequence applications are reported for nitrogen-14 NQR in a plastic explosive.

Organic electroluminescent diodes based on thin organic layers are one of the most promising next-generation systems for the backlighting of the liquid crystal screens. Among other methods to obtain white light, three-layer luminescent devices with each layer emitting one of the three fundamental colours have been studied here. Red, green and blue light were produced by doped with Nile red, and TPD layers respectively. A fourth thin film of TAZ has been inserted between TPD and to control injection of electrons into the TPD. The effect of the layers' thicknesses on the spectral emission of the device has been examined. Results show that the thicknesses of TAZ and doped layers have to be controlled to within a precision of better than 5 Å. The discussion turns on the possibility of applying this technology to screen backlighting.

Plasma diagnostics were performed during excimer laser ablation of graphite in a low-pressure atmosphere using time- and space-resolved optical emission spectroscopy. The laser fluence and nitrogen pressure were set to values typically applied to pulsed laser deposition of thin films. Under these conditions, optical emission spectra were dominated by continuum emission and spectral lines from carbon ions during the early plasma phase , when the carbon vapour is located in the vicinity of the target surface, whereas molecular bands of molecules and CN radicals were essentially observed at later times when the vapour expands through the ambient gas. Emission spectra of , CN and were recorded as functions of time for various distances from the target. From computer simulations of molecular spectra, we deduced rotational and vibrational temperatures. The acquired information about the kinetics of excited plasma species and gas phase reactions contributes to a better understanding of pulsed laser deposition of carbon nitride thin films.