Table of contents

The propagation of surface waves in overdense cylindrical plasmas is studied. The radial and axial inhomogeneities of the plasma are simultaneously taken into account.

The electrical transport properties of the ladder polymer BBL in film forms were studied as a function of pressure. The sample resistance was monitored in two different configurations, perpendicular (transverse) and parallel (surface) configurations. The results reveal a significant difference in the pressure dependence of resistance between the two configurations. Photocurrent as a function of photon energy was measured to determine changes in the electronic structure in the pressurized and released samples. Results indicate an absence of shifts in the band edge but higher photocurrent efficiencies were observed for the films.

Small-scale hole formation in Upilex polyimide and soda-lime glass using TEA laser ablation is reported. Hole dimensions as small as produced in the polyimide suggest optical resolution rather than thermal degradation effects limit the feature size attainable in infrared TEA laser polymer ablation.

Pulsed ion beam implantation with plasma focus has proved to be an effective method of metal surface treatment for tribological purposes. Nevertheless, the pulsed nature and the continuous energy spectrum of the ion beams differ from those of the standard ion implantation processes. In this paper a model of the thermal evolution of the surface layers of stainless steel, titanium and copper, during and after nitrogen and argon ion beam incidence, is presented using the finite-difference method.

In the calculations, the geometry and physical characteristics of the ion beams, the single-ion - solid interaction process and the thermal properties of the materials were used. The results showed a strong thermal effect consisting in the generation of transitory heating slopes and heating speeds as high as and respectively, with maximum temperatures that can reach even the material evaporation point at the surface layers. The cooling down process, through the thermal conduction mechanism at the target bulk, turns out to be fast enough to produce the complete thermal relaxation of the target in only a few microseconds after the end of the ion beam incidence. The results presented are contrasted with experiments performed in similar conditions to those used in the numerical model.

Structural changes induced by post-exposure to oxygen plasma were studied for films deposited at low temperatures (200 - C) by plasma-enhanced chemical vapour deposition from tetraethoxysilane. Carbon- and water-related impurities remaining in the film are decomposed by the oxygen plasma and then disappear. This brings about the disappearance of micropores and structural consolidation and stabilization, through which the degree of waterproofing improves, the relative dielectric constant decreases and the absorption edge shifts towards a higher energy.

In order to investigate the effectiveness and failure of amorphous hydrogenated carbon - nitrogen thin films (a-C:H(N)) as diffusion barriers against diffusion of copper in silicon, we performed a systematic study of films 10 - 100 nm thick. The a-C:H(N) films were grown by plasma-enhanced chemical vapour deposition onto unpatterned p-type (100) Si wafers and overlaid with 100 nm Cu films. The films were annealed in a vacuum quartz tube at temperatures in the range 300 - C. The annealing time was fixed at 30 min and no kind of sequential annealing was involved for each sample. The structural modifications and thin film reactions were followed as a function of the annealing temperature and characterized by nuclear techniques (Rutherford backscattering spectrometry, elastic recoil detection analysis and nuclear reaction analysis), Auger electron spectroscopy and hydrogen effusion experiments. In situ sheet resistance measurements were also performed. Whereas Cu films react completely with Si at C to form , the a-C:H(N) film prevents Cu - Si interaction up to C despite the degradation of the a-C:H(N) film and hydrogen and nitrogen losses that begin at temperatures as low as C.

films were implanted by 80, 120, 200, 270 and 350 keV ions with the same dose of . The depth profiles of fluorine have been accurately measured using resonant nuclear reaction at with width . These true distributions of fluorine were extracted from the experimental excitation yield curves by a proper multiple-convolution method. The range distribution parameters, the average projected ranges and the projected range straggles were then obtained. These experimental parameters were compared with theoretical predictions using the Monte Carlo simulation of TRIM'92. In present work of the F - YBCO system, the experimental values of agree with the theoretical results very well to within %, but the experimental projected range straggles, , are larger than the TRIM'92 predictions by factors of more than 20%. These results may contribute to progress both in ion beam modification in high-temperature superconducting films and range profile theory of ions in polycompound targets.

Thin films of (LSCO) with very smooth surfaces were prepared in situ by pulsed laser deposition on (100) substrates. X-ray diffraction in Bragg - Brentano and four-circle geometry confirmed that full epitaxial LSCO films can be grown for a much wider deposition temperature range, 500 - C, than that reported previously. Resistivity versus temperature measurements revealed that the LSCO films grown at temperatures lower than C were metallic. However, those fabricated at higher deposition temperatures showed a semiconducting transport behaviour, similar to that of oxygen-deficient LSCO films grown at the lower temperatures. X-ray photoelectron spectra of the Sr 3d core level suggested that this change in transport behaviour may be caused by cation disorder as well as oxygen deficiency involved in the high-temperature deposition. An all a-axis oriented (YBCO/LSCO/YBCO) heterostructure was fabricated successfully for the first time, which further confirms that the conductive LSCO film is promising for fabrication of high- superconductor - normal metal - superconductor junctions.

Magnetic flux leakage (MFL) is used for in-line inspection of underground oil and gas pipelines. MFL signals are sensitive to the line pressure which should be taken into account when estimating the sizes of defects. MFL signals have been studied from electrochemically milled pits with 50% penetration in pipeline steel under the influence of different axial or circumferential stresses and a range of magnetic flux densities. Magnetic Barkhausen noise (MBN) measurements have been used to study the changes in the direction of the magnetic easy axis of the pipe wall. These help one to understand the stress-dependent MFL results. MBN measurements have also been used to estimate the directional magnetic anisotropies of the steels.

The problem of radiative transfer in an inhomogeneous finite medium with an internal energy source and bounding surfaces which reflect both specularly and diffusively is solved by using the maximum-entropy technique. The reflectivity R and transmissivity T for plane-parallel media are calculated and compared with results from published calculations that used other methods. The comparison shows that the maximum-entropy results are good and converge to the exact results.

For the removal of material with pulsed laser radiation the distance travelled by the shock or blast wave and the amount of energy released in the plasma state due to the absorption of laser radiation are determined experimentally and theoretically. The distance travelled by the blast wave is detected by schlieren photography, the released energy by monitoring the transmitted laser radiation during the removal process. The theoretical evaluation is performed by numerical simulation using a model incorporating the laser-induced vaporization process and the dynamics of the plasma state. The results obtained from the experiments and the model are compared with that of the Sedov - Taylor scaling. The removal of the oxide layer from austenitic steel is investigated with laser radiation produced by a TEA and a high-power laser device. For the TEA laser with fluences of 5 and 10 J 50 - 80% of the pulse energy is released into the plasma state and the Sedov - Taylor scaling describes the distance travelled by the blast wave in agreement with data from the experiments and the simulation. For the high-power laser with a fluence of 50 J , 6% of the pulse energy is released into the plasma state and the Sedov - Taylor scaling does not describe the data of the simulation. The process of removal of copper and aluminium material is simulated for excimer laser radiation with fluences of 15 and 30 J . For copper 15 - 30% of the pulse energy is released into the plasma state and the Sedov - Taylor scaling is applicable. For aluminium, less than 2% of the pulse energy is released into the plasma state and the Sedov - Taylor scaling is only applicable for the higher fluence.

The scaling of the K-shell line emission of intermediate-valued atomic number pinch plasmas, generated in a plasma focus device, is investigated for currents ranging between 180 kA and 310 kA, a pressure range between 70 Pa and 1000 Pa and various values for the anode radius. It is shown that the transient ionization dynamics can be made visible in the scaling of the 1s - 2p transition of hydrogen-like ions and the 1 - 1s2p transition of helium-like ions. The experimental results for the resonance line scaling are in agreement with the theoretical predictions based on similarity considerations for the magnetohydrodynamics and the ionization process in the pinch plasma.

A spectroscopic study of a low-pressure supersonic jet of laser-heated argon plasma is presented. The experimental set-up consisted of a high-pressure convergent nozzle and a supersonic nozzle. The supersonic nozzle was placed just behind the convergent nozzle and was connected to a low-pressure chamber. A continuous wave laser with output power of 2 kW was used to maintain the plasma in the stream of argon gas flowing from the convergent nozzle. The plasma then expanded through the supersonic nozzle. Emission spectra from the laser-sustained plasma and supersonic jet were measured with a 1.3 m focal length spectrograph and 1254 silicon intensified target (SIT) detector connected to an EG&G PARC optical multichannel analyser (OMA) III. We found that the supersonic stream of argon plasma had an electron density of - and a temperature of 6 - 7 kK.

Resistive hose growth for moderate or large skin depth differs from that derived from a conductivity model. Asymptotic growth is calculated for the Bennett equilibrium, incorporating the inductive component in the plasma return current, with phase mixing accounted for via the `distributed-mass' model. Analytic scalings are checked with numerical solutions of the linearized model. For a ratio of skin depth to beam radius of less than 1/10 the conductivity model appears quite adequate. When this ratio exceeds 1/4 inductive corrections appear.

When a load requiring a very fast rising current is fed from a flux-compression generator, it is necessary to introduce a conditioning circuit in order to reduce the rise time of the generator output current substantially. The final stage of this circuit will include a plasma erosion opening switch, which is the fastest known opening switch for use at the current levels involved. This paper presents results obtained during the development of a novel two-stage conditioning circuit and compares the experimental performance of the circuit with results provided by a computer simulation. A time compression of the rise time of the currents from microseconds to less than 100 ns was obtained, representing a 40-fold increase in the corresponding signals.

This paper is aimed at calculating the onset voltage of negative corona in rod - plane gaps as influenced by the presence of a dielectric barrier located either parallel or normal to the gap axis. The effect of the barrier thickness, permittivity and location with respect to the stressed rod on the calculated onset voltage is investigated. The method of calculation is based on the criterion of self-recurring single electron avalanches developed in the gap when stressed negatively. The electric field values used for avalanche growth are evaluated using a combined technique based on boundary-element and discrete-charge simulations. In this technique, the surface charge on the rod is simulated by fictitious discrete charges while the surface charge on the faces of the barrier is simulated by surface charged boundary elements. The electric field assumes values higher than those in the absence of the barrier whatever the position of the barrier, parallel or normal to the gap axis. The smaller the distance between the barrier and the rod, the larger the thickness and the higher the relative permittivity of the barrier, the lower is the corona onset voltage.

Young's moduli of green and sintered unstabilized - ceramics have been determined by measuring compression and shear velocities through the material and, from separate measurements, the associated bulk density. Young's modulus and sintered density of - ceramics can be enhanced by increasing the compacting pressure when forming the green ceramics and with the addition of <5 wt% of unstabilized . For a particular green compacting pressure, the trend in the diametrical compressive fracture stress is similar to that of Young's modulus. The fracture stress also increases with a higher green compacting pressure at a constant wt% .

A new approach to the non-equilibrium distribution function for carriers in multi-valley band structures is presented. The approach is derived from the evolution process of the kinetic distribution function in momentum space as a result of scattering and a rapid change in electric field. This physics-based approach offers a unique and efficient model to obtain non-equilibrium and hot-carrier distribution functions without directly solving the integro-differential Boltzmann transport equation. The fast transient distribution functions of electrons in multi-valley GaAs and are studied using the resultant model. A Monte Carlo (MC) simulation is also included to verify the validity of the developed approach. It is shown that the distribution function derived from the developed method can respond, as fast as the average velocity, to a drastic change in field. It can account for effects of velocity overshoot/undershoot and includes the highly non-Maxwellian nature of the kinetic distribution function in extreme non-equilibrium situations.

On the basis of a series of experimental investigations reported in the literature, electrode microscopic surface roughness was dismissed as a factor influencing breakdown levels in compressed , irrespective of field non-uniformity. This conclusion appears to be tenable if one restricts observations to the investigations in question. In the present communication, we contend that the scope of these studies formed an insufficient basis on which to invoke such a general conclusion. To clarity this contention, the role of surface roughness in relation to the breakdown characteristics of compressed is recalled and its domain of influence brought into focus.

The effect of gaseous impurities such as water vapour and oxygen on the dielectric strength of compressed may be due to either gas composition or electrode surface protrusions. The assumption of a local field enhancement due to protrusions has been rejected due to the actual electrode roughness observed microscopically. It has been shown that the gaseous impurities lead to the creation of initiatory electrons through electron detachment from hydrated negative ions involving water vapour and oxygen, inducing changes in the breakdown regimes. Moreover, without hydration, electrode surfaces are passivated (fluorine deposition) and behave as covered with an insulating layer.