Table of contents

6 MeV electrons and Co-60 -rays were used for grafting vinylidene chloride (VDC) onto high-density polyethylene (HDPE) samples. The HDPE samples were immersed in vinylidene chloride and irradiated either with Co-60 -rays or with 6 MeV electrons. In both cases, the radiation dose was varied in the range 1.25-7.5 kGy. The grafted samples were characterized by IR spectroscopy to obtain information about the chemical bonds and with the 14 MeV neutron activation analysis technique for estimating the number of chlorine atoms. The formation of stable bonds between the VDC molecules and the polymer chains could be achieved either with 6 MeV electrons or with Co-60 -rays. Both the number of chlorine atoms and the sample-surface conductivity increased with the radiation dose but the increases achieved with 6 MeV electrons were greater than those achieved with Co-60 -rays.

Photoacoustic (PA) heat transmission measurements were used to study thermal transport in n-type polycrystalline CdTe films doped with metallic indium. Thermal diffusivity (TD) at room temperature was determined using an open cell PA technique. The TD obtained for each sample was correlated with x-ray diffraction measurements. It can be shown that the TD of the undoped films under investigation is significantly reduced compared with corresponding doped films. This reduction is a result of the high concentration of indium atoms and defects depending on the deposition parameters. It is shown that the effects of CdTe lattice shrink produced by indium doping, induces an increase in phonon scattering reflected in the large TD decrease even with moderated indium concentration. We have calculated the relation between the TD and the lattice parameter as a polynomial function (cm² s^-1) = -35225.2+14259a-1532.7a²-27.9a³+8.4a⁴.

We prepared organic light emitting diodes (LEDs) with alternately deposited dye-doped aluminium quinoline (Alq3) and diamine derivative (TPD), and studied their electroluminescence (EL) and photoluminescence (PL) properties. The alternate deposition structure changed the energetic position and full width at half maximum (FWHM) of the EL spectra for the organic LED with alternately deposited undoped Alq3 layers, but did not change those for the organic LED with alternately deposited dye-doped Alq3 layers. On the other hand, the EL efficiency of the dye-doped specimens, despite the use of sample dyes with high PL quantum yield, was lower than that of the undoped specimen. Although the location of an emitting Alq3 layer depends on electron injection, the emitting region in a 5 nm thick Alq3 layer was estimated to be localized near the TPD layer on the anode side by a partial dye-doping method. To explain the conflict between the electron injection dependence of EL and the location of the emitting region, we propose recombination in the TPD layer and the direct energy transfer from TPD to the sample dye without the excitation of Alq3.

Multilayered thin-film structures consisting of soft magnetic layers and well conducting spacers exhibit high sensitivity to external magnetic fields. We develop the model theory of giant magneto-impedance in such a structure. Expressions for the tensor of surface impedance are obtained and the problem of sandwich miniaturization under conditions which keep the sensitivity is analysed. The effect of giant magneto-impedance manifests itself in miniaturized sandwiches largely in non-diagonal components. The effect of nondiagonal magneto-impedance shows promise as a basis for developing submicrometre highly sensitive magnetic sensors.

In this paper we report on the giant magnetoresistance effect and oscillatory exchange coupling in electrodeposited Co₈₇Fe₁₃/Cu compositionally modulated alloys. The alloys are compositionally modulated over nanometre length scales with ferromagnetic Co₈₇Fe₁₃ (Cu) alloy layers and non-magnetic Cu layers. Co₈₇Fe₁₃/Cu multilayered thin films were electrodeposited from a single sulfate plating solution containing all metallic ions of interest under computer-controlled potentiostat switching on (111)-textured Cu buffers previously evaporated on Si(111). Electrodeposits present a polycrystalline character with coexistence of face-centred cubic (fcc) and hexagonal close-packed (hcp) structures. Magnetoresistance effects as high as 8% were observed at room temperature. The dependence of the magnetoresistance effect on Cu spacer layer thickness shows an oscillation period around 1.0 nm.

The angular and potential dependence of giant magnetoresistance in magnetic multilayers is discussed. The functional dependence of the giant magnetoresistance on magnetic configuration variation is obtained by considering both interface and bulk magnetization contributions. The results show that the giant magnetoresistance in magnetic multilayers varies with magnetization angle and differs for different layer thicknesses. We also clarify the interface and bulk contribution of the giant magnetoresistance in magnetic multilayers for various exchange potentials and impurity scattering potentials.

The dynamical behaviour of the laser beam fusion cutting process of metals is investigated. Integral methods such as the variational formulation are applied to the partial differential equations for the free boundary problem and a finite dimensional approximation of the dynamical system is obtained. The model describes the shape of the evolving cutting kerf and the melt flow. The analysis is aimed at revealing the characteristic features of the resultant cut, for example, ripple formation and adherent dross. The formation of the ripples in the upper part of the cut, where no resolidified material is detectable, is discussed in detail. A comparison with numerical simulations and experiments is made.

This paper is the second step in the study of deviations from equilibrium in models of decaying SF₆ arcs. The first step was based on a kinetic approach, which allowed us to study the influence of deviations from chemical equilibrium. Departures from equilibrium are shown for a simplified geometry, and we find results similar to those of in the literature for the influence of pressure or intensity. In order to build the basis of the two-temperature model, we calculated the two-temperature composition, the transport coefficients and thermodynamic properties, and the energy exchange term between electrons and heavy particles through elastic collisions.

Electron-ion collisions contribute to the main part of the energy exchange term, S⁺ and S₂⁺ having the greatest contributions to this term. Our results show that taking departures from thermal equilibrium into account leads to a slower cooling rate of the plasma. The evolution of temperature departures during extinction is in agreement with experimental results.

Time-varying intensities of N₂ and N₂⁺ bands under discharge and post-discharge conditions of a pulsed dc 2-H₂ diode plasma have been analysed. It is shown that, at a constant discharge current, the discharge voltage and the substrate temperature continuously decrease with the introduction of H₂ into N₂. As a consequence the degree of ionization n_e/[N₂] keeps a nearly constant value. Under such conditions, a V-V excitation of N₂(X,v) by H₂(X,v) explains small increases in intensity of the N₂ second positive system and N₂⁺ first negative system in the discharge with about 5% H₂ in N₂. In the afterglow, the N₂ and N₂⁺ band intensities decrease with the amount of H₂ let into N₂ but a vibrational excitation of N₂(C,v´) radiative states has been observed in the N₂-H₂ afterglow, just like in pure N₂, indicating that pooling reactions of N₂(X,v) vibrational ground-state molecules are always active in the post-discharge regime.

This paper considers the fundamentals of the variational approach to the charge-drift equations as part of the generalized field theory of electrical discharges in gases. It is in furtherance of the published theory on charged gaseous flows in which some variational results have been given based on continuity principles. These results were developed as part of the Lagrangian approach to charge drift, which is the equivalent of the more commonly used Eulerian continuity equation. A complete and exhaustive set of optimizing principles, on which finite-element methods can be based, would be of considerable help to any problem solver using Lagrangian methods; and it is with the global search for such expressions that this work is concerned. The author has previously succeeded in showing that solving the governing equations of charge drift is equivalent to finding minimizing electric potentials for certain integrals in which the charge distributions are known. The dual of these principles, in which optimal charge distributions are sought for given potentials, was not given in earlier work as an appropriate integral could not be found. This situation is investigated, and proofs are given of the non-existence (degeneracy) of these dual principles for both single and multiple ionic flows. The work is put into the general context of the search for solutions of ionic flow problems in a gaseous medium and is of particular relevance to corona discharges and their applications, aerial ionization phenomena and gas-insulated systems. It is of decisive importance in revealing the existence or non-existence of full finite-element solutions to charge-drift problems, as it clearly reveals when this method can give results and when not. It further indicates how the finite-element approach can be used jointly with other numerical methods. The paper has other fundamental implications, for it shows whether or not variational proofs can be constructed of major results in the theory of charge drift which have already been derived in the literature by other means.

For atomistic simulation of vacancy-assisted dopant diffusion in silicon one needs details of the dopant-vacancy interaction, i.e. the potential as a functional of dopant-vacancy separations. In this paper, we present a detailed study on the energetics of As-vacancy reaction in silicon and the lattice distortions surrounding the As-vacancy defect by using an ab initio plane-wave pseudopotential method and the density functional theory (DFT). A potential-energy diagram as a function of As-vacancy separation, which can be used in the atomistic diffusion simulations, is provided. We also calculate the binding energy and the formation energy of various complexes such as AsV, As₂V and AsV₂ (V represents a vacancy). We find that the stable configuration of As₂V is As-V-As, whereas the stable configuration of AsV₂ is As-V-V. The nature of the binding between As and a vacancy is explained in terms of the lattice distortions and the change of chemical bond configuration introduced by the As-vacancy complex.

CdTe films with large grains were prepared by rapid thermal processing (RTP) of a room temperature evaporated CdTe film used as the precursor. RTP was carried out at different temperature ramps and the films, thus produced, were characterized by measuring the optical and microstructural properties to optimize the deposition conditions for the preparation of large grained CdTe films. Photoluminescence (PL) measurements were carried out to derive information on the defect structures in these films.

In order to clarify the reasons for the contradictory results regarding quadratic electrostriction in alkali halides reported by various authors, we developed an improved capacitive dilatometer. Employing the frequency-modulation technique, the resolution of the experimental set-up reaches l 2×10^-13 m. Various possible sources of errors could be detected, including sample mounting, calibration faults and, in particular, electro-mechanical resonances caused by strong Coulomb interactions between certain components of the dilatometer. From frequency-dependent measurements in the range 60-1200 Hz we determined the complete tensors of the quadratic electrostriction of LiF, NaCl, NaBr, KCl, KBr, KI, RbCl, RbBr and RbI at room temperature. The results are in reasonable agreement with values derived from sophisticated lattice-theoretical models. Furthermore, we studied the influence of the real structure of Li-doped KCl crystals on their electrostrictive properties.

Thermoluminescence glow curves calculated from three physically meaningful models are fitted into the empirical general-order (GO) kinetics expression to find the fitted values of activation energy E and the kinetic order b. The results show that the figure of merit of the fit deteriorates progressively as the best fitted value of b deviates from 1 and 2. At the same time the fitted E value also departs from its true value. This result is used to reinterpret the observed change in E of glow peak 5 of LiF (TLD-100) in post-irradiation annealed samples. It is concluded that the application of GO kinetics to glow peak 5 of LiF (TLD-100) leads to inconsistencies and that the changes in E found by GO fitting may not be real.

When they are recrystallized from the melt, natural plant or insect waxes tend to form solid phases with a nematic-like structure (i.e. a parallel array of polymethylene chains with little or no aggregation of the molecules into distinct layers). An electron diffraction study of carnauba wax and two types of beeswax has shown that the degree of molecular organization into lamellar structures can be enhanced by annealing in the presence of benzoic acid, which also acts as an epitaxial substrate. Nevertheless, the resultant layer structure in the annealed solid is not the same as that found for paraffin wax fractions refined from petroleum. Probably because of a small but significant fraction of a very long chain ingredient, the lamellar separation is incomplete, incorporating a number of `bridging molecules' that span the nascent lamellar interface.The same phenomenon has been described recently for a low molecular weight polyethylene.