Table of contents

The morphology and growth mechanism of silver films approximately 150 Å in thickness on Si(001) substrates have been studied by atomic force microscopy and x-ray reflectivity. The thin films prepared by dc sputtering at room temperature are composed of islands of silver. The shape and size distribution of these islands are studied using these two complementary measurement techniques.

The energy dependence of the electron - electron scattering rate in copper is numerically calculated with the use of Monte Carlo integration. The screening by d-band electrons, exchange interaction and the non-equilibrium electron distribution are taken into account. We also compute the rates of laser-stimulated electron - phonon collisions with the consideration of umklapp processes. It is shown that in the absence of direct interband transitions, and for energies higher than the Fermi energy of the metal, laser absorption is determined by electron - phonon umklapp processes.

Photoluminescence properties of SiGe/Si single wells with fluctuating structural parameters are studied. Four SiGe/Si single wells have been grown on Si(001) at 750 by disilane and solid Ge molecular beam epitaxy with varied disilane cracking-temperatures. Intense NP and TO-phonon replicas are detected up to 70 K in the photoluminescence spectra and the activation energy of the thermal quenching of the photoluminescence is meV. The high growth temperature and purposeful introduction of fluctuation of structural parameters may be responsible for the improvement of the thermal quenching property.

The effect of the discharge current density has been studied in order to obtain fundamental information about the growth of diamond films by a hot-filament-assisted chemical vapour deposition method with positive substrate bias. It is found that the application of a positive bias to the substrate improves the deposition rate and maintains control of the film's quality. Optical emission spectroscopy and mass spectroscopy have been employed to investigate in situ the effect of the discharge current density on a gas-phase environment. The increase in discharge current density significantly leads to an enhancement of the conversion of methane to carbon-containing species such as , CH, and . In addition, the density of H atoms also increases with increasing discharge current density. The accelerated electrons are likely to play an important role in these effects. These results suggest that the influence of the discharge current density on diamond growth is primarily due to a change in the gas composition.

We report in this work the behaviour of the magneto-impedance in twisted wires of amorphous that have been subjected to a current annealing with an applied tensile stress and have various induced anisotropies and saturation magnetostriction coefficients. The samples were annealed at 0.5 A for 1 min, with applied stresses in the range 100-800 MPa. The magneto-impedance is studied in the best frequency and current-amplitude ranges. High sensitivities to the applied magnetic field (up to ) and to the torsion (around ) are obtained.

The crystal structure and magnetic properties of ribbons prepared by melt-spinning and subsequent heat treatment were studied, where M represents Cu, Nb, Zr, Ti, V and Mo. The as-spun ribbons have an almost amorphous structure, and the annealed ribbons consist of 2:17 carbides and a small amount of - phase. Additions of Nb, Zr, Ti, V and Mo prevent crystalline grain growth. A significant coercivity enhancement was found only in ribbons with , and the maximum coercivity at room temperature was obtained for melt-spun ribbons with x = 1 annealed in vacuum. The coercivity can be further improved for ribbons of higher carbon content annealed in a Sm atmosphere. Additions of , V and Mo do not obviously change the coercivities in ribbons annealed below 1173 K, but the coercivities for and Ti ribbons decrease greatly. A small Cu addition has little effect on the lattice parameters and Curie temperature, but decreases the saturation magnetization and the magnetocrystalline anisotropy field. Additions of Nb, Zr, Ti, V and Mo decrease the Curie temperature, the magnetocrystalline anisotropy field and the saturation magnetization.

Radiation qualities of mercury high-frequency electrodeless light sources (HFELSs) of natural and 202 isotope abundance of 99.8% have been studied in order to optimize filling and operation of the source. The optimal mercury vapour pressure in a high-frequency electrodeless inductive coupled discharge is estimated. A qualitative explanation of the excitation and ionization processes is given. An application of nonlinear multiparameter chi-square line shape fitting in order to find the true profile of spectral lines and equipment influence is presented. We demonstrate that, by appropriate selection of both the HF-oscillator working mode and Hg vapour pressure, it is possible to change the intensity and profile of the spectral lines quickly, making the use of the mercury HFELSs in various applications possible.

This paper reports the results of the detailed and comprehensive experimental and theoretical treatment of the rf gas breakdown. We give the measured breakdown curves of the low-pressure rf discharge in argon, hydrogen and air in a broad range of gas pressures and interelectrode distances. The different processes of generation and loss of charged particles participating in the rf gas breakdown are discussed. We suggest to distinguish the following sections on the rf discharge breakdown curves: multi-pactor, Paschen, diffusion-drift and emission-free ones. The analytic gas breakdown criterion of the combined (rf plus weak dc electric field) discharge taking into account the anisotropy of electron diffusion in the electric field is obtained. A novel method for determining the electron-drift velocity from the measured rf breakdown curves is suggested. The electron-drift velocity data in argon, hydrogen and air obtained with this technique in the range -2000 V are given and compared with those got by conventional means.

The plasma density and electron temperature of the plasma generated in a pulsed low-pressure arc operated with Ar gas filling at p = 2 and 10 mbar have been determined employing a spherical Langmuir probe located in the outer region of the arc channel. A theoretical model has been used for the interpretation of the probe signals, which predicts the plasma structure resulting from the interaction of the metallic ions generated at the cathode spots with the neutral gas. Both collisionless and high-pressure (diffusive) theories have been employed to infer time-averaged plasma parameters from the probe signals. A reasonable agreement is found between the determined plasma density, electron temperature and ion flux attenuation with the corresponding values predicted by the theoretical model.

The plasma of a dielectric barrier discharge normally splits into a number of single filaments statistically distributed over the electrode area. In this paper we show how a single filament can be observed. Excited states of atoms in this filament are probed by infrared absorption spectroscopy. Absorption profiles of and transitions are measured for various pressures. The decay rates and density of Xe and Xe are calculated from time-resolved transmission measurements. The decay rates agree well with values found by other groups. The maximum density of excited atoms is found to increase with pressure much faster for the metastable state than it does for the resonance state. The strong increase of the Xe density with pressure can be attributed to a power increase and to recombination of atoms in higher states.

A technique is proposed for determining the location of an arc-discharge filament in a circuit breaker or a plasma torch utilizing only three photo-detectors, with the same spectral sensitivity, to observe the optical radiation emitted from the arc. The three detectors are placed at different azimuthal positions perpendicular to the central axis of the arc filament and are arranged symmetrically with respect to the central axis of the arc chamber and with their angular responses non-orthogonal. Outputs from the photo-detectors are analytically processed to yield two chromatic parameters, (the nominal radial mode) and (the dominant azimuthal mode), which define the arc location in the laboratory frame (, ). and are defined by algorithms used in chromatic processing. As an illustration, the technique has been applied to interpret some experimental results for determining the location of an arc filament lying within the nozzle of a gas-blast circuit breaker.

A two-dimensional numerical model is used to investigate cataphoresis (demixing driven by electrical fields) in free-burning arcs in mixtures of argon with helium, hydrogen, nitrogen and oxygen at atmospheric pressure. The method of inclusion of electrical field effects in the combined diffusion coefficient treatment of diffusion and demixing is presented. Cataphoresis is found to lead to large increases in helium concentration near the anode in argon-helium arcs and smaller decreases in hydrogen concentration near the axis in argon-hydrogen arcs. There is no significant effect in argon-nitrogen and argon-oxygen arcs. The effects of cataphoresis on other arc properties are generally small and are significant only in argon-helium arcs.

Energies of the ground and some excited states of on-centre donors in spherical quantum dots are calculated, within the effective mass approximation, as functions of the R dot radius and for different potential shapes. We propose an exact numerical solution for the radial Schrödinger equation in a quantum dot with any arbitrary spherical potential by using a trigonometric sweep method. An evident increase in the binding energy is found as the soft-edge-barrier potential model is considered. It is found that the binding energy increases as the dot size decreases up to a dot radius critical value and then, for R slightly smaller than , the impurity wave function spreads to the barrier region and the 3D character is rapidly restored. The properties of the shallow donors in a quantum dot with a double-step potential barrier and multiple barriers are analysed, and two peaks in the binding energy are found. Our results for the spherical-rectangular potential are in good agreement with previous calculations obtained using other methods.

We present a method of calculating the interaction between two particles in a single chain and between two chains in different structures in a non-polar liquid by using the equivalent conductivity plate concept. With this method, we obtain the quasi-static shear force-strain relationships and yield stresses of single-chain, 2D close-packed, rectangular and 3D BCT structures. By comparing the yield stresses with that of a single chain, we draw the conclusions that the interactions between chains in 2D close-packed and BCT structures enhance their yield stresses and that the enhancement becomes more significant as the number of chains increases, whereas the interactions between chains in a 2D rectangular structure weaken its yield stress. These results reveal the significant and distinct contribution of the structure of an electrorheological fluid to its yield stress.

The effect of temperature (22-) on the conductivity of silicone oil was determined employing three heating-cooling schedules. In all cases the conductivity was super-ohmic with a good fit to the equation based on Onsager's dissociation theory, namely

where is the conductivity at low electric field and A and are constants which define the field-enhanced ionic dissociation. The parameters , A and varied with temperature; however, the major effect of the heating-cooling schedules was on the parameter A. An analysis of the dissociation process gave that the valence of the conducting ions was in the range 1-2. The observed anomalous effect of temperature on the conductivity of the silicone oil was attributed to the gain and loss of water which occurred during a given heating-cooling schedule. We found good agreement between the measured anomalous temperature dependence of the yield stress (in dc field) of a zeolite-silicone oil suspension and that predicted by the conduction model when the variation of the conductivity of the oil with temperature was taken into account.