Table of contents

As soon as power is applied, the distributed electron cyclotron resonance (DECR) plasma rapidly dissociates the hexamethyldisiloxane (HMDS) and tetraethoxysilane (TEOS) parent molecules. At low power, the daughter molecules methane, acetylene, and ethylene are observed, but at higher power these molecules are dissociated as well. Starting the DECR plasma in HMDS and TEOS increases the pressure by an order of magnitude. When correctly operated, the DECR plasma fully dissociates the HMDS and TEOS parent molecules into their constituent atoms. At the chamber wall, the H atoms recombine to form molecules, whereas the Si, C, and O atoms stick to the surface and contribute to film deposition.

The etching of hydrogenated amorphous silicon (a-Si:H) and microcrystalline silicon by hot tungsten filament generated atomic hydrogen has been investigated. Room-temperature etch rates of 27 Å for amorphous and 20 Å for microcrystalline silicon have been achieved. Boron doping decreases the etch rate, whereas phosphorus doping does not affect it. No surface roughening occurs, even for the highest a-Si:H etch rates. In the initial phase of the etch process, however, a bond structure modification arises close to the surface. An increase of microcrystalline silicon etch rates towards the substrate/film interface reflects the coalescence of the microcrystalline nuclei. Hot filament atomic hydrogen etching provides high etch rates of amorphous and polycrystalline silicon with a high selectivity against metals and thermal oxide. Due to its simple setup and control, this kind of hydrogen etching is very interesting for applications in semiconductor technology where F- or Cl-etchants are to be avoided.

A parametric study of the thermal radiative properties of thin-film selective emitters used in thermophotovoltaic applications has been performed. It has been found that the effective directional emittance depends strongly on the physical thickness, refractive index and spectral extinction coefficient of the films. The emissivity exhibits a saturation, for an optical depth greater than unity, which is dependent on the refractive index and extinction coefficient of the material, namely the higher the refractive index and extinction coefficient, the lower the saturation value. For transparent films, the thickness required to achieve saturation is of the order of tens of micrometres whereas much lower thicknesses are required for absorbing films. Significantly, an anomalous increase in emittance at low thickness for high-index films has been observed, which might be of particular interest in thermophotovoltaic applications. The emittance has also been found to be strongly dependent on the emissivity and reflectivity of the substrates and on the direction of propagation of radiation. The total hemispherical emittance of the films has been found to increase with increasing temperature and total directional emittance, for the wavelength range . The data presented provide a design model for the optimum thickness of a thin-film thermophotovoltaic emitter.

This paper describes a new mathematical procedure for the determination of the force acting on a direct current in a horizontal loop moving in a vertical direction, with simple periodic motion, above a conductive plate of finite thickness and conductivity. The density of eddy currents induced within the plate due to the harmonic motion and the electromagnetic field outside the plate are utilized in the calculation procedure of the force. A general expression for the force is given in the form of Fourier integral series. A graph of the force versus periodic motion frequency is presented.

This paper provides a theoretical analysis of guided lateral modes in broad-area (BA) semiconductor lasers with modal reflectors formed by patterning the reflectivity of the front facet. The analysis has been performed by using the model based on the effective-index method and the concept of the effective facet reflectivity. The numerical results include mode threshold conditions and far-field patterns of the lasing modes for various reflector configurations.

A theoretical analysis of the heat transfer from a moving elliptical cylinder is carried out and general solutions in elliptical coordinates are obtained for aspect ratios , both and . The heat-flux distribution and total heat-flow rate are calculated, investigated for a wide range of parameters and presented graphically. The results obtained are useful for applications concerning thermal processes (laser cutting, welding, heat treatment and so on). A comparison of a moving circular cylinder with a numerical model of laser cutting is considered and discussed.

An experimental study of the origin and hitherto unexplored structure of the pressure - tension cycles accompanying the cavitation of liquids under dynamic stressing by tension is presented. The results of this study are relevant to certain problems in engineering and medicine, and the potential for application of the improved `tube-arrest' apparatus described here to those fields is considered.

In an effort to understand the dynamic behaviour of the streaming electrification phenomenon better, a computational model has been prepared. This paper describes the development and behaviour of the simulation for the development of charge-density profiles in space and time subsequent to the initiation of flow in a channel. Results are provided to demonstrate the functionality of the model and its effectiveness in clarifying the nature of the phenomenon.

By a two-dimensional numerical simulation of positive streamers in atmospheric air in sphere - plane gaps, the G-values (numbers of radicals per 100 eV of input energy) for the production of oxygen and nitrogen atoms are obtained. Calculated G-values weakly depend on the applied voltage and parameters of the gap and are about 3 - 4 and 0.3 - 0.4 respectively.

In the frame of the qualitative theory of streamer propagation in nonuniform electric fields, approximate formulae for G-values in streamer corona discharges are derived. The G-values are determined by the magnitudes of the reaction rate coefficients at electron energies corresponding to the maximum of the electric field in the streamer head. The formulae obtained describe well the relations between the G-values for different plasma chemical reactions and can be used for estimations of the absolute G-values with an accuracy up to a factor of two.

Using the relaxation continuum (RCT) model, numerical analysis of oxygen rf glow discharges between parallel plates with laser irradiation parallel to the electrode was performed. The oxygen discharge sustained by a sinusoidal wave voltage at a frequency of 13.56 MHz, amplitude of 200 - 230 V and pressure of 0.5 - 1.0 Torr is irradiated by the laser with a power of 300 W, width of 2 mm and wavelength of . Under these conditions, laser-induced photodetachment occurs with a large enough rate to affect the discharge structure significantly. When the plasma is irradiated continuously, the number density of ions in the incident region decreases by about 30%. The electron number density and the flux in the discharge when the pulsed laser is turned on and off every ten rf cycles, show prominent temporal variation with the variation of the electric field. Electron cooling is enhanced during the laser irradiation.

This paper is dedicated to the description of an interesting experimental phenomenon that was discovered in irradiated polymethyl methacrylate (PMMA). The breakdown voltage and electric-tree inception (initiation) time in PMMA were investigated under 50 Hz AC voltage after inhomogeneous proton irradiation. An anomalous relationship among , and the proton free length (the depth of irradiation) R in PMMA was found.

Submicron superconducting tunnel junctions were fabricated for submillimetre wavelength heterodyne detection. To this end three types of Pb alloy electrodes were investigated. All have shown good I - V dc characteristics but only the Pb - In - Au alloy produced stable and reliable junctions in vacuum and thermal cycling. Au-free junctions were found to be unreliable and would fail, i.e would form a short circuit, when placed in vacuum by desorption of water from the oxide barrier. This effect was subsequently stopped by alloying the electrode with 1% wt of Au leading to cathodic corrosion which in turn protects the junction from failing in vacuum.

Thermoluminescence glow peaks are calculated numerically for a one-trap - one-recombination-centre model using a generalized approach. Except in extreme cases the peaks are seen to change in position and shape with a change in dose. These glow peaks are fitted to the general-order kinetics model and the values of the kinetic parameters, namely the activation energy, pre-exponential factor and order of kinetics are determined by finding the best fit. In this way an attempt is made to correlate the empirical parameters with the physically meaningful ones in the framework of the adopted model. The fitted value of the activation energy matches reasonably its input value used in the generalized approach model calculations. The fitted values of the order of kinetics and the pre-exponential factor parameters change with the initial occupancy of the traps (dose) in all cases in which the order of kinetics (KO) is found to be in the range in which 1< KO< 2. The KO decreases with increasing trap occupancy whereas the pre-exponential factor increases. The latter parameter undergoes a change also in its units. It is observed that, when the found value of the KO is such that 1< KO<2, the best fitted general-order kinetics peak deviates significantly from the computed peak. A better fit is found with two peaks, one of which is approximately of first order and the other approximately of second order. The KO parameter at saturation dose has been correlated with the ratio of the re-trapping and recombination cross sections. These theoretical results are discussed in the perspective of experimental observations in general. Plausible reasons for disagreements between theory and experiment are also discussed.

The thermally stimulated discharge behaviour of vacuum-deposited polyvinyl fluoride films (about thick) studied as a function of polarization temperature (313 - 453 K) and polarization field (1 - ) shows a single relaxation peak whose peak temperature, charge, activation energy and so on depend strongly on the polarization parameters. The peak has been attributed to space-charge distributed polarization due to the migration of the charge carriers, injected from the electrodes or present inherently, over macroscopic distances and their subsequent trapping; the trapping levels being distributed in the range of energies 0.55 - 0.69 eV.

The purpose of the present work was to compare enhanced field emission from broad-area surfaces in DC and RF regimes. Geometrical defects, known to be field emitters, were created artificially by solid contact on copper and niobium samples. Each sample was tested successively in a re-entrant RF cavity, then in a DC diode housed in a specially equipped scanning electron microscope (SEM). When the sample was out-gassed carefully and exposed to a limited field and a limited current to avoid irreversible modifications of the emitter geometry, the Fowler - Nordheim parameters extracted from the experiment were the same in DC and RF regimes.

A general formalism for hopping electron transport over insulators sustained by secondary electron emission is presented. Steady-state electron transport takes place when the charging of the insulator, which turns out to be self-stabilizing, is such that the average secondary electron yield becomes equal to unity. The steady-state potential distribution for the electron transport is determined for various insulating geometries with the aid of Monte Carlo calculations and compared with the low-hopping approximation. The Monte Carlo results show that the steady-state potential distribution can exhibit several interesting features such as spontaneous symmetry breaking of statistical origin and the occurrence of local repulsive parts in the geometry. In several cases the numerical results, including the above two features, are found to agree well with the results of experiments.

The three-dimensional molecular dynamics simulation method has been used to study the dynamic responses of an electrorheological (ER) fluid in oscillatory shear. The structure and related viscoelastic behaviour of the fluid are found to be sensitive to the amplitude of the strain. With the increase of the strain amplitude, the structure formed by the particles changes from isolated columns to sheet-like structures which may be perpendicular or parallel to the oscillating direction. Along with the structure evolution, the field-induced moduli decrease significantly with an increase in strain amplitude. The viscoelastic behaviour of the structures obtained in the cases of different strain amplitudes was examined in the linear response regime and an evident structure dependence of the moduli was found. The reason for this lies in the anisotropy of the arrangement of the particles in these structures. Short-range interactions between the particles cannot be neglected in determining the viscoelastic behaviour of ER fluids at small strain amplitude, especially for parallel sheets. The simulation results were compared with available experimental data and good agreement was reached for most of them.