Table of contents

The main magnetic characteristics regarding the domain structure and magnetization processes (axial, circular and Matteucci and inverse Wiedemann effects) of amorphous wires and glass-coated microwires are analysed. Magnetic bistability, spontaneously observed in samples with large enough ratio magneto-elastic anisotropy with axial easy axis to shape anisotropy, is the main source for a number of sensor applications in pulse generators, position and field sensors, encoded security tags, rotational counters, magnetostrictive delay lines, and so on. The relevant perspectives of the novel giant magneto-impedance effect recently reported and observed in non-magnetostrictive samples are also introduced.

Systematic microstructural studies of hot pressed HDDR, fully dense magnets have been carried out. A fine grained, hard magnetic phase structure with a grain size of a few hundreds of nanometres is the most outstanding microstructural characteristic of these magnets. Apart from the compact fine grained microstructure with hardly any Nd-rich phase, partially isolated, fine hard magnetic grains with a Nd-rich surrounding were also found. Abnormal grains were observed, arising from the early stages of growth. These grains had a close contact to small neighbouring grains as well as larger abnormal grains of up to with straight borders. Other phases identified were the and intergranular platelets.

The homogenization of impedance-matched chiral-in-chiral (IMCIC) composites is shown in essence to involve nothing more than the smoothening of a scalar Helmholtz equation with a non-uniform wavenumber. A wealth of simple effective medium relations and complicated numerical techniques are shown thus to become available for IMCIC composites. Using the Maxwell Garnett as well as the Bruggeman approaches, we show that equal enhancements of the permittivity and the permeability of an achiral or chiral isotropic material by dispersing a specific chiral particulate material in it are possible.

We develop a simple method leading to the determination of important parameters for the praseodymium-doped fluoride fibre amplifier (PDFFA), such as the non-radiative energy transfer upconversion coefficient or pump-excited state absorption cross section . We apply this method to five ZBLAN bulks of different concentration (from 10 000 down to 500 wt ppm) and to a ZBLAN: 500 wt ppm single-mode fibre. The resulting non-radiative energy transfer upconversion coefficients are at 500 wt ppm and at 1000 wt ppm. When the pump wavelength is set at 1017 nm, is very weak: less than . We measured that the population varies according to the pump power raised to the power 2.7. We conclude that the upconversion mechanism leading to the excitation of states in the PDFFA is different from all that which has been previously suggested and we propose a three-photon process. The application of our method requires the measurement of radiative emission branching ratios from levels and that we compare to the values calculated with the Judd - Ofelt analysis. We show that this analysis has to be used very cautiously with ions. Finally, we discuss the distribution of ions in ZBLAN glass. The fitting of fluorescence decay curves from level with the Inokuti-Hirayama model shows that the distribution of ions in ZBLAN is nearly homogeneous and no clustering effects are detected. Nevertheless, the non-exponential fluorescence decay curve of level even at very low concentrations is explained by the fact that the ions do not all have exactly the same environment in the glass.

A class of irreversible refrigeration cycles is investigated to determine the maximum coefficient of performance in the heat pump mode and the refrigerator mode. For the purpose of generality and simplicity of the results, finite-time heat transfer in the condenser and evaporator is expressed in terms of arithmetic mean temperature differences. The generic source of internal irreversibility is measured by a single irreversibility factor which transforms the Clausius inequality into an equality to simplify the cycle model. These optimum cycle performances are obtained as closed form analytical expressions in which the irreversibility factor has been shown to be simply related to the ratio of the actual and endoreversible cycle coefficients of performance.

In this work, the problem of the thermal characterization of two-layer systems by means of the photoacoustic technique is discussed. For a two-layer system under rear-side illumination conditions, we have applied the Rosencwaig and Gersho model for calculating the pressure fluctuation in the photoacoustic gas chamber. The limiting cases in which both layers are thermally thin, thermally thick and one layer is thermally thin and the other is thermally thick are discussed. When both layers are thermally thin, a consistent equation for the heat capacity is obtained and an effective thermal diffusivity equation is derived when both layers are thermally thick. In order to test our theoretical results, we apply them to two-layer systems consisting of AlGaAs layers of different Al concentrations, grown by liquid phase epitaxy on GaAs substrates. The results of our measurements are in good agreement with the theoretical predictions. Our results show the general character of the expression for the effective thermal diffusivity of two-layer systems reported by Mansanares et al (1990 Phys. Rev. B 42 4477).

The influence of finite-rate heat transfer and regenerative losses on the performance of a Stirling refrigerator using an ideal or Van der Waals gas as the working substance is investigated. The cooling rate and the coefficient of performance are derived. The optimal relation between the cooling rate and the coefficient of performance is obtained. The maximum cooling rate and the corresponding coefficient of performance are determined for different cases. The problem of optimizing other parameters is also discussed. The results obtained here will be useful for the further understanding and the selection of the optimal operating conditions of a Stirling refrigerator.

The results of measurements of the microhardness on chalcogenide glasses of the system (where x = 0, 11, 16, 21 and 50 atomic wt%) are reported. The dependence of on composition shows a drastic decrease in the hardness upon the addition of sulphur at the expense of arsenic. It is also found that the microhardness of the ternary system increases, with a maximum at the crystallization temperature on isothermal annealing at different temperatures. The glass transition temperature of the glassy composition was identified mechanically.

A previous drag force study for a spherical particle immersed into a rarefied plasma flow has been improved upon, based on a more detailed analysis concerning the interaction between the charged sphere and ions and electrons. Revised analytical expressions are presented for the drag force acting on a non-evaporating or evaporating particle for the extreme case of the free-molecule flow regime and a thin plasma sheath. Both metallic and non-metallic limiting cases of the particle materials (with infinite and zero electrical conductivity, respectively) are considered. It is shown that the ion component of the drag force is appreciably less than the previous result and that the drag coefficient for a non-evaporating particle becomes identical to that derived for the case of non-ionized gases. The drag force on a spherical particle is directly proportional to the square of the particle radius and to the relative velocity between the particle and the bulk plasma at low speed ratios. Evaporation enhances the drag force acting on a particle due to the additional contribution to the drag force caused by the reaction of non-uniform evaporated mass flux outflowing from the evaporating particle. This evaporation-added drag force is more significant for particle materials with lower latent heat of evaporation and lower vapour-molecular mass. For the case without evaporation, there is almost no difference between metallic and non-metallic particles in their drag forces. However, a marked difference may exist between metallic and non-metallic evaporating particles in their drag forces because the different floating potential distributions on the surfaces of the two types of particles cause different distributions of the local heat fluxes along the particle surfaces.

We report temperature measurements in a low-pressure hydrogen microwave plasma. Translational temperatures both of H and of (using Doppler broadening), as well as the rotational temperature of , are simultaneously determined. It is first shown that the rotational temperature of the excited state is not in equilibrium with the translational temperatures of the neutral particles. Then, using a high-resolution Fourier transform spectrometer, we show that the H atom kinetic temperature is higher than the one. This result is interpreted in considering the mechanisms of relaxation of the hot H atoms, produced by electron impact dissociation of , in the molecules and on the tube walls.

RF glow-discharge plasmas provide mild energetic ion bombardment of exposed surfaces. The characteristics of a 10 MHz RF glow-discharge Ar plasma are studied by particle-in-cell simulation. The model simulates a spherical plasma device using a one-dimensional plasma model. The code is used to determine the breakdown voltage, , for a given pd, where p is the gas pressure and d is the plasma discharge length. These values are then compared with Paschen's law for the DC case. Also, the breakdown voltage as a function of driver frequency is investigated. Due to the nonlinear capacitance of the plasma, the current and voltage waveforms are found to contain higher harmonic components and sub-harmonic components. Above a certain power level of the driver, sub-harmonics which are indicative of a period-doubling (PD) bifurcation are found to become dominant. The PD thresholds for varying pd, the magnitude of the current and the voltage of the Fourier-analysed components as a function of applied RF voltages are calculated. The PD threshold is always higher than the breakdown threshold. Finally, the pressure-dependence of the sheath width is discussed.

The probability, , of losses of N and O atoms on Pyrex walls was determined from a fit of calculated to measured concentrations [O] and [NO] in a low-pressure glow discharge in , for percentage concentrations . The kinetic model used for calculations includes a detailed description of the processes occurring in the discharge bulk and of the surface reactions of O and N atoms. It was found that and are functions of the ratio and the wall temperature, . The values of were found to increase from about to about as increases from 1% to 90% (corresponding to ). The probability was found to be independent of and to depend only on in the range . For , however, depends on , its magnitude increasing by a factor of 2 - 5 as . The kinetic model developed here for surface reactions provides closed expressions for and in terms of the rate constants and the activation energies for these reactions. It is shown that the behaviour of and is well explained by the model under the following conditions: (i) the main surface processes for the low wall temperatures involved are reversible adsorption followed by surface diffusion of the adatoms to active sites, where they may either be irreversibly adsorbed or recombine; and (ii) there exist two independent systems of active sites, with different reaction probabilities.

A freely localized discharge is excited by a powerful microwave beam in argon, hydrogen and nitrogen. All processes of gas discharge production, maintenance and decay are volumetric in nature. The plasma decay is determined by diagnostic microwave beam attenuation. In the initial post-discharge stage the decay is close to an exponential law in nitrogen and hydrogen and to a linear law in argon. The decay adheres to the `recombinational' law only during the final stage of relaxation. Possible mechanisms for such behaviour are discussed.

Previous investigations of capacitive rf plasmas by means of Langmuir probes have shown unusually low mean electron energies of the order of a few tenths of an eV. We have developed the Thomson light scattering technique for its application to such plasmas in order to see whether those unusual plasma conditions can be confirmed by an independent experimental technique. Because impurities can affect helium discharges considerably, the plasma was operated in a UHV set-up. The symmetric electrode arrangement consisted of two aluminium discs of 70 mm diameter each and 40 mm spacing between them. The experimental set-up is described and it is pointed out how the particular problems of investigating such plasmas were solved. From the light scattering spectra of uncorrelated electrons both mean energies between 0.5 and 2 eV and densities in the vicinity of were derived as a function of rf voltage for a pressure of 40 Pa. Comparison with Langmuir probe measurements in the literature shows excellent agreement of values within their error limits including the steep rise and onset voltage of the transition. With respect to values reported from modelling calculations, agreement within error brackets has been found to apply for densities only.

The azimuthal component of the force, which establishes rotation in vacuum arc centrifuges, is investigated. It is found that the design of the anode grid is one important factor influencing rotation. A range of tungsten-wire grids have been studied experimentally in a vacuum centrifuge operating with a magnesium cathode, and angular velocities have been determined by cross correlation of voltage probe signals. It has been verified that angular velocity increases when grids with higher effective electrical resistivity are used, as predicted theoretically. Grid heating during the 14 ms operating pulse increases resistivity and should also increase angular velocity; this effect has been observed experimentally and agrees with predictions.

Optically stimulated luminescence (OSL) was excited at LNT by monochromatic light in x-irradiated natural quartz crystals. Excitation maxima appeared at 290 and 310 nm. The phototransferred thermoluminescence (PTTL) of these crystals showed excitation maxima at the same wavelengths, indicating that carriers are optically stimulated from the same traps. This is supported by the finding that the same wavelengths are most efficient for optical bleaching caused by prolonged illumination. The effects of thermal annealing to gradually increasing temperatures on the OSL were investigated and a correlation to thermoluminescence (TL) peaks was found. The OSL intensities showed sharp decreases after annealing to 160, 190 and 280 K; these temperatures coincide with the temperatures of the main TL glow peaks. It appears therefore that the OSL and the main TL peaks between liquid nitrogen temperature (LNT) and room temperature (RT) are due to the same donor levels. The emission spectrum of the OSL showed that this emission is composed of some bands, which appear also in PTTL as well as in x- and photoluminescence, indicating that the same luminescence centres are responsible for these emissions.

A novel method is described for preparing high-quality thin films which exhibit an abrupt resistivity change of 4 - 5 orders of magnitude at about ; this is the best result among those so far prepared on non-crystal substrates. To show the difference from the ordinary sol - gel method which uses vanadium alkoxide as precursor, this method has been called (by the authors) the inorganic sol - gel method, for it uses powder as precursor. This newly developed method shows some advantages in that it produces high-quality thin films (adherent, crack-free, and with good switching properties) in a cheap, simple, and reproducible way. The method consists of four processes: quenching, coating, drying and vacuum heat treatment. These processes show strong effects on the properties of the final films. In this paper, the effects of the drying process on the film blistering and the effects of film thickness, quenching temperature, and heat treatment time on the resistivity switching property were studied, and DSC, XRD, ESCA, and SEM were utilized to study the drying process and characterize the films. It was found that when the drying temperature was and heating rate was in the drying process, the final films would be blister-free and crack-free (on non-crystal substrates). It was also found that the magnitude of resistivity change at the phase transition of the samples treated at for 10 h under a pressure of 0.8 Pa increased with increasing thickness (in the thickness range 0.4 to ). When the film thickness was about , the magnitude of resistivity change of the samples treated under the same conditions was found to decrease with increasing quenching temperature. In a certain range of treatment time the magnitude of resistivity change of the samples treated at under a pressure of 0.8 Pa was found to increase with increasing heat treatment time.

For any real arrangement of contacts on an electronic device, the resistance obtained from a two-terminal measurement includes effects due to the curvature of current paths near to the contacts as well as the intrinsic bulk effects which are of primary interest and the resistance due to the interface between the contact material and the device material. Provided that the contacts are sufficiently well separated that the geometric curvature effect associated with one contact is negligible at the other then separate contact resistances can be defined for the two contacts. In this case the measured resistance can be interpreted as a series combination of two contact resistances (each including both interface and geometric effects) and a bulk resistance. The object of this paper is to show analytically that the contact resistance associated with a single contact can be obtained from an appropriate three-terminal measurement using a remote voltage probe well away from the current contacts. The limits of validity of this result are examined and are found to be relatively undemanding.

An electro-chemical reaction model is proposed in this paper to describe electrical ageing of solid dielectrics under ac voltage. The present model has the ability to predict not only the scale-invariance property of the electrical ageing function, but also the classical electrical ageing law, i.e. the electric field strength - lifetime inverse power law relationship. The micromechanisms inherent in the model enable a direct physical interpretation of the macroscopic electrical ageing behaviour in terms of the microscopic processes. We argue that the fractal behaviour of electrical ageing and breakdown processes in solid dielectrics are by essence determined by the scale-invariance of the electrical ageing evolution equation.

The method of a posteriori error calculation has been applied to the calculation of the refractive index and thickness of optical thin films from spectrophotometric transmission interference measurements. The refractive index and thickness of transparent or semitransparent thin film deposited on a transparent substrate can be calculated using both Edser - Butler and Swanepoel equations. A least-squares method and smoothing have been used to refine the Swanepoel's estimate and a correlation analysis has been applied to the differences between the two refractive index estimates. The refractive index covariance function is approximated by an exponential function and is then used in the statistical modelling process. The method has been applied to the calculation of the refractive index of a thin film deposited on a quartz substrate. In practice the method is especially useful in view of its ability to detect the deterioration of data caused by instrumental drift.

Semi-insulating GaAs grown by the liquid-encapsulated Czochralski (LEC) method was investigated by means of photo-induced current transient spectroscopy (PICTS). Surface and bulk contributions in the PICTS signal are compared by studying sandwich and planar samples. It is shown that, when using PICTS on materials with a depletion region, it is possible to identify the nature of traps. The used criterion is discussed. In addition the effects of the excitation light wavelength upon positive and negative bias PICTS spectra are reported.

The dual-beam thermal lens technique has been found to be very effective for the measurement of fluorescence quantum yields of dye solutions. The concentration-dependence of the quantum yield of rhodamine B in methanol is studied here using this technique. The observed results are in line with the conclusion that the reduction in the quantum yield in the quenching region is essentially due to the non-radiative relaxation of the absorbed energy. The thermal lens has been found to become abberated above 40 mW of pump laser power. This low value for the upper limit of pump power is due to the fact that the medium is a resonantly absorbing one.

Numerical simulations based on the exact Fresnel equations are used to show that it is possible to determine uniquely the relative permittivity and thickness of a thin lossless dielectric film adsorbed on a gold or silver layer. The calculations, which include the effects of up to 1% random noise on the experimental data, show clearly that there is no degeneracy in the solutions of the Fresnel equations even for films as thin as 2 nm. It is shown that gold is preferable to silver as a substrate when the overlayer properties need to be determined accurately. It is further shown that, if the overlayer is bounded by water rather than air, then the experimental constraints would preclude the use of silver as a substrate but measurements would still be possible with gold.

In situ boron-doped silicon films were deposited by a novel LPCVD process in the gas system. A high deposition rate and good thickness uniformity of films were obtained by the process. The silicon film annealed becomes polycrystalline with strong (111) texture. The polycrystalline silicon films annealed at were made of small grains. A uniform distribution of boron concentration was obtained in the silicon films and penetration of boron into the silicon substrate through the layer was not observed. The resistivity of the boron-doped silicon films was dependent on the annealing temperature and time and the minimum value of the resistivity was . Furthermore, good breakdown characteristics were achieved and the average breakdown field intensity was . This process provides a reliable gate deposition process for a sub-micrometre CMOS device with a surface channel.

A model for evaluating time-resolved acoustic microscopy measurements of cracks in anisotropic solids is presented. Calculations of the time-of-flight traces of acoustic waves reflected from the face of an inclined crack (FR) and the diffracted waves from the crack tip were carried out. Furthermore, the theoretical results for the FR signals are compared with measurements in a Ni superalloy. The most significant effect of anisotropy is the possible appearance of a signal due to shear waves with horizontal polarization.

A cavity in a viscoplastic material will shrink if the surrounding medium is exposed to an external pressure. This shrinkage is greatly influenced by the temperature of the material, because of an Arrhénius-type material law for the creep behaviour. If the temperature is also time-dependent thermal expansion will, in addition, affect the volume change of the cavity. Rock salt behaves like a viscoplastic material. In salt domes used as underground repositories for radioactive waste, temperature differences of about can arise in the salt. For a safety analysis of the repository it is of great interest to know the shrinkage of the cavities, called the convergence. The convergence behaviour is investigated in the case of a hollow sphere and a hollow cylinder. A viscoplastic material with variable time-dependent temperature is assumed. The problem leads to a nonlinear integro-differential equation which is solved analytically in simplified cases and numerically in the general case. The numerical solution shows good agreement with experimental results. An approximate solution for the general case is proposed.

The existence of a singular wave on the boundary of a magnetized plasma has been proved for both dielectric and metal interface. It has been shown that the points of the complex-zone boundary are neither degenerate waves, nor ones with zero field components. It has been proved that the intersection points of the complex-zone loop with the dispersion curve describe singular waves. The correct field components of the singular wave enable one to calculate Poynting's vector, which is essential for the modelling of a plasma sustained by a travelling surface wave.