Table of contents

A giant magneto-inductive effect has been observed at room temperature in nanocrystalline FeCrSiB films prepared by RF sputtering followed by an annealing treatment. The frequency spectra and field dependence of the effect were studied in the frequency range from 1 kHz to 13 MHz and the magnetic field range from 0 to 75 Oe. A maximum reactance change of -110% induced by an applied magnetic field of 75 Oe was obtained at a frequency of 5 MHz. The sensitivity of the magneto-inductive effect at this frequency is about 8.5%/Oe. The field dependence of the effective permeability of the film is also presented.

New analytical results are found for the capillary absorption of a liquid into a porous (sorptive) composite solid composed of n parallel layers of arbitrary thickness and material properties. The analysis is based on the `sharp wet front' model (also known as the the Green - Ampt model) and the results are exact for that model. A contact impedance acting at the interface between layers is included. The physical approximations of the model are discussed. The cumulative capillary absorption as a function of time is expressed in terms of the sorptivity, permeability and porosity of the materials of the individual layers. Experimental data obtained on composite bars of gypsum plaster and plaster/sand materials agree well with model predictions, although they test the model over only a limited range of parameter values. For these composite specimens, there is no evidence of a hydraulic contact impedance at the interface between layers. An asymptotic expression is given for the effective sorptivity of an alternating composite ABAB....

A two-dimensional time-dependent model has been developed for the prediction of droplet formation in gas metal arc welding. The model is a unified treatment of the arc, the welding wire, taken as the anode, and the workpiece, taken as a plane cathode. Predictions are made of the formation and shape of the welding droplets as a function of time, accounting for effects of surface tension, gravity, inertia and magnetic pinch forces. The wire feed rate and gas flow rates are also incorporated into the model. Calculations are made of current densities, electric potentials, temperatures, pressures and velocities in two dimensions both in the arc and also within the molten drop and solid electrodes. For an arc in argon with a mild steel wire of 1.6 mm diameter and a current of 325 A or more, we predict the formation of small drops of diameter 1.2 mm or less and large drop frequencies consistent with the spray transfer mode observed in welding. At currents of less than 275 A, we predict large drop sizes of about 3.8 mm in diameter or more, consistent with the globular transfer mode in welding. At a current of 300 A, in a transition zone between the two modes, we predict the presence of both small and large drops.

Misfit dislocation formation in lattice-mismatched III - V heterostructures both under tensile and under compressive stress has been studied. Layers of GaAs under tensile stress have been grown by metal - organic vapour phase epitaxy on substrates with indium concentrations between 0.1 and 1.1%. Compressively strained layers with indium concentrations between 0.5 and 2.5% have been grown on GaAs substrates. For the layers under tensile stress an asymmetrical dislocation pattern has been observed, whereas the compressively strained layers show a symmetrical dislocation pattern. A model describing the relaxation process by the formation of dissociated hexagonally shaped half-loop dislocations is proposed. A difference in the mobilities of the two possible misfit dislocation types is found to be the origin of asymmetrical strain relief at low growth temperatures. In layers under tensile stress the cross slipping of screw dislocations is counteracted by the shear stress, leading to relaxation in only one direction. In layers under compressive stress the nucleated misfit dislocations can undergo cross slipping, resulting in a cross hatched pattern at the surface. At higher growth temperatures the dislocation patterns become more symmetrical due to the higher dislocation mobilities. Growth hillocks are formed on the surfaces of the layers grown under tensile stress, due to local accumulation of dislocations. This hillock growth is prevented at higher growth temperatures by the higher mobility of the dislocations. It is also shown that the (mis)orientation of the substrate is revealed by non-parallel groups of dislocation lines observed at the surface of a relaxed epilayer.

Polypyrrole (PPy) doped with small anions like or large polymeric anions such as poly(styrenesulphonate) forms a conducting organic solid. The electrical properties of metal contacts to this material were evaluated by current - voltage characteristics and impedance spectroscopy measurements. The I - V characteristics of the -doped device was symmetrical but non-ohmic, while that of the -doped diode was rectifying. The complex impedance spectra of -doped structures showed two partially overlapping semi-circles, which revealed the existence of two distinct regions at the metal/doped PPy junctions. They were modelled by an equivalent circuit consisting of two parallel RC circuits in series representing a thin insulating interfacial layer and a depletion region. The impedance spectra of -doped devices manifested a single semi-circle whose diameter depended on the bias voltage. In this case, the thin interfacial non-conducting layer was absent.

When a piezoelectric element is inserted into a medium, it is now well-established that the viscoelastic properties of this medium can easily be deduced from the measurement of the electrical impedance of this element and by using an appropriate optimization algorithm. This paper essentially deals with the influence of bonding defects at the interface between the piezoelectric sensor and the tested medium. First, a model is proposed to calculate the modifications of the electrical impedance due to defects of this type. The validity of this approach is demonstrated by comparing the theoretical predictions with the results obtained experimentally for different samples with well-defined bonding defects. Then, with this model, it is easy to determine the electrical impedance of an embedded piezoelectric element, whatever the value of the relative area on which the bonding defect occurs. In order to simulate what will happen in practice when we ignore that these defects are present, such simulated electrical impedances are processed with the usual optimization algorithm, assuming perfect bonding. Obviously, the viscoelastic properties of the tested medium are subject to error, as the size of the non-bonded area increases. It is shown that a very efficient tool based on the Kramers - Kronig relationships can be used to check the correctness of the extracted parameters.

The carrier transport mechanism has been studied in a three-layered electroluminescent (EL) device, which consists of poly(9,9-dialkylfluorene), diamine and perylene derivatives. The time response of EL emission in the three-layered device is completely different for the cases of driving by a forwards- or a reverse-bias field. Under the forwards-bias condition, it shows a slow response, whereas there is a fast response under the reverse-bias condition. Mean carrier mobilities have been estimated from the response time of emission. Mobility under the forwards-bias condition is found to increase with increasing applied field, whereas that under the reverse-bias condition remains constant and larger than that under the forwards-bias condition.

The effect of halogen (F, Cl and Br) doping on growth kinetics and structural properties of spray pyrolytically deposited tin dioxide films was studied in detail. The strengths of the halo-acids and hence the electronegativities of the halogens played an important role in governing the reaction processes which controlled the growth kinetics of the films. F doping affected the growth rate of a film the least, whereas Cl and Br doping reduced the growth rate to an increasing extent. The structural properties were less affected by doping. The films were polycrystalline and remained highly textured along the [200] direction irrespective of the dopant as well as of the doping level. The grain size remained essentially the same regardless of the dopant.

The results of studies carried out on the effect of magnetic field on the ageing of island silver films, deposited on glass substrates held at room temperature in a vacuum of Torr are presented in this article. The effect of magnetic field on the occurrence of large scale coalescence (LSC) is studied through the repeated deposition technique. A magnetic field of the order of 100 Oe reduces the ageing rate due to the flattening of islands but variation of the field in the same range does not affect ageing significantly. The effect of magnetic field is more pronounced on smaller islands than on larger ones. The application of magnetic field causes LSC to occur at an earlier stage.

Ion beam nitridation (IBN) of InP at room temperature was studied as a function of both ion incident angle and energy. The InP surfaces were exposed to ion beam in an ultrahigh vacuum environment and the resulting surfaces were characterized in situ by small spot size x-ray photoelectron spectroscopy (XPS) for accurate determination of the surface composition and chemical state. Thin InN reaction layers were formed at all ion incident angles and ion energies whereas the formation of P - N bonds was not observed. However, the degree of nitridation of In decreases with increasing incident angle and ion energy, closely following the reduced incorporation of N at higher angles and ion energies. The variation in nitridation is smaller with ion energy in the 2 - 10 keV range than with ion incident angle. The observed angular and energy dependence of the N incorporation can be explained in terms of sputtering yields, indicating that the growth kinetics can be described as a dynamic process comprising the accumulation of N and sputter removal of the surface layer.

The study of pure and -doped single crystal fibres with x = 0.24 by the LHPG technique is reported. The wavelength for non-critical second harmonic generation phase matching was found to be near 932 nm. Low-temperature spectroscopy reveals that the ions are located in the A2 sites of the tungsten - bronze structure in different environments. The stimulated emission cross section near 1060 nm of the channel and its branching ratio are determined with the help of the Judd - Ofelt analysis.

Most standard tomographic inversion methods require many measurements with a regular coverage of the object studied. A new method has been developed to obtain tomographic reconstructions from measurements by systems with a small number of detectors and an irregular coverage. The method reconstructs values on a regular grid in projection space from the measurements on an irregular grid by an iterative interpolation scheme. It applies a priori information and smoothing between the iterations. Furthermore, consistency of the results is obtained by an iteration between projection space and actual space. The tomographic reconstructions required in this iteration are made by a filtered-back-projection (FBP) method for the regular grid. The algorithm has been tested on assumed emission profiles. For a fan-beam system with a limited number of views the method has been compared with an FBP method for fan-beam systems; it was found to perform equally well. The method has also been applied to the visible-light tomography system on the RTP tokamak, which has only 80 channels and a very irregular coverage. Satisfactory results were obtained both for simulations and for reconstructions of actual measurements. The method appears to be a promising new approach to tomographic reconstructions of measurements by systems with irregular coverage and a small number of detectors.

By using finite-time thermodynamic theory, the optimal performances related to exergy of a Carnot refrigerator under the influence of thermal resistance are studied. The optimal relations between the rate of exergy output and the coefficient of performance and between the rate of exergy output and the rate of refrigeration are derived. Moreover, the main characteristics of the two optimal relations are discussed and some uses of the concept of exergy in finite-time thermodynamic theory are expounded. Some novel and useful results are obtained. Finally, it is pointed out that to extend the traditional exergy analysis using the theory of finite-time thermodynamics is quite important.

In this analysis the generalized kinematic equation for film thickness is derived by the method of perturbation. The equation is then used to investigate the linear stability of molten flow in laser cutting under a transversely applied uniform magnetic field. The effect of phase change is taken into account at the liquid - vapour interface. Firstly, the stationary solution to the variation of molten layer thickness is determined. Furthermore, linear stability analysis shows that the optimum cutting speed can be increased under the magnetic field. The effect of magnetic field revealed that the Hartmann number m stabilizes the flow no matter what values of cutting speed or gas velocity are used. This upgrades the cutting quality in a laser cutting process. The instability could be counteracted by controlling the applied magnetic field.

Electron-magnetized vacuum arc plasma transport in a magnetic toroidal duct is calculated numerically taking in account electron - ion collisions, electron and ion temperatures, and the high conductivity of the duct wall. The longitudinal magnetic field in the duct, the fully ionized plasma density and the electric potential distribution at the torus entrance are given, while the plasma density, electrical field and current, and macroscopic plasma velocity across the magnetic field inside the duct are calculated. Toroidal coordinates are used to describe plasma beam propagation. A Runge - Kutta routine is used for the calculations along the torus while a finite difference method is used across the torus cross section. It is found that plasma loss due to particle flux to the duct wall depends on the electron and ion temperatures and the plasma density distribution at the torus entrance cross section. With an electron temperature of , 30 000 K and 50 000 K, an ion temperature and a Gaussian distribution of plasma density at the torus entrance with a maximum value , we found that the duct efficiency was less than 10% for longitudinal magnetic field strengths of 10 mT and 20 mT. In the case where only the electrons are magnetized, filter efficiency depends only weakly on the magnetic field strength, on , and on .

The use of pulsed lasers to generate ultrasound in the non-contact regime is a well documented technique. A variety of lasers have been used to generate ultrasound in a range of materials, but all so far have allowed the laser to impinge directly on the sample or on a constraining layer in contact with the sample. It is also well known that the plasma generated at the surface of a sample when hit by a fast pulse of laser light is the most efficient mechanism for generation of longitudinal ultrasonic waves. One of the factors that has limited the use of lasers in ultrasonic generation is the fact that they can damage the surface of a sample. This damage can range from pitting or cracking the surface to the removal of a surface coating, such as a paint. We report here a technique that uses the plasma created by a focused pulsed laser beam to generate ultrasound without the sample actually being illuminated directly by the laser light.

High-resolution lineshape analysis of Thomson-scattered laser light was used to determine the centreline temperature and velocity of ions in a free-burning arc. The arc was maintained at in atmospheric-pressure argon. The technique allows direct measurement of plasma gas velocity without disturbing conditions within the plasma - the values found were lower than previously reported using indirect methods and increased with time, over 2 h. On the other hand, the ion temperature was found to drift little over the same period and its value was higher than previously reported for Thomson scattering, yet lower than found by emission spectroscopy. Possible reasons for these differences are examined and, in particular, the role of small concentrations of oxygen is discussed. This preliminary study highlights experimental difficulties that are inherent in this type of measurement.

Some experimental results obtained from a series of firings using a small-bore two-stage plasma armature railgun are presented which contradict assumptions employed in more recent attempts to model plasma armatures in railgun firings. By introducing the current - time behaviour into the equation of motion for the plasma - projectile system, an expression for a limiting exit velocity is obtained. This general expression is dependent upon the rail inductance per unit length when no anomalous effects occur in a firing. Since current diffusion is not significant close to the plasma - projectile system during a firing, the current distribution can be assumed to be in the form of thin sheets along the inner rail surfaces, thereby enabling the rail inductance per unit length to be evaluated. Different values for the height of the current sheets are then used to evaluate the rail inductance per unit length. When introduced into the expression for the limiting exit velocity, all yield significantly higher exit velocities than those recorded in railgun firings. These results explain the relatively poor performance of a railgun without the need to incorporate relativistic effects as in recent work.

The influence of slow ions on the electronic emission of a cathode in a high-pressure electric arc is investigated. As a first approach, a simple model is introduced, where solving the stationary Schrödinger equation is reduced to integrating a one-dimensional second-order differential equation. We have found that the electronic current may be enhanced through two mechanisms: a non-resonant process related to the lowering of the potential barrier and a resonant mechanism involving bound states of the ions. The non-resonant process is found to be dominant. The influence of various parameters such as ionic density, cathode temperature and charge states of the ions on amplification coefficients is analysed.

The dynamics of deformation in cylindrical liners are studied experimentally and theoretically in -pinch geometry, where the cylinders are deformed by a magnetic field created by a current flowing along the axis. This method allows one to obtain one-dimensional deformation and a reliable recording of magnetic field and cylinder deformation. The experiments are performed with a current amplitude of 0.8 - 3 MA and a current rise time of 2.5 - . Aluminium and copper tubes, from 4 to 6 mm in diameter and 0.25 - 1 mm wall thick, are compressed. The deformation rates under study are in the range of . The time dependence of the radii of the copper and aluminium tubes are measured with a streak camera and by the pulsed x-ray technique. The time resolution of the streak and x-ray photographs is 10 - 15 ns, their spatial resolution is .

A rheological model describing the dynamics of compression is developed. The model includes the description of the metal as a plastic medium with moving dislocations in the solid state, and as a viscous medium in the liquid state. The one-dimensional solution to magneto-hydrodynamical equations of the liner dynamics is compared with the experimental results and thus the following rheological parameters of the metal are obtained: , the probability of dislocation generation in plastic deformation; and , the drag stress, the parameter which characterizes a drag force acting on the dislocation.

Correlations for vapour pressure and saturated fluid (liquid and vapour) phase densities have been derived based on several experimental sources of data for R-134a. These equations, which are on ITS-90, use the same parameter in the powers of temperature terms. A method of optimizing this parameter is described. Saturated vapour densities are calculated from the Clausius - Clapeyron equation and experimental data, such that negative or unrealistic densities are not predicted when extrapolated towards the triple point. The method yields internal consistency of the critical properties used in the saturation equations. Results of the analysis are compared with the standard formulations.

We report optically detected cyclotron resonance (ODCR) measurements on two subband occupied electronic systems confined in triangular and square quantum wells. It is shown that the ODCR measurement is a useful tool for the understanding of the luminescence processes, in addition to the characterization of carrier concentration, effective mass and Fermi energy. We find that only one broad photoluminescence (PL) line locates below the energy gap for the triangular well, which is attributed to donor-to-acceptor recombinations. For the square well, two lines with emission energies higher than the bandgap are observed. Each line width is consistent with the Fermi energy of the first and second subband. This suggests that the emissions involve electron transitions from the first and second subbands at all occupied k states to localized holes. We also find that the effective mass of electrons in the first subband is heavier than that of electrons in the second subband in the triangular well due to the effect of nonparabolicity and the electron distribution, while the reverse is observed in the square well. This is explained in part by the nonparabolicity and, significantly, by the barrier leakage of the electron wavefunction. Furthermore, we find that the single particle relaxation time obtained from magnetoresistance measurements and the scattering time from cyclotron resonance are longer for electrons in the upper subband for both triangular and square wells, and the relaxation time is smaller than the corresponding scattering time, consistent with previous transport results.

Experiments of electron-beam-induced current (EBIC) and deep-level transient spectroscopy have been performed on a silicon bicrystal precontaminated with Fe and then annealed at . Contrary to all other similarly heat treated samples, whether they are as-received or deliberately contaminated with the fast diffusing Cu and/or Ni, the slowly cooled sample containing Fe exhibited an enhanced EBIC contrast and barrier effects at the grain boundary level, which have been associated with the formation of iron silicides at the interface. On the other hand, the rapid cooling has been found to `freeze' the moderately diffusing Fe in interstitial sites which act as recombination centres and are then at the origin of the observed general decrease of the EBIC in the bulk. A specific additional treatment of the quenched samples has led to the restoration and even improvement of both the EBIC signal and the minority carrier diffusion length.

Deep levels related to defects in high-resistivity undoped LEC-GaAs, generated during the growth and by low-fluence proton irradiation () are investigated by means of photo-induced current transient spectroscopy (PICTS). In order to compare effects from defects in the volume and defects in the surface of the material on PICTS observations, sandwich Schottky diodes and planar samples with two ohmic contacts on the front face were studied. Five main traps were observed. In addition to apparent activation energies, it is shown that the nature of carrier traps can also be identified. Irradiation with protons results in the creation of a new electron trap at nearly 0.72 eV below the conduction band. It is also shown that significant modifications in PICTS results may occur when changing the wavelength of the exciting light. In order to check the reliability of the deductions made from PICTS related to the nature of the observed traps, deep level transient spectroscopy (DLTS) measurements were performed under a permanent illumination of the sample. A general comparison and discussion are based on the results obtained from these different techniques.

The compound figures among the solid electrolyte materials exhibiting a high oxygen ion conduction. It belongs to the well known BIMEVOX family whose structure originates from the aurivillius phase . The layered structure of these compounds results in a larger bidimensional conductivity in the planes than along the c axis. This physical characteristic is clearly observed in a single crystal, whereas it is completely inhibited in misoriented powders. This paper deals with the means to retrieve this anisotropic conduction from free powders. Powder orientations were obtained using a high magnetic field and a uniaxial pressure. The correlation between the crystallographic texture and the electrical conductivity of this compound is reported here for the first time.

The spatial distribution of charges injected by monoenergetic electrons in Teflon FEP has been determined by two different techniques - the laser-induced pressure pulse (LIPP) technique and the laser-intensity modulation method (LIMM). A new numerical deconvolution technique for the LIMM is used. A comparison of the results provided by the two techniques shows good agreement.

This paper presents an approximate universality displayed by thermally stimulated depolarization currents ruled by stretched exponential relaxations when properly re-scaled. A visually perfect universality occurs especially when the energy and the heating rate are varied. It becomes somewhat poorer when the frequency factor or the stretched exponent changes. Empirical relations between the half widths and other pertinent parameters are given.

Polarization profiles have been measured with a resolution of about in corona poled 95:5 P(VDF-TFE) copolymer by using the piezoelectrically induced pressure step (PPS) method. A polarization peak is observed near the positive side of samples poled in a negative corona by the constant current technique. The distribution of polarization is also nonuniform in the case of a constant voltage poling at , but profiles are rather uniform if a poling field is applied at . In multilayer samples, the upper film bombarded by corona ions remains absolutely nonpolarized. Thin transition nonpolarized zones are seen near surfaces of even well polarized P(VDF-TFE). It is shown that polarization uniformity in P(VDF-TFE) is strongly affected by injection of negative charge carriers from the virtual electrode formed either on the surface bombarded by corona ions, or between two contacting dielectric surfaces. Our data on P(VDF-TFE) are in accord with those reported on other ferroelectric polymers.

This paper describes an investigation into time lags in PMMA at temperatures up to . A impulse waveform was used. Below the time lags were of the order of a few microseconds, but at higher temperatures time lags of hundreds of microseconds were recorded. The results are discussed in terms of Artbauer's recent theory.

The density and wavenumber dependence of the refractivity of in the gas phase has been determined by dispersive Fourier transform spectroscopy in the visible (DFTS-VIS, white-light interferometry). At a temperature T of 870 K (n - 1) can be described via , where is the amount-of-substance density given in and the wavenumber of the measuring light in . The uncertainty in the refractivity is . The range of validity and the limitations of this relationship are discussed in detail.

Cold plasma treatments of polymers induce surface transformations through several mechanisms involving photons, charges, radicals and excited species produced in the discharge. We have isolated the UV interaction contribution to the total luminescence emitted by the polymer after plasma discharge. Spectral and time-resolved light analyses have shown that the emitted light is constituted of the same components as in plasma-induced luminescence, namely photoluminescence, chemiluminescence and charge-recombination contributions. The essential differences were found in the dependence of the emission upon the treatment time. The luminescence intensity following plasma interaction decreased for increasing treatment time, whereas the UV interaction led to increasing emission followed by a steady-state luminescence level. In addition, the spectral distribution after a long exposure to UV did not evolve in an irreversible fashion. Some features of the time-dependence of the total intensity have been explained on the bases of luminescence decay analyses following conventional photoluminescence excitation. Whereas plasma interaction induced strong surface transformations, UV probably acts through more selective processes such as initiation of decomposition of hydroperoxides.

A modified conduction model is proposed for predicting the maximum local electric field, current density and attractive force between two spherical particles in a host oil. The dependence of the conductivity of the host fluid on electric field is expressed by a simplified equation based on Onsager's theory. The model gives the ratio of the maximum local field to the applied field as , where and , A and are the conductivity parameters relating to the host fluid. is the conductivity of the particles and the applied field. Good agreement is found between the predicted and measured values of the current density and the yield stress of electrorheological (ER) suspensions. To obtain a strong ER effect, a high value of the combined conductivity parameter of the host fluid is desired.

We present here a two-dimensional numerical simulation of a hydrogenated amorphous silicon p - i - n solar cell non-uniformly illuminated through the p-layer. This simulation is used to show the effect of the presence of dark regions in the illuminated surface on the electrical behaviour of the device. The continuity equations for holes and electrons together with Poisson's equation, implemented with a recombination mechanism reflecting the amorphous structure of the material, are solved using standard numerical techniques over a rectangular domain. The results obtained reveal the appearance of a lateral component of the electric field and current density vectors inside the structure. The effect of such components is a lateral carrier flow of electrons inside the intrinsic layer and of holes inside the p-layer, resulting in leakage of the transverse current collected at the contacts and an increase in the series resistance.

X-ray diffuse scattering (XDS) is used to detect the lateral structure of organic multilayers of Cd-stearte. XDS from the 30-layer sample reveals a coherence phenomenon dependent on , the half angle between the incident beam and the reflected beam direction: for small , distortions within metallic layers are interpreted as height fluctuations. For increasing , these distortions are seen as mosaicity due to the decrease of the lateral coherence length of x-rays. Usually, the only effect of the finite instrumental resolution is considered to be line broadening of XDS signals. Additionally, we show that the decreasing lateral coherence length of x-rays leads to incoherent scattering from samples. As a striking consequence in scattering experiments, the interpretation of real structure features of samples can change. The inhomogenities of the multilayer structure are described as height fluctuations of Cd layers and mosaicity of molecular clusters.

We explore the possibility of a quantum directional coupler based on -shaped coupled electron waveguides with smooth boundaries. By calculating the transmission spectra, we propose an optimized coupler structure with a high directivity and fine uniformity. The coupler specifications, directivity, uniformity, and coupling coefficient are evaluated.

We have imaged the conducting paths in a metal - insulator composite , with x ranging from 0.24 to 0.576 by conducting atomic force microscopy (AFM). The surface morphology and the electric current between the tip and sample have been obtained simultaneously on the nanometre scale. Measurable changes of current image have been observed for x below and above the percolation threshold . Our observations imply the importance of tunnelling for all samples. The high spatial resolution of AFM combined with a conducting tip provides new insight into electron transport behaviour in metal - insulator composites at the nanometre

Acid-treated carbon nanotubes have been decorated with nanoscale Au, Pt and Ag clusters by employing several procedures. The nature and extent of metal coverage can be varied by changing the concentration of the metal compound or by mild sonication (treatment with ultrasound). The metal clusters seem to get deposited on the acidic surface sites of the nanotubes.