Table of contents

A silicon-based PbTiO₃/Pb(Zr_0.53Ti_0.47)O₃/PbTiO₃ (PT/PZT/PT) sandwich structure is prepared by a sol-gel method. The PT layers in the sandwich structure are used as seeding layers to improve the crystallization of the lead zirconate titanate (PZT) ferroelectric thin films. The maximum dielectric constant of about 950 is obtained at the coercive field 17 kV cm^-1, and the remnant polarization is 19 µC cm^-2. The leakage current density is less than 5×10^-9 A cm^-2 when the applied voltage is below 200 kV cm^-1. Compared with the ferroelectric structures without and with only one PT seeding layer, the processing temperature is reduced greatly, while the electrical properties of the PZT films are further improved.

The increasing information density in magnetic recording, the miniaturization in magnetic sensor technology, the trend towards nanocrystalline magnetic materials and the improved availability of large-scale computer power are the main reasons why micromagnetic modelling has been developing extremely rapidly. Computational micromagnetism leads to a deeper understanding of hysteresis effects by visualization of the magnetization reversal process. Recent advances in numerical simulation techniques are reviewed. Higher order finite elements and adaptive meshing have been introduced, in order to reduce the discretization error. The use of a hybrid boundary/finite element method enables accurate stray field computation for arbitrary shaped particles and takes into account the granular microstructure of the material. A dynamic micromagnetic code based on the Gilbert equation of motion to study the time evolution of the magnetization has been developed. Finite element models for different materials and magnet shapes are obtained from a Voronoi construction and subsequent meshing of the polyhedral regions. Adaptive refinement and coarsening of the finite element mesh guarantees accurate solutions near magnetic inhomogeneities or domain walls, while keeping the number of elements small. The polycrystalline microstructure and assumed random magnetocrystalline anisotropy of elongated Co elements decreases the coercive field and the switching time compared to zero anisotropy elements, in which vortices form and move only after a certain waiting time after the application of a reversed field close to the coercive field. NiFe elements with flat, rounded and slanted ends show different hysteresis properties and switching dynamics. Micromagnetic simulations show that the magnetic properties of intergranular regions in nucleation-controlled Nd-Fe-B hard magnetic materials control the coercive field. Exchange interactions between neighbouring soft and hard grains lead to remanence enhancement of isotropically oriented grains in nanocrystalline composite magnets. Upper limits of the coercive field of pinning-controlled Sm-Co magnets for high-temperature applications are predicted from the micromagnetic calculations. Incorporating thermally activated magnetization reversal and micromagnetics we found complex magnetization reversal mechanisms for small spherical magnetic particles. The magnetocrystalline anisotropy and the external field strength determine the switching mechanism. Three different regimes have been identified. For fields, which are smaller than the anisotropy field, magnetization by coherent switching has been observed. Single droplet nucleation occurs, if the external field is comparable to the anisotropy field, and multi-droplet nucleation is the driving reversal process for higher fields.

X-ray reflectometry allows the determination of the thickness, density, absorption and rms roughness of a stack of thin layers on a substrate from several nanometres to some hundred nanometres. Inversion of the experimental reflectivity data is usually realized by a trial-and-error method based on the theoretical computation of the reflectivity curve after having extracted initial values of the layer thicknesses from the result of a classical FFT of the reflectivity data. However, the order information of the layers is lost during classical FFT. The order of the layers then has to be known a priori. Besides, the classical Fourier transform does not reveal anything about the stack parameters (density, absorption and the rms roughness). As this trial-and-error method is efficient provided that one has a good idea of the stack parameter values, it is important to extract some valuable information directly from the experimental reflectivity. In this paper, it will be shown that the order of the layers can be obtained by the so-called joint time-frequency representations. Furthermore, the continuous wavelet transform allows qualitative determination of the stack parameters and helps in the determination of an appropriate starting model for the trial-and-error method. The points of interest of this method are illustrated by experimental examples.

Both LiB₃O₅and SiN_1.375H_0.603 were implanted by 1.0 MeV Au⁺ ions to a dose of 5×10¹⁵ ions cm^-2 under different angles. The range straggling and lateral spread of 1.0 MeV Au⁺ ions in both LiB₃ O₅ and SiN_1.375H_0.603 were investigated by the Rutherford backscattering of 2.1 MeV He²⁺. The experimental mean projected range, range straggling and lateral spread are 279.7 nm, 54.0 nm and 34.6 nm for the case of LiB₃O₅, and 222.3 nm, 54.6 nm and 31.5 nm for the case of SiN_1.375H_0.603. The results show that the experimental range straggling and lateral spread are much larger than the values predicted by the 1998 version of the Transport of Ions in Matter code (TRIM98). After inelastic effects have been included in nuclear stopping regime, there is a much closer agreement with the experimental values than the original TRIM98 codes have. The maximum differences of the mean projected range, range straggling and lateral spread between experimental and calculated values are less than 3%, 24% and 21%, respectively for both cases.

Simple pictures and discussions are presented concerning the effects of the hole barrier in bilayer organic light-emitting devices. There seems to be an optimal value of the hole barrier height for the maximum device efficiency. The conclusion is quantified by numerical simulations of the heterojunctions. Recent experiments are also analysed and compared to these results.

The electrorheology of silica particles coated with protonated polyaniline or polyaniline base in silicone oil has been studied. The behaviour of suspensions has been compared with those of bare silica particles and polyaniline base powder. For a 1 wt.% suspension of polyaniline base, the low-shear viscosity (at 7.69 s^-1) increased more than 25 times in the presence of the electric field, while the upper-shear viscosity (623 s^-1) approached this value in its absence. In suspensions of coated silica particles, the viscosity increase was much lower, only a little higher than in a suspension of dry silica particles. The electrorheological performance of these systems is discussed in connection with the polarization characteristics resulting from the frequency spectra of permittivity and dielectric loss of suspensions and from the particle dipole coefficient.

A capacitance-type humidity sensor in which a porous silicon layer is used as a humidity-sensing material was developed. This sensor was fabricated monolithically to be compatible with the typical IC process technology except for the formation of porous silicon layer. As the sensor is made as a mesa structure, the correct measurement of capacitance is expected because it can remove the effect of the parasitic capacitance from the bottom layer and other junctions. To do this, the sensor was fabricated using process steps such as the localized formation of porous silicon, oxidation of the porous silicon layer, and etching of the oxidized porous silicon layer. From completed sensors, capacitance response was measured at a relative humidity of 25-95% at room temperature. As a result, the measured capacitance showed an increase over 300% at the low frequency of 120 Hz, and showed little dependence on temperature between 10 and 40 °C.

A Monte Carlo model was used to describe the behaviour of electrons and ions in an argon hollow-cathode discharge under the influence of a transverse or longitudinal magnetic field. The model included calculating the energy distribution of electrons and ions, the electron excitation and ionization rate spatial distributions and the flux and density distribution of electrons and ions. Comparisons were made between these two kinds of magnetic field to primarily distinguish their effects on the hollow-cathode effect and the sputtering process. The results show that the applied magnetic fields influence the characteristics of discharge in the negative glow more efficiently than that in the cathode dark space, and the transverse magnetic field (parallel to the sheath electric field) is more suitable to enhance the hollow-cathode effect and sputtering process than the longitudinal one (parallel to the electrode).

Effects of B addition on the structure and magnetoresistance of as-quenched and annealed Co-Cu granular alloys have been studied. The formation of the Co₂B phase reduces the number of small magnetic particles, which are the centres for spin-dependent scattering. The magnetoresistance of Co-Cu-B granular ribbons decreases with increasing B content.

In this paper, we consider the stimulated transition-radiation emission from a relativistic beam of electrons with short pulse, which passes through a plasma ripple and interacts with a plane wave. A set of self-consistent nonlinear equations is developed to describe the evolution of the radiation field in the plasma ripple. Analytic calculations of the small-signal gain and numerical computations of the nonlinear saturation of this emission are presented. It is shown that this device may provide a short-pulse coherent tunable source ranging from the microwave to the near-infrared regions, with a relatively high extraction efficiency.

We study the synchrotron radiation properties in a nondispersive medium for the case when the charge velocity is smaller or greater than the light velocity in the medium. We show that the space distribution of synchrotron radiation has a spiral-like structure at a fixed moment of laboratory time. As time progresses, this spiral-like structure rotates without changing its form. The space-time domains, where particular polarization components disappear and where they are infinite, are determined. Their dependence on the radius of the observation sphere is also studied.

An analysis of the vector wave equation was conducted. A class of self-similar solutions with inhomogeneous polarization corresponding to the resonator modes is deduced. The modes with inhomogeneous polarization can be selected by a diffraction element with polarization selectivity used as one of the resonator mirrors. Diffraction elements with high polarization selectivity of about 100% are necessary for generating `pure' radially polarized modes. The radially polarized beam provides a higher energy efficiency (the product of the depth of the cut by the cutting velocity) for laser cutting metals than the circularly polarized main mode does under the same conditions. The two limiting cases of resonance absorption on the spherical plasma target could be realized using axially polarized beams: the resonance absorption is maximum in the case of radial polarization and does not occur in the case of azimuthal polarization.

Basic mechanisms influencing the resonant frequency of the RF-discharged slab-waveguide CO₂ laser head are described. An algorithm of calculations to design a laser head resonant frequency is given. The algorithm is experimentally confirmed.

A new integration method is introduced for calculating the thermodynamic potential energy of gases with provided intermolecular potential. An example for hard-sphere molecules is illustrated. The results obtained agree well with the experimental data for oxygen and methane at normal and high temperatures. When the potential energy is applied to the study of gas expansions, such as Joule-Thomson expansion and free expansion, the heating and cooling effects produced by conversions of mechanical work and potential energy into heat energy can be revealed separately. Also, we may find the physical relationships between temperature changes and intermolecular processes.

Time- and space-resolved measurements of an ablative polyethylene capillary discharge using a pinhole camera are presented in this paper. Measurements with and without a 0.1 µm thick polyimide filter allowed us to identify the soft x-ray production zones. The images show that the plasma, mainly composed of highly ionized carbon, was not detached from the capillary wall during the heating phase. This plasma behaviour does not favour the development of a recombination-pumped x-ray laser. For two capillary lengths, the plasma dynamics were observed at constant power density in a first run and at identical current waveform in a second run. In both cases, they were different and could induce errors on gain measurement when varying capillary lengths. To our knowledge, this is the first report of time-resolved pinhole images of ablative carbon capillary discharges used as soft x-ray sources.

A pulse-modulated rf inductively coupled thermal plasma, which has extended control in its applications in pulse mode, was diagnosed both experimentally and numerically to determine the critical values of the duty factor and shimmer current level down to which the pulse mode of the plasma is sustained. Pulse-modulated plasmas were generated for different operating conditions (at atmospheric pressure, 2-20 ms on-time, 60-70% shimmer current level) and corresponding spectroscopic measurements were carried out. For different pulse on-times, the limit of the respective off-times for which pulse mode of plasma exists were determined and, thus, a typical operating zone of pulse-modulated plasma was proposed in both experimental and theoretical efforts. A two-dimensional model was solved numerically at atmospheric pressure (760 Torr) with various duty factors and shimmer current levels. A portion of theoretically predicted results were compared with the experimental results where reasonable agreement was found.

A computational model of a low-pressure discharge having a negative-ion component is developed. Many existing models for this type of discharge consider collisionless positive ions and two negative species each obeying Boltzmann relations. Our aim is to relax the Boltzmann-negative-ion assumption and we use a more realistic model with kinetic positive ions, kinetic negative ions and Boltzmann electrons. Positive and negative ions are created uniformly in the discharge at a constant rate, and lost either to the walls or via volume recombination. This model is solved using a hybrid simulation with particle-in-cell (PIC) ions. The negative-ion distribution function is found to have cold and hot components of nearly equal densities for which T_e/T_-cold≈100 (the creation temperature) and T_e/T_-hot≈5-20. The computed positive ion flux exiting the discharge agrees approximately with those calculated from Boltzmann-negative-ion models when the negative-ion temperature is accounted for correctly. It has been predicted that three electronegative discharge structures can exist: uniform, stratified and double-layer stratified. All three structures are observed in our model. In particular, a double-layer stratified discharge is observed when the effective negative-ion temperature is sufficiently low, in qualitative agreement with Boltzmann-negative-ion models.

A measurement of the positive streamer charge has been performed at atmospheric conditions in a quasi-uniform electric field where the discharge was electrically triggered. By applying a square impulse voltage to the trigger electrode, which was close to, but electrically isolated from, the anode, a positive streamer discharge with one discharge event was produced. The voltage, current and luminosity associated with the streamer discharge were measured simultaneously. By placing a photographic film at the cathode, the number of individual streamers hitting the cathode was estimated within one discharge event. The amount of net charges in streamer discharges has been evaluated for different background electric fields. From the results, it has been deduced that each individual streamer channel contains a charge represented by an excess of 1.1-2.0×10¹¹ positive ions m^-1. The lower value corresponds to a background field of 400 kV m^-1 and the higher one to 600 kV m^-1. The streamer has also been simulated using a simplified streamer model. The results of the measurement and the calculation are compared and discussed.

During a lightning strike to an aircraft in flight, the lightning channel becomes deformed in the airflow and displaced along the aircraft, a so-called swept stroke. The deformation and the displacement are caused by the interaction between the aerodynamic flow and the plasma properties of the channel together with the properties of the surface. The main part of the lightning current is a continuous current with a magnitude of hundreds of amperes and a duration of hundreds of milliseconds. The objective of this article is to analyse the properties of the lightning channel during this continuous current phase in order to parametrize them; this parametrization is used in a companion paper (Larsson et al J. Phys. D: Appl. Phys.33 1876-83) for complete swept-stroke simulations. A model of the thermodynamic evolution of a lightning channel during its continuous current phase is developed and numerically solved. In this model, the channel is assumed to have axial symmetry. A quantitative analysis of the influence of failing axial symmetry is also included. The main conclusions are that the steady-state conditions are rapidly reached and that the channel can be considered to be a free-burning arc subjected to increased thermal losses due to transverse aerodynamic flow.

During a lightning strike to an aircraft in flight, the lightning channel gets deformed in the airflow and displaced along the aircraft, a so-called swept stroke. The deformation and the displacement are caused by the interaction between the aerodynamic flow and the plasma properties of the channel together with the properties of the surface. We give a theoretical analysis and a numerical modelling of the swept-stroke processes. Some numerical simulations of the swept stroke are presented and the results are compared with existing experimental data with satisfying agreement.

Electrical aspects of an rf planar magnetron discharge in noble gases at pressures below 50 mTorr are discussed. The electrical parameters of the experimental device are measured by a diagnostic system consisting of two probes, a capacitive voltage divider and a current loop. The measurements of the rf current and voltage and the fast Fourier transform treatment of recorded signals are used to verify the validity of the `subtraction' method in order to estimate the power deposited into the plasma. This technique shows a better power coupling with a metallic target, up to 90% of the rf delivered power, than for an insulating target for which the power efficiency hardly reaches 50%. In addition, the elementary mechanisms sustaining the rf planar magnetron discharge are analysed. A transition from a combination of α (`wave-riding') and γ (secondary electron emission) regimes above a critical pressure to an α dominant regime at very low pressure is pointed out. This phenomenon is explained by the results of a particle-in-cell Monte Carlo collision simulation.

The strain energy density behaviour is studied at room temperature, for 100 phr (parts per 100 parts of rubber by weight) FEF carbon-black-loaded styrene-butadiene rubber (SBR), natural rubber (NR), butadiene-acryle nitrial rubber (NBR), butyl rubber (IIR) and butadiene rubber (BR). This behaviour is also studied for 100 phr of different types of carbon-black, (intermediate super abrasion furnace) (ISAF), high abrasion furnace (HAF), fast extrusion furnace (FEF), semi-reinforcing furnace (SRF) and easy processing channel (EPC)-)loaded SBR rubber vulcanizates and for different concentrations of FEF carbon-black-loaded SBR rubber vulcanizates.

The shear modulus for all composites is also obtained and discussed. These data are used to calculate the strain energy density using the equation proposed by Blatz et al (1974 Trans. Soc. Rheol.18 145-61), based on the n-measure of Sethe.

It is found that the n-measure is still a material constant, even after the addition of carbon black, but with higher values than that for unloaded rubber.

The structure of boron nitride bamboo-like tubular whiskers grown from boron nitride powder is investigated by high-resolution transmission electron microscopy. Despite the relatively small size of the tubes (20-200 nm in diameter), they all exhibit rhombohedral-like ordering in their layer stacking. The tubular sheets also tend to have their [100] direction parallel to the fibre axis. Particles of iron alloys are commonly found encapsulated inside or at the end of the filaments. It is suggested that iron plays an active role in the growth of the fibres.

The analysis of the NMR relaxation function for microheterogenous systems usually starts with the decomposition of the relaxation function to discrete components, or finding a continuous distribution of the components. Several approaches can be applied to do this: linear least-squares fitting, non-linear least-squares fitting or inversion of the data, based on the Laplace transformation. The spin-grouping technique - a correlated analysis of the spin-lattice relaxation function (recovery or decay) and spin-spin relaxation decay (free induction decay or Carr-Purcell decay) - usually enables a decomposition of relaxation data into a proper set of discrete components. In our paper, we present CracSpin, a program for one and/or two-dimensional analysis of the relaxation function in the time domain. It uses Marquardt's algorithm for non-linear least-squares fitting. The results of analyses of simulated data containing discrete as well as continuous distributions of the components are shown. CracSpin resolves the components of FID even if the ratio of their relaxation times is as small as 2, for comparable component magnitudes (at least about 10% of total signal) and for signal-to-noise ratio (S/N) >100. If the ratio of component relaxation times is higher than ~3, the decomposition is satisfactory for S/N >10, even for a component magnitude of about 1%. The noise level is defined here as equal to the three standard deviations of the normal distribution. The two-dimensional analysis significantly improves the quality of the multicomponent decomposition, for composed decays or in the case of close values of the relaxation time of the components. The representative examples of the analysis, starting from spin-lattice relaxation curves, as well as from spin-spin relaxation curves, are presented and discussed.

The dielectric properties of semicrystalline nylon 11 (mixture of γ and α phase, degree of crystallinity 62%) were investigated in wide ranges of frequency and temperature by broadband dielectric relaxation spectroscopy, thermally stimulated depolarization current techniques and triangular voltage measurements. The main interest was focused on characterizing the relaxation processes in nylon 11, so measurements were, in general, limited to temperatures lower than about 100 °C. The secondary γ and β relaxations, in order of increasing temperature in isochronal measurements, the primary α relaxation, associated with the glass transition of the amorphous polymer, and a process at about 95 °C, related to a structural phase transformation from triclinic α phase to pseudo-hexagonal γ phase, were observed and studied in detail. Absorption of water was found to have a significant effect on the secondary relaxations, giving, in particular, rise to splitting of the β relaxation into two relaxations, β₁ and β₂ in order of decreasing temperature in isochronal measurements. The γ relaxation is assigned to the motion of methylene sequences involving adjacent dipolar amide groups and the β relaxation to motion of water-polymer complexes of different molecular configurations.

The ferroelectric domain morphology of PbTiO₃ single crystals has been investigated at room temperature by electrostatic force microscopy (EFM) and piezoelectric force microscopy (PFM) in addition to atomic force microscopy (AFM). While EFM is shown to reveal 90° a-c-domains via susceptibility contrast and 180° c-domain walls via their stray fields, PFM is used to visualize and to write 180° c-domain patterns. Owing to stabilizing negative space charges provided by the n-type PbTiO₃ only negative written c-domains are stable against backswitching.