Table of contents

Snapback behaviour, with well-defined conduction states involved, has been observed in the ramped-current current-voltage (I-V) characteristics of ultra-thin silicon dioxide films after the occurrence of hard breakdown. The comparison of the snapback behaviour with the switching behaviour observed in the ramped-voltage measurement shows that the two behaviours are similar, suggesting that they can be explained by the same mechanism. The I-V relationship of each conduction state involved in either the snapback or the switching behaviours was found to follow a power law. These observations are consistent with the percolation model, and they can be easily explained in terms of the on/off of conductive percolation paths due to detrapping/trapping or neutral trap generation at certain SiO₂ lattice sites (strategic positions) during the measurements.

Three-dimensional (3D) modelling results are presented concerning a direct current (dc) non-transferred arc plasma torch with axisymmetrical geometrical configuration and axisymmetrical boundary conditions. It is shown that the arc is locally attached at the anode surface of the plasma torch, and the heat transfer and plasma flow within the torch are of 3D features. The predicted arc root location at the anode surface and arc voltage of the torch are very consistent with corresponding experimental results.

Basic physics and current technologies of magneto-optical recording are reviewed. The development owes much to the discovery of amorphous rare earth-transition metal (RE-TM) films, which exhibit quite uniform magnetic and optical properties in the scale of practical interest. The RE-TM films also exhibit a wide variety of thermomagnetic properties on adjusting their composition, which resulted in the recent development of high-density recording using multilayer films. In amorphous RE-TM films it is possible to record thermomagnetically marks some several tens of nanometres in size. In order to readout such small recorded marks, further development of new readout techniques is necessary.

A review is given on arc cathode spots, mainly based on the investigation of arcs in a vacuum with cold cathodes. For the latter and after a short description of general features and theoretical concepts, experiments are presented that study the temporal and spatial behaviour of the spots with high time and space resolution of less than 10 ns and less than 5 µm, respectively. With the help of these observations the various spot types described in the literature are ordered into three levels: level A corresponding to the proper spot with typical diameters of 50-100 µm, level B associated with spot fragments having a size of 10-20 µm and level C comprising a substructure of the fragments. The structures undergo periodic fluctuations of brightness and position with characteristic times that can be arranged in a hierarchy from a few nanoseconds through about 100 µs. The analysis of these fluctuations shows that the spot operates in cycles that include both extremely non-stationary periods with time constants of less than 10 ns and more stationary periods in the microsecond range. In the presence of an external magnetic field, the latter periods lead to unstable plasma configurations that give rise to retrograde motion. Finally, for vacuum arc spots the basic parameters are summarized. After that, the peculiarities of spots in gases with cold electrodes are discussed, followed by a presentation of spots with hot cathodes at high pressures.

A published theory for `coupled diffusional/displacive transformations' is extended to alloyed steels in order to examine the nonequilibrium growth of partially supersaturated ferrite plates as a function of the carbon concentration. The model utilises three interface response functions i.e. the diffusion-field velocity, the interface mobility and the Aziz solute trapping function to enable the estimation of the three unknown quantities: supersaturation, velocity and the composition of austenite at the interface. It is found that the theory correctly predicts the variation in the martensite-start temperature with carbon concentration, but fails to estimate the corresponding variations in the bainite-start temperatures, the reasons for which are not clear.

CuIn_1-xGa_xS₂ films were synthesized by graphite-box annealing of In/Ga/Cu stacked elemental layers (SEL) in the presence of sulphur vapour. The effects of the ambient gas, annealing temperature and duration of annealing on the microstructure of the films synthesized during annealing were studied. The films were characterized by measuring the microstructure and the optical and electrical properties. The effect of grain boundary scattering on the electron transport process was also studied.

The effect of ion implantation on mechanical stress in a-Si:H films was studied with the aim of separating the contributions that the hydrogen content and structural defects make to the intrinsic compressive stress. The a-Si:H films were prepared by plasma-enhanced chemical vapour deposition. Silicon ions with an energy of 160 keV were implanted and the implantation-induced structural damage was studied by means of Raman backscattering spectroscopy. The stress in the films was compressive and its value correlated with the short and intermediate range orders. The results have shown that the value of compressive stress in the material could be lowered by changing the structural order of the silicon network without changing the hydrogen content.

Analytical solutions for determination of the real part of the refractive index and the absorbance of a weakly absorbing film on an opaque substrate by measurement only reflectance of the polarized light at certain characteristic incident angles (grazing angle and the Brewster angle at the ambient-film interface) are derived in the framework of the interferenceless film model. For a thick transparent film and transparent substrate in the polychromatic light of a constant spectral distribution, the adopted method allows determination of the refractive index of a film using only the normal incidence reflectance measurement. This approach may be especially useful for monitoring the refractive index and its variations in the process of deposition of mixtures to produce intermediate indices. An interferenceless blurred film model corresponds to the linear thickness variation over the illuminated sample area or the rectangular spectral distribution of the polychromatic light.

The luminescence of Ce³⁺ doped in stillwellite-type SrBPO₅ and LaBSiO₅ matrices is reported. This novel luminescent system exhibits several unusual features such as the characteristic 5d→²F_5/2,7/2 doublet emission of Ce³⁺ at short wavelength around 320 nm, a high ion-lattice coupling strength (S~30), which is six times the usual value and a high Stoke's shift (~5000 cm^-1). These unusual features appear to originate from the unique crystal chemistry aspects of the stillwellite system. Furthermore, when Tb³⁺ is codoped in this system, it gives intense green emission at 542 nm due to the ⁵D₄→⁷F₅ transition of Tb³⁺ which indicates its potential as a green phosphor for lighting applications.

Thin (6-320 nm) indium tin oxide films were deposited by pulsed excimer (XeCl) laser ablation. The lowest electrical resistivity (1.6×10^-6 Ω m) was measured for samples deposited on moderately heated (200 °C) glass substrates. Optical transmissivity of the films in the range 400-1200 nm is higher than 80%. Ultra-thin (~6-9 nm) films were deposited and successfully used as transparent electrodes in optoelectronic devices.

The mechanism of fluid film lubrication in ultra-thin conjunctions under counterformal concentrated circular point contacts is discussed in this paper. The significance of squeeze film action in increased load carrying capacity is highlighted. The numerical predictions made in acceleration-deceleration motion of a ball against a flat race is found to conform with the experimental findings of other research workers for polar branched lubricants down to a film thickness in the region of 20 nm. This conformance with the experimental findings has enabled a fundamental understanding of the multi-physics of film formation when conditions promoting the formation of ultra-thin films of the order of few nanometres have been employed, with the use of a non-polar lubricant. This paper provides the first ever solution of the combined effect of viscous, surface and molecular forces under transient conditions.

The present paper describes the electromagnetic field of a permanent magnet based device comprising parts that have a rotational movement. The equivalence between the field of a permanent magnet and a magnetic dipole constitutes the main assumption. The real device is thus modelled by a hypothetical structure made of magnetic dipoles. To calculate the magnetic and the electric field, the Hertz vector potential approach was used. The magnetic dipole modelling shows a resultant magnetic field which is rotating 15 times faster than its field source, it underlines ways by which the anisotropy of the magnetic field can be greatly enhanced, and it succeeds in providing concise computational formulae for the field and the energy flow within the field that can be related to results of a more traditional approach, such as the finite element method.

Ferrofluid drops are freely suspended for long periods in air in a novel experiment by using magnetic fields to create an attractive force opposing gravity. The suspended drop is then forced to oscillate by perturbing the supporting magnetic field. In addition to small-amplitude behaviour, the driven drop exhibits high order nonlinear modes of oscillation, and can be driven until it splits. A new simplified analytical expression for the general potential for the drop motion is derived, and numerical simulations of the drop behaviour are presented, showing close agreement with the experimental data.

A physical model is proposed to calculate the recoil pressure acting on the surface of an evaporating material irradiated by a high-intensity laser beam, such as encountered in laser material processing. Laser attenuation in the laser-induced plasma plume, reflection at the material surface and the energy consumption for material heating and melting are considered in this model. This evaporation model represents a revised form of that previously employed by Chen Xi (1996, 1997, 1998) to calculate the evaporation-added pressure acting on an evaporating particle exposed to a thermal plasma, but here the special features associated with laser material processing are considered. The calculated recoil pressures compare favourably with available experimental data.

The application of spherical Langmuir probes for measuring the electron temperature and density on ionospheric sounding rockets is discussed with respect to the influence of the geomagnetic field effects and probe contamination. The influence of the contamination layer is thoroughly analysed in the frame of a nonlinear equivalent circuit. When operating the probe in ramp mode, it is found that the distortion of the current-voltage characteristic is different for decreasing and increasing probe voltages. The resulting error of the electron temperature is determined for a range of capacitance (C) and resistance (R) values of the contamination layer. A method is described to determine the parameters R and C from the flight data. Further, a correction algorithm is discussed that allows the true probe characteristic to be retrieved from the measured distorted characteristic.

The flight data of an ionospheric sounding rocket (DEOS campaign flight F06) are evaluated with respect to electron density and temperature profiles. The probe characteristic is analysed in the frame of a model that takes the influence of the geomagnetic field and of a contamination layer into account, as described in part I (Piel et al 2001 J. Phys. D: Appl. Phys.). The electron temperature of the night-time ionosphere is found to be higher (1300 K) than that predicted by the IRI-95 model (Bilitza D 1999 J. Atmos. Terr. Phys.61 167), but in general agreement with the model of Watanabe et al (Watanabe et al 1995 J. Geophys. Res.100 14 581). It is also found that the electron temperature in depleted plasma regions (plasma bubbles) is lower than in the unperturbed plasma. This is a hint at the action of the Rayleigh-Taylor mechanism that convects cold low-density plasma from the bottomside of the F-layer to higher altitudes inside the plasma bubbles. An absolute comparison of the electron density profiles from the analysis of the Langmuir probe and by an independent impedance probe is performed. Excellent agreement of the profile shape and of absolute density values can be achieved over the entire altitude regime. It is demonstrated which steps in the evaluation procedure of the probe characteristic may lead to systematic errors in electron density.

A dynamic force balance model is proposed by introducing the inertial force to predict metal transfer in arc welding. The dynamics of the pendant drop is modelled as a linear time-varying second-order system and the spring constant and electromagnetic force are calculated for the ellipsoidal drop. Two methods are employed to estimate the spring constant: numerical calculation for the ellipsoidal drop and a closed-form equation for the spherical drop at equilibrium. The inertial force is produced by drop oscillation and it is applied to the drop-detaching criterion. Since the inertial force reaches half the electromagnetic force at the transition current, it influences drop detachment with current increase. The proposed dynamic force balance model predicts the resonance frequency and detaching drop size with reasonable accuracy.

The influences of O₂ and N₂ annealing on the dielectric properties of SrBi₂(V_0.1Nb_0.9)₂O₉ (SBVN) ferroelectrics were studied. Ceramic samples were prepared by reaction sintering a powder mixture of constituent oxides at 950 °C for 2 h in air. Some samples were also subsequently annealed at 800 °C for 3 h in O₂ or N₂. With O₂ annealing, the Curie point of the SBVN ferroelectrics changed from ~433 to ~438 °C and the peak dielectric constant increased from ~760 to ~1010 (at 100 kHz). However, no change in the Curie point was found with N₂ annealing. Furthermore, O₂ annealing was found to reduce significantly both the dielectric constant and loss tangent of the SBVN ferroelectrics at frequencies below 1000 Hz. XRD results revealed a small reduction in the lattice constants with O₂ annealing, but no appreciable change with N₂ annealing. In addition, no detectable change in the microstructure of the SBVN samples was found with annealing. These results imply that some V⁴⁺ ions, which are compensated by the formation of oxygen vacancies, existed in the SBVN ferroelectrics prior to O₂ annealing. V⁴⁺ ions were oxidized to V⁵⁺ with O₂ annealing, which resulted in improved dielectric properties.

A uniaxial gas model of polarization spectroscopy signal strength has been developed. Based on this model, theoretical expressions have been derived both for linear and circular polarization cases. The theoretical expressions developed predict that non-zero signal strength may be obtained, for both linearly and circularly polarized pump beams, at the normal intersection of the pump and probe beams. This prediction is particularly useful when polarization spectroscopy is used in imaging applications. The developed expressions have successfully been applied to explain the first orthogonal planar laser polarization spectroscopy imaging of OH radicals in a pre-mixed CH₄/O₂ flame, for both linearly and circularly polarized pump beams (Reppel J and Alwahabi Z T 2001 Orthogonal planar laser polarization spectroscopy, submitted to Appl. Opt.).

The novel derivates of tris(8-hydroxyquinoline)aluminium (Alq₃), tris[5-(methyl-malononitrile)-8-hydroxyquinoline]aluminium and tris(2,3-dimethyl-8-hydroxyquinoline)aluminium were synthesized. The double-layer electroluminescent devices were fabricated with a novel polymer poly(N,N'-diphenyl-N,N'-bis(4-methylphenyl)-1,4- phenylenediamine-1,3-diisopropenylbenzene) as a hole transporting layer and the derivates as an emitting layer, sandwiched between an anode of Mg:Ag and a cathode of indium-tin oxide. Bright blue and yellow electroluminescence emissions were obtained from the devices. The experimental results indicate that a functional group of electron acceptors connected to 8-hydroxyquinoline results in the emission redshift and a functional group of electron donors results in the emission blueshift. Alq₃ and its derivates are expected to be used as an emitter to achieve various colour emissions.

A highly sensitive and tissue equivalent LiF:Mg,Cu,P thermoluminescent (TL) phosphor in powder form has been developed. The TL sensitivity of this phosphor is about 1.5 times that of Harshaw-Bicron LiF:Mg,Cu,P (TLD100-H) by peak height measurements. Its dose against TL response is linear up to 10 Gy. The annealing temperature was found to affect the glow curve shape and sensitivity.

Defect centres formed in the LiF:Mg,Cu,P phosphor after high gamma dose were studied using electron spin resonance. Two centres assigned to (PO₄)^2- and an F-centre were observed at room temperature. Step annealing measurements indicate possible association between the (PO₄)^2- centre and the TL peak at 120 °C. Phosphorus appears in the form of the (PO₄)^3- moiety in the lattice and is responsible for the high TL sensitivity.

Using a generalized scheme of multiple traps, thermoluminescence (TL) glow curves are calculated for different sets of systems parameters. In particular, the conditions under which glow peaks of first-order kinetics are produced are highlighted. The major findings and conclusions are as follows. (1) In the generalized scheme the glow peaks always reduce to first order at low trap occupancies. It is therefore suggested that the peak analysis to determine the parameters should be carried out only at low doses. (2) Glow peaks which follow first-order kinetics can be obtained irrespective of whether the recombination rate is faster, equal to or slower than the retrapping rate (R_ret). (3) Quasi-equilibrium (QE) of free carriers in the delocalized band, which is the essential condition for the derivation of the conventional analytical expressions of TL and thermally stimulated conductivity, can be realized irrespective of whether R_recR_ret. (4) The realization of the QE condition depends on the concentrations of the traps and the recombination centres (RCs) and their cross sections for free carrier capture. It is discussed and shown that, in doped insulating and semiconducting materials, the values of these parameters are sufficiently high for the QE condition to be comfortably held. It is thus concluded that the doubts raised by earlier workers regarding the validity of the QE assumption in the derivation of the analytical expressions are unnecessary as far as these materials are concerned. (5) It is shown that a system in which some of the untrapped charge carriers recombine within the germinate centres and some become delocalized may satisfactorily explain the mechanism of TL emission in most of the phosphors. The properties of first-order, supralinearity and pre-dose sensitization may be easily explained under the framework of this system. (6) Conclusions (2) and (3) above disprove those of earlier workers who had concluded that QE and fast retrapping together do not form a consistent set of conditions and that the apparent dominance of first-order kinetics in nature is due to slow retrapping.

The dielectric behaviour of various carbon black polymer composites has been characterized by the critical frequency ω_c denoting the crossover from the dc plateau of the conductivity to its frequency dependent ac behaviour. The critical frequency can be related to the dc conductivity using a power law, ω_c∝σ_dc^z, with the exponent z. Presently accepted models predict z to be greater than one when varying the filler content. However, in accordance with published experimental results this work shows that z is rather close to one indicating a nearly constant static permittivity. Furthermore, the above power law makes it possible to describe all investigated compounds using a single master curve ranging over ten decades of dc conductivity. These findings are explained by a qualitative percolation model based on electron tunnelling. Increasing the dc conductivity along the percolation curve does not require the establishment of more physical links between carbon black aggregates. Rather, new conduction paths of nearly the same lengths but with higher tunnelling probability due to smaller gaps satisfy the percolation theory. This scenario allows the number of capacitive gaps to be nearly constant making z near one.

The correct form of equation (20) is as follows: