Table of contents

Increasing our ability to design-in specific dielectric properties or tailor specific dielectric behaviour, often under specific conditions of frequency, temperature and field strength, is of central importance in many scientific and technological applications. Liquid crystal TFT displays, that now threaten the extinction of the cathode ray tube, are a prime example. Another is the search for low permittivity insulators for the electronics industry to reduce coupling capacitance—a barrier to computer processing speed. Ironically, then, it is advances in computing power and computational techniques, as well as the discovery of new composite and artificially engineered materials, which are opening up new opportunities for modelling, understanding and then engineering a diverse range of dielectrics and dielectric responses.

This special cluster in Journal of Physics D: Applied Physics comprises selected papers from the 2005 conference of the Institute of Physics Dielectrics Group, held at Homerton College in Cambridge from 6–8 April 2005, which provided a timely overview of activity in the field, highlighting new approaches and tools available to scientists and engineers alike.

Modelling activity has been characterized by phenomenological approaches for many decades; however, ab initio molecular modelling is making a significant impact in many areas of science, notably in chemistry, molecular dynamics and biotechnology. This topic was a key theme of the conference, affording an opportunity to investigate the ways that molecular modelling can be, and is being, extended into dielectric and electrical transport studies to enable dielectric properties to be understood directly in terms of molecular and meso-scale physics.

The conference also included a review session, in which the results of a pilot study by the IOP Dielectrics Group were presented. This study is undertaking a review of the field to identify research trends such that the future activities of the Group are clearly focused on the needs of its community. A summary of this pilot study is included as the first paper in this special cluster.

The conference also covered topics focused on breakdown and field modelling, charge transport and space charge, the design of composite materials, electronic and optical materials, dielectric relaxation and the rapidly growing field of structured and meta-materials.

As is typical of Dielectric Group conferences, the excellent technical programme stimulated much interesting discussion and debate and was perfectly complemented by a small but very strong group of sponsors/exhibitors, namely Accelrys, Ansoft and Novocontrol. Moreover, it was a pleasure to have such a significant proportion of young researchers and students contributing to both the oral and poster sessions, providing the winner of the 2005 Mansel Davies Award for the best paper by a young researcher, Mr Ennio Capria from Cranfield University for his paper on manipulation of PZT fibres using dielectrophoresis.

Finally, I am pleased to note the contributions made to this special cluster by several authors of papers presented at the conference. These papers particularly focus on the theme of designing composite dielectric and electromagnetic materials, providing an excellent historical perspective as well as demonstrating the breadth, depth and diversity of current research activity. I thank the authors for their contributions and hope you enjoy reading them.

This paper presents a top-level review of global, regional and local (UK) research into dielectrics, as materials, and into related dielectric phenomena, measurements, technologies and applications. The review focuses on three questions: 'Is dielectrics research in growth or decline?', 'How is dielectrics research different geographically?' and 'How has the scope of dielectrics research changed with time?'. The analysis demonstrates that the absolute research activity in dielectrics as measured by the volume of publications in the field continues to grow globally, with the fastest rate of growth observed in China and South-East Asia collectively. It is projected that China may lead the field in terms of total published research output in 6–10 years. In contrast, the UK share of publications in the field is seen to be slowly decreasing. The content and makeup of dielectrics research is seen to be similar across the globe, with the UK blend of research in dielectrics being well correlated with both European and global activity. Within the UK, over a 20-year period, there has been a definite shift away from dielectrics research in the areas of polymer science and atomic and molecular physics and a move to applied and condensed matter physics and optics. Research related to electrical and electronic engineering remains very strong and has retained its share of publications. Not surprisingly, the current hot topic in dielectrics is high permittivity (high κ) dielectrics for electronics applications. Emerging hot topics include dielectrics at the nanoscale, especially the role of interfaces, and the characterization of biological tissues.

Basic physical concepts and theoretical ideas concerning dielectric heterostructures are reviewed from a historical perspective. This background for today's theory of dielectric heterostructures is discussed in some detail because the guiding principles for our understanding can be traced to the earliest developments in electromagnetism. To give an impression of the accelerating progress, I shall distinguish five stages in the development of our understanding of the dielectric properties of heterostructures. Historical remarks are included and technical concepts are introduced informally. For each stage, I call attention to synthetic works or compendia created during the interval. The first stage was reached towards the second half of the 19th century with the work of James Clerk Maxwell. Next the second stage was initiated by Bruggeman through the concept of an effective medium. Bounding methods form the third stage, with many investigators involved, beginning with the work of Wiener; the importance and ingenuity of these methods cannot be overstated. The fourth stage was the introduction of the crucial concept of percolation through an infinite cluster of connected particles and the modern approach to criticality which began in the mid-20th century with the work of Broadbent and Hammersley. Finally, the fifth stage we have experienced in the last decades involves the rapidly developing subject of computational electromagnetics: computers have moved the emphasis away from the general theory of macroscopic electromagnetism towards a better look at the detailed features of the randomness and connectedness of heterostructures. It is concluded that computational techniques provide a versatile tool for studying the dielectric properties of complex composite materials and that considerable progress can be achieved by comparing numerical results against analytical predictions for the properties of these models. As the capabilities for performing realistic simulations increase, it might become possible to routinely design on a computer, at least in part, a combination of materials chosen specifically to achieve a desired response to an incident electromagnetic wave for a variety of technological and industrial processes ranging from electromagnetic shielding and capacitive video disk units to mammalian tissue simulants.

Very large networks of randomly positioned resistors and capacitors have been used to simulate the microstructures of real two-phase (conductor–insulator) materials. These networks are found to exhibit fractional power law frequency dependences of dielectric properties and ac conductivity, of the type reported for a wide range of materials. The network results are related to the resistor and capacitor values by a simple logarithmic mixing rule. The same mixing rule is used to model the electrical characteristics of two-phase electrical composites. The results are tested using water impregnated lead zirconate titinate (PZT) ceramics samples that have a microstructure that forms a complex interconnected random array of conducting (water) and insulating regions. Excellent agreement is obtained between the experimental data and the modelling predictions based on the network simulation results. The power law exponents for ac conductivity and relative permittivity are found to be equal to the proportions of the composite occupied by the insulating and conducting phases, respectively. Studies of conducting polymer impregnated PZT are also presented which show less good agreement with modelling predictions.

A practical approach for the modelling of the dielectric constants of thin composite films is presented. A general distribution function for composition fluctuations in the thin composite films is introduced to describe the transition from a non-percolative to a percolative morphology using physically meaningful parameters and is applied to model a wide range of experimental and simulated polymer–ceramic composite film behaviour from the literature, up to ceramic particle filler volume fractions of 75%. The parameters describing the morphologies of the various composites are used to predict effective dielectric properties with good accuracy. The model is applied further to composites that show early percolation behaviour, and the deviation of their effective dielectric behaviour from the standard effective medium theory at high filler volume fractions is discussed.

The dielectric relaxation due to interfacial charges in metal particle-filled composites occurs in the optical (high frequency) regime. However, many applications would benefit from a shift of the relaxation to a much lower frequency regime (e.g. radio or microwave range). This could be achieved by using a filler with reduced conductivity, but there is no continuum of conductivity in naturally occurring materials to allow engineers to readily achieve this aim or to have complete design freedom. Recently, it was demonstrated, experimentally and theoretically, how insulating particles with nano-scale metal coatings enable this relaxation to be shifted to a lower frequency regime. The current work investigates the microstructure of the metal coating, highlighting a semi-continuous coating structure. Therefore, the relevance of a two-dimensional (2D) percolation-based model to describe the effective dielectric properties of the coating is explored. It is demonstrated that a model in which the metal coating is assumed to be near the 2D percolation threshold can provide a reasonable fit to the experimental data. An improved fit is achieved when a distribution of metal area coverage is permitted.

Dielectric measurements accompanied by infrared absorption and photoluminescence (PL) spectroscopy were used to investigate the electrical and optical properties of oxidized porous silicon (PS). As opposed to non-oxidized PS, only high temperature relaxation processes could be resolved for oxidized PS. Two relaxation processes have been observed. The first process is related to dc-conductivity that dominates at high temperatures and low frequencies. After subtraction of dc-conductivity we could analyse a second high-temperature relaxation process that is related to interface polarization induced by charge carriers trapped at the host matrix–pore interfaces. We found that, while the main effect of the oxidation on the PL appears to be a size reduction in the silicon nanocrystals that gives rise to a blue shift of the PL spectrum, its main contribution to the dielectric properties turns out to be blocking of transport channels in the host tissue and activation of hopping conductivity between silicon nanocrystals.

Manganese oxides (R, A)MnO₃ (R = La, Y, Bi or rare earth metal, A = non-trivalent doping element) have been one focus of research for two outstanding properties: (i) conduction electrons (if any) are highly spin-polarized and (ii) competing interactions of several electronic and lattice degrees of freedom lead to extremely rich phase diagrams and complex physics. A better understanding of the latter might result in future technologies using manganites in spin-electronic devices. This review attempts to systematically outline in a phenomenological approach some fundamentals and key experiments on ferromagnetic manganites, partially with respect to thin film structures. Macroscopic magnetic properties (of ferromagnets and glassy manganites) and intrinsic electron transport are described. Preparation and basic properties of thin films, followed by experiments on spin-polarized tunnelling are reviewed. Finally, multiferroic heteroepitaxial film systems of manganites and ferroelectric titanates are addressed, which are promising candidates for significant magnetoelectric phenomena at ambient temperatures.

The fine structure of magnetic nanoparticle periodic chains is studied by considering the competition between magnetic dipolar interaction and elastic interaction. A Peierls phase with a doubled unit cell length can be formed under proper conditions and a Peierls transition can be induced by temperature and by external magnetic field. Due to the coupling between the magnetic state and the structural state, the nanoparticle chains would possess distinct properties and exhibit interesting behaviour.

Vanadium (V)-doped GaAs (GaAs:V) layers grown by metal–organic chemical vapour deposition under different V-doping levels (10¹⁷–10¹⁹ cm⁻³) were annealed in an arsine–H₂ gas mixture up to annealing temperatures of 750 and 850 °C for 30 min. The effect of thermal treatments on their electrical and optical properties was studied by means of the Hall effect, deep level transient spectroscopy and photoluminescence (PL). Annealing at 750 °C induces a thermal conversion from the n- to p-type of weakly V-doped GaAs. The conductivity of highly V-doped materials remains n-type. All the V-doped samples convert from n- to p-type following annealing at 850 °C. A comparison between the PL spectra for materials annealed under different conditions underlines the important role of gallium vacancies and a possible V accumulation at the surface in the case of thermal conversion.

Theoretical aspects of a new technique for the MeV ion microbeam are described in detail for the first time. The basis of the technique, termed scanning ion deep level transient spectroscopy (SIDLTS), is the imaging of defect distributions within semiconductor devices. The principles of SIDLTS are similar to those behind other deep level transient spectroscopy (DLTS) techniques with the main difference stemming from the injection of carriers into traps using the localized energy-loss of a focused MeV ion beam. Energy-loss of an MeV ion generates an electron-hole pair plasma, providing the equivalent of a DLTS trap filling pulse with a duration which depends on space-charge screening of the applied electric field and ambipolar erosion of the plasma for short ranging ions. Some nanoseconds later, the detrapping current transient is monitored as a charge transient. Scanning the beam in conjunction with transient analysis allows the imaging of defect levels. As with DLTS, the temperature dependence of the transient can be used to extract trap activation levels. In this, the first of a two-part paper, we introduce the various stages of corner capture and derive a simple expression for the observed charge transient. The second paper will illustrate the technique on a MeV ion implanted Au–Si Schottky junction.

Here we introduce a new technique called scanning ion deep level transient spectroscopy (SIDLTS) for the spatial analysis of electrically active defects in devices. In the first part of this paper, a simple theory behind SIDLTS was introduced and factors determining its sensitivity and resolution were discussed. In this paper, we demonstrate the technique on MeV boron implantation induced defects in an Au–Si Schottky junction. SIDLTS measurements are compared with capacitance DLTS measurements over the temperature range, 100–300 K. SIDLTS analyses indicate the presence of two levels, one of which was positively identified as the E_c − 0.23 eV divacancy level. The high sensitivity of SIDLTS is verified and the advantages and limitations of the technique are discussed in light of non-exponential components in the charge transient response. Reasons for several undetected levels are also discussed.

Eu-complex organic electroluminescent (EL) devices with a double metal-mirror Fabry-Pérot microcavity structure were constructed to increase luminance efficiency and to improve colour purity. By optimizing the device structure, bright pure red EL from the Eu³⁺ ion was obtained. The peak luminance of 1160 cd m⁻² at 19 V and CIE coordinates of (x = 0.675, y = 0.320) at 12 V were achieved in the cavity device. The narrow-band emission peak was not changed with increasing detection angle, and the colour saturation of the top 45°-off normal EL emission was even better than that of top normal emission in noncavity devices, overcoming the emission colour blue-shift with increasing detection angle in traditional microcavity devices. It was more important that a significant improvement in EL quantum efficiency at high current density was observed in the cavity device and the increasing mechanism of the EL efficiency was also revealed, which should be mainly ascribed to the shortened lifetime of the excited state of the Eu³⁺ ion.

The mineral zircon, ZrSiO₄, is a candidate material for optical dating because it exhibits luminescence after exposure to natural radioactivity. The kinetic model of zircon thermally stimulated luminescence proposed before has been modified and used to investigate optically stimulated luminescence (OSL) of zircon. The purpose is to explore what might be expected from zircon during real experiments because experimentally zircon OSL has not been studied systematically. Any luminescence dating method involves, as a necessary step, a laboratory irradiation at dose rates much higher than the dose rate of natural radioactivity. The model of zircon OSL predicts a significant and complicated dose rate and temperature effects. Our simulation results suggest that this problem may be solved by laboratory irradiation at elevated temperature followed by a preheat. Such a combined treatment allows one to reproduce the dose response expected from the naturally irradiated material (after the same preheat treatment). The shape of the theoretically calculated dose response curve reconstructed in this way exhibits a weak sensitivity to variation of laboratory irradiation temperature for ages younger than a few thousand years. This means that zircon OSL can probably be used successfully for dating of young samples.

Interaction between the plasma and protective coating on the inner side of low pressure mercury lamp bulbs is considered. Under the assumption that the main way of decreasing the transmission of the bulb wall is the implantation of Hg ions within the fused quartz and formation of complexes [HgO] therein, a qualitative model of the attenuation mechanism is offered. The influence of the characteristics of a coating (thickness, close-packed structures, the lattice parameter, mass of atoms) on the transmission of the bulb walls is analysed. On the basis of the suggested model, estimates of the change in minimum transmission of bulb walls were made for lamps with and without protective coating. It is shown that in spite of approximations, the proposed model is in good agreement with experimental data.

We report spectroscopic studies of the zinc plasma produced in air by the three harmonics of a Q-switched pulsed Nd : YAG laser at 1064, 532 and 355 nm. The electron temperature has been determined from the intensity ratio of the transitions (4s4d ³D₃ → 4s4p ³P₂) at 334.5 nm and (4s5s ³S₁ → 4s4p ³P₂) at 481.0 nm of neutral zinc, whereas the electron number density has been evaluated from the Stark broadening of the (4s4d ³D₃ → 4s4p ³P₂) transition at 334.5 nm. It is observed that both these parameters decrease as the distance from the target surface increases and it increases with an increase in the laser irradiance. The power law is fitted to the experimental data.

A dual ion beam system has been used to produce hard nanocomposite TiN/Si₃N₄ coatings on silicon substrate. Mechanical properties have been determined by nanoindentation and tribological properties have been measured by nanoscratch testing. Nanoindentation showed that harder nanocomposites exhibited higher ratios of hardness to modulus (H/E). The dependence of the resistance to plastic deformation (H³/E²) on hardness was approximately linear. The H/E value influenced the nanoscratch behaviour. Coatings with higher H/E showed higher critical loads for elastic–plastic transition and also the total coating failure occurring in front of the probe. However, coatings with higher H/E also exhibited an unloading failure, occurring behind the probe at much lower load than the loading failure. Optimizing this stress-related unloading failure could be more important for tribological applications.

Similarly to laser-induced backside wet etching (LIBWE) with nanosecond ultraviolet (ns UV) laser pulses, the irradiation of the solid/liquid interface of fused silica with sub-picosecond (sub-ps) UV and femtosecond near infrared (fs NIR) laser pulses results in etching of the fused silica surface and deposition of decomposition products from liquid. Furthermore, the etch threshold is reduced compared with both direct ablation with an fs laser in air and backside etching with UV ns pulses. Using 0.5 M pyrene/toluene as absorbing liquid, the thresholds were determined to be 70 mJ cm⁻² (sub-ps UV) and 330 mJ cm⁻² (fs NIR). Furthermore, an almost linear increase in the etch rate with increasing laser fluence was found. The roughness of surfaces backside etched with ultra-short pulses is higher in comparison with ns pulses but lower than that obtained using direct fs laser ablation. Hence a combination of processes involved in fs laser ablation and ns backside etching can be expected. The processes at the ultra-short pulse laser irradiated solid/liquid interface are discussed, considering the effects of ultra-fast heating, multi-photon absorption processes, as well as defect generation in the materials.

We apply linear and nonlinear methods to study the properties of surfaces generated by a laser beam melt ablation process. As a result we present a characterization and ordering of the surfaces depending on the adjusted process parameters. Our findings give some insight into the performance of two widely applied multifractal analysis methods—the detrended fluctuation analysis and the wavelet transform modulus maxima method—on short real world data.

3D numerical simulation of gas heating in a magnetron sputtering system is performed. Pressure, magnetron power density and location of the substrate plane in front of the target are shown to affect the gas temperature profile. For the pressure range under study, maximum gas temperature is shown to increase with pressure. By increasing the separation between the target and the substrate, the maximum gas temperature is shown to increase up to the point when most of the particles are assumed thermalized. Cu shows more gas heating than does Al due to its higher sputtering yield and energy transfer efficiency. Sputtered particles are shown to be the major source of gas heating.

A synchrotron microbeam high-angular resolution diffraction setup based on a phase zone plate and a perfect Si(004) analyzer crystal was introduced to generate an x-ray microbeam with a lateral size of 0.24 µm and an angular resolution of 2 arcsec. The microbeam high angular resolution x-ray diffraction was applied to study InGaAlAs-based multiple quantum well (MQW) ridge-waveguide arrays produced by metal–organic vapour-phase epitaxy in a selective area growth regime with a central waveguide width varying from 1.6 to 60 µm. The analysis of the period T and the strain S in MQW ridge structures determined from the high-resolution diffraction data is presented. It was found that the MQW period is uniform across the ridge within the error bar of ΔT = ± 0.25 nm. Within the waveguide array, the MQW period and strain can be adequately described by a gas-phase diffusion model.

A numerical model for describing bipolar charge transport and storage in polyethylene has been developed recently. The present paper proposes a comparison of the model outputs with experimental data in three different direct current (DC) voltage application protocols (step field increase and polarization/depolarization schemes). Three kinds of measurement have been realized for the three different protocols: space charge distribution using the pulsed electro-acoustic method, external current and electroluminescence. Simulation under AC stress has also been attempted on the basis of the model parameters that were derived from the DC case. Model limitations and possible improvements are discussed.

A theoretical model describing the volumetric homogeneous crystallization of a substance is proposed, which takes into account the formation of nanoclusters in a supersaturated phase and the appearance and growth of nuclei by means of attachment of the nanoclusters. Linear stability analysis is used to show that a system in which such a mechanism is operative may feature self-sustained bound oscillations of the supersaturation of the crystallizing substance, the density of nanoclusters and the solid phase particle size distribution. An equation for a surface of neutral stability of a steady crystallization regime is obtained. The conditions for the appearance of the nonlinear self-oscillations are found.

The purpose of this paper is to present a study of finite-time thermodynamics applied to evaluate the ecological performance of a quantum heat engine which operates between two thermal reservoirs using the working substance of spin-1/2 systems. The quantum heat engine cycle is composed of two isothermal processes, an adiabatic process and an isomagnetic field process. A sequence of time evolution was determined from the quantum angular momentum rate based on the semigroup approach and the quantum master equation. The individual time duration is added to account for the total cycle time. The objective ecological function representing a compromise between power output and irreversibility is maximized with respect to cycle temperature ratio. Effects of thermal reservoir temperature ratio and magnetic field ratio on the ecological function have been discussed. A comparison of quantum heat engine performance under maximum ecological function and maximum power conditions is also presented.

Melt formation during laser cutting of metallic substrates is considered and the melt thickness is formulated using a lump parameter analysis. The droplet diameter is also predicted and compared with the experimental results. A CO₂ laser with variable pulse frequency is used in the experiment. Oxygen, as assisting gas, impinging coaxially with the laser beam, is used at different pressures. SEM and XRD are carried out to obtain micrographs and oxide compounds formed in the dross. It is found that the liquid layer thickness increases with increasing laser output power and reduces with increasing assisting gas velocity. The droplet formed is spherical and the droplet size predicted agrees well with the experimental results.

A recent paper by Bakaev et al (2005 J. Phys. D: Appl. Phys.38 2031–44) reported the study of hydrodynamic regimes of KrF laser interaction with solid and thin-film targets in air. Experiments were performed with 100 J, 100 ns pulses from an ultra-violet excimer laser installation and the experimental data were compared with the results of numerical simulations. Unfortunately, an error was made in the simulation. In this addendum we develop a new numerical method and obtain good agreement between computational and experimental results.