Table of contents

This special cluster in Journal of Physics D: Applied Physics comprises papers submitted by participants at the 2006 conference of the Institute of Physics Dielectrics Group, held at the University of Leicester during 10–12 April 2006. The conference focused on the interaction of non-ionizing electromagnetic (EM) fields with biological materials at all scales (tissues down to molecules) and at all frequencies. The use of dielectric techniques and theories in biological studies and in the pharmaceutical and biotechnology industries is increasing, and we hope that this conference helped to facilitate this trend and to further an understanding of the value of dielectric studies in biology—both in science and in applications in industry and medicine.

An important policy of the Dielectrics Group is to promote the multidisciplinary nature of dielectric studies, and so we welcomed and received papers and posters from biologists, chemists, engineers, industrialists, medical professionals and physicists in the biotechnology and health care fields. The programme comprised 32 oral presentations, including the keynote opening address `Bio-dielectrics and bio-impedance' by Dr Ø G Martinson of the University of Oslo, and 7 papers given by invited speakers. 27 high-quality posters were also exhibited.

The Mansel Davies Award, for the best presentation by a young researcher under the age of 30, was bestowed on Mr Sun Tao from the University of Southampton. His work, describing time domain analysis applied to dielectric spectroscopy of single cells, forms the subject matter of the first paper in this cluster. The remaining papers are presented in order of the session themes, namely Dielectric Spectroscopy and Techniques, Theory and Modelling, and Electrokinetics. On behalf of the Dielectrics Group, I thank the authors for their contributions, and the Institute of Physics for excellent administrative and editorial assistance.

Dielectric spectroscopy is a powerful tool for investigating the dielectric properties of biological particles in suspension. For low volume fractions, the dielectric properties of the particles are related to the measured properties of the suspension by Maxwell's mixture equation. A number of different techniques can be used to measure the dielectric spectrum in the frequency domain or the time domain. In time domain dielectric spectroscopy, data can be converted into the frequency domain using convolution or Fourier transform, prior to data analysis. In this paper, we present a general method for transforming Maxwell's mixture equation from the frequency domain to the time domain allowing analysis of cell dielectric properties directly in the time domain. The derivation is based on the Laplace transform of the single shell model for a spherical particle, and can be extended to the multi-shell model. For a single shelled cell two characteristic relaxation time constants are derived. The results are compared with published analytical models. We show that the original frequency dependent mixture equation can be recovered by Fourier transform back to the frequency domain. As a result, a general relationship for the dielectric response of a mixture of particles is presented which links the frequency and time domains.

Tetrapolar electrode systems are commonly used for impedance measurements on biomaterials and other ionic conductors. They are generally believed to be immune to the influence from electrode polarization impedance and little can be found in the literature about possible pitfalls or sources of error when using tetrapolar electrode systems. In this paper we show that electrode polarization impedance can indeed influence the measurements and that also other phenomena such as negative sensitivity regions, separate current paths and common-mode signals may seriously spoil the measured data.

In this paper, we report on the influence of D- and L-glucose on the dielectric properties of native shaped (biconcave) human erythrocytes using time domain dielectric spectroscopy. The dielectric spectra of biconcave cells were analysed using a modified form of the model originally reported for spheroid particle suspensions (Asami and Yonezawa 1995 Biochim. Biophys. Acta.1245 317–24) The observed increase in the specific membrane capacitance of the biconcave erythrocytes was correlated with an increase in the concentration of D-glucose. In contrast, no associated correlation was found to changes in the membrane capacitance with increasing concentrations of L-glucose. A similar analysis of the dielectric response of osmotically swollen erythrocytes to changes in D-glucose concentration revealed a significantly different calculated specific cell membrane capacitance at elevated (>12 mM) D-glucose concentrations. The paper outlines and discusses the possible biochemical mechanisms that could be responsible for the measured dielectric properties of the erythrocyte membrane capacitances.

Electrowetting of water drops on structured superhydrophobic surfaces are known to cause an irreversible change from a slippy (Cassie–Baxter) to a sticky (Wenzel) regime. An alternative approach to using a water drop on a superhydrophobic surface to obtain a non-wetting system is to use a liquid marble on a smooth solid substrate. A liquid marble is a droplet coated in hydrophobic grains, which therefore carries its own solid surface structure as a conformal coating. Such droplets can be considered as perfect non-wetting systems having contact angles to smooth solid substrates of close to 180°. In this work we report the electrowetting of liquid marbles made of water coated with hydrophobic lycopodium grains and show that the electrowetting is completely reversible. Marbles are shown to return to their initial contact angle for both ac and dc electrowetting and without requiring a threshold voltage to be exceeded. Furthermore, we provide a proof-of-principle demonstration that controlled motion of marbles on a finger electrode structure is possible.

With an aim to reveal the mechanism of water–protein interaction from the dielectric response of a model fibrous protein, the dielectric constant ε' and loss factor ε'' have been measured in air dried and vacuum dried samples of bovine tendon collagen in the frequency range 30 Hz–3 MHz and temperature range 30–200 °C. An anomalous low frequency dispersion (LFD) and an intermediate frequency strong α-dispersion peak were the two main dielectric responses observed in the air dried sample. The LFD followed the fractional power law of frequency while the α-dispersion conformed to the Cole–Cole modified Debye equation. These dispersions, respectively, have been attributed to percolation of protons between and within the clusters of hydrogen bonded water molecules bound to polar or ionizable protein components. In the vacuum dried sample, however, a very weak high frequency α₂-dispersion peak was observed, which was hidden below the strong α-dispersion in the air dried sample. This peak may be attributed to reorientation of polar components of the collagen molecule.

Temperature dependence of the dielectric data shows release of bound water as a four-step process with discrete peaks at 50, 90, 125 and 160 °C. These peaks have been attributed to the onset of the release of adsorbed surface water, water bound to exposed polar sites, water bound to internal polar sites and very strongly bound structural water, respectively.

This paper describes the application of a novel electric potential sensor to the measurement of the propagation delay of electrical pulses in a saline environment. This is achieved non-invasively through weak capacitive coupling to a novel electric field sensor. An experimental test cell is used to demonstrate that in an environment consisting of a polar liquid we are able to localize the position of a pulse, as well as determine its amplitude and shape. These are the basic requirements for implementing an imaging system based on this technology. Results are presented which show a spatial resolution of better than 0.23 mm using this propagation delay method. The paper includes a discussion of the effect of salt concentration on the electrical conductivity, propagation delay and velocity. The applicability of the sensor to the detection of signals originating from nerve fibres is discussed with preliminary data acquired from a 100 µm diameter glass coated micro-wire immersed in saline.

This paper is the first in a series devoted to the study of dielectric properties of lyophilized disaccharides with a range of moisture contents. The paper addresses a number of methodical issues with frequency-domain dielectric measurements of low-loss powders, such as lyophilized sugars, in the frequency range from 10⁻¹ to 10⁶ Hz. The principle issue that one encounters with such measurements stems from the perturbation introduced by the apparatus function, which can mask the response of the sample above 10 kHz. Two methods of correction of this apparatus function are investigated. In the first (the 'subtraction' method) a low temperature spectrum of the sample is used for correction. In the second (the 'reference' method) additional measurements of two non-dispersive references are used for correction. Both methods are shown to extend the experimental frequency range. The upper frequency limits for the subtraction and reference methods are 100 kHz and 1 MHz, respectively. Other issues, such as the selection of an optimal measurement cell capacitance (∼4.5 pF), the optimal amount of sample (∼0.3–0.5 g) and the accurate compensation of the stray capacitance (∼2 pF) are discussed.

In this paper we describe theoretical modelling and experimental measurements of miniature coaxial probes with flat and conical end profiles, suitable for dielectric spectroscopy measurements on biological tissue samples. Various analytical solutions are compared with the results of simulations using CST Microwave for the sub-millimetre diameter probes operating over a range 500 MHz–40 GHz. Very good agreement was found between the theoretical and experimental data and it has been shown that analytical models for the infinite flanged coaxial probe case are applicable to small diameter flangeless probes, provided the outer conductor diameter is about twice that of the dielectric bead in the coaxial transmission line. Data are presented for a range of sample media including reference liquids and liver tissue.

Various chemical reactions occur simultaneously in barrels during the fermentation processes of alcoholic beverages. Chemical analyses are employed to monitor the change in chemical components, such as glucose and ethyl alcohol. The tests are carried out with extracted specimens, are costly and require time. We have developed a permittivity measurement system for liquid specimens in the frequency range from 2.6 to 50 GHz, and applied the system to fermentation monitoring. Experimental results proved that the observed change in complex permittivity suggests a decrease in the amount of glucose and an increase in alcohol content, which are the key chemical components during the fermentation process.

Over the last century a number of techniques have been developed which allow the measurement of the dielectric properties of biological particles in fluid suspension. The majority of these techniques are limited by the fact that they only provide an average value for the dielectric properties of a collection of particles. More recently, with the advent of microfabrication techniques and the Lab-on-a-chip, it has been possible to perform dielectric spectroscopic experiments on single biological particles suspended in physiological media. In this paper we review current methods for single cell dielectric spectroscopy. We also discuss alternative single cell dielectric measurement techniques, specifically the ac electrokinetic methods of dielectrophoresis and electrorotation. Single cell electrical impedance spectroscopy is also discussed with relevance to a microfabricated flow cytometer. We compare impedance spectroscopy data obtained from measurements made using a microfabricated flow cytometer with simulation data obtained using an equivalent circuit model for the device.

It is known that careful engineering of dielectrophoresis (DEP) forces can be strong enough to move microparticles towards regions of higher or lower field strength. While many of the microdevices exploit differing electrical properties between cells to enact separation, the use of DEP as a generic electrical technique to position and move cells is still under investigation. Our work focuses on developing a robust numerical tool based on calculation of the Maxwell stress tensor (MST) both in a 2D and in a 3D formulation that aims towards providing a deeper understanding of cells interaction using DEP as a handle to position and manipulate cells for fundamental cell biology. The complex Laplace equation is first solved to obtain a value for the potential everywhere on the structure under investigation. The electric field is then obtained by a simple finite difference approach and the time-averaged DEP force exerted on a cell immersed in a medium with complex permittivity and subject to a sinusoidal electric field is calculated using the MST technique. MST is compared with a more approximate method and the ability of the approach to model a cell trajectory from a random initial point within the vicinity of an electrode system, in addition to cell–cell interaction, is also demonstrated.

Dielectric characterisation of polarisable particles, and prediction of the forces and torques exerted upon them, relies on the knowledge of the effective, induced dipole moment. In turn, through the mechanism of depolarisation, the induced dipole moment of a particle is strongly dependent upon its shape. Since realistic shapes create modelling difficulties, the 'spherical particle' approximation is often invoked. However, in many cases, including biological dielectric spectroscopy and dielectrophoresis, this assumption is a poor one. For example, human erythrocytes are essentially oblate spheroids with indented sides, while viruses and bacteria often have elongated cigar shapes. Since shape-dependent polarisation both strongly influences the accuracy of conventional dielectric characterisation methods using Maxwell's mixture formula and confounds accurate prediction of dielectrophoretic forces and torques, it is important to develop means to treat non-spherical particles. In this paper, we demonstrate a means to extract the dipole moment directly from numerical solutions of the induced electrostatic potential when a particle is placed in a uniform electric field. The accuracy of the method is demonstrated for a range of particle shapes: spherical, ellipsoidal, truncated cylinders and an approximation of an erythrocyte, the red blood cell.

The retarded dispersion interaction (Casimir interaction) between two dilute dielectric media at high temperatures is considered. The excited atoms are taken into account. It is shown that the perturbation technique cannot be applied to this problem due to divergence of integrals. A non-perturbative approach based on kinetic Green functions is implemented. We consider the interaction between two atoms (one of them is excited) embedded in an absorbing dielectric medium. We take into account the possible absorption of photons in the medium, which solves the problem of divergence. The force between two plane dilute dielectric media is calculated at pair interaction approximation. We show that the result of quantum electrodynamics differs from the Lifshitz formula for dilute gas media at high temperatures (if the number of excited atoms is significant). According to quantum electrodynamics, the interaction may be either attractive or repulsive depending on the temperature and the density numbers of the media.

Cell biology applications, protocols in immunology and stem cell research, require that individual cells are handled under strict control of their contacts to other cells or synthetic surfaces. Dielectrophoresis (DEP) in microfluidic chips is an established technique to investigate, group, wash, cultivate and sort cells contact-free under physiological conditions: microelectrode octode cages, versatile dielectrophoretic elements energized with radio frequency electric fields, stably trap single cells or cellular aggregates. For medical applications and cell cultivation, possible side effects of the dielectrophoretic manipulation, such as membrane polarization and Joule heating, have to be quantified. Therefore, we characterized the electric field-induced warming in dielectrophoretic cages using ohmic resistance measurements, fluorometry, liquid crystal beads, infra-red thermography and bubble size thermometry. We compare the results of these techniques with respect to the influences of voltage, electric conductivity of buffer, frequency, cage size and electrode surface. We conclude that in the culture medium thermal effects may be neglected if low voltages and an electric field-reducing phase pattern are used. Our experimental results provide explicit values for estimating the thermal effect on dielectrophoretically caged cells and show that Joule heating is best minimized by optimizing the cage geometry and reducing the buffer conductivity. The results may additionally serve to evaluate and improve theoretical predictions on field-induced effects. Based on present-day chip processing possibilities, DEP is well suited for the manipulation of cells.

The influence of a number of parameters on the height of cell aggregates formed by positive dielectrophoresis was systematically investigated. It was found that the aggregate height could be increased by following a number of simple rules. Interdigitated electrodes with oppositely placed castellations gave higher aggregate heights than interdigitated parallel electrodes. The optimal frequency was identified to be 1 MHz. To obtain the highest aggregates, the conductivity of the suspending medium should be kept to the lowest value obtainable, as should the fluid flow rate through the chamber. Aggregate height increased with increasing voltage, but the effect of increasing the voltage diminished as higher aggregate heights were reached. Optima were observed in the aggregate height as a function of the electrode characteristic size, which depended on the cell type and cell size. It was shown to be possible to create aggregate heights of over 150 µm for all the three cell types (bacteria, yeasts and mammalian cells) employed, using voltages of only 20 V_pk–pk.

The controlled manipulation of molecules is a crucial prerequisite for the emerging field of molecular nanotechnology. AC electrokinetics provide a powerful mechanism for both positioning and inducing conformational changes in molecules. In this paper, we investigate the elongation of fluorescently-labelled DNA strands, which are covalently tethered by one end to gold microelectrodes arranged in an opposing-finger geometry, when exposed to strong ac electric fields. We found that the elongation of the DNA molecules is restricted by the geometry of the gap, and that the observed contour of the elongated DNA molecules coincides with the electric field line pattern. Further, we discuss a potential elongation mechanism and provide evidence that the major contribution to the elongation originates from the ac electrokinetic torque, which is supplemented by a small bias force provided by the electric-field-induced fluid flow.

This paper gives a review of recent papers which have led to the capability of the prediction of weld depths for gas tungsten arc welding, for any given arc current, electrode shape or separation and welding gas. The methodology is given for deriving plasma composition as a function of temperature and pressure from basic atomic and molecular properties. Transport coefficients of density, specific heat, enthalpy, electrical conductivity, thermal conductivity, viscosity and radiation emission coefficients can then be derived as a function of temperature. The conservation equations of fluid dynamics are then used to derive weld profiles for stainless steel for welding gases such as argon, helium, carbon dioxide and a 10% mixture of hydrogen in argon. The markedly different weld depths which are obtained are related to basic material functions such as specific heat, electrical and thermal conductivity. The temperature dependence of the surface tension coefficient has a marked effect on weld depth and profiles because it can influence the direction of circulatory flow in the weld pool. Electric arcs in helium and carbon dioxide are more constricted than arcs in argon and as a consequence the magnetic pinch pressure of the arc, transmitted to the weld pool, can force strong downward flows in the weld pool and thus lead to a deep weld. It is found that because of the interactions of the arc and the weld pool through effects such as viscous drag forces of the plasma on the weld pool, it is necessary to treat the arc, the electrode and the weld pool in a unified system.

Nanocomposite hard magnetic materials (Nd,Dy)_4.5Fe_77.5B₁₈ (No. 1) and (Nd,Dy)_4.5Fe₇₆B₁₈Nb_1.2Cu_0.3 (No. 2) have been prepared by crystallizing amorphous ribbons, fabricated by single roll melt-spinning. The evolution of a multiphase structure was monitored by an x-ray diffractometer and by thermomagnetic measurement. We observed that, at annealing temperatures below 670 °C, there is crystallization of soft phase Fe₃B and a small amount of hard phase Nd₂Fe₁₄B. At annealing temperatures above 670 °C, crystallization of α-Fe and probably Dy₂Fe₁₄B phases with large magnetocrystalline anisotropy led to a drastic enhancement in the hard magnetic properties of the materials. The maximum value of H_C is found to be 4.2 kOe for sample No. 1. For sample No. 2, with co-doping of Nb and Cu, nanostructure refinement yields a strong enhancement in exchange coupling between the component phases. Thereby, we obtained high reduced-remanence of 0.78, high remanence of 1.15 and a high (BH)_max value up to 16.2 MGOe.

A giant magnetocaloric effect was found in La_0.7Ca_0.3MnO₃ manganite at low magnetic fields. The magnetic entropy changes caused by a magnetic field change of 0.5 and 1.0 T were as large as 5.04 and 6.25 J kg⁻¹ K⁻¹, respectively, which exceed those of perovskite-like magnetic refrigerants or elemental Gd by a factor of 2–3. The extremely high values of the magnetocaloric effect are attributed to a sharp drop in the magnetization at a first-order ferromagnetic–paramagnetic phase transition and S-shaped magnetization versus field dependence.

We report the investigation of high energy ion beam irradiation on Si (1 0 0) substrates at room temperature using a low energy plasma focus (PF) device operating in methane gas. The unexposed and ion exposed substrates were characterized by x-ray diffraction, scanning electron microscopy (SEM), photothermal beam deflection, energy-dispersive x-ray analysis and atomic force microscopy (AFM) and the results are reported. The interaction of the pulsed PF ion beams, with characteristic energy in the 60–450 keV range, with the Si surface, results in the formation of a surface layer of hexagonal silicon carbide. The SEM and AFM analyses indicate clear step bunching on the silicon carbide surface with an average step height of 50 nm and a terrace width of 800 nm.

The evolution of the sheet resistance (R_s) in δ-doped layers in GaAs during He ion irradiation was investigated. The R_s increases with the dose accumulation in a similar way that occurs in layers with much wider dopant profiles, produced either by ion implantation or epi-growth. The R_s becomes higher than 10⁹ Ω/sq after the so-called threshold dose (D_th) is accumulated. The values of D_th closely correlate with the ratio of the estimated number of replacement collisions at the depth of the δ-doped layer and the original sheet hole concentration. The maximum thermal stability of the isolation, i.e. the persistence of R_s at values above 10⁹ Ω/sq after a subsequent thermal annealing is of about 550–600 °C.

The influence of the doping level on the radiative recombination properties of GaSb:Se crystals has been investigated by cathodoluminescence (CL) microscopy and spectroscopy in the scanning electron microscope. CL images evidence a high dislocation density and dopant segregation around the dislocation cores in highly-doped crystals. A progressive reduction of the Se content leads to a lower dislocation density and a more uniform luminescence spatial distribution. CL spectra reveal the existence of three Se-related emission bands, centred in all the samples investigated at about 765, 740 and 719 meV, whose relative intensity is influenced by the doping level. Measurements carried out at different temperatures and excitation densities indicate that these bands can be attributed to transitions from the conduction band to deep acceptor levels.

We present the electron field-emission (FE) characteristics of conical boron nitride nanorods grown on a (1 0 0) n-type silicon substrate. The emission current can be up to ∼60 µA at an applied voltage of ∼3 kV. Two distinct slopes are evident in the Fowler–Nordheim (FN) plot. The FE characteristics can be explained using a site-related tunnelling-controlled mechanism. The occurrence of two FN slopes is attributed to the switchover from tip emission to side emission, which results from the differences in interface barrier, geometry, as well as the total emission area of the two emission interfaces.

Thermophoresis of axially symmetric bodies is investigated to first order in the Knudsen number, K n. The study is made in the limit where the typical length of the immersed body is small compared with the mean free path. It is shown that in this case, in contrast to what is the case for spherical bodies, the arising thermal force on the body is not in general anti-parallel to the temperature gradient. It is also shown that the gas exerts a torque on the body, which in magnitude and direction depends on the body geometry. Equations of motion describing the body movement are derived. Stationary solutions are studied.

Breakdown in a discharge tube is investigated by means of a fluid model. The discharge tube is similar to a compact fluorescent lamp tube, containing argon at 3 Torr and mercury at a few millitorr. It was found that the minimum breakdown voltage is decreased substantially compared with a tube containing pure argon. Penning ionization of mercury via an argon metastable state plays an important role in this effect. This is illustrated for a lamp operated on a DC voltage, where significant Penning ionization takes place in the wake of the ionization front. Furthermore, contrary to what is suggested in earlier literature, the development of the surface potential of the lamp is shown to be not only determined by surface charges, but also by volume charges.

Investigations of fluorescent lamps (FL) are often focused on the electrodes, since the lifetime of the lamps is typically limited by the electrode lifetime and durability. During steady state operation, the work function lowering emitter material, in particular, barium, is lost. Greater barium losses occur under dimming conditions, in which reduced discharge currents lead to increased cathode falls, the result of the otherwise diminished heating of the electrode by the bombarding plasma ions. In this work the barium density near the electrodes of (FL), operating in high frequency dimming mode is investigated using the high-sensitivity method of laser-induced fluorescence. From these measurements we infer barium loss for a range of discharge currents and auxiliary coil heating currents. We show that the Ba loss can very easily be reduced by moderate auxiliary coil heating.

In order to analyse the effect of the ambipolar potential on the H⁻ ion density recovery in the measurement of the H⁻ ion temperature by the two-laser photodetachment diagnostic technique, the particle-in-cell simulation with a one-dimensional slab model is performed. In particular, a high H⁻ ion density regime with n₋₀/n₊₀ > 0.1 (n₋₀ : H⁻ ion density, n₊₀ : H⁺ ion density before the laser shot) has been studied. The recovery time of the H⁻ ion density becomes shorter as the density ratio n₋₀/n₊₀ increases. The ambipolar potential formed after the laser shot is almost proportional to the density ratio n₋₀/n₊₀. Due to the H⁻ ion acceleration by this ambipolar potential, the H⁻ ion temperature T_−d deduced from the H⁻ ion density recovery tends to be larger than the actual temperature T₋₀. The temperature ratio T_−d/T₋₀ increases with the density ratio n₋₀/n₊₀ and the deduced temperature T_−d becomes about 1.5 times larger than the actual temperature T₋₀ for n₋₀/n₊₀ = 0.9.

The ozone production process in a pulsed positive dielectric barrier discharge (DBD) is studied by measuring the spatial distribution of ozone density using a two-dimensional laser absorption method. DBD occurs in a 6 mm point-to-plane gap with a 1 mm-thick glass plate placed on the plane electrode. First, the propagation of DBD is observed using a short-gated ICCD camera. It is shown that DBD develops in three phases: primary streamer, secondary streamer and surface discharge phases. Next, the spatial distribution of ozone density is measured. It is shown that ozone is mostly produced in the secondary streamer and surface discharge, while only a small amount of ozone is produced in the primary streamer. The rate coefficient of the ozone production reaction, O + O₂ + M → O₃ + M, is estimated to be 2.5 × 10⁻³⁴ cm⁶ s⁻¹.

A layer of tris-(8-hydroxyquinoline) aluminium (Alq₃), which is normally used as an electron-transporting and emissive layer, was incorporated between the hole-transporting layer and the hole-injection layer to balance the electron–hole injection. The Alq₃ layer performed to block the hole current which is a majority carrier in a typical organic light-emitting device. An increase in current efficiency by almost 30%, from 3.1 to 4.0 cd A⁻¹, with a minimum voltage shift was achieved with a 2 nm Alq₃ layer as a hole-blocking layer. A reduction in HTL thickness was observed to reduce the efficiency due to electron leakage to the HIL, whereby an inefficient exciplex emission was observed.

YBa₂Cu₃O_7−δ thin films grown on a Nb-doped SrTiO₃ substrate by a pulsed laser deposition method have been fully characterized by scanning transmission electron microscopy Z-contrast imaging and electron energy loss spectroscopy techniques. The Nb distribution was found to be uniform and unchanged across the interface, ensuring a high quality p–n junction heterointerface. We first observed the coexistence of 124 and 125 YBCO defect structure phases, appearing as planar defects in a YBCO thin film. Dispersive Y₂O₃ nanoparticles have also been observed in the thin film. The interaction of these defect structures and Y₂O₃ nanoparticles is thought to be beneficial for pinning flux through the entire film thickness.

Ultra-water-repellent (UWR) films were prepared by microwave plasma-enhanced chemical vapour deposition using trimethylmethoxysilane and aluminium (III) diisopropoxide ethylacetoacetate (ADE) as raw materials. The film was mainly composed of silica and alumina and was apparently transparent. The film thickness was approximately 500 nm. The sample surface was treated with an organosilane in order to introduce hydrophobic groups. The hydrophobic modification led to a water contact angle of more than 150°, whose value corresponds to the UWR surface. The hardness of film with an optimized Al content was significantly improved compared with that without Al. The maximum hardness was 1.71 GPa. In consequence, we successfully prepared an UWR film in the silica–alumina system.

Structures containing multiple layers of self-assembled InAs quantum dot clusters within a GaAs matrix are investigated on GaAs (1 0 0) by atomic force microscopy. Droplet homoepitaxy (GaAs nanostructures on planar GaAs) is used to create tiny GaAs nano-mound templates elongated along [0 1 −1]. Due to a high density of monolayer steps on the edge of nano-mounds, deposited InAs prefer to form in clusters around the nano-mound templates. By varying the subsequent InAs monolayer coverages and growth temperatures, two distinctive sizes of quantum dots (QDs) are formed around the nano-mounds for the layer stacking. With a fixed GaAs barrier thickness (10 nm) in between the layers, the resulting QDs from the stacked layers show significant improvement in their size uniformity.

Titanium films of different thicknesses ranging from 18 to 210 nm were deposited on glass substrates, at different substrate temperatures (313 to 600 K) under UHV conditions. Their optical properties were measured by spectrophotometry in the spectral range of 200–2500 nm. The optical functions were obtained from the Kramers–Kronig analysis of the reflectivity curves. The effective medium approximation (EMA) analysis was employed to establish the relationship between the structure zone model (SZM) and EMA predictions. There was good agreement between SZM as a function of substrate temperature and film thickness and the values of volume fraction of voids was obtained from EMA analysis. The gettering property of Ti can play an important role in the nano-structure of the film and causes variations in the optical behaviour of thin Ti films, though films were produced under UHV condition and the XRD analysis did not show a detectable amount of oxidation. The over-layer thickness was calculated to be less than 2.0 nm, using the transfer matrix method.

Two novel genetic algorithms implementing principal component analysis and an adaptive nonlinear fitness–space–structure technique are presented and compared with conventional algorithms in x-ray reflectivity analysis. Principal component analysis based on Hessian or interparameter covariance matrices is used to rotate a coordinate frame. The nonlinear adaptation applies nonlinear estimates to reshape the probability distribution of the trial parameters. The simulated x-ray reflectivity of a realistic model of a periodic nanolaminate structure was used as a test case for the fitting algorithms. The novel methods had significantly faster convergence and less stagnation than conventional non-adaptive genetic algorithms. The covariance approach needs no additional curve calculations compared with conventional methods, and it had better convergence properties than the computationally expensive Hessian approach. These new algorithms can also be applied to other fitting problems where tight interparameter dependence is present.

This paper reports the important role of energetic particle bombardment in achieving low temperature deposition of nanocrystalline TiO₂ films by reactive DC magnetron sputtering of Ti targets in a mixture of argon and oxygen. In this work, we studied the effect of particle bombardment in the film deposition process by control of external processing parameters, including total pressure P_t and negative substrate bias V_b. The result shows that the variation of energetic particle bombardment has a significant impact on substrate temperature, crystal structure, surface morphology and refractive index n of deposited TiO₂ films and we believe the process of non-equilibrium atomic scale heating caused by energetic particle bombardment is the main reason for the nanocrystal formation at low temperature (below 75 °C).

The burst mode experiment is commonly used to measure non-linear piezoelectric material properties. However, the theory that is often employed is highly simplified, making use of linear results. Here we represent a more rigorous theory based closely on the underlying non-linear partial differential equations. Since time domain solutions are not available analytically, the approach is in two parts: the PDE is solved in the frequency domain, then an auxilliary non-linear ordinary differential equation is solved in the time domain. Comparison of the two yields the material parameters. Also, we suggest the excitation portion of the I(t) curve be studied rather than the decay part normally used since the former contains more features, has a well-defined initial condition (current and charge both zero) and is less susceptible to experimental artefacts.

Observations of the variation of complex permittivity as a function of frequency have revealed that in some cases a single relaxation process is exhibited while in other cases two or more, or even a distribution of, relaxation times appear to be present. Some of the shortest relaxation times relate to processes which give rise to only small absorptions; these are not always made clearly evident by experimental observations. The suggestion has been made in the literature that they could become more evident if, instead of the usual plot of the variation with frequency with permittivity, a polarizability plot were to be adopted. Although this suggestion was made more than forty years ago, no detailed analysis seems yet to have appeared which elucidates the tangible advantages that would accrue if it were to be implemented and under what conditions. The aim of this paper is to investigate that question. During the course of the investigation, it emerged that the polarizability plot did not merely offer advantages in certain circumstances for the graphical display of experimental data. It is possible that molecular polarizability data might yield additional insights into the physical significance of dielectric measurements made on polar liquids.

La-substituted Bi_1−xLa_xFeO₃ films have been prepared on LaNiO₃/SiO₂/Si(1 1 1) substrates by the sol–gel process. The films with x = 0.00–0.20 were prepared at an annealing temperature of 600 °C. X-ray diffraction patterns indicate that all films adopt R3m structure and different orientation with the increase in x. A Bi₂Fe₄O₉ phase was identified in the films with x = 0.01 and 0.02. Cross section scanning shows that the thickness of the films is about 270 nm. Enhanced ferroelectricity at room temperature was observed by measuring the electric hysteresis loops. The film with x = 0.10 has the largest double remnant polarization of 4.40 µC cm⁻². The double remnant polarizations are 3.35 µC cm⁻², 3.20 µC cm⁻² and 3.49 µC cm⁻² for the films with x = 0.0, 0.05 and 0.2, respectively. Moreover, the films with x = 0.05–0.20 show enhanced dielectric property. Through the substitution of La, the leakage current density is reduced for the films with x = 0.05–0.20 and the films show decreased leakage conduction.

Thermoluminescence kinetic analysis using T_m–T_stop, glow curve deconvolution, variable heating rate and repeated initial rise methods have been carried out on the glow curves of a quartz with a glow peak whose peak temperature goes through a peak as a function of irradiation dose, an unusual feature for quartz. The glow curve of the sample showed four clear glow peaks around 82 °C (peak I), 148 °C (peak II), 200 °C (peak III) and 292 °C (peak IV) when irradiated to 1.8 Gy and read out at 1 °C s⁻¹. The peak temperature of peak IV first increases and later decreases with dose whereas the peak temperatures of peaks I, II and III are independent of dose. T_m–T_stop and glow curve deconvolution (GCD) analyses indicated the presence of at least five peaks at about 80, 146, 199, 295 and 350 °C meaning that the apparently single peak IV may consist of at least two overlapping glow peaks. The activation energy, E, and frequency factor, S, associated with each of the glow peaks are presented. E and T_m values for all the glow peaks in the quartz sample were found to be dose-independent. It was also found, during the use of GCD, that as the irradiation dose increases, the number of thermoluminescence (TL) peaks required to produce the best fit to the glow curve increases although the location of the TL peaks themselves does not change with dose. This effect is explained in terms of the relative intensities of the glow peaks. We have also noted that the ability of GCD to completely isolate all the glow peaks in a glow curve may depend on irradiation dose.

In this study, pulsed-laser deposited (Pb,Sr)TiO₃ (PSrT) films on p-type Si were studied at low substrate temperatures ranging from 300 to 450 °C for metal/ferroelectric/semiconductor applications. The substrate temperature strongly enhances film crystallinity without significant inter-diffusion at the PSrT/Si interface and affects the electrical properties. As the substrate temperature increases, the films have smaller leakage currents, fewer trap states at the electrode interfaces, clockwise capacitance versus applied field hysteresis loops and larger memory windows correlated with superior crystallinity. Conversely, 300 °C-deposited films exhibit a small and counterclockwise loop with a positive shift of the flatband voltage, attributed to more negative trap charges within the films. However, the high substrate temperature (450 °C) may produce serious Pb–O volatilization, incurring more defects and leakage degradation. The analyses of fixed charge density and flatband voltage shift reveal the trap status and agree well with the leakage characteristic. An electron band model of the Pt/PSrT/Si electronic structure is proposed to explain the electrical behaviour. The excellent fatigue endurance with a small variation of memory windows (<11%) after 10¹⁰ switching is also demonstrated.

A three-dimensional mesoscopic method is developed for predicting the effective thermal conductivity of multiphase random porous media. The energy transport equations are solved by a lattice Boltzmann method for multiphase conjugate heat transfer through a porous structure whose morphology is characterized by a random generation-growth algorithm. Our numerical results show that the cell number in the third dimension influences the resulting effective thermal conductivity of three-dimensional porous media. The predicted effective thermal conductivity varies with the cell number in the third dimension following an exponential relationship, and it requires in the examples at least 10 cells along the third dimension before the predictions stabilize. Comparisons with the experimental data show that the effective thermal conductivities measured by the hot-probe and hot-wire techniques agree well with the predicted results by the two-dimensional model, whereas those measured by the transient comparative method agree more with the three-dimensional predictions.

The purpose of this research is to present a theoretical and numerical approach to analyse the unconventional lobe P–V profiles for a heat engine cycle. The unconventional lobe P–V cycle considered here is defined as a cycle consisting of a pressure and volume relation in terms of an angle expression by continuously varying its shape to form the rounded or curved projections of the elliptical cycle. The study is deduced from a principle analysis of thermodynamic first law by using an ideal gas model. The procedure is discussed in detail in this paper, giving particular attention to the consistent evaluation of Q_in and thermal efficiency by determining the adiabatic points first. Multiple adiabatic points have been found for the different lobe configurations. Effects on thermal performances due to different shapes of the lobe cycles are then examined. Finally, investigation into the number of adiabatic points and the critical values to separate different heat transfer regions is also described.

We provide a comprehensive analysis of the nature of emfs that are induced during the operation of a railgun. The main sources of these emfs are changes in rail currents and the motion of the armature. Our experience with the current railgun literature and private communications indicates that the topic of induced emfs is a neglected area of analysis.

Common misconceptions are discussed and new perspectives are presented. It is shown, for example, that there is a wide diversity of conflicting views on the nature of the emf generated by armature motion. We conclude that there is no true motional emf in railguns, and offer a resolution of the conflicting views in terms of localized flux creation.

Finite element modelling is used to illustrate the main concepts and consequences of induced emfs, and to validate the analyses. Experimental data from laboratory railgun tests provide added validation. The results offer insights into many previously unexplained phenomena commonly observed in railguns.

Experimental data and Monte Carlo results of 20–50 keV electron penetration through thin aluminium foils are presented. Transmission ratios as well as energy characteristics of secondary electrons are measured for 3–20 µm thick foils. Implications of these results for the requirements of a radioisotope micro-power sources energy conversion device are analyzed. It is shown that for a given foil thickness, there is a discrete peak in the low energy secondary electron emission. In addition, it is noted that the conversion factor for high energy primaries to low energy secondaries is less than one.

A near resonant two-photonionization scheme , has been investigated for the isotope selective excitation of ⁴¹Ca isotope for its applications as a tracer in bio-medical studies. The ionization efficiency and optical selectivity have been calculated for various powers of the excitation and ionization laser. Under the optimized excitation/ionization laser powers the ionization efficiency and the optical selectivity for the studied scheme are found to be 1.3 × 10⁻⁴ and ∼1.0 × 10⁴, respectively. The ionization efficiency is two orders of magnitude higher than the step-wise excitation process. In combination with a mass spectrometer, an overall selectivity of ∼10¹⁰ can be obtained which is adequate for bio-medical applications.