Table of contents

The issue of the sustainability of energy supply has attracted worldwide concern given the rapid depletion of fossil energy sources amid increasingly worsening environmental pollution and the drive to develop alternative, environment-friendly, renewable energy sources and energy carriers to secure our energy supply and sustainable development. Hydrogen is considered to be among the best solutions available, although technical barriers, in particular effective hydrogen storage, need to be dealt with. Quasi-one-dimensional carbon nanotubes (CNTs) with rich nanosized pore structures are considered to be a potential hydrogen storage medium; however, controversy over and discrepancies in both the experimental and theoretical results do exist. Therefore, the latest research progress in and the current situation pertaining to hydrogen storage in CNTs are reviewed and discussed in detail. Moreover, CNTs can have wide applications as alternative energy storage media, utilizing fully their unique structural characteristics. We summarize and analyse the advantages as well as the research progress made in using CNTs as electrode materials in lithium-ion batteries and supercapacitors. Further, future applications of CNTs in the energy storage field are explored.

The temperature dependence of the electron paramagnetic resonance (EPR) spectra of 'high tension' (HT) and 'low tension' (LT) nylon 6 fibres has been measured in the X-band. The spectra show a characteristic hyperfine structure owing to coupling to the nitrogen nucleus and occur due to nitroxide additives. The linewidth transitions signalling the onset of self-diffusion occur at much higher temperatures than in the proton NMR spectra. The higher resolution of the EPR data allows for discrimination between HT and LT fibres and the observation of the effects of the super-structure induced by different thermo-mechanical treatments on the molecular self-diffusion.

The complex permittivity and permeability of composites consisting of metallic magnetic particles (carbonyl-iron-particles (CIPs)) embedded in a dielectric matrix (epoxy resin) have been studied at microwave frequencies. Composites with different volume fraction (5–60%) of magnetic particles have been fabricated and their complex permittivity and permeability have been measured. The concentration dependence of permittivity and permeability has been analysed using various effective medium theories. We have found that only the general Bruggeman formula describes composites very well over a wide range of concentrations used in this study. The extracted permittivity and permeability of CIPs are consistent with those reported.

Monodisperse face-centred tetragonal (fct) FePt nanoparticles with high magnetic anisotropy and, therefore, high coercivity have been prepared via a new heat treatment route. The as-synthesized face-centred cubic FePt nanoparticles were mixed with salt powders and annealed at 700°C. The salts were then removed from the particles by washing the samples in water. Monodisperse fct FePt particles were recovered with the particle size and shape being retained. Coercivity of the isolated particles up to 30 kOe at room temperature has been obtained.

Existing quadrilayer and trilayer techniques for optimizing the magneto-optical effects from magnetic materials have been applied to new generation recording media to investigate the possibility of maximizing the signal-to-noise readout performance. Various methods are reviewed and the designs they produce are compared with each other and with the working media found in the literature. In order to address a number of inadequacies, a new numerical approach to the optimization of a quadrilayer structure is used to find further solutions that are considered more suitable for the practical recording media. The effects on design and performance of medium of incidence, type of storage layer and wavelength are all considered.

Recent experimental results (Zheng et al 2004 Science303 661) have shown that a 1-3-type BaTiO₃–CoFe₂O₄ composite film exhibited a strong coupling between the ferroelectric and ferromagnetic order parameters. The coupling interaction in the nanostructured multiferroic film could be different from that in a bulk composite because there exists a giant residual stress/strain in the film. In this paper, by considering the influence of the three-dimensional residual strain in the film, the magnetically induced polarization of the nanostructured BaTiO₃–CoFe₂O₄ multiferroic films has been studied using the Landau–Ginsberg–Devonshire thermodynamic theory. The calculation results show that the 1-3-type nanostructured composite film could produce a ferroelectric–ferromagnetic coupling larger than that of its bulk counterpart which is in broad agreement with the experimental results. The 2-2-type nanostructured composite films were found to produce much less coupling interaction in comparison with the 1-3-type film. The dependence of multiferroic coupling on composition and temperature was analysed on the basis of the calculated results.

The magnetoresistive (MR) effect in Bi-2212+MgO composites with proportions 6, 15 and 20 wt% of MgO was observed and compared with the MR effect of pure Bi-2212 and previously reported Bi-2212+USr₂CaO₆. The resistivity of melt textured Bi-2212+MgO composites is characterized by a high sensitivity to an applied magnetic field over an increasing temperature range with increasing MgO addition. X-ray results show that the MgO phase is compatible with the Bi-2212 matrix, stable during the melt texturing process and shows little adverse effect on the superconducting transition temperature. A cryogenic sensor was built using Bi-2212+20 wt% MgO as an active component and tested at 77 K in cycling fields from 0 to 1 T. It showed a high sensitivity and no hysteresis.

The potential of the high-growth rate hydride vapour phase epitaxy technique and laser lift-off for the fabrication of free-standing GaN substrates is explored. Structural and optical properties of 300 µm thick free-standing GaN have been investigated employing different analytical techniques. The x-ray diffraction (XRD) measurements prove good crystalline quality of the material grown. A comparatively low value of (3 ± 1) × 10¹⁶ cm⁻³ of Ga vacancy-related defects is inferred from positron annihilation spectroscopy data. Complete strain relaxation is observed on the Ga-polar face of the free-standing GaN by XRD and Raman spectroscopy measurements. The strain-free homoepitaxy will significantly reduce the defect density, and thus an improvement of the device performance and lifetime can be realized.

The dispersion relation, density of states, wave-functions and single site impurity bound and resonant modes of a photonic crystal slab are computed. The photonic crystal slab is formed by embedding a hexagonal lattice array of dielectric cylinders in a background dielectric. Outside the photonic crystal slab is a uniform, isotropic dielectric medium. The solution of Maxwell's equations for the modes of a free-standing photonic crystal slab are obtained by treating a self-consistent matrix eigenvalue problem that is solved iteratively using a fast computer routine. The properties of single site impurities in photonic crystal slabs are determined using both Green's function methods and effective mass equations based on a Wannier function representation. The impurity dielectric constant supporting an impurity bound state is shown to be a multiple valued function of the frequency of the impurity mode. Asymptotic forms are obtained for the behaviour of impurity bound states at frequencies in the neighbourhood of the band edges. Resonant modes at pass band frequencies are computed for the impurities formed by replacing a single dielectric cylinder of the photonic crystal slab with background dielectric media. Comparison of the theoretical results is made with experiments on an electrically injected photonic crystal microcavity light source.

The effect of ambient gas on the work function of an electron emitter is usually ascribed to the presence of an adsorbed gas layer on its surface. However, in the course of recent unrelated experiments in this laboratory, changes in the electron emission have been observed under conditions of high emitter temperature and a gas pressure so low that significant surface adsorption is impossible. The observed emission changes are the result of two mechanisms that proceed at different rates and that affect the emission current in opposite directions.

An explanation of the phenomenon is proposed in terms of the penetration of gas molecules into the emitter at temperatures sufficiently high for diffusion to be significant. Measurements are presented showing the dependence of the current change on the emitter temperature, the nature of the ambient gas and its pressure.

Studies of the kinetics in the afterglow of three RF discharges having different configurations are presented. Experiments with a slow flow velocity transverse capacitive RF discharge were performed and detailed measurements of the spatial evolution of , O₂(a¹Δ_g), O(³P) and flow temperature were taken. Simulations of three different experimental configurations were in good agreement with the data for the spatial decay of . The simulations also provided reasonable agreement with experimental data for atomic oxygen, O₂(a¹Δ_g) and temperature, where the data were available. Updated electron impact cross-sections for oxygen dissociation were included in the simulations; this proved critical for proper modelling of the production of atomic oxygen and the subsequent decay of . At low oxygen atom densities the decay of was principally from heterogeneous quenching. For the slow flow velocity experiment, O atom recombination and deactivation by the walls play an important role; in the far downstream afterglow region a quasi-stationary concentration was found owing to a near-equilibrium between the pooling reaction and losses to the walls for this slow velocity case.

The electrostatic extraction of nearly monochromatic solvated ions from externally wetted emitters is possible in the case of some ionic liquids or room temperature molten salts. These compact devices are similar to liquid metal ion sources but positive or negative ion beams can be obtained simply by selecting the appropriate polarity for the power supply. dc operation on a single polarity over relatively long periods of time induces electrochemical degradation of the liquid–metal system making voltage alternation at frequencies of the order of 1 Hz necessary to sustain chemical neutrality. This periodic interruption forces a non-steady state behaviour. In particular, the ion current onset is delayed from a square-shaped voltage input signal by a few milliseconds for tungsten metal emitters wetted with the ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate, setting the upper bound for the alternation frequency at about 75 Hz. The dependences of these delays on absolute applied voltages are experimentally explored for this compound, suggesting that viscous drag is the main factor determining the dynamic response.

This paper investigates the microwave breakdown threshold in a circular waveguide excited in the lowest order (TE₁₁) mode, where the electric field strength depends on both the radius and the azimuthal angle. This analysis complements and extends previous investigations of breakdown in cylindrical waveguides and resonators that have been restricted to circularly symmetric waveguide modes so far. A simple analytical approximation of the breakdown threshold of the TE₁₁ mode is found, using a direct variational approach. The predictions are compared with the results of numerical calculations and the agreement is found to be very good.

The transition pressure above which powder formation takes place was experimentally determined in a parallel plate RF silane–hydrogen plasma as a function of the process parameters—power, temperature, gas flow and hydrogen dilution—using the dc-bias voltage as powder formation indicator. The resulting empirical scaling law describes in what conditions powders are formed and in what conditions the plasma is powder-free. Second, a semi-empirical model was developed that treats the nano-particle density in the plasma. This model was applied to analytically describe the transition pressure above which nano-particle coagulation takes place as a function of process parameters. The resulting modelled scaling law shows good correspondence with the experimentally found scaling law. Finally, a series of amorphous silicon films was deposited. The reflection–transmission spectra of the films were measured and modelled through Tauc–Lorentz formalism. The optical analysis shows that at around the plasma transition pressure there occurs also a transition in the properties of the deposited material.

Diode laser absorption studies of aluminium atoms produced in a direct current (dc) magnetron discharge with argon as well as argon/nitrogen and argon/oxygen mixtures as working gas are reported. The measured Al atom density increases with increasing discharge power. The observed temperature being in the range of 340–420 K rises with increasing power but shows little pressure dependence. A small admixture of oxygen gas leads to a complete disappearance of the absorption signal, a result which is not yet fully understood.

Nanosize pore arrays, which have been prepared by the self-organization process of aluminium anodic oxidation, were investigated quantitatively using fast Fourier transformation analysis of scanning electron microscopy micrographs. The results show that the temperature influences the pore domain size and the best self-ordering configuration is obtained at an optimum condition of temperature. The largest domain size was observed for samples anodized around 15°C to 17°C, using 0.3 M oxalic acid. It is also found that the optimum temperature for self-organization of pore oxidation changes in accordance with the concentration of electrolyte.

Based on fundamental principles, a model is presented to describe the influence of materials and fusing on the gloss and colour appearance of images formed on printed documents. The diffuse scattering of visible light from rough-image surfaces will be shown to play a dominant role in glossiness. How the rough-image surfaces are formed depends on the rheology and flow of toner particles at different elevated temperatures in a confined environment (fuser nip) for time greater than the coalescence time. A nondimensional time is emerged from the analysis as a critical scaling parameter, which is a function of interfacial energy, dynamic viscosity, dwell time, coalescence time and the correlation length of rough surfaces. The present model helps us to understand the interactions between rough substrate, toner materials and fusing time and temperature.

The micro-properties (structure and composition) and macro-properties (electrical and optical properties) of zinc oxide thin films deposited on glass substrates using a filtered vacuum arc deposition system were investigated as a function of oxygen pressure (0.37–0.5 Pa) and arc current (100–300 A). The films were polycrystalline and the crystal plane orientation varied with the oxygen pressure and arc current, tending to be aligned parallel to the c-axis. The sizes of the crystallite grains were 10–35 nm. The films were found to be compressively stressed, with stress in the range of −2.5–0 GPa. The stress in any sample decreased as a function of arc current; however, its dependence on the pressure also depended on the applied arc current. The compressive stress in samples deposited with arc current in the range 100–150 A, decreased with the pressure from −2.5 to −1.5 GPa (0.37–0.5 Pa), whereas it increased with the oxygen pressure in samples deposited with arc current ranging from 200–300 A. The compressive stress in all samples deposited with the highest oxygen pressure (0.51 Pa) was in a relatively narrow range of −2.1 to −1.7 GPa.

Film composition, determined by x-ray photoelectron spectroscopy, depended weakly on the deposition parameters. All samples had zinc excess, with a typical oxygen to zinc atomic concentration ratio of 0.7–0.8. Film thickness, in the range of 80–780 nm, depended linearly on both the deposition parameters.

The electrical resistivity (ρ) of the films was in the range of (1–5) × 10⁻⁴ Ωm, depending weakly on the deposition parameters. The electrical resistivity of the films with larger grain size was higher than that of films with smaller grains, whereas it increased with film stress. The optical transmission of the films, expressed by the extinction coefficient, depended strongly on both the deposition parameters (arc current and oxygen pressure). The lowest extinction was obtained with films deposited with higher pressure (P ⩽ 0.5 Pa) and lower arc current (I ⩾ 200 A). The lowest extinction coefficient was ∼4 × 10⁻⁴ nm⁻¹ in the visible and the near-IR range of the spectrum. Films with larger grain size and lower stress had a relatively larger extinction coefficient (∼8 × 10⁻³ nm⁻¹).

In this paper, we describe electric field driven self-propulsion of a water droplet on a solid surface using co-planer parallel-strip electrodes fabricated on a substrate and covered by a hydrophobic coating. A water droplet dispensed on the electrodes, ranging from about 1 nl to 1 µl in volume, takes a nearly spherical shape owing to surface tension and wetting conditions. When the electrodes are energized by either dc or low-frequency single-phase ac voltage, elongation due to the electrostatic force occurs, but translational motion is not expected because the electrostatic potential energy is constant regardless of the droplet's position. However, under certain conditions we observe that the droplet starts moving along the electrodes at speeds of as high as 10 cm s⁻¹. The initial direction of the motion is unpredictable, but once started, it persists until the droplet reaches the end of the electrodes or the voltage is turned off. The motion is of a self-propelling nature; the water droplet leaves behind a moisture layer on the substrate surface, which shields the electric field on the droplet's trailing edge, thus producing an imbalance in the Maxwell stress, which leads to the driving force. The motion seems to be most controllable and regular when the droplet is driven at its hydrodynamic resonance. The mechanism is experimentally verified by real-time measurements of the conductance of the moisture layer.

Nanopattering using atomic force microscope (AFM) has become an important area of research, for both fundamental research and future nanodevice applications. Local oxidation of p-GaAs(100) surface by using a negatively biased conductive AFM tip is a universal method for this purpose. The dependences of the height, aspect ratio and volume on applied anodization times and voltages during which the anodization voltage is applied were studied. We explore the kinetics and mechanisms of the anodization process and how factors such as the electric field strength and the relative humidity influence its growth rate and the contribution of ionic diffusion. The results revealed that the protruding oxide dot's height, aspect ratio and volume increase during longer anodization time and at larger anodization voltage as well as in higher relative humidity conditions. The high initial growth rate (∼300 nm s⁻¹ for 10 V) decreases quickly with decreasing electric field strength and the oxide practically ceases to grow at an order of (2–3) × 10⁷ V cm⁻¹. Auger electron spectroscopy measurements confirm that the modified structures take the form of anodized p-GaAs(100). Also, the contribution of ionic diffusion increases by about 80% at a higher relative humidity. In addition, the nanohardness of the oxide structures was measured with the aid of an AFM-based nanoindentation technique.

A new analytical model for the secondary electron (SE) emission yield, δ, is applied to polymers. It involves a parameter k, k = z_C/R, between the most probable energy dissipation depth, z_C, of primary electrons (PE) and their range R, where k ranges from 0.5 and 0.45 for low-density, low atomic-weight materials. Reduced yield curves (RYC), δ/δ_(max) versus , and normal yield curves, δ versus E⁰, obtained from published experimental data on a wide variety of polymers (polystyrene, PET, polyimide; Kapton; PTFE; Teflon, PMMA, nylon, polyurethane) are compared with the calculated change of δ with PE energy, E⁰. In contrast to the use of the conventional constant loss model where the best fit requires an empirical change in the exponent 'n' in the power law expression of the PE range, R versus E⁰, the present approach is based on the usual choice for n, n = 1.35, and on a choice for k governed by physical arguments. This physical basis then enables one to predict the RYC of other polymers. Finally, values of the SE escape probability and SE attenuation length are estimated for the polymers of interest and a new mechanism is suggested for the contrast reversal in scanning electron microscopy.

A recent analytical model for the secondary electron emission yield, δ, is successfully applied here to graphite and some aromatic hydrocarbons (xylene, anthracene, phenanthrene and biphenyl). In contrast to the use of conventional constant loss model, this model takes a more realistic account of the in-depth generation of the secondary electrons and permits a good description of the reduced yield curves, δ/δ_(max) versus E°/E°_(max), via a suitable choice of the most probable energy dissipation depth, z_C, of primary electrons in these low-density, low atomic-weight materials. Physical information on escape probability and on attenuation length of secondary electrons propagating in the investigated specimens is deduced from the good fit between calculated and experimental yield curves, δ = f(E°).

110 nm thick SrTiO_{(3 ± y)}–(SiO₂)_x thin films with x = 0–0.45 were prepared on Pt/Ti/SiO₂/Si substrates using the chemical solution deposition method and then annealed at temperatures ranging from 600°C to 900°C for 1 min. The dielectric and electrical properties of the SrTiO_{(3 ± y)}–(SiO₂)_x were obviously affected by the annealing temperature and composition. The dielectric constant of the thin films increased with increasing annealing temperature and decreased with an increase in Si content while the leakage current density decreased with an increase in Si content. The 700°C annealed SrTiO_{(3 ± y)}–(SiO₂)_x thin film with x = 0.25 has a suitable dielectric constant of 94.8 and a low leakage current of 1.27 × 10⁻⁸ A cm⁻². The time-dependent dielectric breakdown curve of the 700°C and 800°C annealed SrTiO_{(3 ± y)}–(SiO₂)_x films with x = 0.25 have an expected lifetime of over 10 years at electric fields higher than 0.6 MV cm⁻¹.

The dielectric behaviours of numerous specimens near the morphotropic phase boundary (MPB) of the 0.3Pb(Zn_1/3Nb_2/3)O₃–0.7Pb_0.96La_0.04 (Zr_xTi_{1 − x})_0.99O₃ (x = 0.50–0.53) relaxor ferroelectric system were measured. The results revealed that the poled specimens on the rhombohedral side underwent a rhombohedral–tetragonal transition on heating, and the depoled specimens on the tetragonal side experienced a spontaneous relaxor–normal transition on cooling. A phase diagram based on the dielectric permittivity measurements was proposed for this solid solution. The diagram showed that the polarization made the MPB bend sharply towards the rhombohedral-rich region. On the basis of these results in this and previous similar investigations, some common characteristics of complex relaxor ABO₃ perovskite systems near the MPB were proposed.

This paper is devoted to the study of effective electromechanical properties of piezoactive 0–3 composites based on perovskite-type ferroelectric ceramics. A new model of the 0–3 ceramic/polymer composite is proposed for prediction of the effective properties. This model and the related averaging procedure are concerned with taking into account a hierarchy of inclusions in the polymer matrix and an electromechanical interaction among components. Numerical results are presented for the Pb(Zr, Ti)O₃- and (Pb, Ca)TiO₃-based composites to show the effect of different inclusions on the dielectric and piezoelectric properties. It is also shown that analytical predictions of the effective properties of the studied 0–3 composites are in good agreement with existing experimental data in wide concentration ranges.

The method of Greenwood and Williamson is extended to obtain a solution to the coupled non-linear problem of steady-state electrical and thermal conduction across a crack in a conductive layer, for which the electrical resistivity and thermal conductivity are functions of temperature. The problem can be decomposed into the solution of a pair of non-linear algebraic equations involving boundary values and material properties. The new mixed-boundary value problem given from the thermal and electrical boundary conditions for the crack in the conductive layer is reduced in order to solve a singular integral equation of the first kind, the solution of which can be expressed in terms of the product of a series of the Chebyshev polynomials and their weight function. The non-existence of the solution for an infinite conductor in electrical and thermal conduction is shown. Numerical results are given showing the temperature field around the crack.

In this paper we report the rapid synthesis of Se–Te based chalcogenide glasses through microwave irradiation without the help of metal powders. Mixtures of chalcogens can be made to couple to microwaves when at least one constituent of the mixture has a relatively higher electrical conductivity. Also, this constituent has to be in powder form. The glasses thus prepared have been characterized by thermal analysis and x-ray analysis, and it has been confirmed that the T_g values of our samples are comparable to the already reported T_g values for samples prepared by conventional methods. Thus, this type of rapid synthesis may replace the prolonged conventional procedures for synthesis of these glasses.

Electrical transport and low field magnetoresistance (MR) are reported in the La_2/3Ca_1/3Mn_1−xO₃ (x = 0–0.16) samples, which are prepared by the sol–gel method followed by a sintering treatment at 1100°C. Experimental results show, for x = 0.06, an MR platform is observed in a temperature ∼200 K under the magnetic field of 0.5 T. With an increase in x, the MR effect gets augmented. For the sample with x = 0.16, its MR peak is as high as 50%.

For most metals, evaporation owing to electron beam heating proceeds in an efficient manner at temperatures substantially higher than the melting point. This is particularly true for aluminium, which has a large separation of melting and boiling point (>1000 K). This leads to situations where convective heat transfer plays an increasingly dominant role with increase in incident e-beam power and puts a limit on the surface temperature (and consequently the atomic flux). To mitigate this heat drain, a porous tantalum rod (∼35% porosity) was placed at the point of e-beam impact to act as a convection arrestor and a wick within the aluminium melt pool. The molten aluminium around the porous rod was found to ooze through the capillaries of the porous rod to emerge as a vapour stream. On measuring the atomic flux and surface temperature at e-beam powers (below a value where tantalum softens), it was found that ∼50% higher temperature was reached with the tantalum rod than without it. Also, for generating the same atomic flux, the required e-beam power in the case of the porous rod was about one-sixth of the e-beam power required without the rod. Such an efficient evaporation has been reported earlier but without any qualification on the ion fraction of the vapour stream. In our experiment, the ion content in the vapour stream was measured. It was found that the ionization yield in the case of the porous rod was about five times the yield without the rod. Estimation of ionization yields owing to various processes led to the conclusion that higher ionization in the case of the porous rod can be attributed to a higher emission of secondary electrons from the porous rod causing enhanced electron impact ionization.

The intensities of single bubble sonoluminescence at several ambient temperatures are computed, based on three well-known light emission mechanisms, namely, electron–neutral-atom bremsstrahlung, electron–ion bremsstrahlung and recombination radiation using a spatially uniform pressure approximation. These computed values are much smaller than the experimental data obtained by Vazquez and Putterman in 2000. The theoretical results concluded in this paper are also compared with those obtained by some previous researchers and the accuracy of the uniform-pressure approximation is then discussed. It is concluded that the three light emission mechanisms are insufficient in providing the experimentally observed light intensities.