Table of contents

The effect of substituting Sr for Ba on the magneto-transport and magnetic properties of the (La_2/3Sm_1/3)_0.67Ba_0.33MnO₃ system has been investigated. The samples of (La_2/3Sm_1/3)_0.67Ba_0.33−xSr_xMnO₃ (x = 0.0, 0.1, 0.2 and 0.33) are synthesized by the citrate gel route and crystallize in an orthorhombic structure. The unit cell volume decreases while the metal–insulator transition temperature (T_MI) increases with increasing Sr content. The atomic disorder, which is represented by the size variance, increases with Ba content. The small anomaly in ρ(T) due to the atomic disorder which leads to the different magnetic ordering followed by a broad metal–insulator transition is observed in Ba-rich systems. The peak at T^* (small anomaly) is presumed to be due to spin-dependent interfacial tunnelling that causes the difference in magnetic order between the surface and the core. The suppression in the resistivity values with increasing Sr content could be due to the more symmetric MnO₆ octahedra network. The paramagnetic phase coexists with the magnetically ordered phase between T^* (∼T_C) and T_MI. The suppression of the metastable magnetic phase leads to the high magnetoresistance in Ba-rich samples. The transport data has been analysed using a small polaron correlated model. The magnetic behaviour may be understood by the Ising model. The overall magnetic behaviour could be accounted for by the competing antiferromagnetic and ferromagnetic interactions.

This work presents simulation results for the behaviour of different particles in a new magnetic-classifier (MAGCLA™), which is capable of separating and classifying particles according to their magnetic susceptibilities. In a previous article the results for a blank simulation were reported. In this paper the blank simulation is compared with the results obtained for the variation of two of the main processing variables: friction coefficient, μ, and the radius of the particles, r_part, in the outcome results.

Polycrystalline samples of sodium doped lanthanum manganites of the type La_1−yNa_yMnO₃ (0 < y ⩽ 0.15) having nanometric crystallite size have been prepared by microwave processing. The Curie temperature T_C of the prepared pellets is strongly dependent on the sodium content in the compound and ranges between 196 and 312 K. A detailed structural analysis has been performed on the prepared samples using the Rietveld FULLPROF program and important structural parameters are estimated. Close to T_C, a significant change in magnetic entropy has been observed in all the studied samples. The maximum entropy change at 0.8 T field (µ₀H) for the La_0.90Na_0.10MnO₃ compound shows an enhancement by ∼158% over that measured for a sample with Na content of 0.05 and is ∼67% of that known for the prototype magnetic refrigerant (pure Gd). The maximum adiabatic temperature change (ΔT_ad) is estimated to be ∼2 K. The temperature dependence of the magnetic entropy change for La_1−yNa_yMnO₃ compounds, measured under various magnetic fields, could be explained fairly well by including the contributions from the magnetoelastic and electron interaction in the expression for the Landau theory of phase transition.

A group of elastically coupled ferroelectric and ferrite composites with the general formula (x)BaTiO₃ + (1−x)Ni_0.94Co_0.01Cu_0.05Fe₂ O₄ (where x = 0.85, 0.70 and 0.55) was prepared by the standard ceramic reaction method. The x-ray diffraction pattern of the composite reveals a spinel phase formation for the ferrite and perovskite phase formation for the ferroelectric phase without any other phase. The SEM micrographs were taken to determine the average grain size. The sintered composites exhibit typical hysteresis loops at room temperature. The effect of constituent phase variation on the hysteresis behaviour and the dielectric properties was examined. The parameters such as spontaneous polarization (P_s), breakdown voltage (E_b) and saturation magnetization (M_s) of the composites vary with the ferroelectric/ferrite content. The temperature dependence of dielectric behaviour at a frequency of 1 kHz was also studied. With increasing content of BaTiO₃, the dielectric constant increases and the Curie temperature decreases.

We report a study of the magnetocaloric effect in the ternary alloy system Ni₅₀Mn₃₄In₁₆. This system undergoes an austenite–martensite phase transition, and the change in magnetic entropy is found to be quite large across this martensitic transition. This entropy change is due to an increase in entropy induced by the application of an external magnetic field and can lead to a large inverse magnetocaloric effect. Isothermal magnetic field variation of magnetization exhibits field hysteresis in Ni₅₀Mn₃₄In₁₆ across the martensitic transition. But in spite of the hysteresis losses, a large effective refrigerant capacity can be obtained in this material over a wide temperature interval.

This is the first of two linked papers on the analysis of time-resolved optically stimulated luminescence. This paper focusses on a theoretical basis of analytical methods and on methods for interpretation of time-resolved luminescence spectra and calculation of luminescence throughput. Using a comparative analysis of the principal features of time-resolved luminescence and relevant analogues from steady state optical stimulation, formulae for configuring a measurement system for optimum performance are presented. We also examine the possible use of stretched-exponential functions for analysis of time-resolved optically stimulated luminescence spectra.

This is the second in a set of paired papers on the analysis of time-resolved optically stimulated luminescence. This paper compares experimental results and computer simulations with corresponding conceptual models discussed in the first of this set of papers. The evaluation of principal and subsidiary luminescence lifetimes from time-resolved luminescence spectra measured during or after pulsed optical stimulation is illustrated using suitable analogues of exponential functions developed in the preceding paper. Various methods for calculating the activation energies for thermal quenching, thermal assistance and the frequency factor for the thermal quenching process using the temperature dependence of both luminescence lifetimes and luminescence intensity are described, as are techniques for dealing with cases not easily described by the standard Mott–Seitz model of luminescence. The paper then compares continuous and time-resolved optical stimulation methods, where it is shown that, dependent on suitable selection of the pulse-width, stimulation and measurement time, pulsing the stimulation light might give better accuracy in the determination of the luminescence.

Metallic nano-particles embedded in silicon dioxide have optical properties that are of interest for their possible technological applications in the near future. These properties have been found to depend on their size and shape as well as on their surroundings. In this paper we investigate the effect of 308 nm excimer laser irradiation on silver and gold nano-particles embedded in high quality synthetic silica produced by 2 MeV ion-beam implantation followed by a thermal annealing. Laser irradiation induces nano-particle dissolution and diffusion to the surface and eventually loss of the metal accompanied by ablation of the surface. We show by numerical solution of the heat conduction equation that the process can be understood by considering that the nano-particles are responsible for the laser absorption and that nano-particles dissolution, and subsequent diffusion to the surface, take place when the nano-particles melting temperature is reached.

We report conjugated dendrimers that can be used to fabricate efficient (≤1.0 lm W⁻¹ at ∼100 cd m⁻²) deep-blue emission (1931 CIE (x, y) = (0.15, 0.10)) and high luminance (≤6000 cd m⁻²) organic light emitting diodes (OLEDs). Slab waveguide structures of these materials show low amplified spontaneous emission (ASE) thresholds (≥50 nJ for 390 nm, 10 ns, 10 Hz, pulsed excitation). In addition, we report OLEDs based on binary blends of the dendrimers with the green light emitting polymer poly(9, 9-dioctylfluorene-co-benzothiadiazole): these have low turn on voltages (≥2.2 V) and produce high efficiency (18.2 lm W⁻¹ at ∼100 cd m⁻²) green electroluminescence.

Ho³⁺-doped SrWO₄ crystal was grown by the Czochralski method. The polarized absorption and emission spectra together with the fluorescent decay curve were measured at room temperature. The intensity parameters, radiative lifetimes and branching ratios were calculated based on the Judd–Ofelt theory. The stimulated emission cross-sections of the potential laser transitions were determined using the reciprocity method.

Vertically aligned zinc oxide nanorod arrays were grown directly using a zinc foil as both source and substrate in pure water at low temperature by a simple hydrothermal reaction. The morphology and crystal structure of the ZnO nanorod arrays were examined by scanning electron microscopy, transmission electron microscopy and x-ray diffraction, respectively. The nanorods grew along the [0 0 0 1] direction and were 80 nm in diameter and almost 2 µm in length. Directly employing the zinc foil substrate as cathode, the field emission (FE) of the ZnO nanorods presented a two-stage slope behaviour in a ln(J/E²)–1/E plot according to the Fowler–Nordheim equation. The FE behaviour was investigated by considering the action of the defects in ZnO nanorods based on the measurement of the photoluminescence.

Novel phosphors of Eu³⁺, Tb³⁺ and Tm³⁺ doped CaZr(PO₄)₂ were synthesized by solid-state reactions and their x-ray and vacuum ultraviolet–ultraviolet (VUV–UV) spectroscopic properties were investigated. The bands near 147 or 185 nm in the VUV excitation spectra of those doped samples are attributed to the PO₄ absorption and O to Zr charge transfer transition in the host. The excitation and emission spectra indicate that the phosphors can be effectively excited by x-ray or 147 nm and 172 nm and exhibit a satisfactory red, green and blue light performance, respectively. Considering the high luminescent intensity, excellent colour purity and chemical stability, CaZr(PO₄)₂:RE (RE = Eu³⁺ Tb³⁺, Tm³⁺) are attractive red, green and blue emitting x-ray and plasma display panel phosphors.

Organic quantum well structure-like (OQWSL) samples and double-layer structure (DLS) samples were prepared, which consisted of alternate 2-(4-biphenylyl)-5(4-tert-butyl-phenyl)-1,3,4-oxadiazole (PBD) and tris(8-hydroxyquinoline) aluminium (Alq₃). In the case of OQWSL, the distance between the potential barrier material and the potential well material becomes shorter, so the energy transfer from PBD to Alq₃ is increased. We investigate the energy transfer in OQWSL with different periods. This energy transfer goes to saturation when the period number is 4, which indicates that there is an optimal period number for the energy transfer efficiency. The effective distance of energy transfer from PBD to Alq₃ could be estimated.

This paper is aimed at assessing analytically the dc corona induced pressures in wire-cylinder and wire-plate electrostatic precipitator configurations. This calls for solving the equations describing the corona discharge and the force balance for static gas equilibrium provided that the corona onset voltage and the space-charge-free field values are calculable. The calculated pressure and potential distributions along the gap axis in air and nitrogen at atmospheric pressure agreed well with those measured previously. The calculated corona current density values agreed reasonably with those measured for a high-temperature high-pressure wire-cylinder precipitator. The analytically calculated positive and negative dc corona onset voltages for wire-duct precipitators following proposed criteria based on discharge physics are in good agreement with those measured experimentally at atmospheric and lower pressures.

We present results on the development of hydrophobic coatings on polymers in an atmospheric pressure dielectric barrier discharge (DBD). The effects of X + N₂ DBD are studied, where X refers to chlorine- and/or fluorine- containing precursors, aiming at surface modification with chemically bound halogen-bearing entities. The discharge parameters and the treatment conditions were optimized, both in terms of diminution of the oxygen level in the reactor and efficient creation of X + N₂ environments. Surface analysis and characterization were performed using x-ray photoelectron spectroscopy, contact angle measurement and scanning electron microscopy. The deposition of stable hydrophobic coatings, with a complex structure due to polymerization and cross-linking, with contributions from both halogen species, fluorine and chlorine, is demonstrated.

The dc electrical breakdown of long vapour bubbles in capillaries generated by external heating of the capillary is studied. The fluid columns in the capillary on both sides of the vapour bubble serve as electrodes for the electrical discharges inside the bubble. When a dc voltage is applied across a static vapour bubble, a self-pulsing corona regime is observed, which is followed by a transient spark. The sparking or breakdown voltage of the vapour bubble decreases with increasing conductivity of the NaCl solution. After the transient spark a constricted glow-like discharge is observed in the bubble whilst the bubble expands due to the energy deposition of the discharge. Electrical and optical emission properties of the corona, spark and glow-like regime are discussed.

The cathode erosion rate, arc root velocity and output power of a well-type cathode (WTC), non-transferred plasma torch operating in air are studied experimentally in this paper. An external solenoid to generate a magnetically driven arc and a circular swirler to produce a vortex flow structure are equipped in the studied torch system, which is designed to reduce the erosion rate at the cathode. A least square technique is applied to correlate the system parameters, i.e. current, axial magnetic field and mass flow rate, with the cathode erosion rate, arc root velocity and system power output. In the studied WTC torch system, the cathode erosion has a major thermal erosion component and a minor component due to the ion-bombardment effect. The cathode erosion increases with the increase of current due to the enhancement in both Joule heating and ion bombardment. The axial magnetic field can significantly reduce the cathode erosion by reducing the thermal loading of cathode materials at the arc root and improving the heat transfer to gas near the cathode. But, the rise in the mass flow rate leads to the deterioration of erosion, since the ion-bombardment effect prevails over the convective cooling at the cathode. The most dominant system parameter to influence the arc root velocity is the axial magnetic field, which is mainly contributed to the magnetic force driving the arc. The growth in current has a negative impact on increasing the arc root velocity, because the friction force acting at the spot due to a severe molten condition becomes the dominant component counteracting the magnetic force. The mass flow rate also suppresses the arc root velocity, as a result of which the arc root moves in the direction against that of the swirled working gas. All system parameters such as current, magnetic field and gas flow rate increase with the increase in the torch output power. The experimental evidences suggest that the axial magnetic field is the most important parameter to operate the straight-polarity WTC plasma torch at high output power with a limited cathode erosion rate. This emphasizes the importance of an external magnetic field on a WTC torch system for reducing the erosion at the cathode.

A pseudospark (PS) discharge has been shown to be a promising source of high brightness, high intensity electron beam pulses. A PS-sourced electron beam has two phases, an initial hollow cathode phase (HCP) beam followed by a conductive phase (CP) beam. In our experiments, a 22 kV, 50 A HCP beam of brightness 10^9–10 A m⁻² rad⁻² followed by a 200 V, 200 A CP beam of brightness 10^11–12 A m⁻² rad⁻² were measured. Experiments have been conducted with the application of a HCP beam in a Cherenkov interaction with no input seed wave and with post-acceleration of the CP beam. In this paper, a new Cherenkov interaction experiment with an input seed wave from a 20 kW, 35 GHz pulsed magnetron has been designed using the same PS HCP beam. Simulation results of the interaction will be presented and further PS electron beam applications will be discussed.

Using an analytical model, the effect of reactive ion implantation on the state of the target surface during magnetron sputtering is studied. To describe the substrate condition during reactive sputter deposition, the model uses the well-known Berg model approach. However, the target condition is modelled differently, i.e. besides chemisorption the model includes reactive ion implantation. To test this latter modification, the simulation results are compared with the results of oblique reactive ion beam experiments. The good agreement forms the basis of using the model for reactive magnetron sputtering. It is shown that the well-known hysteresis behaviour of the deposition parameters can be described. Although at first sight the model is comparable to other models, it is shown that the kinetics are clearly different. A good description of the kinetics during reactive magnetron sputtering is essential to model, for example, the reactive sputter process using a rotating cylindrical magnetron.

A two-temperature, axi-symmetric, chemical non-equilibrium model has been developed for an oxygen-plasma cutting torch in two dimensions to obtain distributions of different plasma quantities inside the torch. Apart from mass, momentum and potential conservation equations, separate energy balance equations are considered for electrons and heavy particles. The κ–ε model has been used to account for turbulence. Non-equilibrium properties required for fluid dynamic simulations are obtained from a non-equilibrium property code that includes chemical non-equilibrium. The results show distributions of temperature, velocity, pressure, potential, current density and different species densities inside the plasma torch for an arc current of 200 A. Plasma pressure inside the torch varies from several atmospheres to near-atmospheric pressure. It has been observed that the electron and the heavy particle temperatures differ less near the axis of the torch and appreciably near the wall. Interesting features, observed for other investigated quantities, found consistent with the recent experimental observations are discussed.

This paper (paper I) presents the first part of results obtained with the PF-1000 facility for the first time at its upper energy limit (≈1 MJ). Special attention is paid here to plasma ('pinch') dynamics, which was investigated in relation to its electro-technical and radiation (especially neutron) characteristics with the help of a number of diagnostics, both time-integrated and with nanosecond temporal resolution. In these methods we utilized a Rogowski coil for the routine electro-technical measurements, visual multi-frame and streak cameras, soft x-ray pin-hole multi-frame cameras, PIN-diode assembly and PM tubes with scintillators for soft and hard x-rays as well as for neutron investigations together with a set of activation counters. In particular, the temporal cross correlation of different phenomena taking place during the discharge was investigated. The pinch's longevity appears to be 10–15 times larger than the ideal magnetohydrodynamic growth time (ratio of the pinch radius to the ion thermal velocity). It is demonstrated how the 'target' dynamics (pinch plasma of the dense plasma focus (DPF)) depends on and may be controlled by the electrode's size and the geometry of the chamber in this large-scale device. Diffraction of a shock wave together with a current sheath on an obstacle made at the DPF anode cap opens an opportunity for an inertial electrode to be used in future at larger DPF devices.

A large volume post-discharge reactor placed downstream from a flowing N₂–O₂ microwave discharge is modelled using a three-dimensional hydrodynamic model. The density distributions of the most populated active species present in the reactor—O(³P), O₂(a ¹ Δ_g), , NO(X ² Π), NO(A ² Σ⁺), NO(B ² Π), NO₂(X), O₃, and N(⁴S)—are calculated and the main source and loss processes for each species are identified for two discharge conditions: (i) p = 2 Torr, f = 2450 MHz, and (ii) p = 8 Torr, f = 915 MHz; in the case of a N₂–2%O₂ mixture composition and gas flow rate of 2 × 10³ sccm. The modification of the species relative densities by changing the oxygen percentage in the initial gas mixture composition, in the 0.2%–5% range, are presented. The possible tuning of the species concentrations in the reactor by changing the size of the connecting afterglow tube between the active discharge and the large post-discharge reactor is investigated as well.

The plasma cladding waveguide, which is a cylindrical dielectric core surrounded by a plasma cladding, is developed, and the guided modes and their characteristics of this waveguide are displayed through the present detailed theoretical research. The conditions of the single mode existing in the plasma cladding waveguide have been given, and the defined forbidden gap of frequency is discussed. It is found that the usage characteristics of the plasma cladding waveguide vary strongly with plasma frequency, and changing the plasma parameters can control the propagation mode. This paper focuses on exhibiting the basic characteristics and the potential applications of this new type of waveguide.

Numerical simulation of a high-pressure arc discharge has been performed with a self-consistent modelling of most of the components, including the electrodes, and the interactions between them. In particular, the arc column and the cathodic part of the discharge are simulated by means of a two-temperature hydrodynamic model and of a model of nonlinear surface heating, respectively. Simulation results are given for a free-burning arc in atmospheric-pressure argon in the range of arc currents from 10 to 200 A. It is found that the electric power deposited into the near-cathode layer is transported not only to the cathode but also to the arc column, an effect that cannot be described by the local thermodynamic equilibrium (LTE) model. The electron enthalpy transport substantially exceeds the net contribution of thermal conduction by the electrons and heavy particles and is thus the dominating mechanism of energy transfer from the near-cathode layer to the arc column. The predicted gas temperatures along the arc axis in the arc column using the LTE model are much higher than the calculated electron and heavy-particle temperatures (∼1000–2000 K or higher) under the same operation conditions using the non-equilibrium model with the consideration of the near-cathode sheath for the cases studied in the present paper. Studies on the influences of the cathode shapes and metal vapour contaminations on the arc characteristics will be conducted in future work.

The kinetics of destruction of C₂H₂ is investigated in a low pressure pulsed dc discharge in dry air. Tuneable diode laser absorption spectroscopy in the mid-infrared region (1350 cm⁻¹) has been used to measure the influence of (i) the pulse duration, (ii) the pulse repetition rate and (iii) the pulse current on the C₂H₂ concentration in situ the discharge tube. First, it is shown that in the plasma region under flow conditions the time averaged concentration of C₂H₂ depends only on the time averaged discharge current. Second, time resolved measurements have been performed in a closed reactor, i.e. under static conditions. A simple kinetic modelling of the pulsed discharge leads to a good agreement with the experimental results and shows that the oxidation rate of C₂H₂ is mainly controlled by the time averaged concentration of O atoms. Finally, the influence of porous TiO₂ photocatalyst on the C₂H₂ oxidation rate is reported.

Pulsed laser probing using Moiré deflectometry and Normaski interferometry was performed simultaneously to diagnose the electron density in a wire z-pinch plasma. The Moiré deflectometer has a higher sensitivity while the Nomarski interferometer is able to probe higher densities. The advantages of each technique permitted us to measure a wider range of densities. This includes the low-density coronal plasma with density of an order of magnitude lower (10¹⁶ cm⁻³) than that which can be measured by interferometry. Furthermore, our optical probing presents a low response to mechanical vibrations as it is not necessary to use a separate reference beam as in a Mach–Zehnder interferometer. The experiments were performed on a 160 kA current generator at Imperial College, London, for three different discharge configurations in order to study the initial resistive heating stage of the wire z-pinch.

A millimetre wave antenna array, mounted on a space vehicle re-entering the Earth's atmosphere, encounters a high density plasma around it. At high antenna power, the millimetre wave field heats the electrons nonuniformly. The electron temperature, T_e, follows the antenna pattern, being maximum along the direction of the principal maximum (z-axis) and falling off rapidly across it. The ambipolar plasma diffusion under the pressure gradient force creates a refractive index profile with maximum on the z-axis, leading to self-convergence of the millimetre wave and enhancement in the effective gain of the antenna.

Using a carefully constructed magnetic probe (a B-dot probe) the spatial and temporal evolution of the perturbation in the magnetic field ΔB in an unbalanced pulsed dc magnetron has been determined. The plasma was run in argon at a pressure of 0.74 Pa and the plasma ions sputtered a pure graphite target. The pulse frequency and duty were set at 100 kHz and 55%, respectively. From the ΔB measurements (measured with magnitudes up to about 0.01 mT) the axial, azimuthal and radial components of the total current density j in the plasma bulk were determined. In the plasma 'on' phase, the axial current density j_z has a maximum value of approximately 200 A m⁻² above the racetrack region, while high values in the azimuthal current density j_Φ are distributed in a region from 1 to 3 cm into the bulk plasma with j_Φ exceeding 350 A m⁻².

In the 'off' phase of the plasma, j_z decays almost instantaneously (at least within the 100 ns time-resolution of the ΔB measurements) as the electric field collapses; however, j_Φ decays with a characteristic time constant of about 1 µs. This slow decay can be attributed to the presence of decaying Grad-B and curvature drifts, with their rates controlled by the decay in the plasma density. A comparison between axial and azimuthal current densities in the plasma 'on' time, when the plasma is being driven, strongly indicates that classical transport does not operate in the magnetron discharge.

In this paper, a microscopic approach for the calculation of partial and total power dissipation from energy losses by collisions is considered and applied in the case of N₂O low pressure RF discharges. This approach is based on a Monte Carlo technique in a particle model permitting sampling of the energy deposited by different inelastic electron–N₂O collisions. The calculated power densities presented in this paper are in good agreement with the experimental results and those obtained by the classical macroscopic formula based on spatio-temporal integration of the product of current density and electrical field. This microscopic approach presents, however, a major advantage in comparison with the classical method (which only offers the possibility to calculate the global power dissipation) by making possible the calculation of all the power density terms, thereby permitting one to examine the relative contribution of each collision process in the power dissipation. Its application to N₂O electronegative discharges, at 503 K gas temperature, several RF voltages and two different gas pressures shows how the power is dissipated through electron–gas processes. The power density variation is found to be proportional to the electron density variation brought about by the changes in attachment (i.e. e + N₂O → N₂ + O⁻), detachment (i.e. NO⁻ + N₂O → NO + N₂O + e) and ionization (i.e. e + N₂ O → N₂O⁺ + 2e) processes. The role of each of these processes is fully studied with our particle model in order to explain the dissipated power variation.

Profiling the arc channel of a cascaded arc into an hourglass-like shape results in an extremely high light output intensity (3.5 × 10¹² Wm⁻² m⁻¹ sr⁻¹ in the near-infrared) at an input power of 2.2 kW, a good stability (better than 5 × 10⁻⁴) and a small solid angle of the emitted light beam (Ω = 0.015 sr). These optical properties are advantageous for spectroscopic applications that require a high light intensity over a broad wavelength range in a small solid angle. The absolute light output is measured and is compared with a fast and flexible modelling scheme. These simulations are used to verify the arc performance and to guide arc design. The calculated emitted radiance at moderate arc input power agrees with the experiments within 30% for moderate input power.

Two multilayer antireflection (AR) coating configurations are designed, prepared and characterized. These AR coatings are designed for a 1 mm thick Ge optical window in the 3.25–5.25 µm band. Ta₂O₅ and TiO₂ are used as high index materials along with SiO₂ as low index material. Configuration 1 comprises nine alternating layers of SiO₂ and Ta₂O₅, whereas configuration 2 comprises seven alternating layers of SiO₂ and TiO₂. Post-deposition annealing is also carried out in the temperature range 150–450 °C for 10 h. The prepared multilayered structures are characterized optically and structurally using a spectrophotometer, an atomic force microscope, x-ray diffraction and a scanning electron microscope. Optical characterization shows that multilayered structures have high absorption for as-deposited samples. A considerable improvement in the transmission profiles for the two multilayered configurations is observed at 350 °C with peak and average transmission for both the configurations exceeding 90%. The as-prepared samples show predominantly amorphous-like structure with pronounced peaks for configuration 2 only. Delamination (for configuration 1) and cracking (for configuration 2) of the multilayered structures are witnessed at an annealing temperature of 450 °C.

Formation of aerosol nanoparticles as well as carbon nanotubes and nanofilaments is studied during co-pyrolysis of iron pentacarbonyl and propane with argon as a carrier gas in a flow reactor. Gaseous intermediates from propane thermal decomposition (CH₄, C₂H₆ and C₃H₄) and Fe(CO)₅ conversion are monitored by gas chromatography and IR-spectroscopy, respectively. The aerosol morphology is studied by transmission electron microscopy (TEM) and high resolution TEM. The aerosol particle concentration and size distribution are measured by an automated diffusion battery. The crystal phase composition of particles is studied by x-ray diffractometry. The decomposition of the Fe(CO)₅ + Ar mixture resulted in an iron aggregate formation composed of fine primary particles. In the case of lower pyrolysis temperatures, about 450 K, the primary particle mean diameter is about 10 nm, and consequently, the majority of the primary particles are superparamagnetic, thus forming compact aggregates. At intermediate pyrolysis temperatures in the range 800–1040 K the primary particle diameter is about 20–30 nm, and most of the particles are ferromagnetic in nature. The coagulation of these particles results in a chain-like aggregate formation. Finally, at temperatures higher than the Curie point (1043 K) the ferromagnetic properties vanish and the formation of compact aggregates is observed again. The co-pyrolysis of Fe(CO)₅ and C₃H₈ mixed with Ar carrier gas resulted in aerosol aggregate structures dramatically different from those formed by iron pentacarbonyl pyrolysis. In particular, in the temperature range 1070–1280 K, we observed Fe₃C particles connected by long carbon nanotubes (CNTs). The aggregate morphology is described in terms of a fractal-like dimension D_f, which is determined from TEM images on the basis of a scaling power law linking the aggregate mass (M) and radius (R), . The Fe₃C–CNT aggregate morphology is a function of the inlet ratio between propane and iron pentacarbonyl concentrations [C₃H₈]₀/[Fe(CO)₅]₀. At the low ratio of [C₃H₈]₀/[Fe(CO)₅]₀ < 80 the fractal dimension of aggregates decreases (from 1.7 down to about 1) with the increasing ratio of inlet concentrations. This effect, as observed by TEM, is due to the increase in the mean nanotube length. Vice versa, in the range C₃H₈]₀/[Fe(CO)₅]₀ > 80 the fractal aggregate dimension is higher for a larger ratio of [C₃H₈]₀/[Fe(CO)₅]₀, which is explained by the larger thickness of growing nanotubes obtained for a relatively large propane concentration. The aggregate formation mechanism includes consecutive stages of iron aggregate formation due to Fe(CO)₅ decomposition, carbon deposition on iron particles from C₃H₈ pyrolysis intermediates, carbon dissolution in iron particles, nanotube nucleation at the carbon concentration of about 60 at.% in Fe–C solution and disruption of the Fe–C aggregates into small pieces by the growing nanotubes.

Carbon nanostructures were synthesized by energetic ion irradiation of Si-based gel films. These polymer-like films with different side groups and C concentrations were prepared by sol–gel chemistry and irradiated with Si or Au ions of different energies in the range 3 MeV–2 GeV. The shape and size of the formed carbon nanostructures was studied by energy filtered transmission electron microscopy. They exhibited a visible photoluminescence emission, due to their semiconducting nature and the confinement of excitons. The changes in the optical properties were correlated with the structural transformation of films, investigated by means of Fourier transformed infrared (FTIR) and Raman spectroscopies. The role of carbon concentration, structure and energy transferred by ions on the luminescence properties are discussed.

WO₃–SiO₂ compound thin films were deposited on glass substrates using the sol–gel method, and then all the samples were dried at 100 °C and annealed at 400 °C in air. The effect of WO₃ concentration on the hydrophilicity of WO₃–SiO₂ compound films was studied for the first time and it was shown that the films containing 85 mol% of the concentration possessed a superhydrophilic surface without UV or visible irradiation. Optical properties of the films such as transmittance, reflectance and bandgap energy were investigated using a UV–visible spectrophotometer. According to atomic force microscopy, the surface ratio was maximized in 85 mol% concentration of WO₃ similar to hydrophilicity. Surface chemical states of the films were studied by x-ray photoelectron spectroscopy, which determined the stoichiometry of the deposited thin films. X-ray diffraction patterns showed that the compound thin films constituted of nanocrystalline tungsten oxide grains with 60–10 nm grain size depending on the WO₃ concentration.

Welding laser modelling requires knowledge about relative changes of many thermo-physical parameters involved in the interaction. The absorptivity of the material is one of the most important. In this study, experimental measurements of absorptivity with an integrating sphere on two alloys (aluminium and magnesium) were made. These results were compared with an analytical calculation that takes into account the trapping of the beam by multiple reflections inside the keyhole. Based on a statistical method, an empirical law is proposed connecting absorptivity with the peak power of the laser and the duration of interaction. During the interaction, two distinct phenomenologies are brought to light. A threshold is then defined after which the physical process becomes stable. Below this threshold, the measurement of absorptivity is problematic, and the values are widely dispersed.

We demonstrate a new nano-processing technique using the near- electromagnetic field around a small transparent particle irradiated by an 820 nm femtosecond laser pulse. We fabricate a 2D nanohole array with negative and positive patterns on a soda lime glass surface by irradiating a monolayer of 790 nm diameter polystyrene (PS) particles, arranged in a close-packed hexagonal lattice, with a femtosecond laser pulse. At the lower laser fluence domain, PS particles act as focusing lenses and/or near-field enhancers due to Mie scattering; it enables nanohole processing just under the particle (positive patterning). Nanoholes with diameters ranging from 84 to 170 nm are fabricated in this regime. At the higher fluence domain, the PS particle acts as a mask; while the positive nanohole formation disappears, then it enables nano-patterning of the surface in gap areas corresponding to the region between particles (negative patterning). Nanoholes with diameters ranging from 65 to 110 nm are fabricated in this case. The switching of negative and positive nano-patterning by simply controlling the incident laser fluence is experimentally demonstrated for the first time to our knowledge. A simple theoretical explanation for the switching of the positive and negative patterning is presented by FDTD simulation of the near-field distribution.

In this work TiO_x (x > 1.8) films are grown reactively from a ceramic TiO_1.8 target employing high power pulsed magnetron sputtering (HPPMS) at a constant average target current. The effect of the pulse on/off time configuration on the target and the discharge characteristics as well as on the film properties is investigated. The target voltage (V_T) increases from 480 to 650 V and the peak target current (I_Tp) increases from 2 to 40 A when the pulse off-time is increased from 200 to 2450 µs, while the on-time is kept constant at 50 µs. This is accompanied by an increase in the number of Ti atoms sputtered from the target, as manifested by time-resolved optical emission spectroscopy (OES) measurements. OES also manifests an increase in the ionization of the sputtered Ti atoms with increasing I_Tp. The above changes in the target and discharge characteristics affect the deposition rate so that the latter increases with increasing I_Tp up to a value of 14 A, above which the deposition rate drops. In all the cases the deposition rates are up to ∼40% higher compared to the rates achieved for films grown by dc magnetron sputtering (dcMS) which are also studied for reference. The increase in I_Tp from 2 to 40 A also affects the films' properties. It is shown that a drop in the surface roughness from 1.1 to 0.5 nm takes place. These values are lower than the surface roughness of films grown by dcMS (1.35 nm). Moreover, films grown by HPPMS are found to have higher densities (up to 3.83 g cm⁻³) and higher refractive indices (up to 2.48) in comparison to the films grown by dcMS (3.71 g cm⁻³ and 2.38, respectively).

A thin film of the ternary chalcogenide glassy alloy (As₂Se₃)₉₀Ge₁₀ has been deposited on a glass substrate by the thermal evaporation technique under vacuum. The optical parameters, refractive index (n) and extinction coefficient (k), have been calculated in the wavelength range 400–1500 nm by analysing the transmission spectrum. The dispersion of the refractive index is described in terms of a Wemple–DiDomenico single oscillator model. The value of the static refractive index has been found to be 2.518. The optical absorption edge is described using a non-direct transition model proposed by Tauc and the optical band gap calculated by Tauc's extrapolation is 1.58 ± 0.01 eV. The dielectric properties and optical conductivity has also been calculated.

Optical emission spectroscopy and Rutherford backscattering spectrometry are combined to determine condensation coefficients for plasma sputtering deposition. The method is applied for palladium deposition onto various substrates and condensation coefficients are found to lie between 0.4 and 0.9.

Electron probe microanalysis (EPMA) of stratified specimens has been intensively developed during the last few decades. Several quantification models (PAP, XPP, X-PHI) have led to many commercial software packages being widely used. However, all these software packages require an accurate description of the analysed sample because they are all based on the fundamental assumption that each layer of the sample is uniform in its structure and its composition. This is useful in the case of local analysis but may be problematic in the case of quantitative scanlines or quantitative maps. Indeed, a sample may not be homogeneous in all the analysed areas; this could lead to variations in the detected x-ray intensities and as a consequence to wrong results.

Therefore, efforts have been carried out to analyse thin films on heterogeneous substrates. A method based on the measurement of the backscattering coefficient during x-ray microanalysis was developed in our laboratory. This method, called 'Auger formalism', gave good results in the case of thickness determination of pure coating on heterogeneous substrates and was also successfully applied in the case of multi-elements coating for concentration determination. However, in the case of concentration determination, this method requires knowledge of the film thickness. Thus, the aim of this work is to develop a new quantification procedure which is based on the same approach as previously adopted. This procedure allows a complete determination of both concentration and thickness from x-ray intensities of the coating associated with backscattering measurement. This method is called 'TF_Quantif'.

The performance of this quantification procedure is illustrated by different examples of application (thickness and composition maps determination of bi-element coatings on heterogeneous substrates).

The pulsed high energy density plasma (PHEDP) is generated in the working gas due to a high-voltage high-current discharge, within a coaxial gun. In PHEDP surface modification, discharge is applied for preparing the amorphous and nanostructured high-melting materials as thin films deposited on various substrates. In this investigation, Ta(C)N films were deposited using PHEDP on stainless steel. Pure tantalum and graphite were used as the inner and outer electrodes of the PHEDP coaxial gun, respectively. Nitrogen was used as the working gas and also one of the reactants. Preliminary study on the films prepared under different conditions shows that the formation of Ta(C)N is drastically voltage dependent. At lower gun voltage, no Ta(C)N was detected in the films; when the gun voltage reaches or exceeds 3.0 kV, Ta(C)N occurred. The films are composed of densely stacked nanocrystallines with diameter less than 30 nm, and some grains are within 10 nm in diameter.

Thermal shock resistance of mullite (3Al₂O₃ · 2SiO₂)-bonded porous silicon carbide (SiC) ceramics with 3.0 wt% yttria (Y₂O₃) addition was evaluated by a water-quenching technique. The thermal shock damage was investigated as a function of the quenching temperature, quenching cycles and specimen thickness. The residual flexural strength of the quenched specimens decreases with increasing quenching temperature and specimen thickness due to the larger thermal stress caused by thermal shock. However, quenching cycles at the temperature difference of 1200 °C have no effect on the residual strength since the same thermal stress was produced in repeated thermal shock processes. The good thermal shock damage resistance of the specimens is contributed mainly by the low strength and moderate elastic modulus. Moreover, the pores prevent the continuous propagation of cracks and alleviate further damage.

Barrier parameters of a thermally grown SiO_x gate oxide are derived by relating the SIMS oxygen concentration profile to the barrier height. Even in the simple analytical form such a graded barrier model agrees with the tunnelling current and its voltage dependence in both directions. Asymmetrical tunnelling I–Vs in the symmetrical n⁺Si–SiO_x–n⁺Si structure are due to both graded barrier and penetration of carriers into the gate oxide at the SiO_x–Si substrate interface.

Helium-containing titanium film was prepared by magnetron sputtering in a gas mixture of helium and argon. This method distinctly differs from traditional helium introduction into metals. A high concentration of helium up to 45 at.% and a uniform distribution in the bulk were shown by ion beam analysis. The process of helium incorporation is considered in which the helium particles are energetically backscattered from the target, fly through the glow discharge zone and are consequently embedded into the growing film. It is virtually a continuous sub-threshold-energy implantation during film deposition based on the plasma technique. The limited partial pressure of argon is to maintain the discharge and sputter the titanium target. The helium content incorporated can be controlled conveniently by adjusting the pressure of the working gases. X-ray diffraction, transmission electron microscopy, Doppler broadening of positron beam analysis and thermal helium desorption spectroscopy revealed the microstructure of titanium films, the state of helium bubbles, the defect characteristic related to helium and thermal release behaviour of helium from the titanium film.

Sol–gel derived SrZrO₃ based metal/insulator/metal (MIM) devices were fabricated to study their reversible resistance switching properties operated by dc voltage sweep and voltage pulses. The leakage-state of the device is changed from the original-state and finally switched between the high leakage-state (H-state) and the low leakage-state (L-state). The resistance ratio between the H-state and the L-state is about 10⁴, and the leakage-states are not changed without power supply, which is suitable for nonvolatile memory application. The conduction mechanisms of the original-state, the H-state and the L-state obey Schottky emission, Frenkel–Poole emission and Ohmic conduction, respectively. The first device resistance switching, called the forming process, changed from the original-state to the H-state. The switching time from the H-state to the L-state is much longer than that from the L-state to the H-state and that of the forming process. The decay behaviours of leakage current after resistance switching are influenced by pulse width and voltage stress directions. The switching time can be accumulated to switch the device from the H-state to the L-state, which could be a guide to multi-level memory applications. The model of conducting paths can well explain the electrical behaviours of our resistance switching devices.

Standard shear samples used for piezoceramic characterization lead to underestimation of the piezoelectric shear coefficients due to its dynamical clamping at resonance. This work presents the application of Alemany et al's automatic iterative method to the resonance of a non-Standard shear sample, in order to determine the related complex parameters of piezoceramics, thus including losses, from impedance measurements. The matrix of dielectric, elastic and piezoelectric complex parameters that fully characterize a piezoceramic, a 6 mm symmetry material, can be obtained from such shear data combined with the application of the method to three other electromechanical resonances, namely: the length extensional mode of long rods or rectangular bars, length poled; the thickness extensional mode of a thin plate or disc, thickness poled; and the radial mode of a thin disc, thickness poled. The shear results obtained here are those of non-Standard samples of a commercial Navy type II piezoceramic, thus solving the underestimation of the coefficients in the Standard shear sample and allowing the improvement of the previously reported characteristic matrix from Standard samples. Three-dimensional finite element analysis (FEA) modelling of the resonances of the three material samples used in the matrix characterization was here accomplished using the improved matrix of dielectric elastic and piezoelectric material coefficients including all losses. The comparison of the experimental resonance spectra of these piezoceramic samples and the FEA results obtained for the elastically, dielectrically and piezoelectrically homogeneous items modelled is presented and discussed here.

A study of thermally stimulated currents (TSC) is applied to α-HgI₂ polycrystalline films grown by physical vapour deposition with various thermal boundary conditions. Five TSC peaks are clearly observed and numerically fitted. The activation energy and the density of the trapping centre that corresponds to each TSC peak are then calculated. Finally, the effects of the deposition conditions on the TSC results are discussed.

The thermomechanical response of electron beam deposited nanoporous silicon dioxide is examined using substrate curvature measurements and nanoindentation. Analysis of the thin film bond angle strain distributions versus temperature indicates that low temperature (T < 100 °C) stress hysteresis and tensioning are primarily attributed to hydrogen bonded water desorption. However, at higher temperatures, the absence of water desorption suggests that the thermomechanical behaviour is related to thermally induced bond angle strain redistributions towards the local bonding environment of quartz and thermally grown silicon dioxide. This is supported by the co-efficient of thermal expansion data that trend lower with higher annealing temperatures. The re-absorption of water into the thin film accounts for the reproducibility of the open-loop stress hysteresis and tensioning observations.

The initial yield process and the subsequent formation of prismatic dislocation loops around a spherical inclusion embedded in a single-crystalline Al matrix are studied by atomistic simulations. In conjunction with linear elastic theory, it is confirmed that the maximum shear stress is created at the inclusion–matrix interface on the {1 1 1} plane intersecting the spherical inclusion at a height of (R_P: radius of spherical inclusion). The critical pressure, shear stress and strain for dislocation nucleation are then quantitatively determined. Afterwards, prismatic dislocation loops, which are constructed by four pure edge dislocations with the same Burgers vector but not on the same slip planes, are formed by energetically unstable interactions around the inclusion. Consequently, analytical considerations and atomistic simulation provide a clear explanation of experimental observations and an instructive insight into the precipitation problem.

In this paper we investigate the reflection of circularly polarized light from the exocuticle of the scarabaeid beetle Gymnopleurus virens. Reflection spectra are deeply modulated, exhibiting a number of relatively narrow well-defined peaks, which differ from previously studied specimens. By comparing model calculations and electron microscopy work with the recorded spectra, we can propose the presence of specific structural defects responsible for the unusual spectra.

The dielectric spectrum of whole blood is markedly changed by aggregation of erythrocytes, the so-called rouleau formation. The dielectric behaviour has been simulated using an erythrocyte model that is a disc covered with a thin membrane and an erythrocyte aggregate model that is a pile of the discs with regular spacing d_s. The effective complex permittivity of a cubic system including one of the models was calculated by a numerical technique based on the three-dimensional finite-difference method. Both the models have anisotropic dielectric properties depending on whether the rotational axis of the separate or the aggregate model is parallel (the parallel orientation) or perpendicular (the perpendicular orientation) to the direction of the applied electric field. The models both showed a single dielectric relaxation, which was different in intensity and characteristic frequency between the two orientations. For the erythrocyte aggregate model, the relaxation intensity Δε increased and the characteristic frequency f_c decreased with decreasing d_s in the perpendicular orientation, whereas the opposite d_s-dependence was found for Δε and f_c in the parallel orientation. Increasing the number of cells in the aggregate model enhanced these effects. The difference in dielectric spectrum between the separate and the aggregate models represented well the dielectric spectrum change caused by rouleau formation.

This paper reports the measurement of the electron drift velocity v_e, the longitudinal diffusion coefficient ND_L and the density-normalized effective ionization coefficient (α − η)/N in pure CF₃I and in the CF₃I–N₂ mixtures, where α and η are the electron impact ionization and attachment coefficients, respectively, and N is the gas density. The E/N range covered was 100–850 Td (1 Td = 10⁻¹⁷ V cm²). The present results were derived from a pulsed Townsend experiment. For pure CF₃I, the values of v_e and (α − η)/N were found to increase linearly with E/N. Moreover, the E/N value at which ionization equals attachment, commonly referred to as the limiting field strength, was found to be E/N_lim = 437 Td, which is greater than that of SF₆ (360 Td), a widely used insulating gas. For the CF₃I–N₂ mixture with 70% CF₃I, this E/N_lim value was found to be essentially the same as that for pure SF₆.

Kubelka–Munk theory is used extensively in a number of industrial applications including colour matching. The main aim of this paper is the derivation of alternative analytical equations, which are more accurate than correspondent Kubelka–Munk formulae for light scattering materials of a finite optical depth. The derived equations are based on asymptotic radiative transfer theory valid for optically thick turbid media with arbitrary phase functions and single scattering albedos.

This paper presents the principal experimental results provided by a preliminary investigation into the possibility of using exploding wire (EW) techniques to shatter the plastic cockpit canopy of a modern jet aircraft. The data provided forms the basis for a qualitative understanding of the physics of interaction between the plasma produced by an EW and the surrounding elasto-plastic material in which the wire is embedded. To optimize the shock-wave 'clean cutting' effect, the significance of the material, the dimensions of the exploding wire and the amplitude of the current and voltage pulses are all considered. This leads to important conclusions concerning both the characteristics of the EW and the optimum arrangement of the electrical circuit, with the single most important optimization factor being the peak electrical power input to the EW, rather than the dissipated Joule energy.

A full-scale system relevant to an actual cockpit canopy shattering is outlined and relevant results are presented and discussed.