Table of contents

Zn nanowires and nanoribbons have been synthesized from Zn powders through a simple thermal-vapour deposition process.

In this paper, we describe the principles of operation of a plasma display panel (PDP) and the physical mechanisms controlling the performances of a PDP in terms of light emission efficiency, lifetime and image quality. Emphasis is put on the physics of the plasma occurring in a PDP cell, on the discharge optimization, and on the analysis of recent results provided by experimental and numerical diagnostic tools. We focus on alternative current PDPs, where the plasma is generated by a dielectric barrier discharge, the configuration adopted by most PDP companies. The recent improvements and the remaining research issues are discussed.

Metalorganic chemical vapour deposition (MOCVD) and atomic layer deposition (ALD) are highly promising techniques for the deposition of dielectric and ferroelectric oxide thin films, which have a variety of applications in electronic devices. A key requirement for both MOCVD and ALD is the availability of precursors with appropriate physical properties and decomposition characteristics, but there are problems associated with many of the existing precursors. Therefore, it is sometimes necessary to `tailor' the properties of the precursor in order to optimize MOCVD and ALD process parameters, such as evaporation temperature, deposition temperature, layer purity and uniformity. In this paper, the design of a number of new, improved oxide precursors is described, with emphasis on the influence of molecular structure on precursor properties and on the growth dynamics of the MOCVD and ALD processes.

In an equilibrium immiscible Au–Co system characterized by a positive heat of formation of +11 kJ mol⁻¹, a non-equilibrium Au–Co phase of hcp structure was formed by 200 keV xenon ion mixing at 77 K in the Au₅₀Co₅₀ multilayered films. Based on the free energy calculation, the excess interfacial free energy stored in the Au–Co multilayered films could provide adequate thermodynamic driving force for alloying between Au and Co and forming the non-equilibrium Au–Co hcp phase. Besides, the average magnetic moment per Co atom in the newly formed hcp structure was reduced by 22% of its equilibrium value, within a measuring error of 8%.

The additive dose, T_m(E_a)–T_stop, repeated initial rise, variable heating rate and computerized glow curve deconvolution (CGCD) methods were used to determine the number of peaks and kinetic parameters (kinetic orders b, activation energy E_a and attempt-to-escape frequency s) associated with the thermoluminescence (TL) glow peaks in unannealed acid purified synthetic quartz produced by the Fluka Company after beta-irradiation between the dose level 0.02 Gy and 2.5 kGy. The E_a–T_stop and CGCD methods indicated that the glow curve of this material is the superposition of at least seven first-order components, which was referred to as P1–P7, in the temperature range between room temperature and 500°C. The results indicated that kinetic parameters vary fairly from method to method. The dose responses and fading process, which are very useful in radiation dosimetry and archaeological dating, of individual TL peaks of this material were also examined. The dose responses of all peaks have similar pattern, first they follow strong linearity and then saturate at different dose levels. Peaks 1 and 2 completely disappeared after 1 month storage in the dark room at room temperature. On the other hand, the intensity of peak 3 was reduced to 27% of its original value whereas the other peaks (P4–P7) were not sufficiently affected during this period.

Modelling results are presented concerning the spatial distribution of plasma parameters in a laser-induced plasma plume with laser welding as the research background. In the modelling, the plasma plume characteristics are affected by many factors, such as the temperature and flow velocity of the metal vapour leaving the welded workpiece surface, the velocity of the shielding gas injected coaxially with the laser beam, the velocity of the assisting gas injected laterally with respect to the workpiece, and the energy absorption and radiation heat loss of the plasma plume. Typical computed distributions of temperature, velocity, vapour concentration, absorption coefficient and the refraction index within the plasma plume are presented with the continuous-wave (CW) CO₂ laser welding of an iron workpiece as the calculation example. The predicted temperatures of the plasma plume are shown to be reasonably consistent with the corresponding experimental data. It is also shown that the metal-vapour/shielding-gas momentum ratio plays an important role in determining the height of the plasma plume formed in the laser welding. Due to the cooling effect of the shielding gas, the dimensions of the plasma plume will become smaller and thus laser absorption and refraction by the plasma plume can be reduced by increasing the shielding-gas velocity. The laterally injected assisting gas may also significantly affect the plasma plume and thus can be used to control the effect of the laser-induced plasma plume on the laser welding process.

Solitary spots on infinite planar cathodes and diffuse and axially symmetric spot modes on finite cathodes of high-pressure arc discharges are studied in a wide range of arc currents. General features are analysed and extensive numerical results on planar and cylindrical tungsten cathodes of atmospheric-pressure argon arcs are given for currents of up to 100 kA. It is shown, in particular, that the temperature of cathode surface inside a solitary spot varies relatively weakly and may be estimated, to the accuracy of about 200–300 K, without actually solving the thermal conduction equation in the cathode body. Asymptotic behaviour of solutions for finite cathodes in the limiting case of high currents is found and confirmed by numerical results. A general pattern of current–voltage characteristics of various modes on finite cathodes suggested previously on the basis of bifurcation analysis is confirmed. A transition from the spot modes on a finite cathode in the limit of large cathode dimensions to the solitary spot mode on an infinite planar cathode is studied. It is found that the solitary spot mode represents a limiting form of the high-voltage spot mode on a finite cathode. A question of distinguishing between diffuse and spot modes on finite cathodes is considered.

The electron drift velocity (W) and the product of the gas number density and the electron longitudinal diffusion coefficient (N D_L) were measured in the ranges of E/N over 1.4–100 Td in the 0.468% c-C₄F₈/Ar mixture, 8–100 Td in the 4.910% c-C₄F₈/Ar mixture, and 170–1000 Td in pure c-C₄F₈, by using a double-shutter electron drift apparatus with variable drift length (1–10 cm). The measured electron transport coefficients in these mixtures indicated that the inelastic processes between electrons and the c-C₄F₈ molecules had a strong influence and the measured electron drift velocity in pure c-C₄F₈ showed substantial deviation from the reported results in the high E/N range. There are no measurements on ND_L in pure c-C₄F₈.

Properties of plasma sheath boundary in multicomponent plasma with negative ions have been investigated experimentally. The modified Bohm sheath criterion derived for thermal electron–thermal negative ion–cold positive ion model predicts the decrease of positive ion drift speed toward the sheath when the negative ion concentration is gradually increased. This modified Bohm criterion has been discussed in this experimental investigation. The experimental parameters (e.g. discharge voltage, discharge current) set for argon plasma production are kept floating during the addition of SF₆ gas. Two important effects caused by the presence of negative ions, e.g. decrease in Bohm speed of positive ions toward the sheath and reduction in plasma density have been observed. The reduction in the ion flux toward the sheath therefore causes the expansion of the sheath. The numerical solution of Poisson's equation, which includes the contribution of negative ions, is compared with the experimental findings.

The radial expansion of an axially flowing plasma column in a constant axial magnetic field is considered for the following cases: (a) magnetized electrons and unmagnetized ions, and (b) magnetized electrons and partially magnetized ions . In case (a), radially escaping ions produce a radial electric polarization field. For a directed axial ion velocity of v₀ = 1.5×10⁴ m s⁻¹, particle concentration n₀ = 10¹⁸ m⁻³ and magnetic field B = 0.02 T, the azimuthal electron drift velocity in the crossed electric and magnetic fields is 4×10⁵ m s⁻¹, i.e. near to their thermal velocity with T_e = 3×10⁴ K: (kT_e/m_e)^1/2≈5×10⁵ m s⁻¹ and it together with the thermal velocity determines the electron collision frequency. With a neutral gas pressure of 1.3 Pa and a magnetic field strength of B = 0.01 T, the radial electron velocity reaches the radial ion expansion velocity within a time of ⩽8 × R/v₀, where R is the plasma column radius.

If the ions are partially magnetized, the electric polarization field is caused by radially escaping unmagnetized ions, while the electrons, and magnetized ions drift in the crossed electric, and magnetic field. The thermal, and axially directed ion velocities are much less than their azimuthal drift velocity, and thus the azimuthal velocity determines the collision frequency.

An AC-driven, non-thermal, atmospheric pressure air plasma is generated within the gap separating a disc-shaped metal electrode and a water electrode. The ignition phase and the steady-state are studied by a high-speed CCD camera. It is found that the plasma always initiates at the surface of the water electrode. The plasma exhibits different structures depending on the polarity of the water electrode: when the water electrode plays the role of cathode, a relatively wide but visibly dim plasma column is generated. At the maximum driving voltage, the gas temperature is between 800 and 900 K, and the peak current is 67 mA; when the water electrode is anode, the plasma column narrows but increases its light emission. The gas temperature in this case is measured to be in the 1400–1500 K range, and the peak current is 81 mA.

Atmospheric pressure plasmas are commonly used to improve the wetting and adhesion properties of polymers. In spite of their use, the mechanisms for achieving these properties are unclear. In this regard, we report on a computational investigation of the gas phase and surface kinetics during humid-air corona treatment of polypropylene (PP) and the resulting modification of its surface properties while varying energy deposition, relative humidity (RH), web speed, and gas temperature. Using results from a global plasma chemistry model validated against experiments, we found that increasing energy deposition increased the densities of alcohol, carbonyl, acid, and peroxy radicals on the PP surface. In doing so, significant amounts of gas phase O₃ and N_xO_y are produced. Increasing the RH increased the production of peroxy and acid groups, while decreasing those of alcohol and carbonyl groups. Production of O₃ decreased while that of HNO₃ increased. Increasing the temperature decreased the concentrations of alcohol, carbonyl, and acid groups on PP while those of the peroxy radicals increased. For a given energy deposition, higher web speeds resulted in decreased concentrations of alcohols, peroxy radicals, carbonyl, and acid groups on PP.

A probabilistic modelling approach for the study of the cathode spot displacement dynamic in high-pressure arc systems is developed in an attempt to interpret the observed voltage fluctuations. The general framework of the model allows to define simple, probabilistic displacement rules, the so-called cathode spot dynamic rules, for various possible surface states (un-arced metal, arced, contaminated) and to study the resulting dynamic of the cathode spot displacements over one or several arc passages. The displacements of the type-A cathode spot (macro-spot) in a magnetically rotating arc using concentric electrodes made up of either clean or contaminated metal surfaces is considered. Experimental observations for this system revealed a 1/f^∼1 signature in the frequency power spectrum (FPS) of the arc voltage for anchoring arc conditions on the cathode (e.g. clean metal surface), while it shows a `white noise' signature for conditions favouring a smooth movement (e.g. oxide-contaminated cathode surface). Through an appropriate choice of the local probabilistic displacement rules, the model is able to correctly represent the dynamic behaviours of the type-A cathode spot, including the FPS for the arc elongation (i.e. voltage) and the arc erosion trace formation. The model illustrates that the cathode spot displacements between re-strikes can be seen as a diffusion process with a diffusion constant which depends on the surface structure. A physical interpretation for the jumping probability associated with the re-strike event is given in terms of the electron emission processes across dielectric contaminants present on the cathode surface.

The radial and temporal dependences of the metastable 6 ³P₂ (Xe_m) and resonance 6 ³P₁ (Xe_r) state densities are measured in the active phase and afterglow of pulsed discharge in xenon by laser absorption technique at pressure 10 Torr and currents 200–500 mA. It is found that the densities grow by a factor of 25 during the transition from the active discharge phase to the afterglow and there is no decrease of the density after switching the field off. It is shown that the collisional-radiative recombination prevails over the dissociative recombination because of high electron density and relatively low electron temperature in a constricted discharge. The electron cooling after the field switching-off is caused mainly by electron–ion collisions whereas the electron–atom elastic collisions are less effective due to the Ramsauer effect. The quantitative modelling of the active phase and afterglow is performed on the basis of the time-dependent system of balance equations for densities of excited atoms and charged particles, as well as electron temperature. The results of the modelling reflect all peculiarities of the excited atom behaviour both in the active phase and afterglow.

Cathode erosion rate was experimentally investigated for two types of arcs: one with tungsten cathode in nitrogen atmosphere and one with hafnium cathode in oxygen atmosphere. Conditions were typical for plasma arc cutting systems: gas pressure from 2 to 5 atm, arc current from 200 to 400 A, gas flow rate from 50 to 130 litre min⁻¹.

It was found that the actual cathode evaporation rate G is much lower than G₀, the evaporation rate that follows from the Hertz–Knudsen formula: G = νG₀. The difference is because some of the evaporated particles return back to the cathode. For conditions of our experiments, the factor ν could be as low as 0.01. It was shown experimentally that ν depends strongly on the gas flow pattern close to the cathode. In particular, swirling the gas increases ν many times. To explain the influence of gas swirling, model calculations of gas flows were performed. These calculations revealed difference between swirling and non-swirling flows: swirling the gas enhances the gas flow from the cathode. This enhanced flow sweeps the evaporated particles away from the cathode and thus increases the net evaporation rate.

Electrode erosion associated with arc ignition (start erosion) was observed for both types of cathodes. Models of start erosion were suggested. In case of hafnium cathode the start erosion is due to cracking out the hafnium oxide layer, which was created during previous arc operation. In the case of the tungsten cathode the start erosion is produced by a cold cathode arc (vacuum arc), which exists at the cathode during first moments after arc ignition.

Acoustically induced second harmonic generation (AISHG) in hydrogenated amorphous silicon (a-Si : H) films of different morphology has been observed. We have found that with increasing acoustical power, the optical SHG of Gd : YAB laser light (λ = 2.03 μm) increases and reaches its maximum value at an acoustical power density of about 2.10 W cm⁻². With decreasing temperature, the AISHG signal strongly increases below 48 K and correlates well with the temperature behaviour of differential scanning calorimetry indicating near-surface temperature phase transition. The AISHG maxima were observed at acoustical frequencies of 10–11, 14–16, 20–22 and 23–26 kHz. The independently performed measurements of the acoustically induced IR spectra have shown that the origin of the observed phenomenon is the acoustically induced electron–phonon anharmonicity in samples of different morphology.

To improve ZnO thin film quality, the ZnO thin films grown on silicon (100) by plasma enhanced chemical vapour deposition from Zn(C₂H₅)₂ and CO₂ gas mixtures at a low temperature of 120°C are annealed in an oxygen ambient at temperature ranging from 600°C to 1000°C. X-ray diffraction spectra indicate that ZnO films possess a polycrystalline hexagonal wurtzite structure. Atomic force microscopy results show an increase of ZnO grain size with the increase of annealing temperature. The photoluminescence is closely related to the annealing temperature. The free exciton binding energy deduced from the temperature-dependent PL spectra is about 59 meV for the ZnO film annealed at 900°C, suggesting that the film quality can be improved by annealing process.

High solar performance Zr–ZrO₂ cermet solar coatings were designed using a numerical computer model and deposited experimentally. The layer thickness and Zr metal volume fraction for the Zr–ZrO₂ cermet solar selective coatings on a Zr or Al reflector with a surface ZrO₂ or Al₂O₃ anti-reflection layer were optimized to achieve maximum photo-thermal conversion efficiency at 80°C under concentration factors of 1–20 using the downhill simplex method in multi-dimensions in the numerical calculation. The dielectric function and the complex refractive index of Zr–ZrO₂ cermet materials were calculated using Sheng's approximation. Optimization calculations show that Al₂O₃/Zr–ZrO₂/Al solar coatings with two cermet layers and three cermet layers have nearly identical solar absorptance, emittance and photo-thermal conversion efficiency that are much better than those for films with one cermet layer. The optimized Al₂O₃/Zr–ZrO₂/Al solar coating film with two cermet layers has a high solar absorptance value of 0.97 and low hemispherical emittance value of 0.05 at 80°C for a concentration factor of 2. The Al₂O₃/Zr–ZrO₂/Al solar selective coatings with two cermet layers were deposited using dc magnetron sputtering technology. During the deposition of Zr–ZrO₂ cermet layer, a Zr metallic target was run in a gas mixture of argon and oxygen. By control of oxygen flow rate the different metal volume fractions in the cermet layers were achieved using dc reactive sputtering. A solar absorptance of 0.96 and normal emittance of 0.05 at 80°C were achieved.

BaZn_ZCo_2−ZFe₁₆O₂₇ (W-type hexaferrite)/SiO₂ microcrystalline glass ceramics (Z = 0.0, 0.5, 0.8 and 1.1) were prepared by citrate sol–gel process, they were characterized by x-ray powder diffraction, scanning electron microscopy and thermogravimetry–differential scanning carlorimetry. The results show that the crystallizing temperature of W-type hexaferrite in the system BaO–Fe₂O₃–CoO–ZnO–SiO₂ by sol–gel process is about 1200°C, the average grain size of BaZn_ZCo_2−ZFe₁₆O₂₇/SiO₂ microcrystalline glass ceramics is about 0.3 μm. The complex dielectric constant and complex permeability of BaZn_ZCo_2−ZFe₁₆O₂₇/SiO₂ has been studied as a function of the composition, frequency and annealing temperature. The real part of permeability decreases with increase of frequency, increases with increase of annealing temperature for all samples; the natural resonance phenomena are observed in imaginary component of permeability—frequency curves for all the samples annealed at 1200°C, the natural resonance frequency shifts to lower frequency with increase of zinc content.

This paper presents experimental evidence that the percolation threshold in conductor–insulator composites can be a function of the particle size ratio of the constituents, as well as the particle shape. This trend in percolation threshold is to be expected when the conducting particles are excluded from regions of the composite volume (e.g. the core of the insulator particles). The composite system investigated consisted of carbon black powder dispersed in PTFE powder. The system and the method of composite preparation was chosen specifically to promote the realization of this effect. The purpose of this experimental investigation was to provide additional confidence in a recently reported genetic algorithm-based approach to analysing the dielectric spectra of percolative composites. The experimental results are compared to a range of geometric percolation models and one such model is adapted to account for ellipsoidal insulator particles. Good agreement between model and experiment is achieved when this modification is used in conjunction with the actual particle size distribution of the insulator particles.

Electric force microscopy (EFM) testing is a promising test technique for function and failure analysis of integrated circuits, especially in the design phase. It enables contactless, chip internal voltage measurements with simultaneous high temporal and high spatial resolution. Up to now, for EFM-testing of periodic digital voltages the sampling technique was used. Another technique—the heterodyne mixing technique—allows fast two-dimensional voltage contrast measurements, which cannot be done using the sampling technique. Thus, in this paper the suitability of the heterodyne mixing technique for the measurement of periodic digital voltages is investigated.

Thin epoxy resin adhesive samples were ultrasonically measured during cure using normal incidence radially polarized shear wave electromagnetic acoustic transducers (EMATs). Although the EMATs used predominantly generated shear waves (SH) they were designed so that they also generated/detected compression waves allowing the simultaneous measurement of shear and compression wave propagation through a curing polymer in a non-contact regime. The adhesive thickness examined in the experiments was approximately 1 mm, which was optimal for experimental measurement using our apparatus. The epoxy resin systems (rapid cure and a standard cure) described in this paper were supplied in a two-part cartridge form, mixed by injection through a mixing nozzle. Five different samples have been investigated at this stage, and there appears to be a fundamental difference in the way that the elastic moduli develop in the rapid cure and longer cure time epoxies. This can possibly be explained in terms of the reaction kinetics and the development of the structure on a microscopic scale. The rapid cure systems initially develop a shear elastic modulus at a faster rate which suddenly decreases at approximately the same time that the temperature of the adhesive reaches its maximum value during the exothermic reaction. This is consistent with an initial rapid reaction rate which is then greatly reduced as the remaining un-reacted polymer chains require a finite time to move into a position where they can react and join the network.

The absorption of fluid by unsaturated, rigid porous materials may be characterized by the sorptivity. This is a simple parameter to determine and is increasingly being used as a measure of a material's resistance to exposure to fluids (especially moisture and reactive solutes) in aggressive environments. The complete isothermal absorption process is described by a nonlinear diffusion equation, with the hydraulic diffusivity being a strongly nonlinear function of the degree of saturation of the material. This diffusivity can be estimated from the sorptivity test. In a typical test the cumulative absorption is proportional to the square root of time. However, a number of researchers have observed deviation from this behaviour when the infiltrating fluid is water and there is some potential for chemo-mechanical interaction with the material. In that case the current interpretation of the test and estimation of the hydraulic diffusivity is no longer appropriate.

Küntz and Lavallée (2001) discuss the anomalous behaviour and propose a non-Darcian model as a more appropriate physical description. We present an alternative Darcian explanation and theory that retrieves the earlier advantages of the simple sorptivity test in providing parametric information about the material's hydraulic properties and allowing simple predictive formulae for the wetting profile to be generated.

Approximate σ_θ–ε_θ curve of a thin coil section without reinforcement wound from a rectangular conductor exhibiting a linear behaviour after hardening is considered. The influence of the bending stress in the initially elastic coil conductors on their gradation in the plastic state is taken into account. Mechanical work done during plastic deformation of conductors near the mid-plane of the coil is estimated; when the average Lorentz hoop stress in the first energizing reaches a yield point of the coil conductor, irreversible work per unit volume of the coil body is ∼10⁴ J m⁻³.