Table of contents

The fine structures of low-temperature photoluminescence (PL) spectra of TiO₂ thin films with addition of ZnFe₂O₄ (ZnFe₂O₄/TiO₂ composite films) are firstly reported. The films were deposited on quartz substrates by radio-frequency magnetron sputtering method. It is shown that different phase structures are developed for the pure TiO₂ and composite films at different annealing temperatures. There is a very strong broad PL band in the composite films, which consists of some minor peaks besides the main PL peak. It is considered that the main PL peak originates from the transition of the impurity-related centres and the minor peaks come from transition, assisted by phonon replicas, of impurity- and oxygen-related defects in TiO₆ octahedra.

Ion beam etching of surfaces has recently been shown to be an attractive liquid crystal alignment technique for use in the commercial fabrication of liquid crystal displays. Reflectivity and atomic force microscopy measurements suggest the alignment ability of an ion-etched surface is promoted by modifications at the atomic scale. Reflection anisotropy spectroscopy is demonstrated as a real time monitor of the etching process, promising a process control tool for the next generation of liquid crystal devices.

Silicon oxynitride films are grown by plasma-enhanced chemical vapour deposition on single-crystal Si(100) and textured Si solar cells, using a safe organic precursor, hexamethyl-disilazane. Using the Lucovsky-Phillips criterion of bond coordination constraints, we grow high-quality thin (~20 Å) and thick (up to 2700 Å) films which are carbon free (<1.0{%}) as characterized by x-ray photoemission spectroscopy (XPS) and Auger electron spectroscopy depth profiles. Core-level and valence band XPS is used to conclusively identify oxynitride bonding and band gap reduction in SiO_xN_y. For a λ/4 `blue' anti-reflection coating on the solar cells with uniform thickness (870±15 Å) and composition (SiO_1.6±0.1N_0.3±0.05), an efficiency (AM 1) increase of 1{%} is obtained.

We report on the synthesis of high quality La_1/3Sr_2/3FeO₃ (LSFO) thin films using the pulsed laser deposition technique on both SrTiO₃ (STO) and LaAlO₃ (LAO) substrates (100)-oriented. From x-ray diffraction (XRD) studies, we find that the films have an out-of-plane lattice parameter around 0.3865 nm, almost independent of the substrate (i.e. the nature of the strains). The transport properties reveal that, while LSFO films deposited on STO exhibit an anomaly in the resistivity versus temperature at 180 K (corresponding to the charge-ordered transition and associated with a transition from a paramagnetic to an antiferromagnetic state), the films grown on LAO display a very small magnetoresistance behaviour and present an hysteresis around 270 K under the application of a 4 T magnetic field. The changes in transport properties between both substrates are discussed and compared with the corresponding single crystals.

Magnetostriction measurements were performed at different temperatures for Fe₈₁Si_3.5B_13.5C₂ METGLAS^® films using a strained substrate technique. The magnetostriction constant was deduced from magnetic properties measured using a vibrating sample magnetometer. The film strain was varied using a range of curved sample holders. From the change of magnetic anisotropy field as a function of controlled strain, the saturation magnetostriction constant can be determined with sufficient accuracy. The temperature dependence of magnetostriction of METGLAS^® Fe₈₁Si_3.5B_13.5C₂ from 9 to 287 K is reported. It is suggested that a single-ion mechanism of magnetostriction is dominant in this amorphous alloy.

We report the optical and electroluminescent properties of the lithium complex of (2,3-dimethyl-8-hydroxyquinoline) lithium (LiMMq), exhibiting intense photoluminescence (PL), peaked at about 458 nm. As the result of electron-donating methyl groups in 8-hydroxyquinoline, the PL spectrum is blue-shifted relative to (8-hydroxyquinoline) lithium (Liq). The double-layer electroluminescent devices with a novel polymer poly(N,N'-diphenyl-N,N'-bis(4-methylphenyl)-1,4-phenylenediamine-1,3-diisopropenylbenzene) as hole transporting layer and the LiMMq as emitting layer, sandwiched between cathode of Mg : Ag alloy and anode of indium-tin oxide, were fabricated, and the bright blue electroluminescence with luminance of more than 8000 cd m^-2 was obtained. The properties indicate that the LiMMq is a potential blue emitting material for the application in light-emitting diodes.

The influence of the controlled exposure to oxygen of the calcium cathode of polymeric light emitting diodes (pLEDs) is investigated. The LEDs are fabricated with ITO as anode, OC₁C₁₀-PPV as electroluminescent polymer, calcium as cathode and aluminium as protecting layer. The polymer layers of the LEDs are spincoated in a dry nitrogen atmosphere and transported directly into an UHV chamber where the metal electrodes are deposited by evaporation. In order to investigate the influence of the exposure to oxygen of the calcium cathode, the deposition of the calcium layer was interrupted in some cases and the samples were exposed to 30-1000 mbar of oxygen. We determined the amount of oxygen in the different layers of the I-V-light characterized pLEDs with elastic recoil detection analysis and correlated it with the characteristics of the devices. Exposing a part of the calcium layer to oxygen at layer thicknesses equal to or less than 10 nm leads to a total loss of the brightness, while exposing thicker layers or the pristine PPV does not affect the LEDs significantly.

In this work we have studied experimentally the influence of N-O chemistry on radiative emissions from a small DC plasma torch at 1 atm. The plasma torch has been designed for the atomizer of an on-line atomic absorption spectrometer, which is used for the detection of vaporized metals in various process gas flows. The plasma torch was burning in pure nitrogen and an oxygen bearing sample gas was introduced into the plasma jet. The temperature of the plasma jet was determined spectroscopically to be around 2000 K. At this temperature the equilibrium UV radiation of excited atoms or molecules is negligible, but molecules and atoms are effectively excited by collisions with metastable nitrogen molecules formed in the plasma. The emission spectra of the plasma jet were measured in the wavelength range 200-400 nm in various gas mixtures. In pure nitrogen the second positive system of N₂was observed, the intensity of which exceeded the estimated radiation at thermal equilibrium even by 10¹³ times. With a trace amount of oxygen-containing species, such as O₂, CO₂ or H₂O, very intense γ-band radiation of NO was observed. The intensities of the lines were calculated to be around 10⁹ times greater than corresponding equilibrium intensities. High intensities were also observed in atomic resonance lines of several metals. The intensity of the Cu line at 324.75 nm was 5×10³ higher than the estimated equilibrium emission at given conditions. Correspondingly, the emission intensity of Pb line at 283.3 nm was around 5×10⁵ and Cd line at 228.8 nm around 2×10⁷ times more intense than at thermal equilibrium. Our study indicated that the rate of the collisional excitation of metal atoms by metastable nitrogen molecules was roughly the same for all the studied metals. When larger amounts of O₂ or H₂O were introduced into the plasma jet, the emission intensity of molecular lines and atomic lines of metals decreased drastically. We showed that radiative emissions do not interfere with absorption measurements provided that the percentage of O₂ in the plasma jet is above 5 vol% or of water vapour above 2 vol%.

Laser to x-ray conversion efficiencies from solid targets irradiated by KrF laser pulses of wavelength 248 nm are measured. A 16-bit front illuminated open electrode 1024×256 pixel x-ray CCD camera working in single photon counting mode is used to record the x-ray output from Al, Cl, Ag, and Ti emitting in the 1.5-4.5 keV photon energy range. X-ray conversion efficiencies up to values of ~0.2{%} (2π sr)^-1 are obtained with pulses of duration 2 ps irradiating the targets at 12 Hz with peak irradiance of 1.9×10¹⁶ W cm^-2.

A new model for electromagnetic field modelling is proposed for the simulation of inductive plasma torches. Instead of solving the equations of vector potential, the electromagnetic fields are obtained by solving the equations of the magnetic stream function (φ), the contours of which represent the magnetic lines, i.e. the direction of magnetic field. This model is used to calculate the effect of ferrite on the plasma flow when the ferrite is placed around the coil in order to shield the electromagnetic radiation, therefore reducing the losses of RF power. Under the assumption that the permeability of ferrite is infinite, the magnetic line is perpendicular to the surface of ferrite. If the ferrite has infinite permeability, we neednot solve the equations of magnetic stream function in the ferrite and the surfaces of ferrite are taken as the boundary of the magnetic stream function at which the normal derivative of magnetic stream function is set to zero. In this paper, the computational results with different ferrite shapes have been obtained, which show that the role of ferrite is not only to shield electromagnetic radiation but it also increases the power coupling efficiency to plasma torch and reduces the necessary coil current as well. The results of the model clearly indicate how this can be done efficiently in an industrial plasma torch.

A model for an inductively coupled plasma with ferrite around the coil is developed. Vector representation is used for modelling and calculation of the electromagnetic fields. The permeability of ferrite is taken into account (not assumed to be infinite as in a previous work by the authors) but is assumed not to change with magnetic fields. The power dissipation in ferrite is neglected (no imaginary part for permeability). Under these assumptions, the role of ferrite can be completely replaced by the magnetization current density on the surface of ferrite. Through the magnetic field boundary condition on the surface of ferrite, the magnetization current density is derived and added to vector potential equations as a source term. The commercial Computational Fluid Dynamics (CFD) software FLUENT is used to solve the governing equations of plasma flow with vector potential equation and the flow, temperature, and electromagnetic fields. The effect of different shapes of ferrites around the coil was simulated. The results are compared with the results from the same model without ferrite and a previously proposed model with infinite permeability of ferrite. The computation results show that the effect of ferrite is not only to shield the electromagnetic radiation but it also decreases the coil current necessary to sustain the same power plasma torch. Accordingly, it increases the power coupling efficiency as well.

Plasma based ion implantation at elevated temperatures is a technology often used to obtain thick surface layers of several µm by thermally activated diffusion, e.g. nitrogen in steel, titanium or aluminium. By lowering the pulse voltage at constant temperature, the current density can be increased at a constant heat flow. However, an upper limit is given by the ratio of the diffusion rate transporting the implanted ions from the surface towards the bulk and the sputter yield. This sputtering of the surface dominates for very high current densities and limits the maximum achievable layer thickness. Different maximum current densities were found for the four investigated systems - nitrogen in different steel grades, aluminium and titanium, as well as oxygen in titanium - reflecting the varying diffusivities. Additional requirements, besides the maximum current density, as a conformal treatment for complex objects containing small holes or trenches, as well as short heating times, can be solved most effectively by pulsed voltages in the range of 2-5 kV and an additional heating of the sample. The problem of a sample cooling time of several hours after the treatment is recognized. A partial solution would be to increase the gas pressure during the cooling phase for a more effective heat dissipation.

A method is presented for the determination of physical discharge parameters for partial discharges (PDs) of voids in solid insulation. Based on a recently developed stochastic theory of PD processes, a statistical analysis of a measured phase-resolved partial discharge (PRPD) pattern allows the determination of the relevant physical parameters like first electron availability or decay time constants for deployed charge carriers. These parameters can be estimated directly from the measured patterns without the need of performing simulations. Furthermore, error bounds for the parameter values can be given.

The parameter estimation algorithm is based on the analysis of a contiguous region of the PRPD pattern where this region can be chosen nearly arbitrarily. Thus, even patterns with several active PD defects or patterns which are corrupted by noise can be analysed.

The method is applied to a sequence of patterns of a void in epoxy resin. The change in first electron availability in the course of a day can be determined quantitatively from the data while the other physical parameters remain constant.

A three-dimensional numerical ray-tracing code has been developed to consider the effects of optical refraction at VUV and extreme ultraviolet (EUV) wavelengths in the pinhole imaging of capillary discharge plasmas. An experimental pinhole imaging system is modelled and results are compared to images recorded from a fast ablative discharge in short polyethylene capillary. Refractive effects are only observed for electron densities greater than 3×10²⁵ m^-3 at the longest wavelengths. Thus it can be concluded that, for this experiment, electron density profiles can be obtained from pinhole image, and the ring structure observed in experiment is not due to refraction.

We have studied the efficiency of ozone production by pulsed positive corona discharge in coaxial wire-cylinder geometry at atmospheric pressure. A corona discharge was generated by short (~150 ns) high voltage pulses applied between a silver coated copper wire anode and stainless steel cylinder cathode in synthetic air. A pyrex probe and Teflon tube was used for collecting discharge products and an ozone concentration was monitored outside of the discharge chamber by a non-dispersive UV absorbtion technique. The production of ozone was investigated as a function of energy density (10^-4-3×10^-1 Wh l^-1) delivered to the discharge volume by combining the discharge frequency (0.1-10 Hz) and airflow rate (1-32 l min^-1). From ozone concentration measurements we have evaluated the ozone production, yield and production energy cost. The ozone production yield and cost vary in the range of 15-55 g kWh^-1 and 35-110 eV/molecule.

In this paper, we have studied the diffusion process of Cu in V₂O₅ films at room temperature deposited V₂O₅(2000 Å)/Cu/(Si or glass) samples as a function of annealing temperatures in different gas environments. According to our Auger electron spectroscopy, x-ray photoelectron spectroscopy and film resistivity measurements, Cu segregation and accumulation toward the surface of the oxide film were occurred when the vanadium oxide deposited on the Cu buffer layer. The thickness of Cu overlayer was about one monolayer for the deposited samples at room temperature. Annealing treatment at temperatures above 250°C in Ar or N₂ (80%) + H₂ (20%) environment has enhanced the rate of diffusion process. It is proposed that the diffusion mechanism depends on the nature of applied gases and their pressures.

Electrical resistivity of the unplasticized poly(vinyl chloride) copolymer (UPVC) films irradiated with high-energy proton beams was studied with reference to a control sample, as a function of both ion energy and ion dose. Upon irradiation with beam energy ranging from 25 up to 37 MeV and at a beam fluence of 0.225×10¹⁰ ion cm^-2, the room-temperature resistivity of the insulating films decreased by four orders of magnitude from its original value. Furthermore, using 25 MeV proton beams over a wide range of fluence (10¹¹-10¹⁵ cm^-2), the room-temperature resistivity of the films decreased by only three orders. Then, the dependence of the resistivity ρ(T) on the ion energy and fluence was also observed as the temperature Twas progressively increased up to 373 K. The observed behaviour of ρ(T) agrees with the charge transport model, consistent with a hopping mechanism in the polymer. In addition, the changes in the ac electrical resistivity of the irradiated UPVC films have been measured within the temperature range (293-373 K) and at different frequencies (100 kHz-3 MHz).

Maxwell-Wagner piezoelectric, dielectric and elastic relaxations in two-layer or multilayer serial piezoactive media are considered. As distinct from the oversimple model, described in literature, we derive exact solutions by taking into account mechanical boundary conditions, transversal piezoelectric response and elastic properties of layers. We first study the Maxwell-Wagner relaxation of elastic compliances and the contribution from piezoelectric coefficients and elastic constants of two layers to the value of the relaxation time. Methods for strengthening as well as eliminating the relaxations and for the giant enhancement of dielectric permittivity are specially reviewed.

The image force is considered to be one of the non-specific sources of surface charge and origin of the double charge layer in the interface between a non-polar liquid dielectric and a polar solid. It is assumed that there is no interaction between phases, neither chemical interaction nor preferential adsorption, due to their specific chemical nature. Two possible physical mechanisms have been investigated. The first takes into account the existence of a potential barrier to the charge movement as it leaves the surface. Therefore, the charges that are in liquid are attracted to the surface. The second is the reduction of dissociation energy of ion pairs close to the interface in comparison with bulk dissociation. Both mechanisms result in a decrease of recombination rate and a sharp increase of dissociation rate. It has been shown that both these mechanisms could lead to the creation and accumulation of an abnormal non-specific surface charge carrier.

In this paper, we show that highly crystallized and (00l)-textured MoS₂ thin films can be achieved on glass substrates with NaF additive. The thin films have a direct optical bandgap of 1.77 eV and a p-type electrical conductivity of σ≅4.5×10^-2 S cm^-1 at room temperature, which are near those of the MoS₂ single crystals. These properties are required for the application of the MoS₂ in thin film solar cells. The influence of the sodium on the crystallization and texturization process has been interpreted as due to the formation of an intermediate sodium thiomolybdate phase. The decomposition of this compound when T>723 K leads to the achievement of the MoS₂ thin films having large crystallites oriented with their c axis perpendicular to the plane of the substrates. This process of texturization has then been generalized to the case of MX₂ (M: Mo,W; X: S, Se) thin films with Ni and K additives. These results constitute a new step towards the achievement of efficient MoS₂ based solar cells.

We have developed n-type microcrystalline hydrogenated silicon oxide (n-µc-SiO : H) thin films by the radio frequency plasma enhanced chemical vapour deposition (RF-PECVD, 13.56 MHz) method having suitable characteristics for use in the fabrication of single or multijunction amorphous silicon (a-Si) solar cells. The films have been characterized in detail for the study of structural and optoelectronic properties. Transmission electron microscopy, Raman spectroscopy, x-ray diffraction, Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy have been used for the structural studies. The dependence of the structure and optoelectronic properties of n-µc-SiO : H films on the various deposition parameters such as hydrogen dilution, chamber pressure, RF-power density etc have also been studied. Comparison of the properties between n-µc-SiO : H and n-µc-Si : H films have been studied, too, which shows that the former has higher optical gap (2.17 eV) and lower activation energy (0.015 eV) with similar electrical conductivity (12.08 S cm^-1).

In this paper, laser short-pulse heating of gold-chromium two-layer assembly is considered. Since, the heating period is in the order of picoseconds, nonequilibrium energy transport is considered when modelling the heating process. An electron kinetic theory is employed to derive the governing equations of energy transport while elasto-plastic analysis is carried out when modelling the thermomechanical response of the substrate materials. In the analysis, thermomechanical coupling is considered and it is accommodated in the energy transport equation. A numerical method using a finite difference scheme is used to discretize the governing equations. It is found that temperature attains considerably high values across the gold-chromium interface, which in turn results in excessive stress levels in this region.

Suppression of pore defects in keyhole laser spot welding demands for a theoretical description of the fundamental process. Investigating the unbounded keyhole collapse in liquid Zn instead of a solid provided a simplified situation offering several advantages. Improved high speed x-ray transmission imaging due to an enlarged keyhole in the absence of violent melt motion was enabled, which also facilitated the development of a semi-analytical mathematical model. Good correspondence between the experimentally and theoretically obtained transient keyhole and bubble shape permitted physical analysis by the model. Characteristic timescales were identified for post-vaporization, vapour relaxation, cooling, collapse, bubble contraction, oscillations and buoyancy. Recondensation due to rapid cooling turns out to be responsible for shielding gas flow into the keyhole, finally maintaining a spherical bubble. Creation of a convergent keyhole is a possibility to avoid bubbles.

The spatial distribution of the polarization and space charge in thermally poled poly (vinylidene fluoride) is studied using the laser intensity modulation method. Injected space charge, localized near the electrode polymer interface, tends to prevent the formation of uniform polarization in the polymer bulk. The actual amount of charge existing in the poled specimen is determined using hysteresis measurements and thermally stimulated discharge current (TSDC) measurements. By using the peak cleaning technique and by measuring the pyroelectric current during the cooling of the specimen, the contribution of depolarization current and space charge detrapping to the TSDC measurement is considered. From hysteresis measurements a relaxation process was observed around 65°C which was related to the dipolar relaxation in the crystalline phase known as the α_c relaxation. A significant increase of the TSDC at temperatures higher than 130°C was observed meaning that the dipolar charge and the space charge are very stable up to high temperature. In this temperature range, the pyroelectric current is significant. Two relaxation processes were identified for a polarizing temperature lower than 120°C. One is centred around the polarizing temperature and is related to space charge release. The second is related to dipole relaxation in the crystalline phase. The position of the last peak is determined by interaction between the dipoles and the internal electric field, resulting from the charge stored in the sample. We propose to call this as the α_cρ interaction. The higher temperature of the dipolar peak was identified as 86°C with an activation energy of 0.52±0.04 eV.

The simultaneous effect of impact ionization and the concentration of radiation on solar cell performance is analysed. For maximum solar concentration and an infinite number of impact ionizations one obtains a maximum cell efficiency (0.845). This corresponds to an optimum reduced driving force qV/E_g = 0.882, given a ratio of T_s/T_p~300/6000 (q,V and E_g are electron electric charge, voltage and bandgap energy, respectively, while T_s and T_p are ambient and sun temperature, respectively). With full concentration the optimum reduced driving force equals the Carnot factor 1-T_c/T_p exactly (T_c is cell temperature). In the case of no illumination, there is a negative driving force. This is related to the coefficient of performance of a Carnot refrigeration engine. In the limit of an infinite number of impact ionizations, the Carnot factor occurs again, this time as an upper bound to the optimum reduced driving force.

A thermodynamic optimization of a solar mini-dish/stirling system is presented. The solar collector heat losses by convection and radiation are diminished by using optical fibres to transport concentrated solar energy. We analyse an absorber-heater for the solar heat engine to ensure the reduction of the heat losses using the first law and the second law. Taking into account internal and external irreversibilities for the solar heat engine, the optimal operating temperature and the overall efficiency of the system are established.

Photopolymerization of a commercial dental resin has been investigated by ¹H stray-field (STRAFI) magnetic resonance. The resin is a visible light-cured system, included in a new generation adhesive, which is used to bond the restorative material to enamel or dentin. Different methods were used to follow the curing reaction, which involve long and short spin-echo train acquisitions to obtain one-slice and one-dimensional data, respectively. The echo attenuation, in the limit of very short time delays, could be described as the sum of two exponentials. While the intensity of the early echoes in the train appeared mainly governed by spin-spin relaxation, the decay of the last echoes seemed to depend also on spin-lattice relaxation in the rotating frame. The relative amplitude of the long-time component was found to decrease from 84% to 10% with the photopolymerization progress, and a STRAFI degree of conversion of 74% could thus be suggested. The influence of the curing protocol was observed in STRAFI profiles.

A theoretical framework is presented which allows, for the first time, quantitative statements about the temperature dependence of electrorotation (ER): while temperature changes in physiological ranges do not significantly alter the overall shape of the spectrum, all of the characteristic points of the spectra do shift, to varying extends, in both their field frequency and amplitude of rotation. To experimentally verify these predictions, we developed a device which allows for autonomous detection of rotation speed. It is based on the pinhole technique known as MOSPAD [1] but differs in its higher degree of automation, more robust algorithms for signal analysis, and the possible use of an adaptable virtual mask in the video-RAM instead of the solid one in the optical path. Our results are in good agreement with theory and suggest previous ER data without temperature control should be reconsidered. We describe conditions under which physical and physiological effects of temperature in and on cells can be distinguished. Moreover, we broaden the applications of ER from the traditional determination of (rather static) cellular properties to kinetics of cellular processes, to the impact of optical tweezers on the temperature of cells in their focus, or to resonance characteristics of electrode chambers.

The developing interfacial region between a soap bar and water has been studied using a suite of spatially resolved NMR techniques. Stray field imaging (STRAFI) allowed the dynamics of water ingress into a shop-bought, commercial soap to be followed. A simplistic analysis of the data shows the ingress to be a Fickian process (∝t^1/2) in the first 4 h. The T₂ contrast employed in the STRAFI method is not sufficient to resolve detail of the mesophase formation at the interface. However, double quantum filtered ²H spectroscopy at different positions in the interfacial region allowed water concentration (and mesophase distribution) to be mapped over the first 120 h of dissolution. A simple model shows good agreement with the water concentration data. In the isotropic soap solution above the interfacial region, J-cyclic cross polarization was used to selectively interrogate the CH₂¹H of the soap alkyl chains and, in combination with a pulsed field gradient measurement of self-diffusion, suggests a micellar solution in which the hydrodynamic radius of the micelles is ~5nm.

Experiments aimed at investigating the possible factors affecting the temperature performance of thick-film resistors are presented. Particular emphasis is given to the temperature coefficient of resistance (TCR) of thick film strain gauges printed on both alumina and stainless steel substrates. The results confirmed that the resistance versus temperature curve is nearly parabolic, but showed that T_min, the temperature at which the TCR changes to zero, is largely affected by the choice of resistor and substrate materials and also the thickness of the thick-film resistors. A possible explanation is proposed for the observed relationship between resistor thickness and TCR. Other factors, such as the thickness of the substrates, the choice of conductor materials, and whether single- or double-sided printing of the substrate was employed in fabrication were found to make little difference to the temperature performance of the thick-film resistors.