Table of contents

Microphotoluminescence and second-harmonic microscopy were used to study islands formed inside phosphate and fluorophosphate optical glasses with fullerene dopants. Scanning microphotoluminescence and second-harmonic microscopy indicated that fullerene dopants are subjected to strong influence from the glass matrix, which causes distortion of molecular symmetry, enhancement of fluorescence, and occurrence of noncentrosymmetry required by the macroscopic second-order optical nonlinearity.

Recent developments in plasma assisted physical vapour deposition (PAPVD) processes are reviewed. A short section on milestones in advances in PAPVD covering the time period from 1938 when the first PAPVD system was patented to the end of the 1980s is followed by a more detailed discussion of some more recent advances, most of which have been related to increases in plasma density. It has been demonstrated that the state of the art PAPVD processes operate in a plasma density range of 10¹¹ to 10¹³ cm^-3. In this range a substantial fraction of the plasma consists of ionized film forming species. Hence, the energy of the condensing film forming species can be directly controlled, as opposed to utilizing indirect energy control with, for example, ionized inert gas bombardment. For a large variety of applications ranging from ceramic film synthesis at conditions far from thermodynamic equilibrium to state of the art metallization technology, such direct energy control of the condensing film forming species is of critical importance, and offers the possibility to engineer the coating microstructure and hence the coating properties.

Within the framework of the single scattering and the anomalous diffraction approach, the conditions for coherent transmittance quenching for surface ferroelectric liquid crystal (SFLC) droplets have been found. The influence of the droplet polydispersity and the disorientation of their optical axes for the SFLC film for the conditions under which the film coherent transmittance becomes zero is analysed. The contrast ratio and the modulation depth of the SFLC film under the conditions of coherent transmission quenching have been studied. The possibility of a dramatic increase in the contrast ratio at fields of view of a few degrees is shown. Analysis of the contrast ratio and modulation depth of the SFLC film under the conditions of coherent component quenching and at a departure from these conditions has been performed.

A bulk Ge₂₀Te₈₀ glass was prepared using a melt-quench technique. The crystallization mechanism was studied using differential scanning calorimetry (DSC), scanning electron microscopy and x-ray diffraction. DSC was performed at different heating rates under non-isothermal conditions. From the heating-rate dependence of the temperature of the glass transition, T_g, and the peak temperature of crystallization, T_p, the average value of the activation energy for the glass transition, E_g, and the average value of the activation energy for crystallization, E_c, were calculated for the Ge₂₀Te₈₀ glass.

The crystallization mechanism was examined in terms of recent analyses developed for use under non-isothermal conditions. The results indicate that the glassy Ge₂₀Te₈₀ has three-dimensional growth, the average value of the order of the crystallization mechanism, n, is 3.5±0.1. The average values of E_g and E_c are 223.3±5.1 and 134.9±3.6 kJ mol^-1, respectively.

Two-dimensional island gold films (2D-I(Au)Fs) were prepared by a thermal evaporation technique where Corning 7059 glass slides, held at an ambient temperature during deposition, were used as substrates. After exposing the films to air at a room temperature of 300 K, the dc resistance of the films was monitored until the films attained short-term stability, namely, invariance of the resistance over time. The island gold films were identified by the value of their stable surface resistivity (ρ_s); these values are 23, 275, 4.4 × 10³, 23.2 × 10³ and 37.5 × 10³ MΩ/□. The variation of the stabilized surface resistivity with temperature over the range of 100-300 K was studied and the temperature coefficient of the surface resistivity (TCR) was deduced. The films have a negative TCR and for any particular temperature the magnitude of the TCR increases with ρ_s. For films with a certain ρ_s, the magnitude of the TCR increases with a decrease in temperature. The comparison between the magnitudes of the TCRs of the studied films in the present work and those reported by other investigators revealed that our films possess much higher values, and therefore this advantage renders them suitable for being used as temperature sensors. Our results were interpreted, qualitatively, by assuming that the electron transfer between islands takes place by the activated tunnelling mechanism.

Thin film and bulk samples were prepared from synthesized amorphous Te_82.2Ge_13.22Si_4.58 chalcogenide glassy alloy by the thermal evaporation technique. X-ray analysis shows that both synthesized material and thin film forms have an amorphous nature. The electrical and thermal conductivities for the bulk sample were studied as a function of temperature in a range below T_g (T_g = 423 K). The obtained results for electrical conductivity are explained in accordance with the Mott and Davis model. The switching effects in amorphous films were also investigated. The switching phenomenon for this composition was of memory type. The mean value of the threshold voltage _th was found to increase linearly with increasing film thickness (98.9-250.1 nm), while it decreased exponentially with increasing temperature (below T_g). The results obtained are explained in accordance with the electrothermal model for the switching process.

A gold contact with polypyrrole (PPy) doped with the copper phthalocyanine toluenesulfonate (CuPcTS) anion (Au/PPy-CuPcTS) was studied using complex impedance spectroscopy, current density voltage (J-V) and capacitance voltage (C-V) measurements. The J-V characteristics of these junctions are asymmetrical and nonlinear. The junction parameters extracted from the J-V characteristics (the saturation current density, the rectification ratio and the ideality factor) and from the C-V characteristics (the built-in voltage and the charge carrier concentration) are strongly influenced by the thickness and by the preparation temperature of the PPy layer. These Schottky diodes show high sensitivity to NO_x in the parts per million concentration range, which was explained by changes in the contact potential and in the carrier concentration of the PPy layer due to NO_x exposure. The NO_x sensitivity is influenced by the thickness as well as by the preparation temperature of the PPy layer. The junction parameters and the gas sensitivity can be improved largely by increasing the preparation temperature of the PPy films up to the glass transition temperature of PPy.

A solution of the eddy currents problem in a solid conducting cylinder placed in the field of an eccentric circular current loop is presented. The conventional potential theory can only deal with the simple case of rotational symmetry and axially directed exciting wires. If, however, the exciting current loop is placed such that the conventional vector potential has all three components, the vector field equation in cylindrical coordinates cannot be separated, hence no solution can be obtained. An advanced vector potential is therefore introduced to solve the present three-dimensional boundary value problem for the steady-state skin effect, which consists of two vector potentials that give transverse electric and transverse magnetic field components. Formulae for the eddy current distribution in the cylinder due to an eccentric circular current loop are developed and the results are then given in the form of a Fourier integral series. The analysis is then extended to cover an arbitrary current loop in a general position. In addition, the force acting on the conducting cylinder is evaluated and the results are given in the form of a Fourier integral series, which is then presented in a graphical form.

The second-order hyperpolarizability of two multi-adducts of fullerene, C₇₀ 5-aminonitrile and C₇₀ 5-dicyandiamide, was measured by using a femtosecond time-resolved optical Kerr effect at 810 nm wavelength. The magnitude was estimated to be as large as 4.1×10^-32 esu for C₇₀ 5-aminonitrile and 5.8×10^-32 esu for C₇₀ 5-dicyandimide. This showed that the optical nonlinearity of C₇₀ was strongly enhanced by forming a multi-addition charge-transfer complex.

This paper demonstrates that time-integrated space-resolved laser-induced plasma spectroscopy (TISR-LIPS) is a useful technique in the vacuum ultraviolet (VUV) for the quantitative determination of the carbon content in steels. The standard reference samples used were carbon-iron alloys containing a relatively wide concentration range of carbon (0.041-1.32%). In the experiments the output of a Q-switched Nd:YAG (1064 nm) laser, with approximately a 1 J maximum output pulse energy and approximately a 12 ns temporal pulse width, was focused onto the surface of each sample (under vacuum) in order to produce the emitting plasma. A fore-slit mounted in the target chamber allowed spatially-resolved spectral measurements in the axial direction of the plasma and provided emission lines that were almost free of the background continuum. A 1 m normal incidence vacuum spectrometer, equipped with a 1200 grooves mm^-1 concave grating and a micro-channel plate/photodiode array detector combination, was used as the detection system. A particularly interesting feature of this work is the demonstration that VUV spectroscopy allows ionic lines to be used and linear calibration curves were obtained for the five carbon spectral lines (from C⁺ and C²⁺) under investigation. The limits of detection for all lines were determined; the lowest detection limit (87±10 ppm) was obtained from the C²⁺ 97.70 nm line, which compares favourably with the only available value in the literature of 100 ppm.

The interaction of 20 ns, 3 J laser pulses with solid boron nitride targets is studied spectroscopically in the wavelength range from 30 to 300 Å, and by taking pinhole pictures at short wavelengths. The experiments were carried out for different angles of incidence of the laser beam and as a function of the depth of the hole in the target. Typical temperatures are from 22 to 45 eV. It is observed that the heating of the plasma occurs at the bottom of the hole and that the hole is along the axis of the direction of the laser beam.

An infrared heterodyne interferometer has been used to measure the spatial distribution of the electron density in direct current, atmospheric pressure discharges in air. Spatial resolution of the electron density in the high-pressure glow discharge with characteristic dimensions on the order of 100 µm required the use of a CO₂ laser at a wavelength of 10.6 µm. For this wavelength and electron densities greater than 10¹¹ cm^-3 the index of refraction of the atmospheric air plasma is mainly determined by heavy particles rather than electrons. The electron contribution to the refractive index was separated from that of the heavy particles by taking the different relaxation times of the two particle species into account. With the discharge operated in a repetitive pulsed mode, the initial rapid change of the refractive index was assumed to be due to the increase in electron density, whereas the following slower rise is due to the decrease in gas density caused by gas heating. By reducing the time between pulses, direct current conditions were approached, and the electron density as well as the gas density, and gas temperature, respectively, were obtained through extrapolation. A computation inversion method was used to determine the radial distribution of the plasma parameters in the cylindrical discharge. For a direct-current filamentary discharge in air, at a current of 10 mA, the electron density was found to be 10¹³ cm^-3 in the centre, decreasing to half of this value at a radial distance of 0.21 mm. Gaussian temperature profiles with σ = 1.1 mm and maximum values of 1000-2000 K in the centre were also obtained with, however, larger error margins than for electron densities.

The characteristics of planar magnetron discharges of an O₂/Ar mixture are clarified using the particle-in-cell/Monte Carlo method. The simulation is carried out for axisymmetrical magnetic fields under the condition of constant total gas pressure of 5 mTorr and constant applied voltage of 500 V. The fraction of oxygen partial pressure, p_O₂, is changed from 30 % to 70 %. In the case of p_O2 = 50% the order of the magnitude of number densities is n_e>n_Ar⁺>n_O2⁺>n_O⁺>>n_O^-. As p_O2 increases, the electrical field becomes weaker, the cathode sheath becomes thicker, n_Ar⁺ decreases, n_O2⁺ and n_O⁺ first increase and then decrease, and the total flux of positive ions onto the cathode decreases. The effect of the arrangement of a magnet system on the total ion flux is also examined.

Using the technique of a single probe we have measured the distributions of the potential and of the electron concentration, as well as of the electron temperature, inside a complex space-charge configuration formed by excitation and ionization of neutrals, produced by electron acceleration in front of a positively-biased electrode immersed in a neutral gas.

We report the results of a study on the influence of oxygen in the plasma gas used in the plasma arc cutting process on cuts obtained in mild steel plates. Experimental results of shapes of kerfs and the leading edges of the cut front formed while cutting a 6 mm mild steel plate at 100 A with nitrogen, air and oxygen as plasma gases are presented. These results are discussed in the light of the overall energy balance of the process. It is found that the exothermic reaction of oxygen in the plasma gas with the iron in mild steel enables the cutting of mild steel at higher speeds with both air and oxygen than the maximum cutting speed attainable with nitrogen. A comparison of the melting rates for oxygen with those of air reveals that although oxygen can produce more exothermal energy by oxidation, oxygen is not superior to air in melting metal near the bottom of the kerf formed at high cutting speeds.

The study shows that the dross formed at the bottom of the cut is determined by the shape of the cut-front surface over which the molten metal from the cut front flows to be ejected at the plate bottom. Any improvement of metal ejection to be gained with oxygen as the plasma gas may be the result of enhanced superheating of the metal melted from the cut-front surface.

The Al-enriched intermetallic compound DO₂₃-Al₃Zr was directly formed by Zr ion implantation into Al films at a current density of 64 µA cm^-2 using a metal vapour vacuum arc (MEVVA) ion source at a dose of 4×10¹⁷ ions cm^-2. With increasing ion dose the crystallinity of the DO₂₃-Al₃Zr phase was gradually improved, and at a dose of 5×10¹⁷ ions cm^-2 the DO₂₃-Al₃Zr layer was about 100 nm thick. The formed DO₂₃-Al₃Zr phase played a significant role in enhancing the hardness as well as the elastic modulus of the Al films.

The infrared emission in radioluminescence of feldspar crystals determines the received irradiation dose. This recently discovered phenomenon can be used for dating the last light exposure of feldspar grains (e.g. sediments). From the physical point of view, there is particular relevance to the infrared optically stimulated luminescence, because both deal with the same light sensitive electron trap. Data from light stimulation experiments (ultraviolet to infrared) suggest that a localized transition is most likely to be responsible for the infrared optically stimulated luminescence and that this process is possible for only a relatively small proportion of trapped electrons. The infrared radioluminescence signal gives direct information about the trapped charge density of the electron trap. A new model, described in terms of a band scheme, has been successfully used to interpret the observed data.

Impact electrification between an elastic sphere and a metal plate has been studied experimentally. To find out how charge transfers between the contact bodies, the voltage profiles at the impact are measured under various experimental conditions using a digital oscilloscope, and simultaneously the contact deformation of the sphere is visualized with a high-speed camera. The initial charge on the sphere and the transferred charge are obtained from the integrated voltage with respect to the elapsed time of the impact process. The variation of the electrification by repeated impacts is analysed by taking account of the initial charge and charge relaxation with elapsed time. Furthermore, the relationship between the transferred charge and the contact area as a function of the impact velocity is investigated based on the electrification theory and Hertz analysis of elastic contact deformation.

Studies on the dc electrical conductivity of SiO₂/CdSe/SiO₂ nanocomposites in the temperature range of 150-370 K are presented. The existence of a threshold volume fraction of the semiconducting phase for the percolation conduction in the composites was observed. The results are in agreement with the predictions of the theoretical models proposed for granular metals. The temperature dependence of the dc conductivity in the higher temperature range (with T^-1/2 variation) is in good agreement with the model of Sheng and Klafter.

Vanadium oxide is one of the most important optoelectronic materials that are used in optical switching devices, gas and humidity sensors, and secondary Li batteries. It has been recognized that V₂O₅ can be coloured through electro-, photo-, and thermochromism processes. We report here that the surface of V₂O₅ (annealed at 580 °C for 4 h) pellets turned to a deep blue colour upon just one pulse ablation of the XeCl excimer laser (λ = 308 nm, pulse duration = 36 ns, output energy = 100 mJ/pulse). Also we found that when a yellow pentoxide vanadium pellet was exposed to proper excimer laser irradiation, its surface electrical conductivity changed remarkably, that is from an insulator to a semiconductor. The pentoxide vanadium sample, before and after excimer laser irradiation, was analysed with scanning electron microscopy (SEM), UV-visible diffuse reflectance spectral (UV-VIS), x-ray diffraction (XRD), Raman spectrum (RS) and x-ray photoelectronic spectrum (XPS). The presence of a peak at about 830 cm^-1 in the Raman spectrum indicates that the sample after laser irradiation is sub-stoichiometric with an oxygen deficiency. XPS showed the partial reduction of V₂O₅ and the appearance of conduction band electrons. SEM showed that the surface of V₂O₅ became smooth and less porous after excimer laser irradiation. From our experimental results, it was concluded that the laser-induced colouration is attributed to thermochromism.

The procedure for the simultaneous evaluation of correlated physical parameters using covariance least-squares methodology has been implemented. A versatile computer code has been developed for the execution of the evaluation task and for the solution of a wide range of physical data analysis problems including curve fitting, spectral peak location and decay data analysis. The results of a validatory simultaneous cross section revaluation and of the analysis of titanium decay data carried out with the code are reported. The result of the validation test is in good agreement with the original evaluation by Hayes and Ryves.

The decay data have also been analysed using the maximum likelihood method appropriately formulated for a photopeak fed by one decaying nuclide. The result is in good agreement with that obtained via the covariance least-squares method. This confirms the accuracy and consistency of the whole procedure.

Hajossy et al (1999 J. Phys. D: Appl. Phys.32 1058) alleged that the break of a short circuit is preceded by the ignition of an arc because they estimated the relative field strength to be high enough for this to occur. This assertion has proven inconsistent with measured data. In particular, the typical sudden change from progressively rising to sharply dropping voltage contrasts with the alleged gradual commutation, but rather points to a detonation across the isthmus. Concerning the confinement of metal vapour due to inertia, the comment refers to Hess (1991 J. Phys. D: Appl. Phys.24 36-40). There are several substantiated reasons why the minimal diameter of the bridge and also the voltage, required for a bypassing ignition, are actually larger than the values estimated by Hajossy et al, and why the bridge does not simply vanish. Somewhat misleading observations are blamed for the fallacies. The established wire explosion model of re-ignition is certainly valid, even in general. For that reason, there is no hope that the alleged premature ignition could be used for avoidance of the spatter-causing explosion.

It is shown that estimations made in the premature arc scenario are in good agreement with the observed results in spite of some simplifications and uncertainties pointed out by Blumschein. The temperature dependence of electrical resistivity does not influence the geometry of the drop's neck and the magnetic pressure does not suppress the evaporation dramatically. The reached current density casts doubt upon the crucial role of isochoric heating in the arc ignition. The shunting arc, used in plasma-based ion implantation, gives experimental evidence of the premature arc scenario. The relative field strength (600 Td, used also in the premature arc scenario) is sufficient for the shunting arc ignition.