Table of contents

A method of synthesizing bulk amounts of single-walled carbon nanohorns (SWNHs) on a significant low-cost basis is proposed based on the 'arc in water' method with N₂ injection into the arc plasma. It is elucidated that rapid quenching of the carbon vapour in an inert gas environment is necessary to form the delicate SWNH structures. To realize this reaction field, the arc plasma between the graphite electrodes was isolated from the surrounding water by a thin graphite wall with an N₂ flow that excluded reactive gas species (H₂O, CO and H₂) from the arc zone. High concentrations of SWNHs were found as fine powders floating on the water surface. The particle size distribution of the SWNHs produced by this method was evaluated by dynamic light scattering, resulting in an approximately 70 nm peak diameter.

The variation of surface magnetization with corrosion in Fe_73.5Cu₁Nb₃Si_13.5B₉ in the amorphous and nanocrystalline states is investigated. The results show that in the amorphous samples when the oxidized layer increases the surface saturation magnetization decreases. However, in the nanocrystalline samples the surface saturation magnetization does not change significantly with the corrosion process but the approximation to saturation is different in the non-oxidized and oxidized nanocrystalline samples. In the case of non-oxidized samples, the surface saturation magnetization is reached at a low applied magnetic field (1000 Am⁻¹), whereas in the oxidized samples it is reached at a higher applied magnetic field of 7000 and 9000 Am⁻¹ for the samples annealed at 520°C for 60 min and 30 min, respectively.

In this paper the technique of thermoelectric measurements at high pressure was applied for characterization of semiconductor microsamples based on lead chalcogenide compounds (p-PbSe, n-Pb_1−xSn_xSe). The Raman scattering technique at ambient pressure was used as an alternative tool for testing of the samples. Raman measurements have revealed broad peaks at 135 and 265 cm⁻¹ for PbSe and Pb_1−xSn_xSe. Analogous spectra were obtained for PbS, and PbTe-based ternary compounds at higher and lower frequencies, respectively. The peaks have been attributed to the first- and second-order Raman modes. From resistivity and thermoelectric power data the linear decrease in the pressure of the NaCl → GeS structural phase transition with increasing Sn content has been established and the thermopower of high-pressure GeS phases have been determined. Thermoelectric properties of the samples at high pressure have shown high sensitivity to a small variation in the composition of the ternary Pb_1−xSn_xSe compounds, which makes it possible to distinguish semiconductor microsamples whose compositions are very similar.

Torch plasma arcs have useful high-energy and high-current characteristics. Torch plasma arcs can be flexible even if exposed to high-speed laterally flowing gases. This study measured the length, voltage, input power, heat power and heat efficiency of a torch plasma arc to the anode to elucidate their influence upon the plasma torch arc anode attachment with a high-velocity laterally flowing gas. That velocity was varied from 0 to 60 m s⁻¹. The axial plasma gas argon flow rates used were 4, 8 and 12 slpm. Consequently, the input power increased about 8000–16 000 W with these lateral gas air velocities. The heat efficiency decreased with lateral gas air velocity from about 50% to 25% at a current of I = 150 A. The torch plasma arc length, L_a, was ca 1 cm. The results of this study are applicable for providing electrical power from the ground to high-speed vehicles or vice versa and for reducing anode erosion by anode spot movement.

Currently, research fields related to the elaboration of efficient layering methods for ICF/IFE applications are rapidly expanding. Significant progress has been made in the technology development based on rapid fuel layering inside moving free-standing targets (FST) which is referred to as the FST layering method. This paper presents our new results obtained in this area and describes technologically elegant solutions towards demonstrating a credible pathway for mass production of IFE cryogenic targets.

The ratio of intensities of the first negative system and the second positive system of nitrogen as a function of the electric field strength was experimentally determined in atmospheric-pressure air. The non-self-sustained discharge was excited in a parallel-plane gap using the radiation of a pulsed laser. The field strength was varied in the range of 135–285 Td. The peculiarities of the measurement and data processing of signals of very low intensity are described. The results are compared with the theoretical predictions of other authors.

Hydrogen ions (H⁺, , ) from the near-ground-electrode region in dielectric barrier discharge plasmas were characterized using a molecular beam mass spectrometer under a hydrogen pressure of 1–80 Torr. The measured H⁺ current is more than one to a few orders of magnitude greater than the currents of and at a pressure of 1–15 Torr, with a peak-to-peak voltage of 50 kV and 35 kHz ac power source. At a gas pressure range of 15–80 Torr, only the H⁺ ionic signal is observed. The hydrogen ion currents rise with increasing discharge voltage and ac frequency but exhibit a maximum over the H₂ pressure range studied. The H⁻ ionic signal is also detected under certain discharge conditions within a hydrogen pressure of 1.5–35 Torr. The main physicochemical processes of interaction between hydrogen ions, neutrals and electrons in the alternative and temporary cathode sheath near the discharge electrode have been discussed. The dependence of the mean energy of H⁻ ions on H₂ pressure has also been obtained.

A two-dimensional thermal and chemical non-equilibrium model was developed for high-power Ar–N₂ inductively coupled plasmas (ICPs) at atmospheric pressure, which are conventionally assumed to be under local thermal equilibrium condition. The energy conservation equation of electrons was treated separately from that of heavy particles. These equations consider reaction heat effects and energy transfer between electrons and heavy particles as well as enthalpy flow resulting from diffusion due to the particle density gradient. Chemical non-equilibrium effects were also accounted for by solving mass conservation equations for each particle, considering diffusion, convection and net production terms resulting from 30 reactions. Transport and thermodynamic properties of Ar–N₂ plasmas were self-consistently calculated using the first-order approximation of the Chapman–Enskog method at each iteration using the local particle composition, heavy particle temperature and electron temperature. Power balance for the electron energy and the mass balance of atoms and ions in a high-power Ar–N₂ ICP were investigated using the model developed. Calculational results obtained by the present model were compared with results from two other models such as a one-temperature chemical equilibrium model and a one-temperature chemical non-equilibrium model. This comparison supported the discussion of chemical and thermal non-equilibrium effects in the high-power induction plasma.

Etching of SiO₂ rods has been obtained with a dc torch with argon as the process gas in an air environment at atmospheric pressure; the high temperature of the plasma jet causes vaporization of the exposed area. The apparatus and torch operative parameters have been set up to obtain a depth etch rate of up to 0.6 mm min⁻¹ corresponding to 0.826 g min⁻¹.

An enthalpy probe has been employed to monitor the plasma conditions before the thermal plasma etching process and from the experimental etch rate a surface rod temperature of T_sur = 2057 K has been derived. Etching has been obtained with uniformity over the entire exposed area with peak to peak differences below 1%.

The plasma to rod heat transfer has been simulated using a commercial CFD code Fluent©. The model consists of a non-steady two-dimensional simulation for a compressible turbulent fluid, with an adapted grid calculation. Boundary conditions have been set out using the enthalpy probe plasma jet map. In particular for the flow, the continuity equation for chemical species, the species transport equations (Fick's Law), the momentum conservation equations, the energy equation and the turbulent kinetic energy have been solved. In the solid regions the convective energy transfer due to the rotational motion of the rod, the conduction and radiation energies have been considered. The heat transfer between the fluid and the silica walls (continuity temperature between the fluid and the solid) accounts for the energy loss due to surface radiation (q_r) and vaporization (q_v) obtained from experimental data.

A rod surface temperature of 2057 K obtained from experimental etch rate data agrees well with the calculated temperature obtained using Fluent© (T_sim = 2010 K).

The effect of ultrasound waves on the production of ozone by dc electrical discharge in air, at atmospheric pressure, with a single hollow-needle to plate electrode enhanced by the flow of air through the needle for both polarities of the needle, different airflow rates and currents has been studied experimentally. It was found that the application of ultrasound increases ozone generation for the discharge, with the needle negatively biased, and has no effect on ozone production for the discharge when the needle is biased positively. For the discharge with the needle biased negatively, the ozone generation increases with the increase of the ultrasound transducer surface amplitude and decreases with the increased airflow rate through the needle.

A Monte Carlo model of imprisonment of Xe resonant photons and electronic de-excitation of the Xe resonance level, Xe^*, in ac colour plasma displays is developed. The number of resonant photons arriving at phosphor are calculated for various discharge cell heights, discharge thicknesses, Xe mixture ratios, current pulse widths, and drive frequencies in 67 kPa Ne+Xe mixtures. From the calculations, it was found that only 23.2% of the total Xe^* participate in generating photons, which arrive at the phosphor under a typical electron density of 5.0 × 10¹⁹ m⁻³. Photons from 22.5% Xe^* reach the front glass plate where phosphor is not deposited, and 54.3% of Xe^* are de-excited by electronic collisions. Driving the discharge cells at low current density is one of the effective methods of reducing the de-excitation loss. Optimized drive conditions, such as a narrow current pulse drive, can suppress the luminous efficiency degradation. An increase in the height of the discharge cell is preferable provided that the discharge fills the space.

In this paper a preliminary spectroscopic study of a microwave version (2.45 GHz) of the electrodeless QL-lamp from Philips is presented. Different spontaneously emitted lines by the argon and mercury atoms existing in the discharge have been measured. Equilibrium and non-equilibrium concepts are applied to radiating excited atomic levels. This permits us to infer some information about the excitation temperature in the lamp as well as the possible mechanisms of species excitation involved in this system.

The mechanisms for population inversion among the excited states of He I and Ne I in regenerative sooting discharges have been investigated as a function of the geometry and the physical parameters of the graphite hollow cathode sources. The effect of the state of sooting of the hollow cathode, the gas pressure and the role of the cycling of i_dis on the population inversion of the excited He I and Ne I levels have been investigated.

This work is devoted to the study of plasma parameters in the expansion of a microwave discharge sustained within an Ar–N₂–H₂ gas mixture. The plasma expansion in the reactor depends on the wave propagation conditions.

We show that in a pure argon discharge the electron energy distribution function (EEDF) is identical to a Maxwell energy distribution function whatever the distance between the discharge exit and the substrate holder is and whatever the incident power is, ranging between 100 and 400 W. However, results show that the electron density is larger close to the discharge exit than to the substrate holder.

When N₂ or H₂ is mixed with Ar, the discharge shrinks. The EEDF is displaced towards a low electron energy, and this behaviour increases with increasing N₂ or H₂ percentage. The EEDF cannot be compared with a Maxwell energy distribution function for a gas mixture containing more than 10% N₂. Beyond this value, the plasma is unstable 3 cm below the discharge exit, and for larger N₂ concentrations, the wave propagation is not observed in these regions.

When the three gases H₂, N₂ and Ar are all mixed together in the gas mixture, the plasma is more stable and the expansion is detected even for gas mixtures containing a large concentration of (N₂, H₂) mixed with argon, in a 80% Ar–20% (N₂, H₂) or 48% Ar–52% (N₂, H₂) gas mixture. However, when the concentration of H₂ is too low (49% Ar–50% N₂–1% H₂), the plasma shrinks and wave propagation is not observed. This behaviour could be explained assuming that these gas mixtures containing Ar–H₂–N₂ are producing NH_x species in plasma that are low ionization energy species. However, numerical models are necessary in order to study such a complex plasma and to confirm the accuracy of this last assumption.

In this study, the influence of increasing the Al concentration on the electrical, optical and structural properties of spray-pyrolysis-deposited SnO₂ films has been investigated. The SnO₂ : Al films were deposited at a substrate temperature of 480°C using a hydro-alcoholic solution consisting of tin and aluminium chlorides with various Al-doping levels from 0 to 30 wt% in solution. The [Al]/[Sn] atomic ratios were from 0 to 12.1 in films. The results of x-ray diffraction have shown that the deposited films are polycrystalline without any second phases with preferential orientations along the (110), (211) and (301) planes and an average grain size of 28.7 nm. Also, the Hall effect and resistivity measurements of the films show that for a specific acceptor dopant (Al) concentration (8.0 at% in film), majority carriers convert from electrons to holes and p-conductivity dominates. The optical absorption edge for undoped SnO₂ films lies at 4.105 eV, whereas for high acceptor-doped films it shifts towards lower energies (longer wavelengths) in the range of 4.105–3.604 eV.

Thin films of hafnium oxide were deposited by electron beam evaporation. The effects of the substrate temperature and the oxygen partial pressure on the refractive index and carbon monoxide sensing properties of the films were studied. The films were characterized using x-ray diffraction and x-ray photoelectron spectroscopy techniques. Films deposited on unheated substrates were amorphous, whereas those deposited on heated substrates showed a mixture of amorphous and polycrystalline structure. All the films were found to be optically inhomogeneous. The inhomogeneity of the films was taken into account in the determination of their refractive indices. It was found that the porosity (as reflected by the refractive indices) of the films was the main factor that affected the sensitivity of the films in relation to their detection of carbon monoxide.

Theoretical aspects of quantitative diffraction-enhanced imaging of weak objects are considered using the Fourier optics approach. The amplitude and phase transfer functions are introduced by analogy with the well-known case of in-line (holographic) imaging. The inverse problem of the reconstruction of the phase and amplitude of the incident wave from recorded images is solved in the case of non-absorbing objects and objects consisting of a single material and in the general case of objects with uncorrelated refraction and absorption characteristics. A comparison is given between the solutions to the inverse problem obtained using the new formalism and the geometric-optics approximation.

Asymmetrical periodic ('ratchet') potential energy structures have a number of applications, including the dielectrophoretic rectification of Brownian motion, the implementation of quantum tunnelling devices, and as a model of the action of molecular motors such as muscles. The effectiveness of such devices is dependent on the asymmetry of the potential energy, not that of the potential energy generating structures. Using empirical analysis of simulations of electric field ratchets, this paper derives empirical expressions describing, and optimizing, electric field ratchets in terms of the electrode dimensions.

For the first time laser-induced breakdown spectrometry, with laser pulse repetition frequencies of up to 1 kHz, with single pulse evaluation is realized for scanning microanalysis of macroscopic samples. The tightly focused beam of a diode-pumped Q-switched Nd : YAG-laser is scanned with a step size of 20 µm across a sample surface. The emission spectrum of each laser-induced plasma generated by a single laser pulse of 2 mJ energy is guided to a spectrometer of the Paschen–Runge type to detect the line radiation of up to 24 elements simultaneously covering a spectral range from the vacuum ultraviolet to the near infrared. The time resolved spectral signals linked to the respective detector channel are processed to generate maps of the spatial distribution of elements in the sample surface. In a measuring field of typically 1 × 1 cm² 250 000 measurements are performed within 11 min. The spatial resolution achieved, in terms of the diameter of the crater produced by a single laser pulse in steel samples, is better than 15 µm. The experimental system is applied to investigate inclusions in steel samples. These inclusions influence the quality of steel grades for the production of spring steel, thin sheets and wires. They consist of oxides, nitrides or sulfides. Correlating the maps of different elements allows us to identify the type of inclusion, this is demonstrated for aluminium oxide, aluminium nitride and manganese sulfide.

The supersonic jet flows of neutral gas from atmospheric to near-vacuum conditions in the interface region of mass-spectrometer systems is investigated by continuum-based (fluid) numerical simulations. An enhanced understanding of the neutral gas transport is of paramount importance to fully understand flows in the interface region of mass spectrometers, for it is the neutral dynamics that governs and drives the ions from the high pressure ion source through the interface orifice towards the ion optics and detector subsystems. The key features and structure of the complex neutral gas flow are examined and the influence of large pressure differences imposed across the interface region, orifice geometry, and gas skimmer configuration used for flow control are assessed. The flow structure is shown to be that of a classical under-expanded free jet for 'skimmer-absent' cases and very good agreement between the numerical predictions and empirical and experimental values is demonstrated. For the 'skimmer-present' cases, the shock structure downstream of the orifice and skimmer is identified and fully described and its influences on the flow skimming and focusing processes are discussed.

The dimensionless thermoelectric figure-of-merit, ZT, of Bi₂Te₃ based alloys was investigated under a large temperature difference using a recently reported 'open/short circuit' measurement technique. It is shown that the measured ZT decreases with an increase in temperature difference. Theoretical analysis indicates that this dependence can be explained by taking into account the Thomson effect. An equation is obtained for a modified thermoelectric figure-of-merit which is valid for measurement over large temperature differences.