Table of contents

Gold Schottky contacts formed in situ on n-type GaN after a 600 °C anneal have been characterized by current-voltage (I-V) measurements and x-ray photoelectron spectroscopy (XPS). The mean Schottky barrier height and lowest ideality factor were found to be 1.24 eV and 1.03, respectively, as measured by I-V. The highest barrier measured was 1.35 eV with an ideality factor of 1.12. XPS data showed that the 600 °C anneal produced an upward band bending of 0.35 eV, the subsequent gold deposition caused a further band bending of 0.25 eV in the same direction. Our results can be interpreted in terms of the Cowley-Sze model and suggest a high density of acceptor states at the bare GaN surface.

We demonstrate that extremely high aspect ratio patterns can be created at a submicrometre scale using focused-ion-beam etching in a porous material. Thanks to a preliminary microscopic structuration of the etching material, the limiting effects usually observed in bulk material ion-beam etching are strongly reduced. Holes with an overall aspect ratio of 50 are obtained. In combination with the photo-electrochemical etching, this method is successfully used to fabricate three-dimensional silicon photonic crystals up to five periods thick at a submicrometre scale.

This paper discusses the role surface analytical science has played in understanding the complex phenomena occurring during lubrication of modern internal combustion engines. The interactions between the multi-functional lubricant additives and the various metallic surfaces present in the tribological contacts are complex and lead to the formation of inhomogenous multi-layer protective surface films. Surface analysis by ultra-high vacuum (UHV) techniques such as x-ray photoelectron spectroscopy, Auger electron spectroscopy and secondary ion mass spectrometry has allowed model structures for these films to be derived through which the behaviour of the contact can be understood. Non-UHV probes have elucidated the role played by the soluble, partly reacted or degraded film precursors that occupy the interfacial region between the solid surface and the liquid lubricant, and have allowed the mechanical properties of the films to be investigated on a micro- and nano-scale. The use of surface analytical techniques to study interactions between lubricant species and combustion soot is also discussed.

A recently developed new experimental-analytical x-ray diffraction method for the direct non-destructive characterization of single-crystal alloys is applied to map the complex structure-factor of InGaAs/GaAs multi-quantum wells. The technique is based on analytical measurements of the x-ray phase and amplitude changes in a narrow polychromatic region of synchrotron radiation. High-resolution, x-ray Bragg diffraction profiles have been collected at the European Synchrotron Radiation Facility near the absorption edge of Ga. The studies have allowed the observation and preliminary analysis of fine structure of nanoscale sublayers, where the crystal structure factor may noticeably differ from the bulk material. These results might allow direct and quantitative analysis of the exact location and nature of relaxation defects in single-crystal multilayer structures.

Nanosize pore arrays have been prepared by the self-organization process of aluminium anodic oxidation. The symmetry of the pore configuration has been analysed by using fast Fourier transformation. For different anodization temperatures, it has been found that lower temperatures yielded higher symmetry. The linear relation of Lnσ_a versus T reveals that the anodization process is thermally activated with the apparent activation energy, E_c, of 0.52 eV. It was also found that the temperature has less influence on the ordered pore domain size than acid concentration. The largest domain size was observed for samples anodized under the conditions of 0 °C, 40 V, 0.6 M oxalic acid. The surface morphology of the acid solution/alumina and alumina/metal interface indicates that steady growth of alumina film at lower temperatures ceases the uneven local expansion of the alumina and contributes to the high asymmetry of pore arrays.

Some of the physical properties of xCuO-50 PbO-(50-x)B₂O₃ glasses were studied. The transformation temperature shows a minimum value at about 20 mol% CuO. The infrared spectra reveal that in this glass the fraction of four-coordinated boron atoms would be minimal. Up to a content of 30 mol% CuO there is a limited increase in density. Both the electric resistivity and activation energy decrease with increasing CuO content. These changes are correlated with the distribution of the structural units in glass. There are specific changes for a CuO content >30 mol% in the density and the parameters of electric conduction. The changes are due to crystallization effects in such glasses. The electric conduction appears to be ionic with Pb²⁺ and Cu²⁺ as the charge carriers. The change in properties has been correlated with the structure of the glasses.

Contributions of acoustical deformation scattering, ion impurity scattering and grain boundary potential scattering to the conductivity of TCO films have been calculated in order to deduce the intrinsic limit of conductivity of TCO films regardless of precise details of the preparation procedure. The results indicate that the effective mass of charge carriers has a strong dependence on carrier concentration. Based on the effective mass correction, as well as the carrier concentration ionized impurity centre correction, scattering due to ion impurity has been developed to explain the upper limit of mobility or the lower limit of resistivity of TCO films. Two empirical expressions are introduced to depict the dependence of the upper limit of mobility and the lower limit of resistivity of TCO films on carrier concentration. The dependence of transparency on carrier concentration is also discussed.

The switching effects in Sb_xSe_1-x (0⩽x⩽0.9) thin films have been investigated. The annealing of the films at 323 K improves the switching characteristics and decreases the threshold voltage V_th. The threshold switching voltage and threshold activation energy ε_s were found to decrease linearly on increasing the antimony content. Moreover, the threshold switching voltage increased exponentially with temperature.

Time dependence of the switching current produced by reversal of domains was analysed as a function of electric field and temperature using the Avrami theory. By direct observation of the domain pattern during slow polarization reversal by means of nematic liquid crystals it was possible to reveal significant information concerning the mechanism of switching.

By using the matrix method for describing the propagation of electromagnetic waves in multilayers, the intensity distribution of the writing laser beam inside a CD-R as well as its reflectance R_m and transmittance T_m were calculated. Based on the rate of energy absorption derived from the intensity profile, the temperature distribution in the disc layers during the recording was then calculated by solving the heat conduction equation numerically. Due to the interference effects, both the maximum temperature T_max and the optical absorptance 1-R_m-T_m of the multilayer are found to oscillate with increasing thickness d₂ of the dye layer, which accounts for the failing of the writing on discs with d₂-values corresponding to the minima of these curves. Finally, a simple relationship has been derived allowing the prediction of T_max without numerically solving the heat conduction equation.

Stable electron emission from amorphous diamond film at a low threshold field of 6-7 mV m^-1 has been observed using a transparent anode technique. The electron emission characteristics are discussed in terms of the structural properties of films. Using scanning electron microscopy and Raman spectra, the emitting and the non-emitting regions of the amorphous diamond film are analysed. The emitting regions exhibit rougher microstructure in morphology and a stronger Raman peak at 1360 cm^-1 than the non-emitting regions, a signature of having more micro-sp² components. It is suggested that field emission is prone to take place at the regions containing more sp² nanoclusters or nanocrystalline graphite.

We present a theoretical treatment of the fundamental perturbations caused when continuous wave tunable laser radiation is absorbed by the low-temperature plasma of a noble gas positive column. For the first time we present a full theoretical description of the contributions due to the induced changes in the electric field, electron density and radiation trapping, as well as the primary laser perturbations. Comparison of our theory with experimental observation shows that the primary perturbations are generally dominant but in some instances it is the field perturbation which has the greatest effect.

In the present paper, a new approach to modelling the ablation phenomenon using computational fluid dynamics (CFD) tools coupled with a physical radiation model is proposed, implemented and validated for application in circuit-breaker arc studies. The present work shows that the principal characteristics of ablation-dominated arcs can be simulated effectively using CFD tools if the radiation incident at the wall boundaries can be predicted accurately.

A new, more precise and simple semi-empirical formula has been obtained for the prediction of the rotational velocity of magnetically driven arcs in air and nitrogen. The formula is based on the balance between the motive Lorentz force and the aerodynamic drag force and takes into account changes in the gas density value due to the arc rotation and the axial gas velocity. The formula enables the calculation of the arc velocity in electric arc heaters as a function of current, magnetic field, axial gas velocity and gas density. Experimental results are presented for arcs in air and nitrogen, for currents in the range 100-1760 A, magnetic induction values of 0.005-3.9 T and axial gas velocities of 0.2-33 m s^-1. The formula can be useful for the study of cold electrode erosion and engineering calculations of electric arc heaters.

Vacuum arc plasma jet (VAPJ) propagation in a neutral nitrogen atmosphere has been calculated numerically on the basis of a hydrodynamic description. It was assumed that the VAPJ was emitted isotropically from a point source located z₀ = 20 mm in front of the entrance of a straight duct 100 mm in diameter in which an axial magnetic field of 0.02-0.05 T was imposed. Plasma densities of n₀ = 10¹⁸ and 10¹⁹ m^-3 and neutral gas densities n_n0 = 0.001-0.1×n₀ were used as initial conditions at the duct entrance. A three-fluid model was used, with the ion temperature having an initial value at the duct entrance of T_i = 10⁴ K, while constant temperatures of T_e = 3×10⁴ K and T_n = 10³ K were assumed for the electrons and neutrals, respectively.

It was found that the plasma jet decelerates down to the critical point, i.e. where the jet velocity is equal to the local speed of sound. The distance of the critical point from the entrance cross section decreased from z_c = 4×R (R = radius of duct) for n_n0 = 0.001×n₀ down to z_c = R for n_n0 = 0.1×n₀. It was found that increasing the magnetic field also decreased z_c. It was also found that the electrons and ions have rotational motion components, in opposite directions, and that friction with the neutral gas decreases the rotational velocities.

The relationship between the fume formation rate (FFR) in gas metal arc welding (GMAW) and the droplet size that is transferred from the wire to the workpiece is explored. A strong relationship between droplet size and FFR has been found experimentally. This is in agreement with the predictions of recent modelling work. The result could be applied in the design of welding procedures using pulsed GMAW to minimize fume.

Cathaphoresis of Zn evaporated into the positive column of helium and neon discharges was investigated both experimentally and theoretically. The side-light intensity of the Zn-I 518.2 nm transition was recorded along a 4.5 cm long positive column discharge with an inner diameter of 3 mm. The buffer gas pressure was varied between 10 and 25 mbar while discharge currents of 20-60 mA were applied to the tube. Reasonably good agreement was found between the experimental data and the theoretically predicted axial distribution of zinc concentration in the tube. The results can be useful in the design of the cathaphoretic confinement section of the different He-Zn laser tubes and a prospective Ne-Zn laser system, which would operate in the deep ultraviolet region (210 nm).

Dielectric barrier discharges (DBDs) occur in configurations which are characterized by a dielectric layer between conducting electrodes. Two basic configurations can be distinguished: a volume discharge (VD) arrangement with a gas gap; and a surface discharge (SD) arrangement with surface electrode(s) on a dielectric layer and an extensive counter electrode on its reverse side. At atmospheric pressure the DBD consists of numerous microdischarges (VD) and discharge steps (SD), respectively, their number being proportional to the amplitude of the voltage. These events have a short duration in the range of some 10 ns transferring a certain amount of charge within the discharge region. The total transferred charge determines the current and hence the volt-ampere characteristic of each arrangement. The microdischarges (discharge steps) have a complicated spatial structure. The discharge patterns on the dielectric surface depend on the polarity and amplitude of the applied voltage as well as on the specific capacity of the dielectric. Experimental findings on DBDs in air and oxygen are presented and discussed.

On the basis of a self-consistent two-dimensional modelling the temporal and spatial development of a microdischarge and discharge step are investigated numerically. The results lead to an understanding of the dynamics of DBDs. Although in VD arrangements cathode-directed streamers appear especially in electronegative gases, their appearance is rather unlikely in SD arrangements.

The application of DBDs for plasma-chemical reactions is determined by the productivity, with which the energy of the electric field can be converted into internal states of atoms and/or molecules. Depending on the desired product it could be both the generation of internal electronic states of molecules or atoms and dissociation products of molecules. The discharge current and current density of DBDs in both the SD and VD arrangements as well as the energy release and energy density distribution in the discharge region are presented. As an example the effectiveness of the energy conversion into ozone production is detailed. Some peculiarities of the discharge parameters, for instance the correlation between discharge patterns (microdischarges or discharge steps) and surface charge density, are discussed.

The discharge plasmas of electronegative gases such as chlorine are often used for etching poly-Si in the ultralarge-scale integrated (ULSI) manufacturing process. In the present work, systematic self-consistent particle-in-cell/Monte Carlo simulations are performed for a weakly ionized chlorine plasmas produced by a radio frequency discharge between parallel electrodes. Particle collisions are described using a set of cross section data and effective theoretical models. The effects on the plasma structure of the applied voltage, the gas pressure, the secondary electron emission coefficient, the distance between the electrodes and π-scattering are investigated in detail using a supercomputer.

In this paper, plasma based ion implantation of a diamond-shaped target was simulated using a fluid dynamic model for three different sizes. The effects of the target size on plasma sheath evolution and the implanted ion parameters have been studied. It was found that a larger sized target would result in a faster sheath expansion, and better conformity between the sheath and the target. For all three cases, the ion implanting dose peaked near the corner and decreased at the corner, reminiscent of the sheath characteristic around an independent corner.

A unified model, free of any adjustable parameters, for the size-dependence and dimension-dependence of melting point depression and superheating of nanocrystals is developed. In terms of the consideration of the surface/volume ratio of nanocrystals, the suppression of melting point of nanocrystals and superheating of embedded nanocrystals are predicted. The model predictions for the melting temperatures of nanocrystals are consistent with the experimental results and molecular dynamics simulations.

The structural framework of a medium hardness Fischer-Tropsch wax distillate is established quantitatively by electron crystallography and compared to model paraffin assemblies with a similar Gaussian distribution of chain lengths. The lamellar packing closely resembles the crystal structure of refined petroleum waxes with a similar distribution of defects near the lamellar interface. Nevertheless, clear differences associated with the absorption of smaller chains within the lamellar interface, detected by NMR, are not resolved by these diffraction measurements, perhaps due to artefacts induced by the high vacuum of the experiment and/or specimen preparation.

The potential of photoacoustic spectroscopy to resolve the crystal field levels of Cu²⁺ ions in three polyamine copper complexes, aqua spermine copper sulfate trihydrate [NH₂(CH₂)₃NH(CH₂)₄NH(CH₂)₃NH₂·Cu²⁺·H₂O]·SO₄^2-·3H₂O, norspermine copper sulfate trihydrate [NH₂(CH₂)₃NH(CH₂)₃NH(CH₂)₃NH₂·Cu²⁺·SO₄^2-]·3H₂O, and homospermine copper sulfate dihydrate [NH₂(CH₂)₃NH(CH₂)₂NH(CH₂)₃NH₂·Cu²⁺·SO₄^2-] ·2H₂O, has been explored along with UV/VIS and electron paramagnetic resonance (EPR) spectroscopy. Intense absorption is detected in the photoacoustic spectrum corresponding to the d-d transition band weakly traced in the corresponding optical spectrum. The observed fine structure photoacoustic lines are assigned to the individual d-d transitions of Cu²⁺ ions, which are further exploited to determine the diverse metal-ligand interaction of the studied compound employing simple crystal field analysis.

The positive-definite quantity ß, defined as part of the reverse mapping in equations (8) was found to be incorrect in section 3, and correct in section 8. The correct form of ß is as follows.

The quantity v_i shown in one term of equation (43) should be capitalized as V_i which is consistent with the other terms.