Table of contents

Microwave and RF plasmas are finding increasing use in materials processing, plasma chemistry, chemical analysis, and other fields. This is stimulating the search for suitable plasma sources. In the 1970s, electromagnetic surface waves were put to use to sustain plasmas and an efficient microwave device, called a surfatron, was developed for this purpose. Recent work has shown that such discharges can also operate at radio frequencies. A large number of on surface-wave plasmas experimental data have been accumulated-their modelling is well advanced and they have found applications in various fields of research and technology. This paper reviews the physical principles of operation and the design of surface-wave plasma sources. Since the wave launcher is the central component of the source, this review presents a unified description of several compact, efficient, and easy to operate launchers specifically intended for plasma generation that have been developed over the past fifteen years. It is now possible to sustain such plasmas at frequencies ranging from 1 MHz to 10 GHz, in a pressure domain extending from 10^-5 Torr up to few times atmospheric pressure, and in a rich variety of plasma vessels and reaction chambers.

The flux from foil diffusion sources has previously been shown to contain atoms, ions and clusters which are electronically excited and can be field ionized by weak fields. Pulsed field ionization of the flux from a diffusion source at temperatures between 1200 and 1500 K is studied here at field strengths below 500 V/cm. At field strengths below approximately 60 V/cm, no field ionization is observed for any choice of the parameters. These values would indicate principal quantum numbers of n=28-50 for Rydberg atoms Cs*. The minimum emitter voltage where a time-of-flight peak due to field ionization is observed is recorded under varying conditions, and the flight time of the corresponding ions is observed to be as expected for Cs⁺ ions which have passed the pulsing grid after it has returned to its high voltage. Theoretical expressions are derived which describe the field ionization giving ions with a total energy just enough to pass this high voltage. The formulae involve characteristic life times of the excited states, that are some average over the distribution of states. The average lifetimes determined from the fit to the experiments vary between 0.7 and 0.3 mu s when the field strength varies from 67 to 450 V/cm, and from 0.7 to 8 mu s when the emitter temperature increases from 1200 to 1500 K.

An optical effect showing focusing and defocusing of a dye laser beam near the atomic resonance of the Tl*6p²P_3/2-7s²S_1/2 transition in Tl vapour produced by photodissociation is reported. The experimental investigation of the effect as a function of detuning, vapour number density, dissociation laser energy and dye laser energy is presented. The effect is attributed to distortion of the dye laser wavefront by anomalous dispersion near the resonance and the inhomogeneous number density of Tl atomic vapour produced by an inhomogeneous intensity distribution of the dissociation laser.

A new method to stabilize the CO₂ concentration in sealed-off CO₂ lasers is presented. Molecular sieves (zeolites) are used to adsorb large amounts of CO₂, allowing compensation of losses of CO₂ arising mainly from oxidation processes, other chemical reactions and O₂ adsorption. The adsorption process of CO₂ and water vapour in zeolites is theoretically described using Langmuir's isothermic equation. The theory allows a determination of the optimum quantity of zeolite and gives a temperature dependence of the adsorptive capacity. A RF-pumped CO₂ waveguide laser is used to test the CO₂ pressure stabilization. The measurements were performed by means of a quadrupole mass spectrometer.

A 193 nm ArF excimer laser is used in the photoablation of bulk YBa₂Cu₃O₇ and the oxides of barium, copper and yttrium. Optical emission from the plume of ablated material is studied from 350 to 630 nm. Emission from ions, atoms and diatomic molecular oxides are observed. The effects of applied electric and magnetic fields on the plume in vacuum and oxygen are discussed. The applied electric field is found to enhance the intensity of all the emitting species enabling identification of the highly congested emission lines in the spectra. The results might help to provide a mechanism for the observed effect of an applied electric field in the production of in situ superconducting thin films of YBa₂Cu₃O₇.

Applying an electric field across a poorly conducting material containing a crack causes a force to be exerted across the crack faces which resists crack opening, giving an electric adhesive effect. This paper presents a theory to account for this phenomenon, based on the idea that the electric potential developed across the opened crack faces by current flow around the crack provides a crack closing pressure which can be calculated. The theory is used to interpret experiments demonstrating adhesion between contacting semiconductors in an electric field. It may also be useful in explaining electrostatic precipitation, electrical adhesion between solid surfaces, and electro-gelation of powders and slurries.

A low frequency DC pulsed plasma used for iron nitriding is studied by means of an electrostatic probe and optical emission spectroscopy. The evolution of the electron density leads to the determination of the electron-ion recombination coefficient. The variations of this coefficient and the measurement of some emission lines of neutral iron and of excited states of neutral and ionic molecular nitrogen as a function of the percentage of H₂ give additional insights into the role of hydrogen during the nitriding process. Thus the presence of vibrational states of nitrogen-N₂(C³ Pi _u, B³ Pi _g, A³ Sigma _u⁺), N₂⁺(B² Sigma _u⁺)-late in the afterglow confirms their importance in such plasma assisted surface treatments.

Experiments on the transient or ion-matrix sheath from 90 degrees convex and concave corners and randomly perturbed objects have been performed. Equiphase contours of ion acoustic waves launched from metallic structures yield results that are in substantial agreement with a numerical simulation and, for the case of the corners, with recent numerical investigations. Differences can be attributed, in part, to inhomogeneities found in the experimental plasma.

The results of experimental investigations of the absorptivity of laser radiation energy in an optical discharge plasma are presented. The plasma was maintained in a stream of argon and nitrogen gases. The contribution of the mixture constituents to the laser beam absorption is considered. The importance of the obtained results for metal surface processing is discussed.

Experimental results concerning the behaviour of leader filaments near the anode are obtained using schlieren techniques in the case of small and large air gaps. Two main phases are studied. The first one, associated with injection of current (active phase), exhibits a perturbation of thermal and electrical properties of the leader near the anode. The study of the second phase, corresponding to a zero current injection (relaxation phase), allows the measurement of the recovery time of air density inside the leader channel.

In SF₆-¹⁸O₂ discharges, mass spectrometric studies have clearly shown the presence of S₂F and S₂F₂ molecules in the case of the use of fluorine consuming materials. Reaction schemes are proposed to explain the formation of S₂F and S₂F₂ molecules. These reaction paths also lead to the S₂ molecule.

Microwave discharges for the excitation of CO₂ lasers have been investigated. A waveguide structure with closed front and end, and with the discharge tube located parallel to the waveguide axis is used. The field distribution within the waveguide but outside the discharge tube is measured before and after ignition of the discharge. The wavelength of the microwave is reduced by the discharge plasma. The side-on light emission is detected. Light emission is detected over a distance within which the measured field strength in the waveguide varies fivefold. The experimental results are compared to the results of a self-consistent one-dimensional microwave discharge model. The model includes an equation for the electron density, the neutral gas density and a simplified wave equation for the electric field. The results show, in accordance with experimental results, a reduction of the wavelength due to the discharge plasma and the discharge excited over a range within which the electric field outside the plasma varies appreciably. In contrast to the electric field outside the plasma, the electric field inside is almost constant within the excited region. This is due to the high plasma conductivity which is a result of the high electron density which reaches values of up to 10¹² cm^-3. This leads to a power density up to several tens of W cm^-3. In order not to overheat the gas the discharge has to be operated in a pulsed mode. Another method of limiting the gas temperature is to use a waveguide structure with a small electrode spacing or with a fast gas flow.

The amplitude-V_KM (V_KM>0) of negative flat-topped pulses required to maintain current flow in a discharge tube is observed as a function of V₊, the amplitude of similar flat-topped positive pulses of duration t₊, which occur at equal intervals of t_q between successive negative pulses. It is shown that the observed reductions of V_KM can be explained by assuming that the positive pulses deposit electrical charge on the inside of the discharge tube, and simultaneously deionize the inter-electrode gas. The wall charges therefore survive until the next negative pulse is applied to the cathode. They also enhance the cathode field strength. The importance of the results is considered for cross-talk between discharge tubes in display systems containing many close packed discharge tubes.

The energy dependence of the emission yield of electrons backscattered from a clean polycrystalline molybdenum sample has been studied using a dispersive hemispherical analyser (incidence angle theta =70 degrees ; collection angle phi =0 degrees ). True secondaries, Auger electrons, elastic peak and background detected in the N(E) mode were investigated. Experimental results related to the elastic scattering of primary electrons are in good agreement with theoretical treatments (simple diffusion model and Monte Carlo simulation of multiple scattering). It is found that elastically reflected electrons mainly arise from single collision processes with a maximum of the emission yield at a primary energy E_p approximately=300 eV. The behaviour of the Mo-MNN Auger signal normalized by the primary current is compared to the energy dependence of the Auger peak/background ratio. These two normalization procedures lead to some differences mainly due to the transfer of the inelastic contribution of the background toward higher kinetic energies when E_p is increased. The dependence on the primary energy of the true secondary emission is closely related to the one recorded for the total backscattered coefficient deduced from the measurements of primary and sample currents. Threshold effects at an energy corresponding to the Mo-3d inner level are hardly detected. Furthermore, a rough estimation of the relative contributions of the different electrons involved in the N(E) backscattered spectra is proposed.

The representation of two- and three-dimensional point response functions by Pearson frequency distribution curves is discussed for the case of energetic ions implanted into homogeneous, amorphous material. Comparisons are made between the Pearson curves and high-resolution Monte Carlo simulations. It is shown that no extra information is required to derive the three-dimensional representation once the two-dimensional representation is known.

Experimental results for the evolution of the TLD-100 glow peaks IV and V during storage at 70 degrees C are presented. These results confirm a previous conclusion on the null incidence of spontaneous release of radiation-induced trapped charges on this evolution. The results at 70 degrees C allow one to extend this conclusion to the whole range of ambient temperatures. Only thermally activated trap modification processes are responsible for the TL yield variations during long duration ambient exposures. The identification of the nature of these variations suggests a rather simple dosimetric procedure requiring only the determination of the dosimeter sensitivity at the end of the exposure interval. Results are given illustrating the effectiveness of this procedure for the accurate measurement of ambient doses up to 70 degrees C.

Copper strips of 2.5 mm thickness resting on stainless steel anvils were normally indented by wedges under nominal plane strain conditions. Inflections in the hardness-penetration characteristics were identified. Inflections separate stages where each stage has typical mechanics of deformation. These are arrived at by studying the distortion of 0.125 mm spaced grids inscribed on the deformation plane of the strip. The sensitivity of hardness and deformation mechanics to wedge angle and the interfacial friction between strip and anvil were investigated within the framework of existing slip line field models of indentation of semi-infinite and finite blocks.

Molecular assemblies were studied at the air-water interface, as were neutral and oxidized Langmuir-Blodgett (LB) films in the mixed (1: n) molecular system of EDTTTF (SC₁₈)₂ (EDTTTF, ethylenedithiodioctadecylthiotetrathiafulvalene) and behenic acid (CH₃(CH₂)₂₀ COOH). At the air-water interface, a possible molecular organization was discussed from the study of the area occupied by EDTTTF (SC₁₈)₂ and n molar fraction of behenic acid at a surface pressure of 30 mN m^-1. EDTTTF (SC₁₈)₂ molecules form dimers and with increasing behenic acid content, a monolayer reorganization occurs. The formation of monomolecular layers including monomer EDTTTF (SC₁₈)₂ molecules was achieved for n>or=2. X-ray diffraction studies were concentrated on samples of Y-type LB multilayered films with n=0, 1 and 3. Throughout the mixed (1:n) system, stacking periodicity was dominantly observed from (001) reflections as 55+or-1 AA for neutral films, 72+or-1 AA for a brown-coloured film after exposure to iodine, and 46+or-1 AA for the stable, conducting and purple-coloured film after a thermal activation process. Possible molecular assemblies based upon centrosymmetrical bilayers were qualitatively discussed based on the calculation of the linear electron density profiles of pure and doped EDTTTF (SC₁₈)₂ LB films. The large variation of the stacking periodicity during the oxidation process was explained by the molecular inclination of EDTTTF (SC₁₈)₂ molecule associated with the insertion of I₃^- ions which intercalate between EDTTTF (SC₁₈)₂ layers.

The dispersion relation for TE polarized waves guided by a non-linear dielectric slab with intensity-dependent refractive index, surrounded on one side by linear media and on the other side by a metallic surface, is found. The dependence of the propagation constant from the energy flux is also investigated. Some examples are investigated in detail.

The electrochemical and optical properties of poly(1,4-naphthalene vinylene) (PNV) during electrochemical p-type doping have been investigated by the cyclic voltammetry and in situ optical absorption spectrum measurements. The evolution of localized states is evidenced by the spectral change with electrochemical doping. These results are discussed in terms of polaron and/or bipolaron models. The band gap of PNV was evaluated to be about 2.3 eV and that of poly(p-phenylene vinylene) (PPV) to be smaller by about 0.4 eV. This result can be interpreted in terms of a more effective resonance interaction between the naphthalene unit and the vinylene unit. The electronic band structure of PNV was determined. The polaron states in PNV appear in the band gap: about 0.5 eV above the valence band and about 0.5 eV below the conduction band. The bottom of the conduction band of PNV is about 0.3 eV lower than that of PPV and successful n-type doping in PNV is expected.

A transport model for ZnTe is formulated. This model includes the contributions of all major scattering mechanisms and screening. The Boltzmann transport equation is solved for this formulation using a variational procedure and assuming generalized Fermi-Dirac statistics. The contributions of component scattering mechanisms to the total electron mobility are discussed as a function of temperature. Inherent mobility limits of about 1500 cm²V^-1s^-1 (300 K) and about 20 000 cm²V^-1s^-1 (77 K) are reported for the first time; these values occur at electron concentrations of about 2*10¹⁸cm^-3 and below 1*10¹⁴cm³ respectively. Special attention is given to assessing the importance of compensation on the transport characteristics of ZnTe. Thus curves are presented which permit compensation ratios to be determined from experimental transport data. Available experimental data are discussed and shown to fall well within the bounds of the present theoretical model.

The formation and electrical properties of the conductive network in RuO₂ thick film resistors were investigated. As a result, a RuO₂ thick film resistor having a high concentration of RuO₂ has conductive chains of RuO₂ and metal-like conduction. However, the resistor having a low RuO₂ concentration has a reactive Layer that allows it to maintain its conductivity even though there are no conductive paths by mutual contact of RuO₂ particles; it also has amorphous, semiconductor-like characteristics.

Thermal endurance characterization of XLPE cable models is realized by applying conventional procedures and an analytical method. The latter method is based on oxidation induction time measurements to estimate the activation energy of the degradation reaction and then the slope of the thermal endurance line. The conventional life test at an intermediate temperature is used to determine the ordinate intercept of the same line. The estimates of temperature indices, obtained by different diagnostic properties and end-point selections on the basis of both conventional and analytical techniques, are fairly close, thus revealing the ability of appropriate analytical procedures to characterize reliably the thermal endurance of XLPE cables, with the advantage of shortening test times with respect to conventional methods. A discussion is presented on the choice of diagnostic properties and end points, in order to achieve thermal endurance lines and indices which provide actual information on cable performance under service stresses. Analysis of the possible choices is performed with reference to the results of multiple-stress tests which simulate service stresses and by investigating the aging mechanisms. Finally, considerations of the compensation effect applied to life lines, with reference to both Eyring and Arrhenius models, are made. Checks relevant to different property end points reveal very good agreement of the experimental results with the aging compensation effect.

With respect to frequently desired actuators, high-signal electrostrictive deformation is an electromechanical alternative to the piezoelectric effect. Several disadvantages, which conflict with general applications, are investigated. Possibilities to overcome or reduce such disadvantages are discussed and suitable materials presented. General remarks on the high-signal electrostriction are made to explain the qualitative differences in the shapes of the strain-field curves.

For pt.I see J. Phys. C, vol.2, p.6807 (1991). The method of measuring optical activity and linear and circular dichroism in birefringent crystal sections is successfully applied to three materials.

Optical third-harmonic generation (THG) at 1064 nm and wavelength dispersed degenerate four-wave mixing (DFWM) have been performed on substituted polyphenylacetylenes (PPAS). Strong changes in the linear and nonlinear optical properties can be achieved by varying the substituent. Resonant values of chi ⁽³⁾(-3 omega ; omega , omega , omega ) up to 10^-11 esu and chi ⁽³⁾(- omega ; omega , - omega , omega ) of more than 10^-9 esu with ultra-fast response times were observed. A linear relationship between chi ⁽³⁾(- omega ; omega , - omega , omega ) and the absorption coefficient alpha was found. This is compatible with an inhomogeneous broadening of the absorption band or with phase-space filling by one-dimensional excitons. Model calculations are presented that relate the modulus and phase of chi ⁽³⁾(-3 omega , omega , omega , omega ) to the linear optical properties of PPA and indicates a direct two-photon interaction with the absorption band. This may be due to a non-centrosymmetric electronic structure of the PPA backbone.

Optical properties of poly(oxyisophthaloyloxy(2-methoxy-p-phenylene)methylid- ine(2-oxo-1,3-cyclohexanediylidene)methylidene(2-methoxy-p-phenylene)) I and poly(oxysebacoyloxy(2-methoxy-p-phenylene)methylidene(2-oxo-1,3-cyclohex- andeiylidene)methylidene(3-methoxy-p-phenylene)) II polymer films were studied. Transmission and absorption measurements were carried out in the energy range 1.9 to 3.2 eV at 300 K. Absorption coefficient data were analysed and interpreted in terms of the Tauc model ( alpha h(cross)w)¹2/= square root B(h(cross)w-E_g^opt). Analysis of experimental results shows that the absorption characteristics give a good fit to the Tauc model. This indicates that both polymers (I and II) have an indirect band gap. The values of the optical gap E_g^opt and the slope of Tauc plots square root B were determined. The study shows that the indirect allowed optical transitions are predominant in the absorption process. Correlation between the optical band gap and polymer structure was observed and discussed.

In a preliminary study the energy of the thermally stimulated exoelectrons emitted from single crystals of LiF and KBr was measured using a 127 degrees cylindrical deflecting analyser (CDA). Under this set-up the energy of the electrons emitted (E₀) is directly proportional to the potential difference ( Delta V) between the cylinders of the CDA E₀=3.24e Delta V where e is the electronic charge. The energy of the exoelectrons emitted was observed to be in the range of 2-4 eV. A plausible explanation for their high energy is suggested.

A new technique has been developed using a millimetre-wave radiometer to measure the concentration profiles of H₂O and O₃ in the lower stratosphere from a balloon platform. The technique differs from previous microwave remote sensing techniques in being able to carry out measurements with much greater resolution, allowing it to resolve the finer structure in the vertical distributions of H₂O and O₃. The first flight of the new instrument took place from the French launch site at Aire-sur-l'Adour during the 1983 MAP/GLOBUS campaign. The basic principles of the new technique and the method of data analysis are described in the paper together with the results from the first flight. The results obtained were found to exhibit many of the important features seen by previous workers and are discussed in detail in the paper.

An analysis of the excitation of two space-charge waves in a cylindrical metallic waveguide filled with a relativistic electron beam is presented. The wiggler electrostatic potential is spatially periodic along the guide axis and has a radial dependence. A formula for the growth rate in the laboratory frame is derived in terms of an appropriate radial average of the wiggler potential amplitude. Effects of finite beam electron temperature are included and extension to a partially filled waveguide is discussed.