Table of contents

Intensive entrainment and concentration of ferromagnetic aerosols along an upper boundary of a laser light beam in a magnetic field is described. A screen interposed in the path of a light beam compels these particles to stop at a certain distance and keeps them in the position for an indeterminately long period of time. A possible causality relation between this phenomenon and magnetic charge of the particles is examined.

Nanoscale Fe/Mo multilayers were synthesized by means of ion beam sputtering. The microstructure of the multilayers was investigated by low-angle and high-angle x-ray diffraction, cross section and plan view transmission electron microscopy, and Mossbauer spectra. Fe layers in the films become continuous when their thickness is more than 9 AA. The Fe/Mo interface roughness was observed to be less than 3 AA. In this system the enhanced magnetization (as much as 26%) was measured by a vibrating sample magnetometer at a certain range of the individual layer thickness of the two components. An anomalous dependence of Fe saturation magnetization against the thickness of Mo layer was found in the series of Fe 25 AA/Mo films.

The use of digital techniques is becoming increasingly popular in a wide variety of situations. These methods allow one to implement sophisticated measurements in an easy and flexible way, with minimum hardware requirements. Here, a digital approach to low-energy spectroscopy with HgI₂ microdetectors is discussed. Its results are compared with a Monte Carlo simulation adapted to the geometry of these crystals and the electronics used with them.

An exact formulation for the internal field equation of an assembly of small spherical particles irradiated by an electromagnetic wave is presented. It is demonstrated that the formulation is reduced to the existing solutions by suitable approximations of the self-contribution field term and satisfies the energy conservation (optical theorem) requirement. Further analysis shows that the Jones solution, the Purcell-Pennypacker PP and the Iskander-Chen-Penner ICP solutions violate the energy requirement whereas the Goedecke-O'Brien GO solution was found to be the lowest order compatible approximation of the exact solution, and as such satisfies the conservation of energy. Furthermore, the obtained field equation is invariant to coordinate transformation and yields an invariant T matrix which accounts correctly for multiple scattering effects. Comparisons of the results were carried out with the Jones solution, the PP, ICP and GO solutions. In addition, the applicability of the solution to the inversion of light scattering data, especially from sooting flames, is assessed.

In this paper, a general theory of the relativistic asymptotic third-order geometric and first-order chromatic aberrations of a system of combined electrostatic-magnetostatic focusing-deflection sub-systems has been presented, in which relativistic asymptotic aberrations of position and slope of the sub-system, and addition formulae for these asymptotic aberrations of two successive subsystems have been derived. All their aberration coefficients contain no derivative higher than second order. The divergence in Hawkes' theory of asymptotic aberrations has been thoroughly voided. The limitation of equality of object- and image-side asymptotic focal lengths in Hawkes' theory has been erased.

A theoretical investigation of the hydrogen concentration distribution in an aluminium workpiece during welding is presented. The driving force for hydrogen transport is thermal diffusion, whereby a diffusion current is brought about by temperature gradients. The sign of the respective transport coefficient is negative for H in Al, which means that hydrogen will accumulate in the heated regions. An analytical solution is obtained under somewhat restrictive assumptions, which is complemented by a numerical solution allowing for more realistic input. Both solutions agree qualitatively, yielding enrichment factors of two and more for the cases studied. It is predicted that higher processing speeds will result in less enrichment. The significance of these results for the weld quality is discussed.

The fractal dimension of aerosol aggregates has been determined from measurements of the settling velocity of two coagulating particles and the resultant particle. The fractal dimensions for carbonaceous and magnesium oxide smoke aggregates were found to be 1.97-or+0.07 and 1.19-or+0.02 respectively. The measured values agree with those determined from other in situ methods, and are explainable by existing aggregation models.

The linear stability of power law liquid film flows down an inclined plane is investigated. The integral method is used to derive nonlinear evolution equations for film thickness and local flow rate. After linearizing the nonlinear evolution equations, the method of normal mode is applied to study its linear stability. The results reveal that, in the case of fixing the value of power law exponent n, the stability characteristics in terms of generalized Reynolds number Re_n and generalized Weber number We_n are the same as those of Newtonian liquids, i.e. to increase the Reynolds number, or to decrease the Weber number will destabilize the film flow system. Furthermore, decreasing only the magnitude of n will cause more unstable film flow, and make the dimensional wave speed faster.

The transient response of annular fins of various shapes subjected to a constant base heat flux is analysed. The Laplace transform and integral methods are used in the analysis. The inverse Laplace Transform is solved by utilizing the Fourier series technique with modifications. It is shown that the Biot number and the parameters related to shapes play an important role in the heat transfer. The shapes studied are rectangular, triangular and parabolic profiles.

Mobilities of SF₃⁺ and SF₅⁺ ions as a function of E/N in SF₆ gas have been obtained by measuring their drift velocities at room temperature using a pulsed ion-transit-time method. The transverse and longitudinal diffusions for both ions were then calculated by using the parameterized three-temperature version of the generalized Einstein relations.

Using an ionization chamber with a high time-resolution the initial current caused by free electrons liberated during pulsed irradiation was measured. From the decay of this current after a short radiation pulse the electron swarm parameters lifetime (time until attachment to O₂) and drift velocity may be determined in dependency on the collecting field strength. Attachment rate coefficients for three-body attachment to O₂ are calculated for different O₂-N₂ mixtures and compared with literature values obtained from drift chamber measurements. The results show that, concerning the O₂-N₂ mixtures used the energy distribution in the electron swarm probably diverges from the Maxwell distribution assumed in the literature for vanishing O₂ content.

A multiphoton (2+1) absorption laser-induced fluorescence diagnostic is employed for determination of the spatial distribution of atomic hydrogen density in the post-discharge of a low-pressure microwave-induced H₂ plasma, using one pulsed frequency-doubled dye laser. H atom density profiles are described by a simple diffusion equation and the probability of recombination of H atoms on silica is deduced from the profiles.

Electrical and mass-spectrometric studies of a glow discharge produced by a direct current positive voltage applied to a point-to-plane gap in low-pressure dry air have provided many useful results, which help to clarify the interaction of the underlying physical mechanisms. Systematic studies of this discharge show that electrical parameters and gas pressure influence drastically the cold plasma behaviour. A discharge state similar to that of Townsend is obtained for a restricted region of operation while, outside this region, similarity rules seem not to be fulfilled. The main ions detected during the Townsend-like discharge are O₂⁺ and NO⁺ while, after breakdown, dissociation products such as O⁺ and N⁺ as well as N₂⁺ ions are detected. It has been found that ion detection depends strongly upon cathode dark space structure.

This paper reviews measured and theoretical data relating to the low-pressure discharge breakdown in DC and uniform RF fields and their combination. The original results on determination of molecular constants of various gases from breakdown curves obtained by the authors are given. We have investigated the effect of the DC electric field on the RF breakdown pattern. In particular the influence of the DC electric field on the ambiguity region of the RF discharge breakdown curves has been determined. Breakdown equations in combined fields have been derived and comparison has been made between these equations and measured data. Simple analytical criteria for gas breakdown for a wide range of parameters have been given.

An investigation of in-resonator gas breakdown for electron cyclotron resonance condition was performed for various magnetic field configurations, gas pressures and compositions. The dependence of the threshold power of breakdown on the magnetic field value has more than one minimum. One of the minima corresponds to the case when the ECR condition takes place in the centre of the resonator (microwave (MW) electric field is maximal). The other minima correspond to the position of the ECR zone near the resonator edges (MW electric field is rather small). This is valid if the magnetic field configuration inside the resonator is a magnetic mirror. The presence of the edge minimum may be explained by the increase of maximal energy which the electron can attain during stochastic heating. This compensates the decrease of MW electric field near the resonator edges.

By studying the non-stationary transport properties of a semiconductor gas discharge (SGD) structure used for the spatial and temporal conversion of infrared radiation into the visible wavelength range, we observed the phenomena of spontaneously excited ionization waves under strong light excitation of the converter structure. The waves propagate normal to the electric current flow and, by increasing the supply voltage, their velocity increases and can exceed that of acoustic waves in the gas filled region of the structure. Wave interaction is also found to be followed by interference effects. This dynamical instability of the homogeneous state can probably be explained by a nonlinear oscillator model.

A simplified theoretical expression has been developed for a glow discharge to show how the average cathode erosion rate (expressed as the number of atoms per ion of the total bombarding flux) varies with primary sputter yield, pressure, 'diffusion length' and sputtered atom 'stopping' cross section. An inverse pressure dependence is predicted which correlates well with experiment in the <1 to 3.5 Torr range. Observed sputtering efficiency variations with the discharge gas show that Xe<Kr<Ar, which is shown to be in good agreement with theoretical differences in the low-energy primary sputter yield expected on the basis of the mass of the bombarding particle flux. There is a change at higher pressures because the rate levels off and the rates for the same cathode in different gases, including N₂ and He, tend to converge. It is suggested that this could be due to a change in the mechanism to self-sputtering. Under constant conditions, the erosion rates of different cathode materials still correlate quite well with the differences in their primary sputter yields.

A mathematical model is developed to calculate the flux and average energy of fast neutrals in a glow discharge based on the charge transfer model used to describe the energy distribution of ions. According to this model the average energy and relative distribution functions of both fast atoms and ions are found to be independent of pressure. Using experimental values found in the literature it is found that the fast atom flux is at least twice as large as the ion flux, but with an average energy similar to the ions. The sputter erosion of the cathode is therefore probably caused mainly by fast atom bombardment.

Experimental results of the development of a negative discharge in a 16.7 m rod-plane air gap are presented. Similarities with the cloud-to-earth discharge are found and some characteristic parameters are compared. Use of an image converter linked to two still cameras allows quite accurate analysis of the discharge propagation. Information relative to the space leader inception is provided. The current pulse shapes are related to the mechanisms of propagation and the thermal channel diameter of the discharge in the vicinity of the rod, which is measured with the help of schlieren records.

A spectroscopic investigation of an atmospheric pressure high-power transferred argon arc operated over a wide range of experimental conditions revealed the existence of interesting physical characteristics. It was shown that local thermodynamic equilibrium (LTE) was established in the column. However, in the immediate vicinity of the cathode tip, the absolute intensity of some atomic lines do not remain constant on a given isotherm. This phenomenon is not observed on ionized argon lines. Owing to the high temperatures occurring and due to column stability downstream of the cathode tip, the discharge was used to determine transition probabilities of ions.

A simultaneous detection analysis of thermostimulated luminescence (TSL) and electrical conductivity (TSC) is made using the approximate analytical models of first- and second-order kinetics. Some characteristics are developed and a new approach for evaluating the trapping depth is proposed and tested in the case of an alpha -alumina monocrystal.

The unambiguous interpretation of measurement results obtained by scanning electron acoustic microscopy (SEAM) investigations of GaAs specimens is often not possible since the mechanisms which cause the measurable electron acoustic signals are not known exactly for GaAs. Therefore the signal generation within the often used low-frequency range from f=1 kHz to 100 kHz has been evaluated for semi-insulating, undoped and n-doped GaAs substrates in order to broaden the knowledge about the importance of the different possible signal generation mechanisms. It has been found that in n-doped GaAs substrate only the thermoelastic signal generation mechanism is dominant, whereas in a semi-insulating GaAs substrate an additional contribution of the piezoelectric sound generation mechanism exists.

The effective Schottky barrier height of n-In_0.53Ga_0.47As is increased by a 200 nm thick Fe-doped InP layer grown by metal-organic vapour-phase epitaxy. Schottky diodes fabricated by this method exhibit an effective barrier height of 0.57 eV and a very low reverse-current density of 5*10^-4 A cm^-2 at 10 V. Current in the reverse direction is caused by thermionic emission, whereas a complicated transport mechanism, with generation-recombination and tunnelling components, determines the current when the structure is forward biased. Besides peaks clearly related to Fe levels in InP and In_0.53Ga_0.47As, deep level transient spectroscopy also shows a donor-like level with Delta E_a=0.77 eV of an origin that has so far remained unresolved.

The effects of Al and Zn on the critical current density, upper critical field and pinning force of in situ prepared Cu-Nb wires have been studied. Doping this system by 1 wt% of these impurities results in a change in critical current density and pinning force. The critical current density increases at lower fields for both additives but decreases at high fields. The upper critical field H_C2 shows a decrease for both additives. We have modified the Kramer flux pinning law for these two additives. It is found that the value of n, which is a constant in the scaling law of Fietz and Webb with a value of 2.5, varies in the case of these additives and does not remain constant.

The mean potential difference V_B and the frequency F_B of Bakhausen jumps were investigated for polycrystalline Ni_1-xMg_xFe₂O₄ where x=0, 0.2, 0.4, 0.8, 1.0. NiFe₂O₄ shows the lowest values of V_B. The addition of Mg enhances the irreversible motion giving rise to higher values of V_B and F_B. When Mg content exceeds 0.4, the number of jumps begins to decrease. Mg addition affects the energetic situation of the domain walls.

The scanning potential microscope (SPM) is a new form of scanning microscope, which maps distributions of spatial potential by direct measurement. The SPM may be used to study, non-invasively, the electrical properties of samples through the potential distribution created near the sample in response to an applied electric field. Spatial resolution and sample to SPM spacing are both close to 1 mu m at the present stage of development of the instrument. We present an SPM study of a test sample comprising three dielectric layers with differing relative permittivities: a 35 mu m film of cellulose acetate (CA, epsilon _r approximately=5); a 25 mu m film of polyvinylidenefluoride (PVDF, epsilon _r approximately=8.4); and a 50 mu m film of polytetrafluoroethylene (PTFE, epsilon _r approximately=2-2.1). In the experimental set-up a small, audio-frequency electric displacement was applied through the sample. SPM mapping of the resultant potential distribution close to the sample yielded values of relative permittivity that were within 2% of the material specifications.

A new Ag⁺ ion conducting superionic glass system X(0.75AgI:0.25AgCl):(1-X)(Ag₂O:B₂O₃), where 0.1<or=X<or=1 in mol wt(%), has been prepared. A quenched (0.75AgI:0.25AgCl) mixed system was used as host in place of the conventional host compound Agl. The molar composition 0.7(0.75AgI:0.25AgCl):0.3(Ag₂O:B₂O₃) exhibited the highest conductivity sigma approximately=4.4*10^-3 S cm^-1 at 27 degrees C. An ionic transference number approximately=1 was obtained for this composition. Direct measurement of ionic mobility mu was carried out using transient ionic current (TIC) technique and the mobile ion concentration n was calculated from sigma and mu data. The temperature dependence of sigma , mu and n followed the Arrhenius type behaviour. The mobile ion concentration n was found to increase whereas the mobility mu decreased with increasing temperature. Attempts have been made to explain our results on the basis of a cluster-bypass model as well as incorporating other theories proposed for ion conducting glasses. The cell performance of solid state batteries fabricated using the optimum composition glass as solid electrolyte has also been investigated.

We describe a very efficient source of H atoms generated by a : low-pressure (1 Torr) pulsed microwave discharge (2.45 GHz). We show that the low mean microwave power density applied in pulsed discharge limits considerably the heating of the discharge tube wall, and hence, the loss of H atoms by wall recombination. The H atom molar ratio, measured by actinometry, increases from 30% in continuous power to nearly 100% in pulsed power, for the same instantaneous power. We present a comparison between continuous and pulsed power, both for electron density (and discharge balance parameters) and for H atom density.

The large-amplitude nonlinear plasma wake wave driven by ultra-relativistic electron beams of different lengths and densities is studied using the analytical theory of the ultra-relativistic fluid equations. The approximate analytical solution for the wake wave is obtained and how to obtain large-amplitude wake waves is discussed.

Films of Li_xVO_2.5 were produced by reactive direct current magnetron sputtering followed by galvanostatic lithiation from an electrolyte. Infrared absorption bands, measured by spectrophotometry, showed x-dependent changes that could be reconciled with structural expansion and contraction.

Aspects of electromagnetic theory proposed recently point to a possible new mode of radio communication. Such communication would occur via a 'companion wave', a heretofore unknown wave behaviour associated with a radio wave propagating in a superimposed magnetic field. A method of realizing this mode of communication within conventional radio science is outlined.