Table of contents

General expressions for the frequency-dependent dielectrophoretic force and electrorotational torque have been derived for electrically polarized particles that either do or do not exhibit dielectric dispersions. Particles with n dielectric dispersions can, at most, exhibit (n+1) rotational maxima as a function of frequency, and these coincide with regions of maximum frequency-dependence of the dielectrophoretic force. Argand diagrams can be employed to examine the relationships between the dielectrophoretic and electrorotational behaviour of colloidal particles. These results are of relevance to the further understanding of published experimental data and to the application of these two phenomena in the manipulation and characterization of biological cells.

The optical propagation in linear tapered waveguides is studied using both the beam propagation method as a non-modal technique and for local normal mode analysis. The comparison between the results obtained by the two techniques gives a good physical understanding of the transient behaviour of the optical field in the taper, which enables the use of the taper as a collimating element in planar integrated optics. For experimental verification, tapered waveguides were formed by K⁺-Na⁺ ion exchange in glass. A linear taper with an angle of 0.08 degrees has an output beam of 40 mu m width with a divergence angle of 1.13 degrees .

A new analytical model has been developed on the basis of a previous model (by Abe et al.) to simulate resist heating in electron beam lithography. Temperature distributions in both the resist and the substrate have been calculated for a single flash of a shaped beam and for a beam scanning a pattern, showing that the pattern size, the beam current density and the thermal conductivity of the substrate are key factors affecting the temperature rise in resist.

Combined radiation and heat conduction in a plane parallel medium is investigated using a special integro-differential form of the radiative transfer equation as a starting point. Opaque reflecting boundaries are assumed; steady and time-dependent cases are considered. The solution technique used is efficient in computer time and can be extended to treat much more complicated problems.

For pt.I see ibid., vol.25, p.393-400 (1992). The flow of a viscous incompressible fluid between two non-conducting cylinders is investigated. A strong radial magnetic field is applied parallel to the free surface of the liquid. The problem is treated by means of matched asymptotic expansions (as in part I) and the leading terms of the different asymptotic expansions are obtained for M to infinity , where M is the Hartmann number.

The stability conditions of an ionization-produced spherical double layer are analysed on the basis of a criterion discussed recently by Song et al. (1991). The dynamics of an exploding double layer is also investigated. Some experimental evidence is presented, which is generally supportive of the authors' theoretical model.

Reports the DC electrical breakdown data of SF₆ in crossed magnetic fields. The sparking potentials are measured between coaxial cylindrical electrodes over the P(R₂-R₁) range of 0.26<or=P(R₂-R₁)<or=28 torr cm with the perpendicularly applied magnetic field varying from 0 to 13000 G.

Electron number density measurement devices working under the conditions of non-steady-state high-pressure Thomson discharge are discussed. The necessary conditions for evaluating the electron number density and the production rate of the external ionization using Ohm's law are qualitatively stated. In addition, an algorithm for the space charge influence on the electrostatic field applied is derived. The theoretical estimations and some preliminary experimental results show the predictions of this algorithm to be sufficiently good. Some advantages and possibilities of use of the method are emphasized and discussed. Using the results obtained and/or summarized in this work, an easy interpretation of other results obtained using Ohm's law, neglecting the influence of avalanche ionization, is possible.

A standing surface wave discharge can be obtained by reflection of a TM₀₀ surface wave from a short circuit. A standing wave system provides modulation of plasma characteristics. Wave propagation is studied assuming a plasma in which the electron density is modulated whereas the power for plasma maintenance and the electrical field inside the plasma do not depend on the density, as is the case for traveling wave discharges. Then, the authors determine the conditions for the generation of a standing surface wave pattern. Finally, a comparison of experimental results with the model shows that plasma characteristics can be suitably predicted.

The authors present a systematic investigation of the effects caused by electron-electron collisions on the electron kinetics in Ar under the action of DC and microwave fields. The analysis is based on solutions to the homogeneous electron Boltzmann equation using the effective field approximation, i.e. assuming that the electron energy distribution function is time independent. The calculated electron transport parameters and ionization coefficient are used together with a generalized charged particle balance equation to derive the characteristics for the maintenance field and the mean absorbed power per electron for steady-state DC and microwave discharges in Ar. Results are provided for the cases of (i) single-step ionization; (ii) multi-step ionization, via the metastable and the resonance levels of Ar.

Small-angle scattering of X-rays from polycrystalline assemblages of metals, alloys and other crystalline materials can be due to double or multiple Bragg scattering in addition to the 'true' small-angle scattering. Separating these two components of small-angle scattering (SAS) is a necessary requirement for proper interpretation of SAS data. This has been achieved in this work by considering the polarization ratio of X-rays scattered by polycrystalline assemblages. The proportion of 'true' SAS has been expressed as a function of the total diffracted intensity and the polarization ratio. Application to polycrystalline assemblages of aluminium and several Cu-Al alloys shows that the proportion of double Bragg reflection (DBR) is small compared to that of 'true' SAS.

Two methods for the deconvolution of ESR spectral lines and the evaluation of the area under these lines are presented. The first method makes use of Gautschi's algorithm (1970) for the evaluation of the derivative of the Voigt function and then it is least-squares fitted to the experimental first derivative resonance line. The second method uses as input data the maximum, the minimum and their separation on the second derivative of the resonance line. Both methods are applicable to single-crystal lines, low viscosity liquid lines, and completely isotropic-powder or frozen solution spectral lines. A couple of relationships between the area under the resonance curve and parameters obtained in each method are found. The two methods presented here improve on previous deconvolution procedures proposed, since no extra low-temperature measurements are required and a fitting criterion is used for the comparison with the experimental spectrum, including the background.

The ion-induced modifications of the water dissolution process and sodium release have been thoroughly investigated in sodium beta "-alumina single crystals by applying depth profiling techniques (Rutherford backscattering spectrometry, elastic recoil detection analysis and resonant nuclear reactions) for the characterization of leached surfaces. The authors observe modifications of etching and leaching rates in the case of irradiated samples, both depending on the energy deposited by the projectile. Combined with new results of the sodium profile modifications induced by ion implantation, such ion-induced effects give additional information on the processes which govern the surface modification of irradiated beta "-alumina crystals and which could be detrimental for the use of ion implantation in the development of micro-ionic devices.

Solar control coatings required for architectural glazing applications in tropical locations warrant much attention due to their vital role in energy conservation. The solar control properties of Cu₂Se thin film coatings were investigated and the results are presented. It was observed that Cu₂Se coatings have moderate optical transmittance and low reflectance in the visible region and high reflectance and low transmittance in the IR region. These characteristics are useful for the above purpose. The evaluation of their solar control parameters in the visible and IR region showed that they exhibit superior solar control characteristics in certain respects over the metallic and PbS coatings and have comparable characteristics with Cu_xS films.

The excess charge relaxation in electret structures based on Teflon-FEP films, particularly the charge behaviour in the region of polymer-metal contact, has been investigated. Measurements were made using both the standard electret techniques and a special experimental method, based on observation of the partial recovery of voltage of sandwich electret structures during reheating after forced corona-discharge. It has been found that a specific macro-non-uniformity region exists near the FEP-Al interface, where deep trapping of charges drifting through the FEP film occurs. Using experimental measurements and an appropriate analysis, the authors determine the energy distribution of the traps located near the FEP-Al interface estimate the dimensions of this region to be about 0.3.-0.75 mu m from the Al electrode.

New experimental values of the three independent electrostriction coefficients of the alkaline earth fluorides CaF₂, SrF₂ and BaF₂ are presented. Measurements are performed with improved measuring equipment. With this equipment the electrostrictive expansion of a sample is measured with an interferometer system whereby the influence of spurious displacements of the sample holder is eliminated so that more reliable results are obtained. Relatively low positive values are observed for the electrostriction coefficients gamma ₁₁ and gamma ₁₂ and a much higher positive value for gamma ₄₄. The experimental data are in reasonable agreement with results based on theories of the electrostriction of the alkaline earth fluorides.

New experimental data on the electrostriction coefficients of silicon and diamond are presented. Measurements have been performed by means of an interferometer system to ensure a high reliability of the measured dilatation. The value reported here of the electrostriction coefficient of diamond differs from one reported earlier. The difference is due to the use of the improved measurement set-up. The electrostrictive dilatation of diamond is measured on a 0.5 mm thick diamond crystal. The electrostriction of silicon is determined from the measurement of the dilatation of a reverse-biased n⁺p-junction of a silicon diode.

This paper presents a new method (the relative transmission fringe depth (RTFD) method) of determining the optical constants and the thickness of semitransparent thin films. It has the following distinctive features: high precision, simplicity, and a self-examining function for the measured results. In order to meet the needs of application and engineering design, the n-F diagram (F is a new parameter which expresses the relative transmission fringe depth) is drawn. From it, n, k and d of films can be determined conveniently and precisely. With this method, the constants and thicknesses of SnO₂:I heat mirror coatings, plastic films used in agriculture, and micasheets were determined. The results are in complete agreement with those obtained using a polarimetric meter. Also, the calculated T- lambda curves agree well with the T- lambda curves obtained using a spectrophotometer.

For alkaline-earth-based thin film electroluminescent devices, several reports indicate the change of the emission spectrum within one excitation period. This effect has been attributed to the existence of different luminescent centres, efficiently excited at different times. In the present paper, it is shown that wide-angle interference effects can be responsible for considerable spectral changes in the electroluminescent emission of a thin film structure. Such a change reflects the variation of the position of the emitting centres within one excitation period. Thus, wide-angle interference may provide an explanation for spectral shifts, alternative or complementary to models invoking different luminescent centres.

Fixed electrode poling of 20% DAN doped bisphenol-A polycarbonate at moderate poling temperature (80 degrees C) gives a linear electro-optic (EO) coefficient, r₃₃ of 1.12 pm V^-1 for an applied poling field, E_p, of 27 V mu m^-1. This value is found to be ten times larger than that predicted using a simple thermodynamic model. The long term stability of the EO response was found to be unexpectedly good for a guest-host system and approaches that of some side-chain-type materials. At room temperature, a decrease of only 25% was seen in the linear EO response over a period of 21 days. The enhanced response and its unexpected stability is thought to be due to guest-host interactions and particularly to hydrogen bonding. Poling is performed 70 degrees C below the glass transition temperature of the host and is assisted by a beta -relaxation process identified at 80 degrees C.

Polycrystalline thin films of Cu_1-xAg_xSe (0<or=x<or=1) have been deposited by a 'solution growth' technique. As-deposited films have been annealed at different temperatures up to 500 K and the appearance of electrical conductivity has been observed. The electrical conductivity of annealed films shows an exponential dependence on temperature, and two thermal activation energies have been calculated. Excluding x=0, all the films displayed n-type conductivity. Carrier concentration, mobility and thermoelectric power measurements of these films have been carried out as a function of composition. X-ray analysis indicates that CuSe and AgSe films have a cubic crystal structure while films with 0.1<or=x<or=0.9 possess a tetragonal structure with axial ratio approximately 1.25. Films of stoichiometry 0.1<or=x<or=1 show both a direct and an indirect optical bandgap E_g from 1.4 to 1.37 eV and from 1.19 to 0.99 eV respectively. Other parameters such as absorption coefficient alpha , refractive index n, dielectric constant epsilon , and extinction coefficient k have also been computed from reflectance and transmittance spectra.

A theoretical and experimental study of passive, microwave beam modulation is presented using a planar dielectric multilayer structure in the frequency range 26-40 GHz. The structure is shown to exhibit both spectral and angular filtering properties with respect to plane waves. The same filter is also demonstrated to function as a collimating aperture and apodizer when combined with a conventional antenna. In addition the filter is used to steer a beam through a few degrees of arc by sweeping the source frequency from approximately 27 to approximately 29 GHz.

In an attempt to produce polymeric pyroelectric Langmuir-Blodgett films, three derivatives of a hexadec-1-ene-maleic anhydride alternating polymer and two poly-(vinyl pyridine) derivatives have been deposited as alternate-layer films using a two-compartment trough. 1-Docosylamine and 22-tricosenoic acid were also alternated with some of the above polymers. Pyroelectric coefficients measured by the quasi-static technique were found to have a maximum value of 0.8 mu C m^-2 K^-1, comparable to that of other Langmuir-Blodgett structures. Relative permittivity and dielectric loss values of pyroelectric films (in the range 10 Hz-100 kHz) were typically 4 and 0.06 respectively. Finally, these parameters are compared with those of commonly used pyroelectric organic materials.