Table of contents

The propagation characteristics of surface acoustic waves (SAW) in perovskite-type ferroelectric films/MgO/GaAs structures were investigated theoretically. Phase velocities of the layered structure are larger than those of the and PZT/MgO/GaAs layered structures for the same hK value of the perovskite-type ferroelectric film. Large coupling coefficients can be obtained when the interdigital transducer (IDT) is on top of the perovskite-type ferroelectric film, with and without the floating-plane electrode at the perovskite-type ferroelectric film - MgO buffer layer interface; and peak values of the coupling coefficients of the PZT films (2.8 - 3.8%) are higher than those of the (1.9 - 2.5%) and films (1.5 - 2.3%). There exists a minor peak of the coupling coefficients for the PZT and films when the hK value of the perovskite-type ferroelectric film is about 0.5, but not for the films, if the IDT is on top of the perovskite-type ferroelectric film with the floating-plane electrode at the perovskite-type ferroelectric film - MgO buffer layer interface. The minor peak values of the coupling coefficients for both PZT/MgO/GaAs and layered structures all decrease when we increase the hK value of the MgO buffer layer from 0 to 0.25. The results could be beneficial for combining ferroelectric devices, semiconductor devices and SAW devices on the same GaAs substrate.

Measurements of optical absorption and photoconductivity (steady state, frequency dependent, time dependent) were made on an n-type CdTe single crystal and on an evaporated CdTe thin film. For the single crystal the standard steady state photoconductivity showed an intrinsic peak at 1.4 eV. The lifetime calculated from ac photoconductivity measurements was in the range (1.1 - 5) s. The lifetime showed a minimum at exactly the same photon energy at which the photocurrent was maximum. The decay time was always longer than the lifetime. Optical absorption measurements revealed a direct transition and an optical gap of 1.47 eV at 80 K. Polycrystalline thin films of CdTe were grown by vacuum evaporation on glass substrates held at . The films showed a peak in the spectral distribution () curve at 1.65 eV. Direct and indirect transitions were again observed and found to be temperature dependent.

Measurements of the reflectivity and the transverse Kerr effect for sputtered iron films on flat and structured substrates reveal, for the first time, anomalies in both the optical and magneto-optical behaviour of the structured samples. The presence of anomalies in the transverse Kerr effect measurements, for various orders of diffraction, is much clearer than in those of reflectivity. The results are discussed in terms of the anticipated Rayleigh condition for optical anomalies and the condition for the generation of surface plasmons in iron.

Wear-out and breakdown of polymers used as insulating materials are closely related to the dissipation of electrostatic energy in space charge regions. A fraction of this energy is radiated off by electroluminescence which can be considered as a pre-breakdown warning and provides a probe to investigate the mechanisms leading to structural degradation. Electroluminescence emission from two aromatic polyesters is studied - poly(ethylene terephthalate) and poly(ethylene 2,6-naphthalate). We investigate the excitation processes of the luminescent centres, the nature of the centres, and the relationship of the emission features to electrical ageing. Sample electroluminescence is excited by dc and ac voltages under a uniform field configuration. The discussion relies on the analysis of the charge transport process in the luminescent regime, the acquisition of electroluminescence and photoluminescence spectra, and the investigation of the field effect on photoluminescence.

Using a Monte Carlo simulation scheme, we model the effect of gas phase collisions on the evolution of a gas cloud desorbed by a pulsed laser beam from a target surface. As a special feature, we assume that the desorbed particles belong either to a cold or to a hot species with prescribed temperatures. This allows us to assess qualitatively the effect of an ionic component (hot particles) on the evolution of a neutral gas cloud (cold particles). We find that an admixture of hot particles has a deleterious influence on the ablation jet formed: it is less strongly peaked towards the surface normal and fast particles are not so strongly focused towards the jet axis. Simultaneously, a higher percentage of desorbed particles is scattered back towards the surface. This deteriorated jet structure is due to the spatial segregation between hot and cold particles in the desorbed gas cloud, such that cold particles are found predominantly in its near-surface part.

In order to prepare high-quality hydrogenated amorphous silicon carbide () films with a wide band gap, we propose use of a separately excited plasma CVD (SEPCVD) system composed of two independent plasma chambers and one deposition chamber. This method enables control of methane and silane plasmas independently. The optical and electrical properties and structure of films prepared by the SEPCVD method were evaluated with visible - ultraviolet absorption spectroscopy, infrared transmission spectroscopy, x-ray photoelectron spectroscopy and measurements of the photo- and dark conductivities. The carbon content and the optical band gap increased with increasing the rf power on both the methane side and the silane side. films with a carbon content above 0.6 and an optical band gap above 2.8 eV could be prepared by the SEPCVD method even though hydrogen-diluted gas was used. The SEPCVD method proved useful in preparing films with a wide gap. Both fourfold-coordinated carbon atoms and threefold-coordinated carbon atoms existed in films with carbon content from 0.5 to 0.6. However, the atomic percentage of threefold-coordinated carbon in films prepared by the SEPCVD method is smaller than that obtained by the conventional method. was 0.1 - 0.3 and increased with increasing rf power. and decreased with increasing rf power on the methane side, but they were not dependent on the rf power on the silane side. For films with an optical band gap between 1.8 eV and 2.0 eV, the photoconductivity and the photosensitivity were and respectively, and films with high photoconductivity could be prepared. However, the photoconductivity of the films with an optical band gap above 2.2 eV was about .

Experiments on the analysis of the wear debris produced during the polishing of diamond and the rapid sliding of diamond upon diamond using a high-speed sliding machine are presented. The debris was studied by electron energy loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM) and by transmission electron microscopy (TEM). The aim of the work was to improve understanding of the polishing process. It was found that the debris produced when polishing diamond in a direction on a plane consisted of less dense forms of carbon. Diamond debris was instead found in the experiment with the high-speed sliding machine, but the wear track showed markedly different features from those observed on a surface after conventional polishing. The results suggest that the polishing of diamond in the soft directions occurs by a process in which diamond transforms to less dense forms of carbon, after which the transformed material detaches.

This paper demonstrates that the positive streamer corona may be useful for the detection of electronegative impurities in gas (ambient air). The measurements of the repetition rate of streamers are carried out in a point-to-coaxial cylinder gap where DC voltage and AC voltage at a frequency of up to some kilohertz (the so-called `mixed voltage') are applied simultaneously. The repetition rate of streamers is investigated depending on the airflow rate, on the amplitude and frequency of the AC voltage, on the level of gas preionization and on the amount of moisture and impurities of different kinds in air. Results presented in the form of counting-rate characteristics of streamers show that under the action of halogens the detectable changes in characteristics take place if the halogen concentration exceeds 1 - 10 ppb. Principles of operation of the proposed detector and possible basic physical mechanisms of the influence of impurities on the counting response are discussed. It has been demonstrated that a simple statistical model for the inception of streamers under the conditions of a mixed voltage enables calculation of the counting-rate characteristics of streamers in satisfactory agreement with the experimental results.

Arc cathode spots in vacuum with Ti- and Cu-cathodes have been studied by using the high-speed framing camera IMACON 468 in the time range down to 10 ns. The spots exhibited an inner structure that indicates the existence of fragments. At currents of 70 A their number was 5 - 7. These structures showed high dynamics, attracting and repelling one another with speeds up to . This was associated with quasi-periodic fluctuations of the spot brightness, yielding a new explanation for the brightness fluctuations reported in a preceding paper. One of the fluctuations, occurring every , had a most probable duration (width of the light pulse) of 200 - 300 ns. The spatial resolution, per pixel, was sufficient to allow observation of surface craters in situ. So it turned out that the fragments are located at crater rims and that the crater structures may change in times <100 ns. As a consequence of periodic attracting and repelling of the fragments, the spot displaces at random. The mean square displacement was measured to be for observation times of 100, 200 and 500 ns. From the time scale of surface changes it is concluded that the main energy source for crater formation is surface bombardment by the plasma ions rather than Joule heating of the crater volume.

A particulate composite medium in which the host and the spherical inclusions are made of uniaxial dielectric - magnetic media with parallel crystallographic axes is considered. The polarizability dyadics of a single inclusion are obtained, showing in detail the significant role played therein by the degree of anisotropy of the host medium. The derived expressions are used to set up the Maxwell Garnett and the Bruggeman formalisms for homogenization of the particulate composite medium. Numerical results are presented to show that the degree of anisotropy of the homogenized composite medium (HCM) is a non-trivial function of the degrees of anisotropy of the constituent media. Shifts in axial and transverse Fröhlich resonances are also predicted.

On examine, dans ce travail, certains fondements des modèles usuels d'interprétation de la conductivité électronique , dans les états localisés des solides désordonnés, répartis dans une bande B d'énergie, uniforme et de largeur , placée au milieu de la bande interdite. Cette partie I résume d'abord les hypothèses de base de ces modèles, ainsi que les expressions de qui en découlent. Puis, une analyse critique des méthodes d'intégration utilisées est effectuée et ses conséquences en sont tirées. Ainsi, un traitement approprié des équations conduit d'une part à modifier la dépendance de vis-à-vis de la température T et de , comme conséquence d'une correction apportée à une intégration sur les énergies; d'autre part à étendre jusqu'aux très basses fréquences la validité de l'approximation des paires, du fait d'un changement introduit dans la méthode d'intégration vis-à-vis des temps de relaxation.

Nous avons proposé, dans la partie I, une formulation plus complète de la conductivité dans les états localisés, ce qui a permis d'étendre jusqu'au régime continu l'intervalle d'application de l'approximation des paires. Nous analysons ici, d'une manière plus approfondie: (i) les conditions de validité de cette approximation, et nous mettons en évidence les raisons pour lesquelles elle doit être écartée lorsqu'interviennent des interactions coulombiennes; et (ii) les restrictions qui doivent être imposées à l'hypothèse de déconnexion entre états localisés et étendus, qui conditionne l'écriture des équations d'échanges entre les éléments d'une paire et donc aussi l'ensemble des expressions théoriques.

Samples of (R = Y and Fe; x = 0.0 and 0.05) were prepared by the usual ceramic method. X-ray diffraction studies indicated the presence of a single phase. The samples were studied by differential scanning, calorimetry, electrical resistivity and thermoelectric power. An intimate relation between the electrical properties and the different transitions in was found. The partial substitution of Y or Fe for La in has a slight effect on the transition temperatures; it was found to inhibit the phase recombination supposed in the unsubstituted sample at 410 K. Finally the effect of substitution of Y or Fe was found to increase both the electrical resistivity and thermoelectric power markedly.

The temperature-dependence of specific contact resistance for temperatures between room temperature and liquid-helium temperature () has been investigated for Al-to-boron- and Mg/Al-to-phosphorus- doped-silicon contacts. The specific contact resistance of these high-doping-density Si contacts was as low as , even at low temperatures. The resistivity was found to increase slightly as temperature decreased, in contrast with previous predictions.

Using a high- superconducting harmonic mixer at 77 K and a phase-locking loop, a signal source (a Gunn oscillator in the 3 mm waveband) was directly phase-locked to a local oscillator for frequencies less than 1 GHz and harmonic numbers up to 120. The phase-locked Gunn oscillator achieved a frequency instability of less than Hz, with the counting time of 1 s, while the phase noise at intermediate frequency 40 MHz was ( kHz) for 120th harmonic mixing and ( kHz) for 42nd harmonic mixing. The output of this phase-locked signal source was applied to a Josephson junction array used in a voltage-standard system against which a solid-state voltage source (a Zener voltage reference) was measured. The experimental results showed that the quality of this phase-locked microwave source was good enough to justify its use in the quantum voltage standard.

Characteristics of spontaneous polarization reversal have been studied in detail for the first time in crystals subjected to a pulsed electric field in the range 15 - 70 kV . The switching process has been observed by recording a transient switching current and subsequent piezoelectric probe mapping and optical and secondary electron microscopy methods. The measured value of spontaneous polarization is . The ionic potassium DC current was observed to have a strong effect on the polarization switching. The developed experimental set-up has made it possible to fabricate a periodic domain structure and to generate an optical second harmonic power.

When sol - gel synthesized silica glass containing about 260 ppm of OH groups is irradiated with an ArF excimer laser, photoluminescence appears at 1.9 eV (650 nm). From measurements of luminescence lifetime, the absorption spectrum and electron-spin-resonance spectroscopy, the luminescence is thought to be due to a non-bridging oxygen hole centre, a kind of point defect in silica glass.

Using the Einstein relation for a grain boundary, the creep controlled by grain boundary diffusion is compared with that controlled by grain boundary viscous flow. It is found that the creep rate controlled by viscous flow has the same order as does that controlled by grain boundary diffusion. This suggests that the creep controlled by grain boundary viscous flow may have the same mechanism as does that controlled by grain boundary diffusion.

In a recent paper, Sihvola and Pekonen introduced a systematic way of computing the effective medium properties of bi-anisotropic composites. In this comment, we will show that the `strong generalization' presented in their paper is indeed a `bold conjecture' without any theoretical proof.

We reply to the comment by Shanker regarding the validity of our conjecture that generalizes electromagnetic mixing rules. Our reply also emphasizes the fact that a correct conjecture is always more useful the bolder it is.