Table of contents

Heat transport at a Fermi-gas/Fermi-liquid (FG/FL) interface is investigated on the basis of a simplified model of a semiconductor-metal interface. The results indicate that the Peltier heat-pumping rate can be increased due to the additional heat exchange at the FG/FL interface associated with the electron phase transition between the Fermi gas and Fermi liquid. The electronic latent energy is defined as a measure of the energy absorption or emission accompanying a phase transition. It is proposed that a thermoelectric system which incorporates FG/FL interfaces may exhibit a higher thermoelectric efficiency than that of a conventional thermoelectric system.

We have studied the interface morphology of a strained and of a relaxed layer system grown on top of a relaxed buffer on a Si(001) substrate. The strain state of the layers was determined by grazing incidence diffraction (GID). Surfaces have been investigated by atomic force microscopy (AFM) and exhibit anisotropies of RMS roughness and lateral correlation length along the and directions, which are parallel and diagonal to the cross-hatch pattern, respectively. Diffuse x-ray scattering under grazing incidence and exit close to the forwards direction revealed conformal roughness of the interfaces at lateral correlation lengths of about 1 m. To deal with the large RMS roughness of up to 40 Å, the concept of interfaces without a lateral cut-off length was used to describe the diffuse x-ray scattering within the Born approximation. In the case of a relaxed layer, additional roughness on a lateral length scale of 30 nm was observed at a buried interface by diffuse scattering out of the plane of incidence.

We report on the persistent photocurrent (PPC) in p-type nitrogen-doped ZnSe epilayers grown by molecular beam epitaxy on GaAs. Its time-evolution scale ranges from several minutes to hours. The PPC is observed with a non-exponential decay up to room temperature in some samples. A typical decay is composed of an initial transient, which is well described by a stretched exponential, and a subsequent slower transient. The time constant of the first transient has a thermal activation energy of about 0.35 eV. Annealing samples at C decreases both the magnitude of the initial transient of the PPC and the height of a deep-level transient spectroscopy (DLTS) signal from the interface states between ZnSe and GaAs, suggesting that there is a correlation between the persistent photocurrent and the interface states. Also the dependence of the PPC on the wavelength of the illumination suggests that the initial transient originates from the hetero-interface. From current-temperature measurements, we estimate the barrier at the heterojunction to be 0.8 eV. This large value indicates that holes are trapped in a two-dimensional quantum well at the heterojunction to the GaAs substrate. We conclude that the PPC has two origins; namely the presence of metastable centres in the ZnSe layer, close to the hetero-interface, which are similar to DX centres in GaAlAs, and tunnelling of trapped holes from the two-dimensional quantum well through the barrier.

Dye-sensitized fully solid state cells having the structure of rough n-type semiconductor film comprising zinc and tin(IV) oxide/Ru-bipyridyl complex/p-CuI are found to generate high short-circuit photocurrents and open-circuit voltages in contrast to the cells of same type made with a single oxide (tin(IV) or zinc). The mechanism involved is explained as suppression recombinations of photogenerated carriers and dye ions resulting from interparticle charge transfer.

Thin film epitaxial heterostructures consisting of and /Si have been studied theoretically with interdigital transducer (IDT) electrodes at various locations. The thickness of each individual layer has been optimized for achieving an efficient SAW performance with a high electromechanical coupling coefficient. The structural feasibility and practical implications of various device configurations for an acousto-optical device are discussed. The introduction of a thin non-piezoelectric over-layer onto a piezoelectric film is found to enhance the electromechanical coupling coefficient . In a symmetrical /IDT/ waveguide structure the maximum value of is found to increase from 2.438 to 9.23% for a variation in the thickness of the over-layer in the range 0-0.12. Symmetrical and asymmetrical waveguide structures formed with and thin films in combination have been examined and a symmetrical waveguide structure (/IDT//Si) is found to exhibit a high acousto-optical figure of merit and % for a device operating with the fundamental mode at wavelength m.

A method of determining an average refractive-index of a transparent inhomogeneous film on a transparent substrate is proposed. It requires making measurements at normal incidence of the transmittance from the sample using a readily available spectrophotometer. The usefulness of the technique is demonstrated by successful application to thermally evaporated zirconia samples, a type known to present troublesome examples of optical inhomogeneity. Depth profiles of the zirconia films obtained by optical and Rutherford backscattering spectrometric techniques support an earlier model of an inhomogeneous film with a columnar structure. In that reported model it is suggested that the film retains the hexagonal array of closely packed circular bases of the columns and that the columnar diameters decrease with the distance from the substrate side of the film.

Lorentz electron microscopy and micromagnetic modelling have been used to gain insight into the magnetization reversal of CoNi/Pt multilayers supporting perpendicular magnetization. Experimental observations were made in a highly modified transmission electron microscope as a function of the field magnitude and elapsed time. With appropriate selection of parameters, in particular the domain-wall energy and the activation volume, Monte Carlo simulations were able to reproduce most of the experimental results. Both of these quantities are difficult to measure directly. Finally, we note that pinning sites had to be introduced into the model to account for the very irregular manner in which the magnetization reversal proceeded.

In continuation of an earlier paper on the application of the bilocal approximation (BA) within the framework of the strong property fluctuation theory (SPFT), an important restriction on the covariance function is lifted and the consequences numerically examined.

Dual-beam transient thermal lens studies were carried out in aqueous solutions of rhodamine 6G using 532 nm pulses from a frequency-doubled Nd:YAG laser. The analysis of the observed data showed that the thermal lens method can effectively be utilized to study the nonlinear absorption and aggregation which are taking place in a dye medium.

Micromachined reflection phase gratings operate via the electrostatic deflection of reflective microbeams. We develop a lumped parameter model for predicting the transient motion of these microbeams, taking into account electrostatic and tensile forces and viscous air damping via squeeze-film theory. We use this model to determine the time required for a deflected microbeam to return to its undeflected state. Our analysis shows that this re-set time is approximately one order of magnitude greater than the activation time.

We investigate the linear stability of a fluid flowing down an inclined permeable plane by studying the evolution in time of infinitesimal disturbances of long wavelength. We assume that the flow through the porous medium is governed by Darcy's law, and determine the critical conditions for the onset of instability in the case when the characteristic length scale of the pore space is much smaller than the depth of the fluid layer above. The results reveal that increasing the permeability of the inclined plane destabilizes the flow of the fluid layer flowing above.

Studies of laser-induced breakdown in molecular nitrogen were carried out to investigate the dependence of the threshold irradiance on the wavelength at various pressures. The analysis was based on the numerical solution of the time-dependent Boltzmann equation for the electron energy distribution function (EEDF) and a set of rate equations describing the rate of change of the excited states population. The rate coefficients and cross-sections as functions of the electron energy were introduced into this analysis in order to probe the exact contribution of each physical process to the breakdown phenomenon. The calculations were performed under the experimental conditions of Davis et al. In this experiment the breakdown of nitrogen was measured at wavelengths of 1064, 532, 355 and 266 nm, over gas pressures in the range 25-760 Torr, with laser irradiances in the range to . The computed thresholds were found to be in good agreement with the measured ones at all wavelengths. The calculated EEDF and its parameters showed that, at nm, vibrational losses are dominant. Collisional ionization of ground and excited state molecules was found to make a minor contribution to the breakdown phenomenon at 532, 355 and 266 nm. However, the contribution to this process at 1064 nm was more effective. Therefore, the breakdown phenomenon proceeds via an electron-cascade process that converts the molecules only into the excited states, whence multiphoton ionization plays its role.

An investigation of wave propagation in a plasma slab bounded by dissimilar dielectric media has been made numerically in the magnetohydrodynamic approximation. It has been shown that four families of waves can propagate: plasma, cyclotron, anisotropic and waveguide modes. It has been proved that singular waves propagate at the crossing points of the waves with a complex zone boundary. We have analysed the influence of the bounding dielectric media, the width of the waveguide and the magnetization of the plasma on the spectrum of the waves. The distributions of the fields, the energy density and the Poynting's vector of different modes along the dispersion curves have been analysed. The passing of energy from dielectric to plasma with increasing wavenumber has been shown.

Monte Carlo simulations are widely used for computing statistical growth processes such as the development of electron avalanches in gases, but typically require excessively long computer times. In this paper, a method based on intermediate statistics is developed and shown to give results in agreement with a full Monte Carlo treatment with a reduction by a factor of about 100 in computer time. This method could be extended, for example to the computation of the resolution of proportional counters as a function of energy and so help to resolve the discrepancy among existing experimental data. This method should be used for situations in equilibrium (in space and time).

Microwave expansion of a plasma is certainly a promising process by which to obtain a large-diameter plasma profile; however, it generates instability regions and local inhomogeneities. The purpose of this work is to study the wave-propagation conditions and plasma-expansion profile in a pure argon discharge and in argon-methane mixture. Spatially resolved plasma parameters are measured using an array of electrostatic probes (simple and double) moving along the discharge axis. This device gives radial and axial measurements which are correlated to the spatially resolved Ar(420 nm) emission line intensity. We show that, as expected, the wave-propagation conditions are satisfied within the luminous part of the discharge. In this region the electron energy distribution function (EEDF) can be roughly approximated by using a Maxwell distribution function of low temperature (about 1000 K). The absorbed microwave power is mainly transferred to electrons as potential energy. Instabilities appear at the edge of this luminous region, where the wave-propagation conditions are not satisfied. In this region the EEDF is strongly disturbed and cannot be approximated using a Maxwell distribution function. The microwave incident power is mainly reflected, so the potential energy of electrons decreases strongly. Nevertheless, the kinetic energy of electrons increases because of stochastic electron heating due to strong inhomogeneities in the charged particle density producing local electrical fields. When methane is mixed with argon, the energy necessary to maintain an electron free in the plasma increases with increasing frequency of inelastic collisions. Consequently, the plasma expansion length decreases with increasing percentage of methane added to argon.

The models of a positive column of an inert gas discharge at low pressures and small currents are developed in the frameworks of nonlocal kinetic and local fluid theories. Both models are based on the joint solution of the corresponding kinetic equation, ion-motion equation and Poisson equation that permit one to describe bulk plasma and near-wall sheaths of space charge. The theories differ principally in the descriptions of the electron component of a plasma. In the fluid theory the radial flux of electrons is a combination of field and diffusive fluxes, but in the kinetic model a similar representation is impossible. A comparison of the distribution functions and macroscopic properties calculated by kinetic and fluid theories for the discharge under the same conditions is performed. This comparison is carried out for the models of the positive column developed under the assumption of plasma quasi-neutrality and with regard to the deviations from quasi-neutrality. The use of the fluid theory beyond its application range (low pressures and small currents) does not reflect the physical picture of discharge sustenance and leads to incorrect results with respect to several parameters.

The afterglow of a 1 kA, 10 ns duration discharge in neon at 1.1-4.0 bar pressure containing up to 30 mbar of reactant admixture Xe was studied by time-resolved emission spectroscopy. Destruction frequencies of neon ions have been determined experimentally both from the selectively excited fluorescence of and from the radiation of excited xenon atoms. These data confirm the existence of a termolecular charge-transfer reaction of with Xe, the corresponding rate coefficient being . Also the fact that vibrationally excited ions play an important role was confirmed. A persistent source of ionization at late afterglow times has been studied in some detail and was interpreted in terms of collisions between xenon atoms in their first excited states and . The decay processes of these atoms were identified as partially trapped resonance radiation and three-body conversion to dimers.

This paper reports the modelling and initial results of a complete self-consistent physico-chemical model for a circuit-breaker arc plasma. We calculate the free-recovery temperature decay and species densities in a uniform zero-dimensional space according to a collisional-radiative plasma model in combination with an energy balance for pure , pure and an equimolar mixture of the two. Cooling by radiation, thermal conduction and diffusion is considered by using simple models. Among the vast amount of results, it is found that the electron-removal processes like attachment and recombination in a plasma are far less efficient than those in a plasma. Besides this, heating of the recovering plasma caused by exothermic associative reactions dominates over cooling. All this indicates a low current-interruption capability when it is applied in gas circuit breakers. In order to estimate this interruption capability we will use this model in combination with Boltzmann analysis to determine whether the arc plasma recovers or re-ignites under the influence of electron-impact processes and the inherent electrical field strength in part II of this paper.

This paper reports the initial results of a complete physico-chemical modelling of a circuit-breaker arc. The time-dependent results of a collisional-radiative model combined with Boltzmann analysis to determine the electron transport properties in a uniform zero-dimensional space are given. Microscopic processes leading to extinction of the arc under the influence of the electrical circuit are evaluated and discussed. It is shown that, under some conditions the electron temperature is elevated considerable over the gas temperature driven by the electrical field strength inherently built up by arc-circuit interaction after current zero. The related electron-impact, recombination and association processes, which are decisive for the failure or success of the current interruption by the circuit breaker, are studied in detail. Whereas exhibits entirely favourable physico-chemical properties for current interruption, nitrogen requires additional cooling by a mechanical blast because of a combination of highly exothermic association reactions, inefficient electron removal and efficient ionization of atomic nitrogen.

Studies have been conducted on the ferroelectric properties of -, a solid solution of the antiferroelectric oxides and . X-ray diffraction shows that at room temperature this solid solution has a tetragonal perovskite crystal structure. Evidence for a diffuse phase transition in this material is provided from measurements of the dielectric and piezoelectric properties and the form of the P-E hysteresis loop. A Fröhlich-type model for the relaxation time spectrum is shown to model the complex dielectric constant as a function of temperature satisfactorily. Cole-Cole plots of the experimental real and imaginary parts of the dielectric constant, and , as a function of temperature and curves of polarization as a function of temperature suggest a freezing temperature of 152 K and 173 K respectively, in contrast to Vogel-Fulcher fits of the temperature dependence of the maxima in and which suggest a freezing temperature of 310 K and 308 K respectively. The nature of this diffuse phase transition has been interpreted in terms of a glass-like behaviour.

In powdered phosphor screens, a large fraction of incident UV light is reflected from the surface of individual particles, with the remainder penetrating the phosphor surface to generate photoluminescence. The reflected UV photons entering the screen are randomly scattered throughout the particulate structure, resulting in photoluminescence down to, for example, 10 layers deep from the surface. An optimum number of layers within a screen for luminance in reflection and transmission modes can be calculated after determination of the absorption and scattering coefficients per layer in a practical phosphor screen. Good agreement has been obtained between the calculated and experimental results.

To study the characteristics of the plasma plume generated by KrF excimer laser irradiation of graphite, optical emission spectra (OES) of plasma species have been recorded for different distances from the target and for various ammonia pressures. The laser fluence and the ammonia pressures were set to values typically applied during the deposition of carbon nitride thin films. Emission spectra of CN, CH and NH radicals were recorded as a function of time for different deposition conditions. The experimental vibration-rotation bands were fitted to a synthetic spectrum of CN, CH and NH radicals. Rotational and vibrational temperatures deduced from the analysis of CN emission spectra were found to be equal, indicating that a collisional equilibrium was reached among the heavy particles of the plasma plume. Comparison of rotational and vibrational temperatures deduced from the spectra recorded in nitrogen atmosphere is also presented.

The glass-forming regions in the -Se-ZnTe, Se-Se-ZnSe and -ZnTe-ZnSe chalcogenide systems have been determined. The temperatures of phase transformations (the glass transition, crystallization and melting), the density and the microhardness have been studied. The crystalline phases which can be formed in these glasses have been specified. The established correlation between the properties and the composition has been explained with respect to the specific roles of the compounds involved. The results obtained have been compared with those for the similar ternary -Se-ZnSe system.