Table of contents

The effect of illumination on silver diffusion in Ag-CdS diode structures at room temperature was investigated by using radiotracer technique. The effect of photostimulated Ag diffusion in CdS at room temperature is equivalent to thermal diffusion of silver at about . The influence of silver photodiffusion on electrical, photoelectrical and optical characteristics of Ag-CdS diode structures was studied. A decrease in the photosensitivity, rectifying characteristics of Ag-CdS diode structures and an increase in the electron concentration in the near-surface region of the CdS substrate and in the junction width and optical transmission of the structure were discovered after illumination. The possible mechanisms of photostimulated silver diffusion in CdS and degradation of characteristics of Ag-CdS diode structures are considered.

We report the fabrication of a high-concentration Er-doped phosphate-niobate glass. The glass composition has been optimized for doping with erbium and for ion-exchange processing. Formation and modelling of planar ion-exchanged waveguides with silver and potassium dopants are also presented to confirm that this glass is a prospective candidate for active integrated optics.

A quantitative thermal conductivity measurement technique, the method, is applied in a scanning thermal microscope (SThM) with a resistive probe for the determination of thermal properties with a high spatial resolution in the nanometre range. With this set-up the quantitative thermal conductivity of materials can be determined with a deviation of less than 2%. Using gold as the reference material, the local thermal conductivities of silver and a CVD diamond film have been measured with a spatial resolution of approximately 30 nm.

A new set of swarm data in and helium were experimentally determined by the pulsed Townsend method over the range Td (1 Td V ): the effective ionization coefficient , the drift velocity and the longitudinal diffusion coefficient . The limiting values of -He gas mixtures were derived from the experiment and found to vary linearly with the concentration in the mixtures.

The formula derived by Nobuyasu Sato (1980 J. Phys. D: Appl. Phys. 13 L3-L6), for the current flowing in an external circuit due to the motion of charged particles in a gap is extended to include a time-dependent applied voltage. The effects of negative ions, and electron, positive ion and negative ion diffusion are also included. It is found that Sato's original equation still describes the contribution of charged particle motion to the external circuit current. The total circuit current is determined by adding the displacement current that effectively flows across the gap to the current determined by Sato's equation. Some comments are also made about the interpretation of Sato's equation in three dimensions.

The influence of various preparation conditions such as bath composition, film growth and heat treatment conditions on the properties of chemical bath deposited cobalt II oxide thin films has been studied. The interference fringes on the transmission spectra were used to calculate the refractive index and the average thickness of the films. The effects of surface roughness of the films on the interference extrema are also analysed. The maximum film thickness obtainable in a single deposition cycle is about 700 nm. X-ray diffractometry, energy-dispersive analysis of x-ray fluorescence and electrical resistivity measurements were also used for the characterization of the films. The properties of the deposited films are similar to those of hot-sprayed and sol-gel and baked films but film deposition is simpler and more cost effective than via solution growth procedures.

The magnetically bistable nature of as-quenched amorphous fibre disappeared when the material underwent stress-relief annealing at for 30 min. A reduction of internal stress leading to a lowering of the magnetoelastic anisotropy was the cause of such a change from bistable to normal ferromagnetic behaviour. Cathodic hydrogen impregnation caused the re-appearance of magnetic bistability, the magnitude of which was dependent on the duration of hydrogen charging (and hence on the hydrogen concentration). Perfect bistability was restored when the annealed fibre was charged for 120 min at the charging current density of . Owing to the positive molar volume of hydrogen, internal stresses were generated by hydrogenation, which increased the size of the longitudinal anisotropy region. When this longitudinal anisotropy region was big enough to act as a monodomain at the core of the fibre, bistability with a large switching field was observed.

We studied the effect of grain size on the ferroelectric phase transitions in ceramics (x = 0.3, 0.5 and 0.7) prepared by a sol-gel method. The samples were observed and analysed by SEM, TEM and x-ray diffraction. The phase transitions were investigated by means of dielectric measurements. With the decrease of grain size, the Curie temperature decreases and the Curie peak becomes lower and broader and eventually disappears. The diffuseness of the dielectric response is understood on the basis of a diffuse phase transition model. The size dependence of can be described by , where is the for bulk , D is the grain size, and C and are two constants. This equation gives three ferroelectric critical sizes of 317 nm, 246 nm and 176 nm for x = 0.3, 0.5 and 0.7 respectively.

Propagation through a sparse distribution of lossy particles in a cloud is investigated. Using a discrete modelling technique, a mathematical model to aid in the interpretation of the interaction data obtained by electromagnetic probing of mixed ice crystals and waterdrop clouds is developed. Such clouds can contain many possible crystal forms, most notably thin long cylinders and flat plate crystals. The present work is a simulation of the theoretical aspects of this problem. The attenuation, phase, bistatic scattering patterns and emissivity are computed for waves of selected polarizations passing through clouds with specified sizes, shape and distributions. The results are compared with the literature and good agreement is obtained.

We report the results of quantitative phase-contrast imaging experiments using synchrotron radiation, in-line imaging geometry and a non-interferometric phase retrieval technique. This quantitative imaging method is fast, simple, robust, does not require sophisticated x-ray optical elements and can potentially provide submicron spatial resolution over a field of view of the order of centimetres. In the present experiment a spatial resolution of approximately 0.8 m has been achieved in images of a polystyrene sphere using 19.6 keV x-rays. We demonstrate that appropriate processing of phase-contrast images obtained in the in-line geometry can reveal important new information about the internal structure of weakly absorbing organic samples. We believe that this technique will also be useful in phase-contrast tomography.

Acoustic spectroscopy is a relatively recent method for the characterization of suspensions and emulsions. Measurement of the attenuation of ultrasonic waves is often the first step of such analyses. Coupled with appropriate theoretical models, these data allow one to infer information such as particle size distribution and particle concentration. Several of such models are available, describing the behaviour of isolated particles. However, the validity of the isolated-particle assumption is limited to low particle concentrations, where nonlinear multiple-particle effects are negligible. To investigate this aspect, this paper is concerned with the multiple-particle effects as they arise in concentrated colloidal dispersions of high density contrast between the phases. The mechanism of multiple lossless scattering is demonstrated to be of minor influence in these systems. This suggests the presence of another multiple-particle effect, namely particle-particle interactions in the dissipative energy absorption.

The similarity solutions describing the steady plane (flow and thermal) boundary layers on an exponentially stretching continuous surface with an exponential temperature distribution are examined both analytically and numerically. The mass- and heat-transfer characteristics of these boundary layers are described and compared with the results of earlier authors, obtained under the more familiar power-law boundary conditions.

An inverse model for determining the wall heat flux in filmwise condensation on a horizontal plate is presented. The inverse analysis is based on the film-condensation-thickness readings taken at several different points on the plate. Finite-difference methods are employed to discretize the problem domain and then a linear inverse model is constructed to identify the unknown conditions. This approach taken is to rearrange the matrix forms of the differential governing equation and estimate the unknown surface conditions. Then, the linear least-squares method is adopted to find the solution. In the direct problem, the present study considers that the boundary condition at the plate edge can be directly obtained from the concept of minimum energy inherited from the condensate flow rate rather than arbitrarily assumed. For the condensation problem, the governing equation is nonlinear. This paper proposes a linear transformation for solving both inverse and direct problems. In contrast to the traditional approach, the advantage of applying this method to inverse analysis is that no prior information on the functional form of the unknown quantities is needed, no initial guess is required and the iterations of the calculation process need be done once only.

We describe the application of the photoacoustic technique to the thermal characterization of liquids. An experimental method which allows the experimental determination of the thermal effusivity in transparent as well as in light absorbing samples is proposed. The method is tested by measurements in water, ethanol, diffusion-pump oil, glycerol and petroleum. Our results agree quite well with the literature reported values for these samples.

Within the framework of systematic investigations of the dynamic (time-dependent) optogalvanic (DOG) responses in hollow-cathode discharges (HCDs) the effects of the cooling and extinction of a Ne-As HCD were observed. The extinction took place at a low discharge current close to the critical one. In our experiment in this operating mode the DOG response manifested itself as a damped oscillation. The population of levels of the neon atom was measured and the direct ionization rates were calculated. The population transfer from the level to or levels was found to decrease the energy of the gas-discharge plasma.

Numerical analysis of anode boundary layer was carried out to make clear the physical basis of the anode fall in the atmospheric free-burning argon arc. The governing equations of the dominating processes took account of a physical state of non-local thermodynamic equilibrium, and they were solved by applying the finite difference method. The numerical results showed each anode fall, namely a positive anode fall and a negative one, and also showed the distributions of the temperature and electron number density in the case of each anode fall. We conclude that the gradient of electron number density played the most important role in driving an electron flux toward the anode and also determined the sign and magnitude of the anode fall. Furthermore, the electron density gradient was strongly affected by the relation between arc current density and convective flow in the anode boundary layer.

The present study is focused on predicting fragment number and size distribution in dynamic fragmentation processes. Because of the unloading effect of release waves arising from fracture nucleations, we consider there to be a minimum value for fragment size. Combined with the assumption that the sites of fracture nucleation are distributed randomly in the sample, we have deduced a set of equations with which the fragment number and size distribution curve could be calculated. Different from previous work, the parameters in this work are all physically determined but not fitted. Comparison with expanding cylindrical shell and ring experiments has been made, showing that the theory has a good predictive capability.

A neural network method for quantitative depth profiling of inhomogeneous materials with quasi-continuously varying electrical conductivity profiles is presented. The possibilities and limitations of eddy-current depth profiling are examined on the basis of insight into the physics of eddy currents and of the statistics of simulation results obtained for large sets of inversion examples. Neural network reconstructions of electrical conductivity profiles retrieved from experimental eddy-current data on artificial samples are discussed. The approach presented allows one to study the eddy-current inverse problem in a flexible way thanks to the combination of a versatile profile parametrization and the feasibility of fast neural network performance tests.

The poor quantum efficiency of alkali photocathodes in the near infrared can be improved by multiple total internal reflection. A limit for the improvement attainable by this method is calculated and the maximum ratio of the enhanced over the conventional quantum efficiency is found to be the inverse of the absorptance at normal incidence. A novel, simple way of measuring the absorptance of standard tubes is described. Experimental results for the quantum-efficiency enhancement and the absorptance are presented and agree with the theoretical considerations. The measured ratio of the enhanced over the conventional quantum efficiency for the extended S20 photocathode ranges from 2 at 400 nm to more than 12 at 980 nm. The authors believe that, by combining multiple total internal reflection techniques with the use of dedicated photocathodes, the quantum efficiency in the near infrared can be increased by factors of 20-30.