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This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. Soft x-ray resonant magnetic scattering has been used to investigate the element-selective microscopic magnetization reversal behavior of room temperature perpendicular exchange coupled ferromagnetic∕antiferromagnetic (F∕AF) systems and to study the role of the interfacial coupling strength on it. Different nucleation processes and domain size distributions along the decreasing and increasing branches of the reversal have been found. The size of the magnetic domains during reversal depends on both the F anisotropy and F∕AF coupling strength, decreasing when one of them increases. Evidence of the exchange bias(coercivity enhancement) being induced by pinned (unpinned) uncompensated AF interfacial spins is also shown.

We have carried out deep level transient spectroscopy (DLTS), optical DLTS, and capacitance-voltage measurements on liquid phase epitaxy-grown Er-doped Si to characterize the deep levels present in the material and to identify those related to dislocations and involved in the luminescence activity. The optical properties of the material have been studied by photoluminescence, cathodoluminescence investigations, and two emission lines, labeled A and B, have been found, line A being located at 0.806 eV. We have observed that an actual interaction occurs between dislocations and Er-related emitting centers. © 1999 American Institute of Physics.

The total syntheses of three C37 methyl-alkenones with different degrees of unsaturation and of their 13C-labelled analogues from commercially available starting materials are presented herein for the first time. These molecules are important to improve the reliability of the measurements and reconstructions of the sea surface temperature and salinity.

The analysis of the photoluminescence (PL) spectra of a number of silicon samples plastically deformed or simply thermally annealed was used to understand the rol e of oxygen and oxygen precipitates on the PL emissions in the 0.8-1.0 eV range. The results of this analysis show that it is possible to discrim inate between emissions due to oxygen-associated centres and those due to dislocations. Furthermore, i t has been shown on a sample presenting only (dissociated) 60° dislocations that the 0.807 eV e mission is absent, demonstrating that it comes either from dislocation intersections or from scr ew segments. Finally, it has been suggested that the strain field associat ed to oxide precipitates might be responsible of both narrow and broad bands, systematically present in most of the samples examined, which are therefore interpreted as being due to carr ier confinement effects in localized quantum wells at silicon/silicon oxide interfaces of oxide precipitates.

A light-beam induced current (LBIC) in a planar configuration has been coupled to multiple-internal-reflection (MIR) spectroscopy in order to correlate evidence of the surface recombination velocity changes to contaminants on the silicon surface. We verified preliminarily the chemical evolution of HF-treated silicon surfaces from the hydrophobic to the hydrophilic condition after ageing in the laboratory. We then carried out the analysis of silicon surfaces deliberately contaminated with volatile organie molecules using both LBIC and MIR. The results show that the absorption of organics at the surface involves a significant effect on the surface recombination rate.

It is well-known that the sharp luminescence emission at 1.54 μm from erbium-doped silicon has set off a great interest for this material in view of its applications in the third window of optical telecommunications. It is also known that the erbium luminescence is very poor in the absence of impurities like oxygen, carbon and nitrogen, but in spite of the large amount of research work devoted to this material, it is not yet completely clear what is the local structure of the optically active Er centre in oxygen-doped Er–Si alloys. The aim of this paper is to present and discuss the results of the analysis of the EXAFS spectra of two sets of Er-doped silicon samples, of which one was obtained by erbium and oxygen co-implantation and the other was grown by LPE (liquid phase epitaxy). The EXAFS spectra of these samples were satisfactorily fitted by assuming that Er sits in three different configurations, depending on the presence or the absence of oxygen and dislocations in the epi-layer. The relevance of these results in terms of optical and electrical activity of erbium is discussed in details.

Liquid-phase epitaxy from an Si-In-Er solution at an average temperature of 950 degrees C has been used to grow 2- 4 mu m thick epilayers of erbium-doped silicon onto CZ and FZ silicon substrates in an oxygen-free hydrogen atmosphere. Most of the samples grown on CZ substrates presented detectable, but feeble photoluminescence at 2. K in the spectral range of emission of the Er3+ manifold at 0.8 eV. However, some of the samples presented intense photoluminescence characterized by two bands at 0.807 (at 10 K) and 0.873 eV, of which the first falls almost at the same energy of the Er3+ line, but whose intensity presents a quite remarkable persistence up to 250 Ii. From the energy position of the two bands, from their temperature dependence and from the levels found by deep level transient spectroscopy measurements, associated to TEM examinations, it was possible to attribute these bands, labelled D1 and D2, to dislocation luminescence. It will be shown in this paper that the presence of erbium enhances the D1 luminescence, possibly due to the fact that in these samples erbium is gettered at dislocations in an Er-O local configuration, as it results from EXAFS measurements. Apparently, also, a competition occurs with the Er-induced radiative recombination at dislocations, which is a fast process, and the indirect excitation of the Er manifold, which is the predominant process in dislocation-free materials. (C) 1999 Elsevier Science B.V. All rights reserved.

We investigate optical properties of dislocations in nitrogen-doped and nitrogen-free Czochralski silicon. The dislocations are formed during crystal growth, but not formed during deformation. The results show that in nitrogen-doped samples, a broad band replaced the D1 band of dislocation, regardless of dislocation density. The replacement of D1 band is caused by the non-irradiation combination induced by oxygen precipitation. Moreover, a new emission at 0.975 eV is observed in both the nitrogen-free and doped samples when the dislocation density is lower than 10(4) cm(-2).

A joint theoretical and experimental analysis of the crystalline fraction in nanocrystalline films grown by low-energy plasma enhanced chemical vapor deposition is presented. The effect of key growth parameters such as temperature, silane flux, and hydrogen dilution ratio is analyzed and modeled at the atomic scale, introducing an environment-dependent crystallization probability. A very good agreement between experiments and theory is found, despite the use of a single fitting parameter. © 2009 American Institute of Physics.

A combined theoretical and experimental analysis of the crystalline phase fraction in nanocrystalline films grown by low-energy plasma-enhanced chemical vapor deposition is presented. The effect of the key parameters, such as temperature, silane flux, and hydrogen dilution ratio, is analyzed. An atomic-scale Monte Carlo model is developed, where the crystallization probability depends on the local environment of the nanocrystalline film. Good agreement is found between the experiments and theory, despite the use of a single fitting parameter.

The knowledge and control of the structural details (texture, crystallite environment and size) of nanocrystalline silicon films is a prerequisite for their proper application in various technological fields. To this purpose, nanocrystalline silicon films grown by low energy plasma enhanced chemical vapour deposition (LEPECVD) on different kinds of substrates were submitted to a systematic characterization using Raman spectroscopy, X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). The results showed how the difference in substrate morphology is responsible for a deep difference in the film structural properties, particularly in the case of high silane dilutions.

Defect monitoring and engineering techniques were applied to multicrystalline silicon grown from electronic grade silicon scraps and strained silicon-germanium alloys to test their suitability for low-cost photovoltaics and high-speed electronics, respectively. The combination of lifetime, photoluminescence and electron beam induced current (EBIC) measurements was found a very effective practice for the analysis of the effect of impurities on the electrical activity of grain boundaries and dislocations in multicrystalline silicon. Room temperature photoluminescence has been also used to monitor the effect of various cell fabrication process steps on the local recombination activity of defects. The application of the EBIC technique was found as well a good tool for a quantitative determination of threading dislocation density in Si-Ge alloys, in view of the optimisation of the low energy plasma-enhanced chemical vapour deposition (LEPECVD) used for their growth. © 2006 Elsevier Ltd. All rights reserved.

An increase of about 1% of the delivered power by a mono-crystalline commercial silicon solar cell has been obtained by coating the cell with an active poly-vinylacetate film doped with a light harvesting phenanthroline-Eu3+ Complex. The dopant absorbs the UV component of the solar spectrum, where the silicon-based cells are almost blind, and emits red light that can be converted with an efficiency close to the maximum. This effect, achieved by a low cost encapsulation process, has been proven for the case of Air Mass 0 lighting conditions, and could be exploited also for terrestrial applications with the proper choice of the organic ligand. (c) 2005 Elsevier B.V. All rights reserved.

Nanocrystalline silicon (nc-Si) already attracted a considerable attention as a promising material for photovoltaic applications, while its full optoelectronic potentiality is still under investigation, due to the relatively poor knowledge of the correlations between growth conditions, microstructure and physical properties. This paper aims at the illustration of the preliminary results of a 3 years project, addressed at the demonstration of the multifunctionality of nanocrystalline silicon, via the understanding of the quantitative correlations between growth process parameters and the structural, optical, electrical and physico-chemical properties of nc-silicon. The main topics foreseen and actively pursued were: • The development of a gas phase kinetic model to be used for the simulations of the plasma enhanced chemical deposition (PECVD) process, the development of a kinetic model relative to the interaction of radicals present in the plasma phase at the substrate interface, and last but not least, the development of models relative to the subsequent nc-Si growth. • The growth of undoped and doped nc-Si layers on convenient substrates by the low energy plasma enhanced chemical deposition (LEPECVD) process using silane, phosphine, diborane and hydrogen mixtures. • The quantitative experimental determination of the correlation among the crystallinity fraction, the film microstructure, the grain size/shape/orientation, the hydrogen content, the density of the recombination centres, the optical absorption coefficient the strain/stress state and the carrier mobility and diffusion length in undoped and n-type and p-type films, in view of the optimization of the minority carrier generation and carrier collection. The preliminary results already demonstrate that a proper modelling of the growth process is of great help in the selection of optimised growth procedures for nc-Si films and that a full range experimental characterisation is needed to get the proper inputs to the modelling activity. © 2006 Elsevier B.V. All rights reserved.

Three electric-dipole spin-resonance signals, labeled TU7, TU8, and TU9, were detected after subjecting oxygen-rich silicon samples to two-step annealing procedures at 450 and 650 degrees C for prolonged times. The formation and structural evolution of large interstitial agglomerates, known as rodlike defects, occur in oxygen-rich silicon material during similar annealing procedures. Comparison of parameters and formation peculiarities of the defects, inferred from the investigation of the detected signals, with those previously reported for rodlike defects, allowed the assigning of the TU7, TU8, and TU9 spectra to the line-interstitial defects, the planar defects, and the dislocation dipoles, respectively. Correlations of the spin-resonance signals and peculiarities in the photoluminescence spectra for the samples are reported and analyzed. (c) 2005 American Institute of Physics.

This paper is addressed to the discussion of the effect of the dislocation structure and the impurity contamination on the photoluminescence of Czochralski (Cz) silicon in the range of the D1 emission at 0.8 eV. Two types of dislocation systems were considered. One consists of intersecting hexagonal half loops of screw and 60degrees segments. The other one consists of a set of non-intersecting, parallel 60degrees dislocations. In both cases the plastic deformation processes were carried out at 670degreesC, taking care to avoid unwanted impurity contamination. It is shown that the PL emission of pure 60degrees dislocations in the D1 region is missing the 0.807 eV component and consists of a narrow band at 0.817 eV superimposed onto a broad background centered at 0.830 eV. It is also shown that a system of intersecting half loops presents both the 0.807 eV and the 0.817 eV components. The effect of thermal annealing at 800degreesC was shown to induce oxygen precipitation effects, revealed by supplementary spectral features. It is eventually demonstrated that the set up of the D1 band is not necessarily connected with the contamination of 60degrees dislocations with metallic impurities. The major role of oxygen on the dislocation luminescence is eventually experimentally confirmed.

We have studied the magnetization reversal dynamics of spin valves and magnetic tunnel junctions deposited on step bunched silicon substrates with a strong topological modulation. Our measurements show that the magnetization reversal is dominated by domain wall propagation at low field sweep rates and nucleation processes at high sweep rates. The magnetostatic orange peel coupling present in quasi-static conditions between the magnetic layers disappears when switching by nucleation becomes dominant. Micromagnetic simulations show that this phenomenon can be explained taking into account the modulated topology of the substrate.

The nucleation process of oxygen precipitates in silicon at 650 degreesC was investigated using photoluminescence (PL) measurements, which are demonstrated to provide a highly sensitive tool for the characterization of precipitates differing in structure and shape. The results of this study were first analyzed from a thermodynamic and kinetic point of view in order to explain the effect of minute differences in oxygen concentration on the PL spectra, which indicates that two kinds of nanometric oxides coexist in dynamic equilibrium. Then a hypothesis is advanced about the origin of the oxygen-induced PL bands, which is explained in terms of carrier confinement effects induced by the strain at oxide precipitates. (C) 2004 The Electrochemical Society.

This work deals with the structural properties of nanocrystalline (nc) silicon films for solar cell applications, grown using a new PECVD process based on an arc discharge plasma characterized by low ion energies, called LEPECVD (Low energy PECVD). This process permits to increase the intensity of the plasma discharge in the growth region and thus to achieve higher growth rates while avoiding ion-induced surface damage of films. The structural properties of the LEPECVD grown films were studied as a function of the deposition parameters (substrate temperature, growth rate, hydrogen dilution) by Raman Spectroscopy, SEM, and HRTEM analysis. The results of this work allowed us to identify the process requirements suitable for the growth of nc-grains in an amorphous matrix.

This paper reports the results of a study of the effect of nitrogen on the optical properties of dislocations in nitrogen-doped Czochralski and nitrogen-doped float zone silicon samples here the nitrogen doping was carried out by adding Si3N4 in the molten silicon charge or by nitrogen gas dissolution. Dislocations were introduced by plastic deformation at 550 degreesC. In nitrogen-doped plastically deformed samples. emissions in the range of the D1-D4 bands of dislocations are present with a significant shifting from the energies and intensities of the corresponding bands in nitrogen-free samples. It has been shown that the main effect of nitrogen could be the enhancement of the oxygen precipitation. The results confirm the suggestion of some of the present authors that luminescence at 0.830 eV is associated with some intrinsic properties of oxygen precipitates.

Photoluminescence (PL) and deep level transient spectroscopy (DLTS) measurements were used to study the origin of optical emissions in the 0.8-1.0 eV region of selected oxygen precipitated and dislocated silicon samples. It was shown that the D1 band, present in both types of samples, is the convolution of different sub-bands, narrowly spaced between 0.802 and 0.820 eV. The emission at 0.807 eV, assigned in the literature to dislocations, was found only in samples where dislocations were intentionally generated by plastic deformation or induced by the clustering of self-interstitials generated during the growth of oxide precipitates. A comparison of the results of PL, DLTS, and optical DLTS measurements allows the assignment of levels involved in the radiative recombination processes. (C) 2002 American Institute of Physics.

The photovoltaic industry asks for fast, non-destructive techniques for in-line characterization tools in solar cells production. We shall show in this paper that the use of the light beam induced current technique (LBIC) is capable to get in a few seconds time photocurrent maps of large area solar cells and to correlate these data with the cell efficiency. The samples analysed in this study are industrial 10 x 10cm(2) multicrystalline silicon solar cells. The LBIC setup works with three laser sources at 633, 780 and 830 nm, taking the laser beam power below 1 mW. The laser beams are moved on the wafer surfaces using a galvanometer x-y scanner system and the beam size on the focus has a diameter of about 65 Pm. We demonstrated the possibility to obtain quantitative information about the cell quality in

The results of a systematic photo and cathodo-luminescence analysis of a large matrix of CZ silicon samples on which different nucleation and oxide precipitation anneals have been carried out, are reported and correlated with the results of infrared and TEM analysis on the same sets of samples. The results obtained show that the precipitates are correlated with centres, which are responsible of light emission at 0.8 eV and 0.87 eV. Analysis on intentionally dislocated CZ and FZ samples supported these results and confirm that D3 and D4 bands are intrinsic to dislocations.

The development of new integrated circuits (IC) technologies demands a deeper knowledge of the effects of wet wafer cleaning treatments on microchemical, structural and physical surface properties for better device engineering procedures. In this paper, we report and discuss the results of measurements dealing with the effect of conventional hydrochloric acid peroxide mixture (HPM), ammonia peroxide mixture (APM) and dilute hydrofluoric acid (DHF) treatments on the surface recombination rate, measured using the light beam induced current (LBIC) technique in planar configuration and on surface microroughness by scanning tunnelling microscopy (STM). The results indicate that both APM and HPM produce a stable surface, whose recombination rate (around 10(3) cm s(-1)) remains constant for days after the cleaning. In contrast, the DHF treatment results in a low surface recombination rate (less than 10(2) cm s(-1)), which evolves, after an induction period of several hours, to steady-state conditions characterised by surface -OH termination and a recombination rate of around 10(3)-10(4) cm s(-1). STM images and their derived power spectra are in agreement with the interpretation of the changes in surface recombination rates before and after DHF treatments. (C) 2000 Elsevier Science S.A. All rights reserved.

There is a wide set of literature reports that suggest that over-coordinated oxygen or self-interstitials are, directly or indirectly, the chemical bridge between thermal donors, oxygen precipitates and dislocations, capable of supporting a common origin of their emission features in the 0.7-0.9 eV range. Finding the experimental proof of these suggestions was the aim of this present work, which required both appropriate preparation of samples and their careful optical, electrical and microscopical characterization. We were able to show not only that the photoluminescence emissions from oxide precipitates could be correlated to their density and to the presence of closed dislocation rings around them, but also that the precursors of dislocations are optically active as well. For samples thermally annealed in the range of thermal donors, we were able to show that their optical activity seems to be correlated to a transition from a shallow donor level of thermal donors to a deep level of a CiO2 complex.

In this paper we report results concerning the use of Reflectance Infrared Spectroscopy for the study of film structure and morphology. Analyses were performed on tin dioxide and silicon dioxide thin films. For tin dioxide samples, film thickness and surface roughness could be determined. Also, evidence was obtained of preferential crystallographic orientation, that was confirmed by Transmission Electron Microscopy. On silicon dioxide, usability was proved of infrared reflectance spectra for quantitative analyses of water content in the films.

Some issues will be presented concerning the stability of polycrystalline oxide films to be used as semiconductor gas sensors. They are mostly related to the yet incomplete knowledge and control of inner and outer surface properties. One aspect will be considered in detail, namely the connection of film morphology, grain growth and reshaping with the electrical response stability of the material. Specifically, the correlation is studied between the preparation parameters and the characteristics of SnO2 thin films. Tin dioxide films were deposited by spray-pyrolysis of a metallorganic tin compound at 300-400 degrees C. X-ray line broadening analysis and Transmission Electron Microscopy allowed the evaluation of the grain shape and of their growth under operating conditions. The effect of the deposition conditions on the film morphology and properties was also analyzed, in view of the use of these films as gas sensitive materials.

The durability of a device is determined by the stability of its interfaces. The aim of this paper is to compare and to discuss problems connected with interphase stability, as they reflect on chemical-sensor design and operation. Case studies will be considered, concerning issues such as the degradation of the interface between the electrolyte and the auxiliary layer and interface-related degradation in semiconductor sensors. In the former the active mechanism of response degradation is the formation of an interface at the electrolyte-auxiliary layer interface, while in the latter the slow migration of defects throughout the grain dominates. All discussion will be carried out with reference to the relationship between preparation procedures and device structure and chemistry.

The coordination of Zn2+ and Cu2+ ions in semiconducting phosphate glasses was investigated by EXAFS spectroscopy. A change in Zn coordination occurs when the glass composition deviates from metaphosphate. The results are consistent with the hypothesis that Cu(II) and Cu(I) occupy sites with different coordination geometries, but with entire coordination polyhedra similar for all copper atoms. The consistency of the structural model with the semiconducting properties of the glasses is examined. © 1991.

The radiative recombination processes in dislocated float zone silicon samples deformed under gigapascal stresses were studied by photoluminescence (PL) spectroscopy. The observed shuffle dislocations present a reconstructed core and their generation is accompanied by the introduction of point defects and point defect clusters, whose signature is evident in the PL spectra. A broad band around 1 eV is the only PL feature which could be directly related to shuffle dislocations and it is explained conjecturing strain field induced gap changes, as confirmed by molecular dynamics simulations. (c) 2006 American Institute of Physics.

Point and extended defects introduced in p-type Cz Si by oxygen precipitation and plastic deformation have been investigated with electrical and optical methods. Different materials (oxygen precipitated and/or deformed Cz Si and Fz Si) were examined in order to separate the role of oxygen precipitation, plastic deformation, and metallic contamination on the radiative and nonradiative electronic transitions at defect centers. A deep hole trap, named T1, has been associated with dislocation-related impurity centers; additional deep traps have been related to contamination by grown-in transition metals and to clusters involving oxygen atoms. © 2005 American Institute of Physics.

The effect of single-step annealing at 450, 650, and 1000degreesC under gigapascal hydrostatic pressures on oxygen segregation from Czochralski silicon samples was investigated. It was shown that the effect of applied pressure on the oxygen segregation processes begins to be detectable at 650degreesC and significant at 1000degreesC. Not only was the effect of the applied pressure clearly evidenced, but also that of the dopants. In the first case the presence of a gap level associated to self-interstitial clusters could be argued, whereas in the second case both the oxide particles segregation and the dislocation formation were demonstrated to be enhanced by the pressure and by the type of doping. Furthermore, visible and ultraviolet photoluminescence emission at cryogenic temperatures were observed from silicon dioxide particles or from oxide nuclei contained in the silicon matrix. (C) 2003 American Institute of Physics.

CeO 2 has been used as the active electrode material in a solid state device for the determination of the oxygen partial pressure in CO/CO 2 mixtures. Gaseous mixtures with molar ratio CO/CO 2 from 3:1 to 1:3 have been investigated in the 600–850°C temperature range. The performance of this oxygen electrode has been proved better than that of the porous platinum one, because it shows a comparatively better accuracy and a faster time of equilibration with the gaseous atmosphere.

A method for the accurate standardization of an electrochemical oxygen meter, in the 10−6-10−7 bar range is described. The method is based on the use of an electrochemical oxygen leak and a chemical getter pump. In this manner problems connected with traces of hydrogen, originating from the pyrolysis of water, and traces of oxygen of unknown origin are overcome.

Electron spin resonance and ultraviolet and visible absorption techniques have been used to study the optical and structural properties of RuIII and TiIII in TiO–2 and RuO2-based phosphate glasses as a way of investigating the role of transition-metal oxides on the electronic properties of these glasses. From the spectroscopic and thermodynamic analysis of the results it could be inferred that strong metal–metal interactions predominate in TiO2-containing glasses, while metal–matrix interactions play the major role in RuO2-containing glasses, demonstrating that the distribution of the transition-metal ions inside the matrix is essentially determined by the structure of the matrix.

The electrical conductivity measurement carried out on HTaWO 6 ·H 2 O and HTaWO 6 are reported. The activation energy for the conduction process as well as the diffusion coefficient of hydrogen ion are compared with the results obtained by NMR technique.

The use of an high temperature electrochemical oxygen pump fitted with catalytically active anode material is described. This device is useful for the investigation of heterogeneous oxidation reaction and for the quantitative determination of the concentration of trace amount of organic substances in inert gases.

Copper-containing zinc phosphate glasses have been studied for copper contents up to 15 mol% by changing the non-metal-to-metal ratio of the matrix. Optical measurements in the u.v.-visible range as well as e.s.r. analyses were carried out in order to provide structural information about the copper configuration in the system. Strong evidence was obtained for the existence of two different copper pairs. In view of these results and using a modified form of the equation of Austin and Mott for the d.c. conductivity, an analysis of the role of the spatial correlation of copper centers in fixing the hopping behaviour was performed, which stresses the importance of introducing a realistic description of the coordinative geometry of the transition-metal ion in the conductivity model in order to give a full account of the electrical behaviour of the system.

Thin-film Zn-phthalocyanine (ZnPc) sensors for the analysis of traces of NO 2 in air are prepared using a vacuum evaporation technique, starting from an Eastman Kodak material that has been purified by entrainer sublimation in inert gas. Sheets of Al 2 O 3 are used throughout as substrates. An appreciable sensitivity to NO 2 in the 1 – 100 ppm range is observed systematically, but remarkable differences in sensitivity are found in samples apparently prepared in a similar manner. The results show that the sensitivity depends primarily on the structure and morphology of the active layer. Films consisting primarily of β-Pc with a surface rich in elongated whiskers appear to present the largest sensitivity.

The kinetics of the SO2 to SO3 oxidation reaction at electrocatalytically active Pt and V2O5 electrodes have been investigated by means of the solid state electrochemical technique in the 450-500°C temperature range. The results, reported in terms of the conversion of SO2 to SO3 are compared with that calculated from the equilibrium constant of the reaction {A figure is presented} and show that the electrochemically generated oxygen behaves as an "active" oxygen and that, at the higher current densities, the electrolyte presumably is the catalytically active surface. © 1979.

Segregation of residual impurities within a matrix of solar grade silicon is a process which could take place when a crystallization process is carried out far from equilibrium conditions or residual impurities content exceedes solubility limits. As information on this topic is however very scarce, a systematic investigation has been carried out using MG-silicon or heavily doped EG-silicon as model material and chemical analysis, SEM, x-ray micro analysis and Auger spectroscopy as diagnostic methods. Re suits of this investigation show that residual impurities segregate at the grain boundaries or within the single grains as suicides and that, therefore, chemical bonding is the driving force for excess impurity removal. Grain-boundaries could act as sinks for impurities but it appears as well that infra-granular precipitates tend to Co alesce in a network of sub-grain boundaries. Eventually, the fact that the precipitate composition is constant while the distribution of impurities is inhomogeneous within the crystals shows that the local density of preci pitates varies within the crystals, depending on the thermal history of the crystal.

The use of model electrochemical cells for the purpose of optimizing the design and performances of cells using a ceramic oxide electrolyte is considered. Measurements carried out on these cells are compared with results of polarization experiments with Pt electrodes on an yttria-stabilized zirconia electrolyte. © 1974 Chapman and Hall Ltd.

A novel use of solid-state galvanic cells for the determination of thermodynamic properties of oxides by employing mg amounts of powder instead of presintered pellets is described. The oxides wnich were investigated all belong to the rare earths and actinide family, and present enhanced ionic and electronic mobilities which are essential for performing these kind of measurements. The advantage of this method is to allow a fast and direct sampling of oxide fuel rods which is normally carried out by chemical methods. Some examples of this technique are given. © 1977, The Electrochemical Society, Inc. All rights reserved.

Oxides with metallic conductivity could and have been used instead of noble metals as insert electrodes in aqueous solutions as well as electrodes for high temperature fuel cells and electrolysers and as catalysts for the conversion of exhaust gases from internal combustion engines. The aim of this paper is to report the results of a physico-chemical characterization (structure, morphology, electrochemical behaviour) of Ni-Pr oxides which have been proposed as electrode materials for high temperature fuel cells. The electrochemical characterization was carried out in aqueous solutions at room temperature and with solid electrolytes at high temperature. Evidence has been found in the former case for an oxide electrode type of behaviour. In the high temperature case, very low overvoltage values have been observed during cathodic oxygen reduction, while the electrode undergoes a reaction with oxygen during anodic oxygen evolution. © 1977 Chapman and Hall Ltd.

Results of measurements of x-ray diffraction, electron scanning microscopy and electrical conductivity of thick, polycrystalline RuO 2 films obtained by decomposing ruthenium trichloride are presented and discussed. The influence of the preparation procedure, process temperature, chlorine content and nature of the substrate on electrical and structural properties is also considered.