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Microcrystalline phosphorus-doped hydrogenated silicon alloy films were deposited in a remote plasma CVD (chemical vapor deposition) system. The film properties were studied as a function of RF power density and hydrogen concentration in the reaction gas mixture. The properties of the deposited films are extremely sensitive to the RF power density in the studied range of 250 mW/cm2 to 625 mW/cm2. Very low values of electrical resistivity were obtained. For an RF power density of 500 mW/cm2, ρ = 3 × 10-2 Ω-cm, while ρ = 1.9 × 103 Ω-cm for 625 mW/cm2, indicating the predominance of the amorphous tissue over the microcrystalline phase. High doping efficiencies which can be correlated to large grain size are indicated by the very low values of the activation energy as low as 30 meV for 500 mW/cm2, that were obtained.

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The DC analysis of a series-resonant converter operating above resonant frequency is presented. The results are used to analyze the current form factor and its effect on the efficiency. The selection of the switching frequency to maximize the efficiency is considered. The derived expressions are generalized and can be applied to calculations in any of the switching modes for a series-resonant circuit. For switching frequencies higher than the resonant frequency, an area of more efficient operation is indicated which will aid in the design of this class of converters and power supplies. It is pointed out that (especially for power MOSFETs where ohmic losses dominate) it is more attractive to select switching frequencies that are higher than the resonant frequency because of the possibility of nondissipative snubbers. Slowing down the rise of the gate voltage and, hence, the slow decrease of ON resistance during turn-on is also not a drawback to high-frequency switching. Because of this safer operation, the standard intrinsic diode of the power MOSFET could be used at high frequencies instead of the more expensive FREDFET

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The analysis on the technological and organizational change in the European industry, and particularlly the Portuguese one, has been studied at CESO I&D since its foundation on 1988. Few time after that, started a development project that started from a previous research project on the same topics, and supported by JNICT (Ministry of Science). In that projecto we continued to process data that was then not possible to do in the first one. It was then possible to continue a research programme that was urgent and determinant in the field of industrial sociology in Portugal. It focus again on the processes of technological and organizational change in the manufacturing industry.

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A range of CaO-Al2O3-SiO2 glasses have been prepared by fusion of pure starting materials in platinum crucibles. Compositions containing large amounts on network formers, Al2O3 and SiO2, are difficult to crystallize. If the amount of network former is reduced, glasses will self-nucleate and crystallize more readily, but the products of crystallization tend to react with water. This conflict has been partly resolved by adding MgO and ZnO and tailoring compositions so as to produce a phase, variously designated "Q" or "pleochroite", ideally Ca20Al32-2 vMg vSivO68, with v close to 4. Pleochroite crystallizes with a typically fibrous morphology. Preliminary experiments on fragments and melt-cast glass rods indicate that these compositions can be heat treated without deformation to yield highly crystalline, transparent ceramics. © 1989 Chapman and Hall Ltd.

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Experimental results on structure defects in microcrystalline (μc) n- and p-doped μc-S1-x:Cx:H films deposited on alkali-free glass substrates by spatial plasma separation1 and obtained by electron paramagnetic resonance (EPR) are presented. The technique used for subtracting the substrate effect on recorded spectra is also discussed as well as its quantification. The microscopic structure of intrinsic defects and impurity states and their role in transport mechanisms are studied and correlated with the composition of their films. These results are also related to transport properties of deposited films in order to observe the role of dopant centres, located at conduction band tails, in controlling the electrical properties. © 1989.

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Undoped and doped hydrogenated amorphous silicon semiconductors (a-Si:H) have been produced by a two consecutive decomposition deposition chamber (TCDDC) system assisted by electromagnetic static fields. Through this technique, a spatial separation is achieved between the plasma chemistry and that of the deposition to avoid ion and electron (with high energies) bombardment on the growing surface. Besides this, the use of a static magnetic field perpendicular to the substrate will promote plasma confinement, so avoiding its contamination by residual gases adsorbed on the reactor walls. On the other hand, the use of two grids dc biased in the deposition chamber, will allow control of the main film precursors, responsible for the electro-optical and structural properties of deposited films. In this paper we shall discuss the deposition method used as well as the transport, structural and morphological properties presented by deposited films and its dependence on deposition parameters used. © 1989.

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