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Rheocasting, as a semi-solid process, allows the production of aluminium matrix composites at relatively low temperatures (ca. 580ºC), thus favouring a reduced reactivity at the reinforcement-metal matrix interface. When one considers the possibility of further processing (such as any treatment involving remelting, even if partial) of the material, this trait allows a more rigorous control of the interfaces. Composite samples have been produced using as matrix an Al-7Si-0.3Mg alloy reinforced with SiCp (granulometry: 120 μm; Vr = 0.30). These were rheocast at 583ºC, followed by forging and subsequent water-quenching. A structural characterisation (optical microscopy and XRD) of the as-received matrix material, as well as of the reinforced and non-reinforced rheocast material was performed. The phases identification will provide a basis for the understanding of the further processing where the rheocast material will be used as a raw material to produce functionally graded metal-matrix composites by centrifugal casting.

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Ferroelectric and high dielectric permittivity films are currently being investigated in view of their use as gate dielectrics in MIS structures. Along with the suppression of tunnelling currents at small gate thickness, they provide a memory function to MIS structures, which can be used in non-volatile memory applications. In this work we report fabrication and characterization of novel metal-ferroelectric-amorphous silicon structures. The structures consist of glass/ITO substrates coated with PZT 20/80 films (sol-gel) followed by an active layer (i-a-SiC:H, deposited by plasma enhanced chemical vapor deposition (PECVD)). A strong capacitance hysteresis is observed in C-V curves in electron accumulation region (VG > 0), accompanied with a large increase in the capacitance of ferroelectric-semiconductor structures at low frequencies. Threshold voltage for electron accumulation is about 10 V being dependent on the ferroelectric polarization switching. © 2002 Elsevier Science B.V. All rights reserved.

In this paper we report results of nanocrystalline p-doped silicon films produced by hot wire chemical vapour deposition technique with Ta filaments, using a pre-mixed gas containing silane, diborane, methane, helium and hydrogen. The data obtained show that the films produced exhibit good optoelectronic properties and show a surface morphology dependent on the filament temperature and hydrogen dilution. The increase in the filament temperature, keeping constant the hydrogen dilution (87%), promotes the preferential growth of the crystals in the {220} direction, giving rise to a pyramidal-like surface structure. This behaviour is observed by the SEM micrographs as well as by the micro-Raman and X-ray diffraction analyses. On the other hand, using a constant filament temperature, the increase in the hydrogen dilution contributes to an increase in both {111} and {220} diffraction peaks. Thus, by combining both filament temperature and hydrogen dilution the film surface can be controlled from a smooth to a pyramidal-like structure, without decreasing the crystalline fraction of the films. The structure and morphology is also reflected in the stability of the electrical dark conductivity. We observe that this property depends on the temperature range of the measurements and on the exposition time of films to the atmospheric conditions. © 2002 Elsevier Science Ltd. All rights reserved.

This work analyse mainly the dissociation mechanism of the gas during the hot wire (HW) and hot wire plasma-assisted (HWPA) processes used to produce hydrogenated carbon films and silicon-carbide, using ethylene and silane as gas sources. The results show that ethylene is better decomposed by plasma-enhanced chemical vapour deposition (PECVD) than HW process. The data also show that the HWPA leads to a better carbon © incorporation than HW processes, when silicon carbide alloys are produced and, that the presence of atomic hydrogen (H) is beneficial for all processes. That is, the presence of the plasma and H lead to the formation of higher C radicals such as methylsilane (CH3SiH3), ethylsilane (C2H5SiH3) and silorane (C2H4SiH2), whose contributions are enhanced as the fraction of ethylene (Feth) in the gas mixture increases. © 2001 Published by Elsevier Science B.V.