Coal fly ashes have been vitrified by melting with Na2O and CaO as fluxing additives. Adequate heat treatments on the fly ash derived glass produced attractive dark green glass-ceramics. These glass-ceramics exhibited fine-grained microstructures consisting of esseneite and nepheline crystals, with average size below 200 nm, homogeneously dispersed in a residual glassy matrix. Several properties, such as density, thermal expansion coefficient, bending strength, hardness and brittleness index were determined and the correlation microstructure-properties is discussed. The results suggest that these coal ash-based glass-ceramics have potential applications as structural materials or as cladding materials.

The model presented is based on the heat transfer and energy balance equations that rule the set of physical and chemical interactions that take place on the gas phase of a growth process, assuming that the deposition process occurs under laminar dynamic flow conditions (Knudsen number below 1). In these conditions, the chemistry and physics of the process involved in the growth mechanism of silicon thin films produced by the hot wire or the hot-wire plasma assisted technique can be proper derived by balance equations that supply information about how the plasma density, the gas dilution and the gas temperature influence the growth mechanism and the equilibrium of the concentration of species presented on the growth surface. The model developed establishes a relation between the abundance species formed and the parameters initiators of the process such as the filament temperature and the rf power density used.

This work presents the I-V results of a-Si:H/SiOx/Pd MIS (metal-insulator-semiconductor) structures. The a-Si:H was deposited by non-conventional modified triode PECVD. This new configuration allows the deposition of high quality a-Si:H with a photosensitivity of 106, indicating the presence of low density of defects. Spectroscopic ellipsometry measurements revealed that these films are highly dense and present a very smooth surface so allowing a low defect interface between the Pd and the a-Si:H. As a result, we could make MIS photodiodes with barrier heights of 1.17 eV, which give a high reduction of the reverse dark current, an increase of the signal to noise ratio of 106 and an open circuit voltage VOC = 0.5 V. © 2002 Elsevier Science B.V. All rights reserved.

Transparent conducting ZnO:Al thin films have been deposited on polyester (Mylar type D, 100 μm thickness) substrates at room temperature by r.f. magnetron sputtering. The structural, optical and electrical properties of the deposited films have been studied. The samples are polycrystalline with a hexagonal wurtzite structure and a strong crystallographic c-axis orientation (002) perpendicular to the substrate surface. As deposited ZnO:Al thin films have an 85% transmittance in the visible and infra-red region and a resistivity as low as 3.6×10-2 Ωcm. The obtained results are comparable to those ones obtained on glass substrates, opening a new field for low cost, light weight, small volume, flexible and unbreakable large area optoelectronic devices.

We have produced amorphous intrinsic silicon thin films by hot-wire plasma assisted chemical vapor deposition, a process that combines the traditional rf plasma and the recent hot-wire techniques. In this work we have studied the influence of hydrogen gas dilution and rf power on the surface morphology, composition, structure and electro-optical properties of these films. The results show that by using this deposition technique it is possible to obtain at moderate rf power and filament temperature, compact i-type silicon films with ημτ of the order of 10 -5cm 2V -1, without hydrogen dilution. © 2002 American Institute of Physics.

Rhodium complexes modified by simple trialkylphosphines can be used to carry out homogeneous hydroformylation in supercritical carbon dioxide (scCO(2)). The catalyst derived from PEt3 is more active and slightly more selective for the linear products in scCO2 than in toluene, and under the same reaction conditions [100degreesC, 40 bar of CO/H-2 (1:1)] P(OPri)(3) is also an effective ligand giving good catalyst solubility and activity. Other ligands such as PPh3, POct(3), PCy3, and P(4-C6H4But)(3) are less effective because of the low solubility of their rhodium complexes in scCO(2). P(4-C6H4SiMe3)(n) Ph3-n (n = 3 or 1) and P(OPh)(3) impart activity despite their complexes only being poorly soluble in scCO(2). Under subcritical conditions, using PEt3 as the ligand, C7-alcohols from hydrogenation of the first formed aldehydes are the main products whilst above a total pressure of 200 bar, where the solution remains supercritical (monophasic) throughout the reaction, aldehydes are obtained with 97% selectivity. High pressure IR studies in scCO(2) using PEt3 as the ligand are reported.

The resulting economic integration of industrial processes and manufacturing internationalisation lead several authors to argue that world economy is globalised. In this context, the approach to the divestment concept without an social and económical context, does not show a group of associated practices and representations. Choices and options are motivated by exogenous forces that pushes companies to determine strategies that stop capital investment on new equipment goods, or on other imaterial goods. This type of strategy is designated by "divestment". The social level of consequencies are not due to the closing down or de-localization of production units that are divesting, but can be materialised of efects that are irreversible. This means unemployment, de-skilling, labour precarization and even emergence of new forms of social exclusion in former industrialised regions.

In this work we show that it is possible to control the plasma regime in the region close to the substrate in r.f. silane discharges. The PECVD reactor works in a modified triode configuration, where the control over the plasma regime is performed by polarising a grid electrode, placed close to the r.f. electrode, with a DC power source. Besides that, the DC grid allows also to control the energy of the ion bombardment, because the plasma potential will be a function of the voltage (Vpol) applied to the DC grid. The silane plasma was characterised with a Langmuir probe and an impedance probe. We were able to identify three plasma regimes in the region close to the substrate: γ′ regime for Vpol<0 V; γ′-α regime for 0 V<Vpol<40 V; and α regime for Vpol40 V. The γ′ regime is associated with a high concentration of dust particles in plasma and high electron energy (≈8eV), while the α regime is associated with a free dust plasma and low electron energy (≈2eV). The intermediate regime, γ′-α, is characterised by the presence of smaller particles (≈2-5nm) that can be beneficial for the film's properties. © 2002 Elsevier Science Ltd. All rights reserved.

P- and n-type silicon thin films have been produced using a new hot wire plasma assisted deposition process that combines the conventional plasma enhanced chemical vapor deposition and the hot wire techniques. The films were produced in the presence of different hydrogen gas flow and their optoelectronic, structural and compositional properties have been studied. The optimized optoelectronic results achieved for n-type Si:H films are conductivity at room temperature of 9.4(Ωcm)-1 and optical band gap of 2eV while for p-type SiC:H films these values are 1 × 10-2(Ωcm)-1 and 1.6eV, respectively. The films exhibit the required optoelectronic characteristics and compactness for device applications such as solar cells.

In this paper a set of one-dimensional simulations of a-Si:H p-i-n junctions under different illumination conditions and with different intrinsic layer are presented. The simulation program ASCA permits the analysis of the internal electrical behaviour of the cell allowing a comparison among the different internal configurations determined by a change in the input set. Results about the internal electric configuration will be presented and discussed outlining their influence on the current tension characteristic curve. Considerations about the drift-diffusion and the generation-recombination balance distributions, outlined by the simulation, can be used to explain the correlation between the basic device output, the i-layer characteristics (thickness and DOS), the incident radiation intensity and photon energy. © 2002 Elsevier Science B.V. All rights reserved.

In this work we show that it is possible to control the plasma species present near the substrate surface, from what is usually associated with an α regime (a plasma free of particles) to a γ' regime (a plasma where particles are present) and simultaneously control the energy of the ions striking the substrate during a-Si:H deposition from a silane glow discharge in a modified triode (MT) type PECVD reactor, where a DC mesh electrode biased with Vpol is located in front of the r.f electrode. The presence of large particles in the plasma leads to the deposition of the films with the poorest optoelectronic properties. When the particle size in the plasma decrease the film properties improve, but, when particles are no longer present in the plasma region close to the substrate, like in a α like regime, the properties of the films deteriorate again. The results show that the best transport properties are achieved for the films deposited in the α-γ' transition regime corresponding to 0V<Vpol<51V. Under this condition the films present a dark conductivity, σ d ≈ 10-11 (Ωcm)-1, photosensitivity, S ≈ 107, activation energy, ΔE ≈ 0.9 eV, hydrogen content, CH ≈ 10%, factor of microstructure, R ≈ 0.085 and an optical gap, Eop ≈ 1.77 eV.

Tensile tests were performed on PET films coated with Al doped zinc oxide films by RF magnetron sputtering. During the tensile elongation, the electrical resistance of the oxide was evaluated in situ. The results indicate that the increase in the electrical resistance is related to the crack debsity and crack width, which also depends on the film thickness.