Hall effect measurements are one of the most powerful techniques for obtaining information about the conduction mechanism in polycrystalline semiconductor materials, which is the basis for understanding semiconductor gas sensors. In order to investigate the correlation between the microscopic characteristics and the macroscopic performances exhibited by undoped tin oxide gas sensors deposited by spray pyrolysis, Hall effect measurements were performed at different temperatures, from room temperature up to 500 K, and in the presence of two different atmospheres, air and methane. From these measurements, it was possible to infer the potential barrier and its dependence with the used atmosphere. The obtained results were analysed in terms of the oxygen mechanism at grain boundaries on the basis of the grain boundary-trapping model. In the presence of methane gas, the electrical resistivity decreases due to the lowering of the inter-grain boundary barrier height.

Hall effect measurements are one of the most powerful techniques for obtaining information about the conduction mechanism in polycrystalline semiconductor materials, which is the basis for understanding semiconductor gas sensors. In order to investigate the correlation between the microscopic characteristics and the macroscopic performances exhibited by undoped tin oxide gas sensors deposited by spray pyrolysis, Hall effect measurements were performed at different temperatures, from room temperature up to 500 K, and in the presence of two different atmospheres, air and methane. From these measurements, it was possible to infer the potential barrier and its dependence with the used atmosphere. The obtained results were analysed in terms of the oxygen mechanism at grain boundaries on the basis of the grain boundary-trapping model. In the presence of methane gas, the electrical resistivity decreases due to the lowering of the inter-grain boundary barrier height.

The surfaces of cordierite and glass particles were modified by coating them with an alumina precursor using a precipitation process in the presence of urea. Scanning electron microscopy (SEM), high-resolution transmission electron microscopy, X-ray diffraction, electrophoresis, and rheological measurements were used to characterize the coated powders. SEM and transmission electron microscopy morphologies of the coated powders revealed that amorphous and homogeneous coatings have been formed around the particles. The morphology of the coated powders showed a coiled wormlike surface. The coating Al2O3 layer dominated the surface properties of the coated glass and cordierite powders. The influence of the coating layer on the processing ability of cordierite-based glass-ceramics substrates by tape casting was studied in aqueous media. It could be concluded that the coating of the powders facilitates the processing and yields green and sintered tapes with denser, more homogeneous microstructures compared with the uncoated powders.

The surfaces of cordierite and glass particles were modified by coating them with an alumina precursor using a precipitation process in the presence of urea. Scanning electron microscopy (SEM), high-resolution transmission electron microscopy, X-ray diffraction, electrophoresis, and rheological measurements were used to characterize the coated powders. SEM and transmission electron microscopy morphologies of the coated powders revealed that amorphous and homogeneous coatings have been formed around the particles. The morphology of the coated powders showed a coiled wormlike surface. The coating Al2O3 layer dominated the surface properties of the coated glass and cordierite powders. The influence of the coating layer on the processing ability of cordierite-based glass-ceramics substrates by tape casting was studied in aqueous media. It could be concluded that the coating of the powders facilitates the processing and yields green and sintered tapes with denser, more homogeneous microstructures compared with the uncoated powders.

The new compound [Co(eta(5)-C5H5)(dppf-P,P')I]I, 1, was synthesised by the stoichiometric reaction of the Co(III) complex [Co(eta(5)-C5H5)(CO)I-2], 2, with 1,1'-bis(diphenylphosphino)ferrocene (dppf) in CH2Cl2, and was characterised by multinuclear NMR spectroscopy. Exposure to air of THF or CH2Cl2 solutions of compound 1 gave, in an unexpected way, a polymeric chain comprising bridging 1,1'-bis(oxodiphenylphosphoranyl) ferrocene (dppfO(2)) joining tetrahedral Co(II) units [CoI2(mu-dppfO(2))](n), 3. Attempts to obtain the polymeric chain 3 by the direct reaction of dppfO(2) with CoI2, in CH2Cl2, gave instead the monomeric compound [CoI2(dppfO(2))], 4, in which dppfO2 is coordinated in a chelating mode. The structural characterisation of compounds 2, 3, and 4 was carried out by single crystal X-ray diffraction studies. The magnetic behaviour of [CoI2(dppfO(2))] and [CoI2(mu-dppfO(2))](n) was studied, and the results are consistent with tetrahedral S = 3/2 Co-II, possessing a (4)A(2) ground state, and S = 0 Fe-II. In these compounds, Co-II negative zero field splittings were determined from an analysis of the magnetic susceptibility temperature dependence, with D/k = -13 and -14 K for CoI2(dppfO(2)) and [CoI2(mu-dppfO(2))](n), respectively. DFT calculations were performed in order to understand the electronic structure of [Co(eta(5)-C5H5)(dppf-P,P')I]I, 1, as well as that of the paramagnetic specie [CoI2(dppfO(2))], 4. The [CoI2(mu-dppfO(2))](n) chain was also analysed and found to behave very similarly to the monomeric iodine derivative 4. The calculations showed the unpaired electrons to be localized on the Co(II) centre in all these species. The rather complicated electrochemical behaviour exhibited by the dppf complex [Co-III(eta(5)-C5H5)(dppf-P,P')I]I and by [Co(dppfO(2))I-2] is discussed.

New cationic mono-cyclopentadienyl complexes of Co(III) containing mono or bidentate nitrogen donor ligands of general formula [Co(eta (5)-C5H5)(PPh3)L-2][BF4](2) (L = NC-CH3, 2, and NC = Ph, 3) or [Co(eta (5)-C5H5)(PPh3)(L-L)[BF4](2), [L-L = 2,2 ' -bisimidazole (H(2)biim) (4) and dipyridylamine [HN(NC5H5)(2)] (5) have been synthesised by the stoichiometric reaction of the Co(III) complex Co(eta (5)-C5H5)(PPh3)I-2 (1), with Ag[BF4] and the appropriate ligand in CH2Cl2. Under the same conditions and using;trans-azobenzene as a ligand, an orthometalation reaction took placet giving the new compound [Co(eta (5)-C5H5)(PPh3)(kappa -C,kappa -N-C6H4N=NPh)][BF4] (6) in high yield. The structural characterisation of compounds 4 and 6, and of the starting compound Co(eta (5)-C5H5)(PPh3)I-2 (1) was done by single-crystal X-ray diffraction studies. DFT calculations (ADF program) were performed in order to understand the orthometallation reaction. (C) 2001 Elsevier Science B.V. All rights reserved.

The practical implantation of the concept of dynamic virtual enterprise is still far from expectations due to a number of factors such as the lack of appropriate interoperable infrastructures and tools, lack of common ontology, and the socio-organizational difficulties. However, the creation of industry clusters supported by advanced information and communication tools can meanwhile provide a basis for the rapid creation of dynamic virtual enterprises in response to the market opportunities. A federated service management approach is introduced in this context and its application to the tourism industry is discussed. Finally, the support for the aggregation of simpler services into value-added services, implemented by distributed business processes within different organizations, is presented.

Monitoring systems have traditionally been developed with rigid objectives and functionalities, and tied to specific languages, libraries and run-time environments. There is a need for more flexible monitoring systems which can be easily adapted to distinct requirements. On-line monitoring has been considered as increasingly important for observation and control of a distributed application. In this paper we discuss monitoring interfaces and architectures which support more extensible monitoring and control services. We describe our work on the development of a distributed monitoring infrastructure, and illustrate how it eases the implementation of a complex distributed debugging architecture. We also discuss several issues concerning support for tool interoperability and illustrate how the cooperation among multiple concurrent tools can ease the task of distributed debugging.

In this work, we report the optical and compositional properties of hydrogenated amorphous silicon carbide (a-SiC:H) thin films produced by plasma-enhanced chemical vapor deposition (PE-CVD), hot wire CVD (HW-CVD) and hot wire plasma-assisted CVD (HWPA-CVD) processes. The optical band gap of a-SiC:H films was controlled from 1.85 to 3.5 eV by varying the percentage of ethylene in the silane gas mixture from 3 to 100%. Adding a rf plasma to the hot wire process the carbon gas source dissociation is implemented leading to an increase in bulk carbon incorporation. This evidence is proved by the enhancement of the peak ascribed to the SiC stretching vibration mode, the reduction of the peak related to the SiH wagging modes, the decrease in the refractive index and the increase of optical band gap. The influence of hydrogen gas dilution on the properties of the films obtained by the different methods is also reported. © 2001 Elsevier Science B.V. All rights reserved.

This work deals with the study of the role of intra-gap density of states and films composition on the colour selection of the collection spectrum of glass/ITO/a-Six:C1-x:H/Al Schottky photodiodes produced in a conventional plasma-enhanced chemical vapour deposition (PECVD) system using as gas sources silane and a controlled mixtures of silane and methane. To do so, properties of the films were investigated, especially the one concerning the determination of the valence controllability of the films produced and the density of bulk states. Besides that, a PINIP device was also produced, using the a-Six:C1-x:layer that lead to the best Schottky diode performances. © 2001 Elsevier Science B.V. All rights reserved.

The process conditions of growing thin silicon films by plasma enhanced chemical vapour deposition (PECVD) were presented. The plasma impedance was found to monitor the powders in the PECVD systems and good quality silicon films were grown close to the plasma regime where the powders were formed. The silicon films exhibited properties which were interpreted based on a two-phase model where silicon nanostructures were embedded in a disordered network.

We derive a theoretical expression for the two-photon emission rate of two-electron systems, in a form suitable for easy implementation in numerical calculations. Racah algebra techniques were used to extended previous work on two-photon emission in hydrogen-like systems to more complex ones. The obtained expression is, as far as we are aware, the first general expression that gives the spontaneous two-photon decay rates of helium-like systems for any combination of multipoles.