In this work, we present a study of the effect of temperature, type and concentration of the dopant on the structural characteristics of ZnO thin films produced by spray pyrolysis; the crystallite size has been determined from profile peak shape analysis. These results are compared to the electrical characterisation performed on these materials. The effect of the dopant on the properties of ZnO thin films depends on its characteristics, mainly its ionic radius. Al, Ga and In have been studied as dopants, the best one being In, since it leads to the lowest resistivity.

Space charge in electrically aged LDPE was studied using a recently developed technique combining isothermal charging and discharging with non-isothermal measurements. Samples were aged in a NaCl aqueous solution at 40degreesC for 1500h under an AC field of 6MV/m (50Hz). The samples were then isothermally DC charged and discharged (both currents recorded). Next a non-isothermal experiment with constant heating rate was performed. Finally the sample was kept at the highest temperature and the final isothermal discharge current registered. The last step has to be carried on for long time to ensure an almost complete discharge of the remnant charge so that results become reproducible and possible to analyze. Selective charging (careful choice of the field, temperature and the ratio of charging/discharging times) revealed the presence of different trapping sites. From the analysis of the isothermal and non-isothermal data the relaxation times and activation energies could be obtained.

Space charge in electrically aged LDPE was studied using a recently developed technique combining isothermal charging and discharging with non-isothermal measurements. Samples were aged in a NaCl aqueous solution at 40degreesC for 1500h under an AC field of 6MV/m (50Hz). The samples were then isothermally DC charged and discharged (both currents recorded). Next a non-isothermal experiment with constant heating rate was performed. Finally the sample was kept at the highest temperature and the final isothermal discharge current registered. The last step has to be carried on for long time to ensure an almost complete discharge of the remnant charge so that results become reproducible and possible to analyze. Selective charging (careful choice of the field, temperature and the ratio of charging/discharging times) revealed the presence of different trapping sites. From the analysis of the isothermal and non-isothermal data the relaxation times and activation energies could be obtained.

The crystallization of a commercial borosilicate glass powder has been studied in the temperature range 750-900°C. Crystal growth was investigated by high temperature XRD and cristobalite precipitation was identified. Glass devitrification exhibited a characteristic incubation period that decreased with increasing temperature: 25-30 min at 750°C, 9-12 min at 775°C, 5-10 min at 810°C, and 0-5 min at 840°C. Cristobalite is an unfavorable transformation product in terms of thermal expansion behavior. The precipitation of cristobalite in sintered glass compacts was confirmed by dilatometric analysis, where the increase in thermal expansion coefficient due to the presence of cristobalite and its transition from the tetragonal to the cubic phase were verified. Correlation between the XRD results and the dilatometric data from sintered glass compacts showed the partial dissolution of cristobalite when the glass was heated at the highest temperatures.

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.