The effect of annealing treatment (in the presence of different types of atmospheres) on the performances of zinc oxide thin films (intrinsic and doped with In and Al) prepared by spray pyrolysis have been studied, with the aim to determine more adequate conditions to improve the properties of the films. The results show that the annealing treatment leads to substantial changes in the structural, electrical and optical characteristics of ZnO thin films. The most significant improvements were obtained after annealing in forming gas (reduction atmosphere) at 200°C during 2 h. The ZnO:In film after heat treatment was the one that exhibited the lowest resistivity (p=5.2x10-2 ωcm) and a high transmittance (T=86%). © 2001 Elsevier Science Ltd. All rights reserved.

In this work we present preliminary results on the sensitivity to methane gas of zinc oxide thin films deposited by spray pyrolysis. It was found that using highly resistive (above 104 Ω cm) thin films and by performing the measurements at 200°C a sensitivity better than one order of magnitude was found to detect 2000 ppm of methane. A linear dependence on the sensitivity between 100 and 2000 ppm of methane was also obtained. © 2001 Elsevier Science Ltd. All rights reserved.

{In this work we report how it is possible to control the plasma regime near the substrate surface, from predominantly α to predominantly γ', passing trough and intermediate α-γ' regime, 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 type PECVD reactor. To do so, we apply a DC voltage (Vpol to a set of grids placed in front of the r.f. electrode and by doing this, we control the energy of the ions striking the substrate during the film's growth and the plasma regime near the substrate. Under a plasma of the γ' regime, the surface roughness is high and the films are poorly compact. In the α-γ' regime, the ion bombardment is moderate and the films are highly smooth and compact. In the α regime the ion bombardment is higher and so the films can become more compact but the surface roughness increases and the electrical properties deteriorate. The results achieved show that the best transport properties are achieved for the films deposited in the α-γ' regime corresponding to a Vpol of 38 V. Under this condition the films presented a dark conductivity, σd = 6.2×10-12 (Ωcm)-1, activation energy, ΔE ≈ 0.9 eV, hydrogen content

In this work a study of the influence of the annealing treatment (atmosphere and temperature) on the properties of zinc oxide thin films (intrinsic and doped with indium and aluminum) prepared by spray pyrolysis is presented. The result shows that the type of atmosphere (reduction or oxidant) has an important role in the changes observed in the structural, electrical and optical properties of the ZnO thin films. The ZnO thin film doped with indium, presents the lowest resistivity (ρ = 5.8×10-3 Ωcm) associated to a high transmittance (T = 86%), characteristics required for application on optoelectronic devices.

This paper presents results of the role of the oxygen concentration (CO) and the deposition pressure (pd) on structural and electrical properties of indium tin oxide films produced by r.f. magnetron sputtering. The films were annealed in air, followed by a reannealed stage in hydrogen, aiming to improve the film's transparency and conductivity. The results achieved show that the films texture grain size, structure and compactness is more influenced by CO than by pd, the same does not happen with the electrical properties.

The choice over the Portuguese case studies was based on the sample constructed for the application of the firm questionnaires, during the second year of the SOWING project, 1999. This sample was fulfilled of firms among several activity sectors: textile, manufacturing, electronics, transports and software industry, based on NACE – codes (2 – digit level). Thus, we agreed to include in a new database the remaining questionnaires and construct a sample with 113 observations. Concerning the organisational change we make a distinction of three categories of change. First we analyse changes taking place at the inter-firm level (outsourcing, subcontracting, geographic relocation), followed by changes at the organisational level (deconcentration/decentralisation, reduction of hierarchical levels, introduction of cost and profit centres). The third kind of changes analysed will be those taking place at the workplace level (job enlargement/enrichment, changing character of work, work load). The Portuguese studied companies presents a relative uniform pattern considering the variables social competencies, practical knowledge, responsibility and specialized professional qualifications.

We examine the most important processes leading to the creation of excited states from the ground configurations of Ar8+ to Ar16+ ions in an electron-cyclotron resonance ion source, which lead to the emission of K x-ray lines. Theoretical values for inner-shell excitation and ionization cross sections, including double KL ionization, transition probabilities and energies for the de-excitation processes, are calculated in the framework of the multi-configuration Dirac-Fock method. With reasonable assumptions about the electron energy distribution, a theoretical K x-ray spectrum is obtained, which reproduces very closely a recent experimental result.

Measurements of electron impact ionization of neutral Al, Ga, and In show large cross sections compared to other elements in the same rows of the periodic table. Semiempirical and classical calculations of direct ionization cross sections are all substantially smaller. Calculations by McGuire [Phys. Rev. A 26, 125 (1982)] for aluminum that include excitations to autoionizing 3s3p2 doublet levels are 2.5 times higher than experiment at the peak. We report the direct ionization cross sections based on the binary-encounter-Bethe model of Kim and Rudd [Phys. Rev. A 50, 3954 (1994)], which is an ab initio theory. We add the autoionization contribution using scaled plane-wave Born cross sections as recently developed by Kim [Phys. Rev. A 64, 032713 (2001)] for excitations to the first set of autoionizing levels. Dirac-Fock wave functions are used for the atomic structure. Our results are in excellent agreement with experimental values and support substantial contributions from excitation-autoionization to the total ionization cross sections for these elements. We also compare the total ionization cross section of boron to available theories, though no experimental data are available.

The role of the deposition pressure and hydrogen dilution in the production of p-type Si:H films by hot wire chemical vapor deposition, was investigated. The system used permits to obtain uniform and homogeneous films properties over a 10cm×10cm substrate area. As heated filament we used Ta, since Ta filaments have longer life period without deteriorating than the W filaments ones. In this work, we show that the electrical properties of the films produced are dependent on the process gas pressure. In the pressure range of 13.3 Pa (0.1 Torr) to 66.5 Pa (0.5Torr), the film's coplanar electrical conductivity at room temperature varies by more than two orders of magnitude, for films produced at same hydrogen dilution and filament temperature, reaching values of about 0.1 (Ωcm)-1, at deposition pressures of about 40-53Pa (0.3-0.4Torr). On the other hand, the increase in hydrogen dilution (from 87% to 96%) promotes the surface roughness due to an enlargement of grain sizes in the direction of the {220} diffraction planes as observed by SEM micrographs without changing the crystalline fraction (48-50%) obtained by micro-Raman analysis.

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.

The periplasmic hydrogenase of Desulfovibrio vulgaris (Hildenbourough) is an all Fe-containing hydrogenase. It contains two ferredoxin type [4Fe-4S] clusters, termed the F clusters, and a catalytic H cluster. Recent X-ray crystallographic studies on two Fe hydrogenases revealed that the H cluster is composed of two sub-clusters, a [4Fe-4S] cluster ([4Fe-4S]H) and-a binuclear Fe cluster ([2Fe]H), bridged by a cysteine sulfur. The aerobically purified D. vulgaris hydrogenase is stable in air. It is inactive and requires reductive activation. Upon reduction, the enzyme becomes sensitive to O(2) indicating that the reductive activation process is irreversible. Previous EPR investigations showed that upon reoxidation (under argon) the H cluster exhibits a rhombic EPR signal that is not seen in the as-purified enzyme, suggesting a conformational change in association with the reductive activation. For the purpose of gaining more information on the electronic properties of this unique H cluster and to understand further the reductive activation process, variable-temperature and variable-field Mossbauer spectroscopy has been used to characterize the Fe-S clusters in D. vulgaris hydrogenase poised at different redox states generated during a reductive titration, and in the GO-reacted enzyme. The data were successfully decomposed into spectral components corresponding to the F and H clusters,and characteristic parameters describing the electronic and magnetic properties of the F and H clusters were obtained. Consistent with the X-ray crystallographic results, the spectra of the H cluster can be understood as originating from an exchange coupled [4Fe-4S] - [2Fe] system. In particular, detailed analysis of the data reveals that the reductive activation begins with reduction of the [4Fe-4S]H cluster from the 2+ to the If state, followed by transfer of the reducing equivalent from the [4Fe-4S]H subcluster to the binuclear [2Fe]H subcluster. The results also reveal that binding of exogenous CO to the H cluster affects significantly the exchange coupling between the [4Fe-4S]H and the [2Fe]H subclusters. Implication of such a CO binding effect is discussed.