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In this work we present the results of a study concerning the role of the properties of zinc oxide thin films deposited by spray pyrolysis on its sensitivity to methane or ethane. It was found that using highly resistive thin layers leads to an increase in the film sensitivity. The variation of the operating temperature of the film leads to a significant change in the sensitivity of the sensor and the ideal operating temperature dependence of the gas used. The sensitivity of the ZnO thin films changes linear with the increase of the gas concentration. However these films seem to be more appropriated for the detection of methane than for ethane since the value of sensitivity obtained are higher and its variation with the gas concentration more pronounced. After the annealing treatment performed the films sensitivity decreases.

The influence of doping on the properties of zinc oxide thin films deposited by spray pyrolysis has been studied. The results show that the doping affects the properties of the films, mainly the electrical ones, function of its concentration and nature. The most significative improvement were observed for films doped with 1 at.% of indium exhibiting a resistivity of 1.9 × 10-1 Ω m associated to a transmittance of 86%, characteristics required for applications on the optoelectronic devices. © 2001 Elsevier Science Ltd. All rights reserved.

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This work presents a fast method to determine qualitatively the uniformity and the thickness of transparent or semitransparent thin films in the visible to near-infrared region. The method proposed is based on the information recorded by a colour scanner in the form of coloured regions, due to the constructive interferences caused by multibeam wavelength light sources as function of the film thickness and refractive index. The method is well applied in transparent films, where the uniformity cannot be seen by visual inspection. This paper shows that the results obtained for ZrO2 films are satisfactory enabling the application of this technique to determine the films uniformity in fast and cheap way.

In the recent past, multiple techniques and tools have been proposed and contributed to improve the distributed debugging functionalities, in several distinct aspects, such as handling the non-determinism, allowing cyclic interactive debugging of parallel programs, and providing more user-friendly interfaces. However, most of these tools are tied to a specific programming language and provide rigid graphical user interfaces. So they cannot easily adapt to support distinct abstraction levels or user interfaces. They also don’t provide adequate support for cooperation with other tools in a software engineering environment. In this paper we discuss several dimensions which may contribute to develop more flexible distributed debuggers. We describe Fiddle, a distributed debugging tool which aims at overcoming some of the above limitations.

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Water trees result from ac electrical aging of the polymeric insulation of medium and HV power cables in a humid or wet environment. As suggested by their name, they arise from penetration of water in the polymer. Visual observation with the help of an optical microscope shows tree (bush) type structures. This suggests that water trees might be fractal objects. Calculation of the fractal dimension from experimental samples may confirm the fractal characteristics and also give information on the damage caused to the polymer. In this work images of water trees taken under the optical microscope, dyed by methylene blue and etched for scanning electron microscopy (SEM), were studied in order to estimate the fractal dimension using a box-counting algorithm. The photographs, made using an optical microscope (scale of 100 mum), of the dyed samples were obtained from laboratory-aged low-density polyethylene (LDPE) specimens using accelerated techniques. Different field amplitude and frequency and also time of aging were used and the dimension values were compared. SEM images resulting from aged cross-linked polyethylene (XLPE) cables revealed a structure at a different scale (similar to 3 mum). Each photograph was analyzed to compare regions with and without water trees.

Water trees result from ac electrical aging of the polymeric insulation of medium and HV power cables in a humid or wet environment. As suggested by their name, they arise from penetration of water in the polymer. Visual observation with the help of an optical microscope shows tree (bush) type structures. This suggests that water trees might be fractal objects. Calculation of the fractal dimension from experimental samples may confirm the fractal characteristics and also give information on the damage caused to the polymer. In this work images of water trees taken under the optical microscope, dyed by methylene blue and etched for scanning electron microscopy (SEM), were studied in order to estimate the fractal dimension using a box-counting algorithm. The photographs, made using an optical microscope (scale of 100 mum), of the dyed samples were obtained from laboratory-aged low-density polyethylene (LDPE) specimens using accelerated techniques. Different field amplitude and frequency and also time of aging were used and the dimension values were compared. SEM images resulting from aged cross-linked polyethylene (XLPE) cables revealed a structure at a different scale (similar to 3 mum). Each photograph was analyzed to compare regions with and without water trees.

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In this work a new structure is proposed for position sensitive detectors consisting of glass/Cr/aSi:H(n+)/a-Si:H(i)/ZnO, where the ZnO forms an heterojunction with the a-Si:H(i). The results show that this structure works with success in the fabrication of linear position sensitive detectors. The devices present a good nonlinearity of ≈ 2% and a good sensitivity to the light intensity. The main advantages of this structure over the classical p-i-n are an easier to built topology and a higher yield due to a better immunity to the a-Si:H pinholes, since the ZnO does not diffuse so easily into a-Si:H as the metal does, which are the cause of frequent failure in the p-i-n devices due to short-circuits caused by the deposition of the metal over the a-Si:H. In this structure the illumination is made directly on the ZnO, so a transparent substrate is not needed and a larger range of substrates can be used.

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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.

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{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.