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2004
Lanca, M. C., and J. Marat-Mendes. "Dielectric breakdown statistics of polyethylene for progressively-censored data." Advanced Materials Forum Ii. Eds. R. Martins, E. Fortunato, I. Ferreira, and C. Dias. Vol. 455-456. Materials Science Forum, 455-456. 2004. 602-605. Abstract

The dielectric breakdown of thin films of low-density polyethylene (LDPE) electrically aged in an aqueous solution of NaCl under an AC electric field was investigated. A two-parameter Weibull function was used for the dielectric breakdown time to failure. The probability of failure for a sample was obtained by the White method for progressively censored data. Samples aged at different temperatures were compared. The results show that initially the samples aged at lower temperature (approximate to25degreesC) are more prone to fail, while those aged at higher temperature (50degreesC) fail at longer times. This was attributed to a competition between oxidation and diffusion.

Lanca, M. C., and J. Marat-Mendes. "Dielectric breakdown statistics of polyethylene for progressively-censored data." Advanced Materials Forum Ii. Eds. R. Martins, E. Fortunato, I. Ferreira, and C. Dias. Vol. 455-456. Materials Science Forum, 455-456. 2004. 602-605. Abstract

The dielectric breakdown of thin films of low-density polyethylene (LDPE) electrically aged in an aqueous solution of NaCl under an AC electric field was investigated. A two-parameter Weibull function was used for the dielectric breakdown time to failure. The probability of failure for a sample was obtained by the White method for progressively censored data. Samples aged at different temperatures were compared. The results show that initially the samples aged at lower temperature (approximate to25degreesC) are more prone to fail, while those aged at higher temperature (50degreesC) fail at longer times. This was attributed to a competition between oxidation and diffusion.

Lanca, M. C., J. Marat-Mendes, R. Martins, E. Fortunato, I. Ferreira, and C. Dias. "Dielectric breakdown statistics of polyethylene for progressively-censored data." Advanced Materials Forum Ii. Vol. 455-456. 2004. 602-605. Abstract
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Zhang, S.a b, Liao Xu Martins Fortunato Kong X. a Y. a. "The diphasic nc-Si/a-Si:H thin film with improved medium-range order." Journal of Non-Crystalline Solids. 338-340 (2004): 188-191. AbstractWebsite

A series of silicon film samples were prepared by plasma enhanced chemical vapor deposition (PECVD) near the threshold from amorphous to nanocrystalline state by adjusting the plasma parameters and properly increasing the reactions between the hydrogen plasma and the growing surface. The microstucture of the films was studied by micro-Raman and Fourier transform infrared (FTIR) spectroscopy. The influences of the hydrogen dilution ratio of silane (R H = [H2]/[SiH4]) and the substrate temperature (Ts) on the microstructural and photoelectronic properties of silicon films were investigated in detail. With the increase of RH from 10 to 100, a notable improvement in the medium-range order (MRO) of the films was observed, and then the phase transition from amorphous to nanocrystalline phase occurred, which lead to the formation of diatomic hydrogen complex, H 2 * and their congeries. With the increase of T s from 150 to 275 °C, both the short-range order and the medium range order of the silicon films are obviously improved. The photoconductivity spectra and the light induced changes of the films show that the diphasic nc-Si/a-Si:H films with fine medium-range order present a broader light spectral response range in the longer wavelength and a lower degradation upon illumination than conventional a-Si:H films. © 2004 Elsevier B.V. All rights reserved.

Mateus, O., T. Laven, and N. Knotschke. "A dwarf between giants?: A new late Jurassic sauropod from Germany." Journal of Vertebrate Paleontology. 23 (2004): 90. Abstract
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Mateus, O., T. Laven, and N. Knotschke. "A dwarf between giants?: A new late Jurassic sauropod from Germany." Journal of Vertebrate Paleontology. 23 (2004): 90. Abstract
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Fernandes, M.a, Vieira Martins M. a R. b. "Dynamic characterization of large area image sensing structures based on a-SiC:H." Materials Science Forum. 455-456 (2004): 86-90. AbstractWebsite

The working principle of silicon p-i-n structures with low conductivity (σd) doped layers as single element image sensors is based on the modulation, by the local illumination conditions of the photocurrent generated by a light beam scanning the active area of the device. A higher sensitivity is achieved using a wide band gap a-Si:C alloy in the doped layers, improving the light penetration into the intrinsic semiconductor and reducing the lateral currents in the structure, which are responsible by an image smearing effect observed in sensors with high σd doped layers. This work focuses on the transient response of such sensor and on the role of the carbon (C) content of the doped layers. A set of devices with different percentage of C incorporation in the doped layers is analyzed by measuring the scanner-induced photocurrent under different bias conditions, (ranging from -1.5V to 1V) in order to evaluate the response time.

Aguas, H., L. Pereira, I. Ferreira, A. R. Ramos, A. S. Viana, J. Andreu, P. Vilarinho, E. Fortunato, and R. Martins. "Effect of an interfacial oxide layer in the annealing behaviour of Au/a-Si: H MIS photodiodes." Journal of non-crystalline solids. 338 (2004): 810-813. Abstract
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Aguas, H., L. Pereira, I. Ferreira, A. R. Ramos, A. S. Viana, J. Andreu, P. Vilarinho, E. Fortunato, and R. Martins. "Effect of an interfacial oxide layer in the annealing behaviour of Au/a-Si: H MIS photodiodes." Journal of non-crystalline solids. 338 (2004): 810-813. Abstract
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Águas, H.a, Pereira Ferreira Ramos Viana Andreu Vilarinho Fortunato Martins L. a I. a. "Effect of an interfacial oxide layer in the annealing behaviour of Au/a-Si:H MIS photodiodes." Journal of Non-Crystalline Solids. 338-340 (2004): 810-813. AbstractWebsite

This work presents a study on the effect of an interfacial silicon oxide layer placed between Au and a-Si:H MIS (metal-insulator-semiconductor) photodiodes in their performances, by stopping the Au diffusion towards the a-Si:H. The results show that the Au diffuses very easily to the oxide free a-Si:H surface, even at room temperature, degrading the photodiode performance. On the other hand, the MIS photodiodes with the interfacial oxide show an improvement of their characteristics after annealing, function of its thickness, and degree of film's compactness. This effect is associated with the presence of oxide of thicknesses ≥5 Å at the Au/a-Si:H interface that prevents the Au diffusion and improves the photodiode characteristics, which does not happen when the interfacial oxide is absent. © 2004 Elsevier B.V. All rights reserved.

Pereira, LuÍs, Isabel Ferreira, Rodrigo Martins, Paula M. Vilarinho, Hugo Águas, Elvira Fortunato, A. R. Ramos, A. S. Viana, and J. Andreu. "Effect of annealing on gold rectifying contacts in amorphous silicon." Materials Science Forum. 455 (2004): 96-99. Abstract
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Aguas, H.a, Pereira Ferreira Ramos Viana Andreu Vilarinho Fortunato Martins L. a I. a. "Effect of annealing on gold rectifying contacts in amorphous silicon." Materials Science Forum. 455-456 (2004): 96-99. AbstractWebsite

This work presents a study performed on several Au contacts deposited by evaporation on oxide free and oxidised (5-20Å of oxide) a-Si:H surfaces. The characterisation of the films was performed on as deposited, aged and annealed at 150°C structures. SIMS and RBS measurements show that the Au diffuses very easily on oxide free a-Si:H surfaces, even at room temperature, resulting in the formation of an oxide at the device surface that acquires a blue colour instead of the gold colour of the contacts. This was also visible in the SEM pictures of the cross section of the structures produced and on the changes of the surface morphology observed by AFM measurements. On the other hand, when the Au is deposited on oxidised a-Si:H surfaces, the results show that the oxide prevents the Au from diffusing and the nature of the contact is preserved. That is, better rectifying and stability performances are obtained in MIS like structures than in Schottky structures.

Águas, Hugo, Lu{\'ıs Pereira, Isabel Ferreira, A. R. Ramos, A. S. Viana, J. Andreu, Paula M. Vilarinho, Elvira Fortunato, and Rodrigo Martins. "Effect of annealing on gold rectifying contacts in amorphous silicon." Materials Science Forum. Vol. 455. Trans Tech Publications, 2004. 96-99. Abstract
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Pinheiro, C., J. A. Passarinho, and C. P. Ricardo. "Effect of drought and rewatering on the metabolism of Lupinus albus organs." Journal of Plant Physiology. 161 (2004): 1203-1210. AbstractWebsite
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Pinheiro, C., J. A. Passarinho, and C. P. Ricardo. "Effect of drought and rewatering on the metabolism of Lupinus albus organs." Journal of Plant Physiology. 161 (2004): 1203-1210. AbstractWebsite
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Águas, H., Raniero Pereira Fortunato Martins L. L. E. "Effect of the discharge frequency and impedance on the structural properties of polymorphous silicon." Thin Solid Films. 451-452 (2004): 264-268. AbstractWebsite

This work presents a study performed on the deposition of pm-Si:H by plasma enhanced chemical vapor deposition using excitation frequencies of 13.56 and 27.12 MHz, where the interest of increasing the excitation frequency relies on higher plasma dissociation and reduced energy of ion bombardment, thus allowing the deposition of superior grade material at higher growth rates. The plasma impedance, which allows the monitoring of particle formation in the plasma, was correlated to the film properties, characterized by spectroscopic ellipsometry and hydrogen exodiffusion experiments. The set of data obtained show that by using the 27.12-MHz excitation frequency the hydrogen dilution and the r.f. power density needed to produce pm-Si:H can be reduced. Growth rates above 3.1 Å/s were obtained, the films being more dense and chemically more stable than those obtained with the standard 13.56 MHz. © 2003 Elsevier B.V. All rights reserved.

Águas, H., L. Raniero, L. Pereira, E. Fortunato, and R. Martins. "Effect of the discharge frequency and impedance on the structural properties of polymorphous silicon." Thin solid films. 451 (2004): 264-268. Abstract
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Palma, A. S., VA Morais, AV Coelho, and J. Costa. "Effect of the manganese ion on human alpha 3/4 fucosyltransferase III activity." Biometals. 17 (2004): 35-43. Abstract
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Águas, H., L. Perreira, R. J. C. Silva, E. Fortunato, and R. Martins. "Effect of the tunnelling oxide growth by H 2 O 2 oxidation on the performance of a-Si: H MIS photodiodes." Materials Science and Engineering: B. 109 (2004): 256-259. Abstract
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Águas, H., Perreira Silva Fortunato Martins L. R. J. C. "Effect of the tunnelling oxide growth by H2O2 oxidation on the performance of a-Si:H MIS photodiodes." Materials Science and Engineering B: Solid-State Materials for Advanced Technology. 109 (2004): 256-259. AbstractWebsite

In this work metal-insulator-semiconductor (MIS) photodiodes with a structure: Cr/a-Si:H(n+)/a-Si:H(i)/oxide/Au were studied, where the main objective was to determine the influence of the oxide layer on the performance of the devices. The results achieved show that their performance is a function of both oxide thickness and oxide density. The a-Si:H oxidation method used was the immersion in H2O2 solution. By knowledge of the oxide growth process it was possible to fabricate photodiodes exhibiting an open circuit voltage of 0.65V and short circuit current density under AM1.5 illumination of 11mA/cm2, with a response times less than 1μs for load resistance <400Ω, and a signal to noise ratio of 1×107. © 2003 Elsevier B.V. All rights reserved.

Águas, H.a, Goullet Pereira Fortunato Martins A. b L. a. "Effect of the tunnelling oxide thickness and density on the performance of MIS photodiodes." Thin Solid Films. 451-452 (2004): 361-365. AbstractWebsite

In this work we present results of a study performed on metal-insulator-semiconductor (MIS) diodes with the following structure: substrate (glass)/Cr (2000 Å)/a-Si:H n+(400 Å)/a-Si:H i (5500 Å)/oxide (0-40 Å)/Au (100 Å) to determine the influence of the oxide passivation layer grown by different techniques on the electrical performance of MIS devices. The results achieved show that the diodes with oxides grown using hydrogen peroxide present higher rectification factor (2×106) and signal to noise (S/N) ratio (1×10 7 at -1 V) than the diodes with oxides obtained by the evaporation of SiO2, or by the chemical deposition of SiO2 by plasma of hexamethyldisiloxane. However, in the case of deposited oxides, the breakdown voltage is higher, 30 V instead of 3-10 V for grown oxides. The ideal oxide thickness, determined by spectroscopic ellipsometry, is dependent on the method used to grow the oxide layer and is in the range between 6 and 20 Å. The reason for this variation is related to the degree of compactation of the oxide produced, which is not relevant for applications of the diodes in the range of ±1 V, but is relevant when high breakdown voltages are required. © 2003 Elsevier B.V. All rights reserved.

Aguas, H., A. Goullet, L. Pereira, E. Fortunato, and R. Martins. "Effect of the tunnelling oxide thickness and density on the performance of MIS photodiodes." Thin solid films. 451 (2004): 361-365. Abstract
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Paula, A.S., Canejo Martins Braz Fernandes J. P. H. G. "Effect of thermal cycling on the transformation temperature ranges of a Ni-Ti shape memory alloy." Materials Science and Engineering A. 378 (2004): 92-96. AbstractWebsite

Shape memory alloys (SMA) represents a class of metallic materials that has the capability of recovering a previously defined initial shape when subject to an adequate thermomechanical treatment. The present work aims to study the influence of thermal cycles on the transition temperatures of a Ni-Ti alloy. In this system, small variations around the equiatomic composition give rise to significant transformation temperature variations ranging from 173 to 373 K. SMA usually presents the shape memory effect after an annealing treatment at ca. 973 K. The optimisation of the thermomechanical treatment will allow to "tune" the material to different transformation temperature ranges from the same starting material, just by changing the processing conditions. Differential scanning calorimeter (DSC) and in situ high-temperature X-ray diffraction (XRD) have been used to identify the transformation temperatures and the phases that are present after different thermal cycles. The results concerning a series of thermal cycles with different heating and cooling rates (from 1.67×10-2 to 1.25×10-1 K/s) and different holding temperatures (from 473 to 1033 K) are presented. © 2004 Elsevier B.V. All rights reserved.

Muşat, V. a, B. b Teixeira, E. b Fortunato, R. C. C. b Monteiro, and P. c Vilarinho. "Effect of thermal treatment on the properties of sol-gel derived Al-doped ZnO thin films." Materials Science Forum. 455-456 (2004): 16-19. AbstractWebsite

This paper presents preliminary results on Al doped ZnO thin films prepared by the solgel method. The thin films were produced by a dip-coater technique on glass substrate, using zinc acetate dihydrate, aluminium chloride hexahydrate, 2-methoxyethanol and monoethanolamine as raw materials. The ZnO thin films were analysed by XRD, Hall effect and SEM measurements. In order to determine the influence of the thermal treatments on the film properties, a set of four different heat treatments (atmosphere and temperature) were studied. All the films are polycrystalline presenting a crystallographic c-axis orientation (002) perpendicular to the substrate. The best results were obtained for films pre-heated at 400°C and post-heated for 1 hour in air at 600°C, after annealing under a reduced atmosphere of forming gas, where a resistivity of 3.9×10-3 Ωcm, a Hall mobility of 34.1 cm2/Vs, a carrier concentration of 4.7×1019 cm-3 and an optical transmittance of 90% were achieved.

Ferro, M. C. a, M. H. V. a Fernandas, C. F. M. L. b Figueiredo, M. S. J. G. b Alendouro, and R. C. C. b Monteiro. "Effect of TiO2 on the crystallization of fly-ash based glass-ceramics." Materials Science Forum. 455-456 (2004): 831-834. AbstractWebsite

A batch of coal fly-ash, soda and lime was melted, quenched to a glass and then devitrified, by one-step heating cycles, forming coarse fibrous microstructures with pores and cracks, resulting in low strength materials. The crystallization behaviour of the based glass was further studied by adding a nucleating agent, TiC2. The resulting structural and microstrutural changes were investigated by differential thermal analysis, scanning electron microscopy, x-ray diffraction, dilatometry and density measurements. The results indicated that the addition of TiO2 could provide a finer grained microstructure, suitable for the production of structural materials.