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2004
Alendouro, M.S.J.G.a, Monteiro Figueiredo Martins Silva Ferro Fernandas R. C. C. a. "Microstructural characterization and properties of a glass and a glassceramic made from municipal incinerator bottom ash." Materials Science Forum. 455-456 (2004): 827-830. AbstractWebsite

A glass was made using bottom ash produced by a Portuguese municipal solid waste (MSW) incinerator. The bottom ash was the single batch material used in the formation of the glass, which was obtained through a conventional melt-quenching method. The glass was then converted to glass-ceramic for further recycling to construction materials. After submitting the glass samples to several heat treatments, between 820 and 1050°C and during different times, it was verified that the optimum heat treatment schedule for the ceramization of the glass was at 1000°C for 10h, as confirmed by microstructural observation and by X-ray diffraction. The major crystalline phases precipitated in the glass-ceramic were wollastonite (CaSiO3) and diopside (Ca(Mg,Al)(Si,Al)2O6). Microstructural analysis of the glass-ceramic revealed that the crystalline phases were present as dendrites and fiber-like structures that were homogeneously distributed in the material. The glassceramic showed good mechanical properties with a hardness of 5.6 MPa and a bending strength of 101 MPa. This material had a density of 2.8 gcm-3 and a thermal expansion coefficient of 9.10-6°C-1. The glass and the glass-ceramic showed an excellent chemical stability against leaching in acidic solution and in alkaline solution. In summary, both the glass and the glass-ceramic have good chemical and mechanical properties and can, therefore, be applied as construction materials.

Alendouro, M. S. J. G. a, R. C. C. a Monteiro, C. F. M. L. a Figueiredo, R. M. S. a Martins, R. J. C. a Silva, M. C. b Ferro, and M. H. V. b Fernandas. "Microstructural characterization and properties of a glass and a glassceramic made from municipal incinerator bottom ash." Materials Science Forum. 455-456 (2004): 827-830. AbstractWebsite

A glass was made using bottom ash produced by a Portuguese municipal solid waste (MSW) incinerator. The bottom ash was the single batch material used in the formation of the glass, which was obtained through a conventional melt-quenching method. The glass was then converted to glass-ceramic for further recycling to construction materials. After submitting the glass samples to several heat treatments, between 820 and 1050°C and during different times, it was verified that the optimum heat treatment schedule for the ceramization of the glass was at 1000°C for 10h, as confirmed by microstructural observation and by X-ray diffraction. The major crystalline phases precipitated in the glass-ceramic were wollastonite (CaSiO3) and diopside (Ca(Mg,Al)(Si,Al)2O6). Microstructural analysis of the glass-ceramic revealed that the crystalline phases were present as dendrites and fiber-like structures that were homogeneously distributed in the material. The glassceramic showed good mechanical properties with a hardness of 5.6 MPa and a bending strength of 101 MPa. This material had a density of 2.8 gcm-3 and a thermal expansion coefficient of 9.10-6°C-1. The glass and the glass-ceramic showed an excellent chemical stability against leaching in acidic solution and in alkaline solution. In summary, both the glass and the glass-ceramic have good chemical and mechanical properties and can, therefore, be applied as construction materials.

Águas, H., Pereira Raniero Fortunato Martins L. L. E. "MIS photodiodes of polymorphous silicon deposited at higher growth rates by 27.12 MHz PECVD discharge." Materials Science Forum. 455-456 (2004): 73-76. AbstractWebsite

This work presents a comparative study between MIS photodiodes produced using high quality amorphous silicon (a-Si:H), deposited by PECVD at 2Å/s, using 13.56 MHz frequency and polymorphous silicon (pm-Si) deposited at 3Å/s using a 27.12 MHz frequency. The results show that the pm-Si:H outperforms the a-Si:H MIS photodiodes by having a rectification ratio of 107, and photosensitivity at AM1.5 conditions of 107, under 1V reverse bias. Apart from that, the pm-Si:H photodiode presents a higher open circuit voltage and better fill factor than a-Si:H MIS photodiode. These results prove that quality devices can be produced at high growth rates by using pm-Si:H. In this work the photodiode performances were correlated to the films properties, aiming to determine the characteristics responsible for the performances exhibited by the pm-Si:H devices.

Águas, Hugo, Lu{\'ıs Pereira, Leandro Raniero, Elvira Fortunato, and Rodrigo Martins. "MIS Photodiodes of Polymorphous Silicon Deposited at Higher Growth Rates by 27.12 MHz PECVD Discharge." Materials Science Forum. Vol. 455. Trans Tech Publications, 2004. 73-76. Abstract
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Hettmann, T., R. A. Siddiqui, C. Frey, T. Santos-Silva, MJ Romão, and S. Diekmann. "Mutagenesis study on amino acids around the molybdenum centre of the periplasmic nitrate reductase from Ralstonia eutropha." Biochemical and Biophysical Research Communications. 320 (2004): 1211-1219. Abstract
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Fortunato, E., A. Gonçalves, A. Marques, A. Viana, H. Águas, L. Pereira, I. Ferreira, P. Vilarinho, and R. Martins. "New developments in gallium doped zinc oxide deposited on polymeric substrates by RF magnetron sputtering." Surface and Coatings Technology. 180 (2004): 20-25. Abstract
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Fortunato, E.a, Gonçalves Marques Viana Águas Pereira Ferreira Vilarinho Martins A. a A. a. "New developments in gallium doped zinc oxide deposited on polymeric substrates by RF magnetron sputtering." Surface and Coatings Technology. 180-181 (2004): 20-25. AbstractWebsite

Gallium-doped zinc oxide (GZO) thin films have been deposited onto polyethylene naphthalate (PEN) substrates by r.f. magnetron sputtering at room temperature. The influence of the film thickness (from 70 to 890 nm) on the electrical, structural and morphological properties are presented. The lowest resistivity obtained was 5 × 10-4 Ω cm with a Hall mobility of 13.7 cm2/Vs and a carrier concentration of 8.6 × 1020 cm-3. These values were obtained by passivating the surface of the polymer with a thin silicon dioxide, so preventing the moisture and oxygen permeation inside the film. © 2003 Elsevier B.V. All rights reserved.

Fortunato, E., A. Goncalves, A. Marques, A. Viana, H. Aguas, L. Pereira, I. Ferreira, P. Vilarinho, and R. Martins. "New developments in gallium doped zinc oxide deposited on polymeric substrates by RF magnetron sputtering." Surface and Coatings Technology. 180 (2004): 20-25. Abstract
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Fortunato, E., P. Barquinha, A. Pimentel, A. Goncalves, L. Pereira, A. Marques, and R. Martins. "Next generation of thin film transistors based on zinc oxide." Integration of Advanced Micro-and Nanoelectronic Devices-Critical Issues and Solutions. Eds. J. Morais, D. Kumar, M. Houssa, R. K. Singh, D. Landheer, R. Ramesh, R. M. Wallace, S. Guha, and H. Koinuma. Vol. 811. Materials Research Society Symposium Proceedings, 811. 2004. 347-352. Abstract
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Fortunato, E., Barquinha Pimentel Gonçalves Pereira Marques Martins P. A. A. "Next generation of thin film transistors based on zinc oxide." Materials Research Society Symposium Proceedings. Vol. 811. 2004. 347-352. Abstract

We report high performance ZnO thin film transistor (ZnO-TFT) fabricated by rf magnetron sputtering at room temperature with a bottom gate configuration. The ZnO-TFT operates in the enhancement mode with a threshold voltage of 19 V, a field effect mobility of 28 cm2/Vs, a gate voltage swing of 1.39 V/decade and an on/off ratio of 3×105. The ZnO-TFT present an average optical transmission (including the glass substrate) of 80% in the visible part of the spectrum. The combination of transparency, high field-effect mobility and room temperature processing makes the ZnO-TFT a very promising low cost optoelectronic device for the next generation of invisible and flexible electronics.

Fernandes, M.a, Vieira Martins M. a R. b. "Novel structure for large area image sensing." Sensors and Actuators, A: Physical. 115 (2004): 357-361. AbstractWebsite

This work presents preliminary results in the study of a novel structure for a laser scanned photodiode (LSP) type of image sensor. In order to increase the signal output, a stacked p-i-n-p-i-n structure with an intermediate light-blocking layer is used. The image and the scanning beam are incident through opposite sides of the sensor and their absorption is kept in separate junctions by an intermediate light-blocking layer. As in the usual LSP structure the scanning beam-induced photocurrent is dependent on the local illumination conditions of the image. The main difference between the two structures arises from the fact that in this new structure the image and the scanner have different optical paths leading to an increase in the photocurrent when the scanning beam is incident on a region illuminated on the image side of the sensor, while a decreasing in the photocurrent was observed in the single junction LSP. The results show that the structure can be successfully used as an image sensor even though some optimization is needed to enhance the performance of the device. © 2004 Elsevier B.V. All rights reserved.

Neagu, R., E. R. Neagu, J. N. Marat-Mendes, R. Martins, E. Fortunato, I. Ferreira, and C. Dias. "Observations concerning relaxation parameters for polarisation decay and their distributions in the range of glass transition." Advanced Materials Forum Ii. Vol. 455-456. 2004. 703-706. Abstract
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Delgado, Manuel, V{\'ı}tor H. Fernandes, Stuart Margolis, and Benjamin Steinberg. "On semigroups whose idempotent-generated subsemigroup is aperiodic." Internat. J. Algebra Comput.. 14 (2004): 655-665.Website
Vaz, D.C.a b, Van Buijtenen Borges Spliethoff J. P. a A. "On the stability range of a cylindrical combustor for operation in the flox regime." Proceedings of the ASME Turbo Expo 2004. Vol. 1. 2004. 511-516. Abstract

The implementation of flameless combustion in gas turbines is a recent research topic motivated by the potential for ultra-low NO x emissions and improvement of the combustion acoustics. This paper presents preliminary results of the implementation of flameless oxidation in a laboratory model of a cylindrical combustor (in view of stationary and micro gas turbines). Guidelines are given for the start-up of this combustion system. The experimental study then assesses, for atmospheric conditions, the combined effect of the air-to-fuel ratio, wall temperature and jet velocity on combustion stability. Global volumetric heat releases up to 16 MW/m 3, and air preheat up to 265 °C are attained. The numerical simulations give insight into the recirculating pattern of the flow and the state of mixing of reactants and products in the near-nozzle region. The turbulence-chemistry interaction is accounted for by means of the non-premixed flamelet-PDF approach (including finite rate chemistry and scalar dissipation rates up to the extinction limit).

Godinho, M. H., AC Trindade, J. L. Figueirinhas, D. Vidal, LV Melo, and P. Brogueira. "Organized structures obtained from urethane/urea elastomers." Synthetic metals. 147.1 (2004): 209-213. Abstract
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Pauleta, Sr., F. Guerlesquin, C. F. Goodhew, B. Devreese, J. VanBeeumen, AS Pereira, I. Moura, and G. W. Pettigrew. "Paracoccus pantotrophus pseudoazurin is an electron donor to cytochrome c peroxidase." Biochemistry. 43 (2004): 11214-11225. AbstractWebsite

The gene for pseudoazurin was isolated from Paracoccus pantotrophus LMD 52.44 and expressed in a heterologous system with a yield of 54.3 mg of pure protein per liter of culture. The gene and protein were shown to be identical to those from P. pantotrophus LMD 82.5. The extinction coefficient of the protein was re-evaluated and was found to be 3.00 mM(-1) cm(-1) at 590 nm. It was confirmed that the oxidized protein is in a weak monomer/dimer equilibrium that is ionic- strength-dependent. The pseudoazurin was shown to be a highly active electron donor to cytochrome c peroxidase, and activity showed an ionic strength dependence consistent with an electrostatic interaction. The pseudoazurin has a very large dipole moment, the vector of which is positioned at the putative electron-transfer site, His81, and is conserved in this position across a wide range of blue copper proteins. Binding of the peroxidase to pseudoazurin causes perturbation of a set of NMR resonances associated with residues on the His81 face, including a ring of lysine residues. These lysines are associated with acidic residues just back from the rim, the resonances of which are also affected by binding to the peroxidase. We propose that these acidic residues moderate the electrostatic influence of the lysines and so ensure that specific charge interactions do not form across the interface with the peroxidase.

Trindade, AC, M. H. Godinho, M. Simoes, and J. L. Figueirinhas. "Pattern formation in a bi-soft segment urethane elastomer." Molecular Crystals and Liquid Crystals. 412.1 (2004): 93-101. Abstract
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Pereira, L., Marques Águas Nedev Georgiev Fortunato Martins A. H. N. "Performances of hafnium oxide produced by radio frequency sputtering for gate dielectric application." Materials Science and Engineering B: Solid-State Materials for Advanced Technology. 109 (2004): 89-93. AbstractWebsite

The search for new dielectric materials to be used in metal-insulator- semiconductor (MIS) structures to replace the silicon oxide (SiO2) has been growing up. The aim is to have materials with high dielectric constants that could allow the use of thicker films and so, to reduce the role of leakage currents that happens in devices using very thin SiO2 layers or to allow the MIS devices to support high currents, besides having a retain memory effect. In this work, we present data concerning the production of hafnium oxide (HfO2) thin films by radio frequency (rf) sputtering that present suitable characteristics to be used as a gate dielectric, taking advantage of its high dielectric constant and stoichiometry reached under certain deposition conditions. Data concerning the role of the deposition parameters in the films structure and in the electrical properties of the films produced using capacitance-voltage (C-V) and current-voltage (I-V) measurements will be shown, together with data concerning the degree of films' compactness measured by spectroscopic ellipsometry (SE). © 2003 Elsevier B.V. All rights reserved.

Pereira, L., A. Marques, H. Águas, N. Nedev, S. Georgiev, E. Fortunato, and R. Martins. "Performances of hafnium oxide produced by radio frequency sputtering for gate dielectric application." Materials Science and Engineering: B. 109 (2004): 89-93. Abstract
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d Cui, H.-N.a, Teixeira Monteiro Fortunato Martins Bertran V. a A. a. "Physical properties of sputtered ITO and WO3 thin films." Materials Science Forum. 455-456 (2004): 7-11. AbstractWebsite

Electrochromic coatings are used in a wide range of technical fields. This paper refers to the properties of amorphous Indium-tin-oxide (ITO) and WO 3 thin films obtained by dc-magnetron reactive sputtering in different oxygen partial pressures (PO2) at room temperature (RT). SEM, XRD and UV-Vis-NIR spectroscopy characterized the films prepared in terms of morphology, structure, and optical and electrical properties. The maximum of the optical transmittance in the visible range for the ITO and WO3 films was above 97% and 98%, respectively. These films were incorporated into ECDs (electrochromic devices) whose performance was assessed by optical methods.

Inacio, P., J. N. Marat-Mendes, and C. J. Dias. "A piezoelectric pseudo-composite polymer film for the detection of proteins." Advanced Materials Forum Ii. Eds. R. Martins, E. Fortunato, I. Ferreira, and C. Dias. Vol. 455-456. Materials Science Forum, 455-456. 2004. 411-414. Abstract
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Pereira, L., Águas Martins Fortunato Martins H. R. M. "Polycrystalline silicon obtained by gold metal induced crystallization." Journal of Non-Crystalline Solids. 338-340 (2004): 178-182. AbstractWebsite

The aim of this paper is to study the role of gold (Au) induced crystallization on amorphous silicon (a-Si) films produced by low pressure chemical vapor deposition (LPCVD) at low process temperatures (550 °C) to allow the use of glass substrates. Concerning the crystallization process Au was deposited by e-beam thermal evaporation over the silicon (Si), using different metal thickness, from 5 to 100 Å. The samples were then annealed at 450, 500 and 550 °C and the crystallization time was changed from 5 up to 30 h. The structure of the films was analyzed by X-ray diffraction (XRD) and spectroscopic ellipsometry (SE) while electrical conductivity measurements were performed to obtain the electrical properties of the films produced, namely the activation energy (EA) and how it changes with the Au thickness used. The data achieved show that the increase of the metal layer thickness decreases the time needed to get full crystallization. However this leads to lower conduction activation energy (EA) meaning that there is also an increase of Au incorporation that leads to the production of doped films. © 2004 Elsevier B.V. All rights reserved.

Pereira, L., H. Aguas, R. M. Martins, E. Fortunato, and R. Martins. "Polycrystalline silicon obtained by gold metal induced crystallization." Journal of non-crystalline solids. 338 (2004): 178-182. Abstract
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Pereira, L.a, Águas Martins Vilarinho Fortunato Martins H. a R. M. "Polycrystalline silicon obtained by metal induced crystallization using different metals." Thin Solid Films. 451-452 (2004): 334-339. AbstractWebsite

The aim of this paper is to study the role of different metals (aluminium, molybdenum, nickel and titanium) in inducing crystallization in films produced by LPCVD at high and low temperature processes and to compare the structural, morphological, optical and electrical properties of the various films produced. This work envisages the use of the most suitable conditions that lead to the production of films for optoelectronic applications such as solar cells. © 2003 Elsevier B.V. All rights reserved.

Pereira, L., H. Aguas, R. M. S. Martins, P. Vilarinho, E. Fortunato, and R. Martins. "Polycrystalline silicon obtained by metal induced crystallization using different metals." Thin Solid Films. 451 (2004): 334-339. Abstract
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