Advanced Materials Forum III

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Authors: Márcia C. Neves, Angela S. Pereira, Marco Peres, Andréi L. Kholkin, Teresa Monteiro, Tito Trindade
Abstract: Cadmium chalcogenide quantum dots (QD’s) were synthesised using a single source approach while zinc oxide QD’s were obtained by a colloidal technique. In both situations the dots were surface capped with tri-octylphosphine oxide (TOPO) hence leading to nanodispersed systems in organic solvents such as toluene. The organically capped QD’s (CdSe, CdS and ZnO) were used as building-units to fabricate LbL (layer-by-layer) films on glass and quartz substrates. A linear increase in the visible light absorbance (due to the QD’s) with the number of deposited layers indicates that multi-layered systems have been fabricated. In order to investigate the effect of the LbL manipulation on the integrity of the QD’s, comparative studies on the optical properties of the starting QD’s and the nanostructured films have been performed. The observation of quantum size effects in both cases suggests minimal degradation of the QD’s though clustering had probably occurred, a point which was further confirmed by AFM analysis.
Authors: M.Fátima Cerqueira, Margarita Stepikhova, Maria Losurdo, Teresa Monteiro, Manuel J. Soares, Marco Peres, Armando Neves, Eduardo Alves
Abstract: Erbium doped nanocrystalline silicon thin films were produced by reactive magnetron r.f. sputtering. Their structural and chemical properties were studied by micro-Raman, spectroscopic ellipsometry and Rutherford backscattering spectroscopy. Films with different crystalline fraction and crystallite size were deposited by changing the deposition parameters. The impact of the composition and structure of Erbium ions environment on the 1.5 µm photoluminescence is discussed.
Authors: Alexandra Fonseca, Eduardo Alves, Joaquim P. Leitão, Nikolai A. Sobolev, M. Celeste Carmo, Alexander I. Nikiforov
Abstract: Monolayer (ML) thick Ge deposition on (100) Si substrates by molecular beam epitaxy (MBE) technique using an ultrathin SiO2 interlayer has been studied by ion beam analysis and photoluminescence (PL). The dependence of the Ge layer growth mode on the amount of the deposited Ge and the SiO2 thickness has been investigated. Atomic hydrogen treatment has been performed in order to passivate non-radiative recombination channels and to enhance the PL intensity. We conclude the formation of Ge quantum dots for the sample with the thickest Ge and SiO2 layers (9 Å and 1 ML, respectively).
Authors: Carla Leer, Olga S. Carneiro, José A. Covas, João M. Maia, Ferrie W.J. van Hattum, Carlos A. Bernardo, László Péter Biró, Zsolt E. Horváth, Imre Kiricsi
Abstract: The effect of the dispersion state of carbon nanotubes in polycarbonate on the rheological, mechanical and electrical properties of melt-extruded compounds is presented. The dispersion state was monitored by means of grey values distribution histograms of optical micrographs of the composites. Increasing the processing residence time, and hence the deformation induced by the surrounding polymer, increased the level of dispersion of CNTs in the matrix. This, in turn, resulted in a large improvement of the CNTs reinforcement effect and decreased composite electrical resistivity. Rheological behaviour is in agreement with these observations.
Authors: Jeremy Sloan, Robin Carter, Angus I. Kirkland, Rüdiger R. Meyer, Alexis Vlandas, Malcolm L.H. Green, John L. Hutchison
Abstract: Restored high resolution transmission electron microscopy (HRTEM) images have been recorded from 1D semiconductor crystals formed within narrow diameter (ca. 1.4 nm) single walled carbon nanotubes (SWNTs). Two unique projections were obtained from separate crystal fragments encapsulated within separate nanotubes that has facilitated the reconstruction of the three dimensional arrangement of atoms within the two encapsulated fragments.
Authors: Filipa L. Sousa, Paula C.R. Soares-Santos, Helena I.S. Nogueira, Rute A. Sá Ferreira, Ana M.V. Cavaleiro, Luís D. Carlos, Tito Trindade
Abstract: A layer-by-layer assembly method was employed to fabricate multilayered films containing the terbium heteropolyanions K6[Tb(BW11O39)(H2O)3]·32H2O and Ky[Tb(XW11O39)2]·nH2O (X = Si and P) and the polyelectrolytes poly(4-styrenesulfonate) and poly(allylamine hydrochloride). A comparative study on the optical properties of the films containing distinct polyoxometalates and different types of multilayers was carried out. The photoluminescence of the solid polyoxometalates and of the resulting films was investigated.
Authors: Ana P. Piedade, Guenis Gomez, M. Teresa Vieira, Mariana Staia
Abstract: In this research work, sputtering was used to deposit silver thin films under different deposition parameters, namely by changing deposition pressure, substrate bias and discharge gas. The main objective of the present work was to study the influence of the textured grain in the mechanical behaviour of the modified surfaces. The deposition rate, chemical composition (EPMA), morphology (SEM) and hardness were also assessed. In the slide alternating wear tests, where poly(tetrafluoroethylene) (PTFE) was used as counterbody, the loads varied from 10 to 30 N. One of the major conclusions of this work is that the thin films with the strongest (111) preferential crystallographic orientation correspond to the highest deposition rate. These sample present higher hardness and lower wear coefficient if compared with other orientations
Authors: José M. Teixeira, Rui F.A. Silva, João Ventura, A. Pereira, João P. Araújo, M. Amado, Francisco Carpinteiro, João Bessa Sousa, S. Cardoso, R. Ferreira, Paulo Freitas
Abstract: A MOKE magnetometry unit simultaneously sensitive to both in-plane magnetization components, based on an intensity differential detection method, allows us to observe the uniaxial anisotropy impressed during CoFe-deposition and to discriminate the magnetization processes under a magnetic field parallel and perpendicular to such axes. Our MOKE imaging unit, using a CCD camera for Kerr effect domain visualization provides direct evidence on the dominant M-processes, namely domain wall motion and moment rotation. Further magnetic information was obtained by AMR measurements due to the dependence of the electrical resistivity on the short-range spin disorder and also on the angle between the electrical current direction (I) and the spontaneous magnetization (MS).
Authors: Anibal Portinha, Vasco Teixeira, Joaquim Carneiro, Rachel Newton, H. Fonseca
Abstract: Zirconia (ZrO2) exhibits three different polymorphic phases as a function of the thermal and pressure conditions (cubic, tetragonal and monoclinic). The use of zirconia coatings at high temperatures requires it to be stabilized at room temperature in order to maintain the high temperature phases when subjected to thermal cycles. For this purpose, this work reports different ways to stabilize ZrO2 coatings produced by DC reactive magnetron sputtering. We have produced stabilized ZrO2 coatings by doping with other metallic and rare earth oxides (Y2O3 and Gd2O3), depositing nanostructured ZrO2 crystallites in an amorphous Al2O3 matrix and using a ZrO2/Al2O3 nanolaminated structure. A comparative study of the coatings produced is presented along with their structural stabilization using different approaches. For the doped coatings the tetragonal or cubic phases were obtained as a function of the dopant percentage and for the nanostructured and nanolayered structures the stabilization mechanism is related to the constraining of the zirconia nanocrystallites and the capacity to maintain its size under certain value.
Authors: Talaat Moussa Hammad
Abstract: Sol gel indium tin oxide thin films (In: Sn = 90:10) were prepared by the sol-gel dipcoating process on silicon buffer substrate. The precursor solution was prepared by mixing SnCl2.2H2O and InCl3 dissolved in ethanol and acetic acid. The crystalline structure and grain orientation of ITO films were determined by X-ray diffraction. The surface morphology of the films was characterized by scanning electron microscope (SEM). Optical transmission and reflectance spectra of the films were analyzed by using a UV-visible spectrophotometer. The transport properties of majority charge carriers for these films were studied by Hall measurement. ITO thin film with electrical resistivity of 7.6 ×10-3, Hall mobility of approximately 2 cm2(Vs)-1 and free carrier concentration of approximately 4.2 ×1020 cm-3 are obtained for films 100 nm thick films. The I-V curve measurement showed typical I-V characteristic behavior of sol gel ITO thin films.

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