Sofia Rodrigues

Impedance spectroscopy study of a compositionally graded lead zirconate titanate structure

The dielectric response of a compositionally graded lead zirconate titanate (PZT) structure prepared by pulsed laser deposition was studied as a function of frequency and temperature (from room temperature up to 419 °C) using impedance spectroscopy. The analysis of combined impedance and modulus spectroscopy, as well as complex plane plots, revealed that the bulk grain relaxation was the dominant relaxation process over the frequency and temperature range studied. The calculated bulk grain capacitance of the graded structure shows an anomalous behavior near temperatures related to the phase transition temperatures of the corresponding PZT compositions. The hopping conduction obeying the “universal power law” and an exponent equal to 0.88 was observed to dominate in alternating current conductivity over the entire frequency range from 10 Hz to 2 MHz at room temperature. At higher temperatures the relaxation spectrum was found to be much influenced by the increased direct current (dc) conductivity. The meas...

Development on Time

Temporal control is considered the fourth dimension in embryonic development and it sets the pace to attain the correct molecular patterning of the developing embryo. In this chapter we review one of the best-studied time dependent events in embryogenesis, which is the formation ofsomites. Somites are the basis of the future segmented framework of the vertebrate adult body and their reiterated appearance during the early stages of embryo development establishes the proper temporal and physical template from where other structures will develop and consequently shape the segmentation pattern of the embryo. Several models have been proposed over the last few decades to explain the mechanism(s) regulating somite periodicity, but no molecular evidence seemed to back up any of the postulated models. Remarkably, in 1997 the first evidence that the formation of the somites depended on an intrinsic molecular clock was at last provided through the description of oscillating gene expression in the tissue from which somites are generated. Since then, a huge amount of data has been and continues to be provided that is gradually revealing the ever more complex molecular mechanism underlying this segmentation clock. We are also beginning to learn about embryonic structures other than the somites which exhibit oscillations of gene expression suggesting they too are dependent upon a segmentation-like clock. This is in itself the clearest evidence that there is still a long way to go before we unveil the myriad of molecular mechanisms that lead to the time control of embryonic development.

Dielectric nonlinearity in a compositionally graded lead zirconate titanate structure

The dielectric response of a compositionally graded lead zirconate titanate (PZT) structure was studied as a function of frequency and amplitude of measuring field. The nonlinear behavior was observed above “threshold” value Et of electric field strength giving rise to field-dependent dielectric properties. Just above Et the nonlinearity was well fitted by the empirical Rayleigh relations. The values of Rayleigh coefficients were observed to be different from those of homogenous PZT films. The analysis of the nonlinearity allows us to suggest higher density of domain walls and/or their better mobility in graded structure.

Philanthropy in Portugal

At the European Council meeting in Lisbon in 2000, the European Union (EU) established the strategic goal of becoming “the most dynamic and competitive knowledge‐based economy in the world” by 2010 (Fontaine, 2000). To achieve this, each EU member state would be required to increase its investment in research and development (R&D) to 3% of its Gross Domestic Product (GDP), which would necessitate an increase in both public and private investments. An important component of private investment is philanthropy. A group of experts recently proposed several policy recommendations to strengthen the role of philanthropy in financing R&D in Europe (EC, 2005). Their report concluded that the EU must further exploit the potential of philanthropy to achieve the strategic investment goals established in the Lisbon Agenda (EC, 2006a). However, many European societies do not have a well‐established philanthropic framework. This is in contrast to the USA and Canada, which have strong philanthropic traditions including specialized institutions to promote fundraising. For example, from 2003 to 2004 the Faculty of Medicine at the Memorial University of Newfoundland in Canada raised 12% of its research funding exclusively from private donations (Memorial University of Newfoundland, 2005). In Europe, the UK has the strongest tradition of philanthropy in science, with many organizations devoted to attracting non‐governmental funding. University College London (UK), for example, has raised more than GBP£30 million in private donations over the past two years for research and other strategically important areas. Even more well known is the charity Cancer Research UK (London)—the worlds leading independent organization dedicated …

Structural and Electrical Properties of Nanostructured Ba0.8Sr0.2TiO3 Films Deposited by Pulsed Laser Deposition

Barium Strontium Titanate Ba0.8Sr0.2TiO3 (BST) thin films have been deposited on Pt/Ti/SiO2/Si substrates by pulsed laser deposition technique. The X-ray diffraction (XRD) shows that the films crystallize in a perovskite phase. XRD and Atomic Force Microscopy (AFM) characterization reveal that the grains are nano-sized. Rutherford Backscattering Spectrometry (RBS) analysis shows the stoichiometry of the films to be close to the stoichiometry of the target. The Raman spectroscopy shows that the films exhibit the tetragonal structure by the presence of the Raman active modes at 301 cm-1 and 729 cm-1, at room temperature. Leakage current measurements of Au/ Ba0.8Sr0.2TiO3/Pt capacitors have been done, at room temperature, to investigate the conduction mechanisms of the films. We found that there are two different conduction regions in the capacitors, namely, an ohmic behavior at low voltages and a Schottky emission mechanism at high voltages. The Schottky barrier height has been estimated to be 0.99 eV.