Magnetotransport Properties of Ferromagnetic Nanoparticles in a Semiconductor Matrix Studied by Precise Size-Selective Cluster Ion Beam Deposition

The combination of magnetic and semiconducting properties in one material system has great potential for integration of emerging spintronics with conventional semiconductor technology. One standard route for the synthesis of magnetic semiconductors is doping of semiconductors with magnetic atoms. In many semiconductor–magnetic–dopant systems, the magnetic atoms form precipitates within the semiconducting matrix. An alternative and controlled way to realize such nanocomposite materials is the assembly by co-deposition of size-selected cluster ions and a semiconductor. Here we follow the latter approach to demonstrate that this fabrication route can be used to independently study the influence of cluster concentration and cluster size on magneto-transport properties. In this case we study Fe clusters composed of approximately 500 or 1000 atoms soft-landed into a thermally evaporated amorphous Ge matrix. The analysis of field and temperature dependent transport shows that tunneling processes affected by Coulomb blockade dominate at low temperatures. The nanocomposites show saturating tunneling magnetoresistance, additionally superimposed by at least one other effect not saturating upon the maximum applied field of 6 T. The nanocomposites’ resistivity and the observed tunneling magnetoresistance depend exponentially on the average distance between cluster surfaces. On the contrary, there is no notable influence of the cluster size on the tunneling magnetoresistance

Magnetotransport Properties of Ferromagnetic Nanoparticles in a Semiconductor Matrix Studied by Precise Size-Selective Cluster Ion Beam Deposition

The combination of magnetic and semiconducting properties in one material system has great potential for integration of emerging spintronics with conventional semiconductor technology. One standard route for the synthesis of magnetic semiconductors is doping of semiconductors with magnetic atoms. In many semiconductor–magnetic–dopant systems, the magnetic atoms form precipitates within the semiconducting matrix. An alternative and controlled way to realize such nanocomposite materials is the assembly by co-deposition of size-selected cluster ions and a semiconductor. Here we follow the latter approach to demonstrate that this fabrication route can be used to independently study the influence of cluster concentration and cluster size on magneto-transport properties. In this case we study Fe clusters composed of approximately 500 or 1000 atoms soft-landed into a thermally evaporated amorphous Ge matrix. The analysis of field and temperature dependent transport shows that tunneling processes affected by Coulomb blockade dominate at low temperatures. The nanocomposites show saturating tunneling magnetoresistance, additionally superimposed by at least one other effect not saturating upon the maximum applied field of 6 T. The nanocomposites’ resistivity and the observed tunneling magnetoresistance depend exponentially on the average distance between cluster surfaces. On the contrary, there is no notable influence of the cluster size on the tunneling magnetoresistance

Can human biomonitoring studies contribute to improve public health decisions?

Abstract publicado em: J Clin Toxicol 2017, 7:3 (suppl)., 66. Doi: 10.4172/2161-0495-C1-025-005: Disponível em: https://www.omicsonline.org/conference-proceedings/2161-0495-C1-025-005.pdfStatement of the Problem: Our previous work has shown the presence of the hazardous chemicals within a complex mixture of contaminants (e.g., metals, pesticides, polycyclic aromatic hydrocarbons) trapped in sediments of a Portuguese estuary. In that case-study, an epidemiological survey confirmed the exposure of the local population mainly through food chain, suggesting the need of a biomonitoring study that includes the quantification of contaminants in biological fluids as well as biomarkers of early biological effects (e.g., biochemical, genetic and omics-based endpoints) in the target population. Recognizing the knowledge gap between exposure to hazardous substances and health outcomes, not only in Portuguese population, but also throughout Europe, the project European Human Biomonitoring Initiative (HBM4EU) has just started, with the overarching goal of generating knowledge towards the safe management of chemicals. Methodology & Theoretical Orientation: Human biomonitoring will be used to understand the human exposure to chemicals and resulting health impacts. The first steps rely on harmonizing procedures for human biomonitoring across countries, to provide policy makers with comparable data on human internal exposure to chemicals and mixtures of chemicals at EU level. Then, linking data on internal exposure with the hazardous chemicals, will allow to aggregate external exposure and identifying exposure pathways and upstream sources. Conclusion & Significance: By generating scientific evidence on the causal links between human exposure to chemicals and negative health outcomes, an evidence-base will be established to allow the use of human biomonitoring in chemical risk assessment methodologies to data. The risk management and communication with stakeholders and policy makers will ensure that results are applied in the design of new regulations for chemicals and for supporting public health protection policies.HBM4EU project, Grant agreement No: 733032info:eu-repo/semantics/publishedVersio

Nanostructured Electrodes for Low Temperature Solid Oxide Fuel Cells

The reduction of the operating temperatures of solid oxide fuel cells (SOFCs) below 600 °C is one of the primary objectives to make them cost competitive with existing energy conversion technologies. However, the low ionic conductivity of the electrolytes and the sluggish electrochemical reaction rates at the electrodes are the major issues, which limit the performance of SOFCs at reduced operating temperatures. While the effect of limited ionic conductivity of the electrolytes at lower operating temperatures has been compensated by decreasing the electrolyte thicknesses, the utilization of nanostructured electrodes with enhanced electrochemical activities has been one of the most common approaches to overcome the electrode limitations associated with the reduced operating temperatures. The aim of the thesis is to obtain high performance nanostructured electrodes for SOFCs in a cost-effective and easily scalable production method. The state-of-the-art electrode materials of La0.6Sr0.4CoO3-δ (LSC) and Ni-Ce0.8Gd0.2O2-δ (NiO-GDC20) with ultrafine microstructure and high phase purity are synthesized by salt-assisted spray pyrolysis method. Nanostructured electrode thin films fabricated by spin coating of the water-based dispersions of LSC and NiO-GDC20 nanoparticles exhibit a three-dimensional porous microstructure with a grain size of around 50 nm. The electrochemical performances of the resulting electrode layers with thicknesses below 1 µm are optimized in the symmetrical cell configuration for the purpose to integrate them into the micro-solid oxide fuel cell (micro-SOFC) devices, which typically employ costly physical vapor deposited Pt thin film electrodes. The proof of concept for the fabrication of porous micro-SOFC electrodes by spin coating of suspensions of electrode nanoparticles is reported for the first time, and the first set of electrochemical data (12 mW/cm2 at 500 °C) demonstrates the feasibility of the developed thin film electrode fabrication method. Furthermore, the synthesized electrode materials are examined in ceria-based anode supported SOFC design. The promising initial electrochemical results (318 mW/cm2 at 600 °C) set the ground for further optimization of the anode supported LSC|Ce0.9Gd0.1O2-δ (GDC10)|Ni-GDC20 cells

Nanostructured Electrodes for Low Temperature Solid Oxide Fuel Cells

The reduction of the operating temperatures of solid oxide fuel cells (SOFCs) below 600 °C is one of the primary objectives to make them cost competitive with existing energy conversion technologies. However, the low ionic conductivity of the electrolytes and the sluggish electrochemical reaction rates at the electrodes are the major issues, which limit the performance of SOFCs at reduced operating temperatures. While the effect of limited ionic conductivity of the electrolytes at lower operating temperatures has been compensated by decreasing the electrolyte thicknesses, the utilization of nanostructured electrodes with enhanced electrochemical activities has been one of the most common approaches to overcome the electrode limitations associated with the reduced operating temperatures. The aim of the thesis is to obtain high performance nanostructured electrodes for SOFCs in a cost-effective and easily scalable production method. The state-of-the-art electrode materials of La0.6Sr0.4CoO3-δ (LSC) and Ni-Ce0.8Gd0.2O2-δ (NiO-GDC20) with ultrafine microstructure and high phase purity are synthesized by salt-assisted spray pyrolysis method. Nanostructured electrode thin films fabricated by spin coating of the water-based dispersions of LSC and NiO-GDC20 nanoparticles exhibit a three-dimensional porous microstructure with a grain size of around 50 nm. The electrochemical performances of the resulting electrode layers with thicknesses below 1 µm are optimized in the symmetrical cell configuration for the purpose to integrate them into the micro-solid oxide fuel cell (micro-SOFC) devices, which typically employ costly physical vapor deposited Pt thin film electrodes. The proof of concept for the fabrication of porous micro-SOFC electrodes by spin coating of suspensions of electrode nanoparticles is reported for the first time, and the first set of electrochemical data (12 mW/cm2 at 500 °C) demonstrates the feasibility of the developed thin film electrode fabrication method. Furthermore, the synthesized electrode materials are examined in ceria-based anode supported SOFC design. The promising initial electrochemical results (318 mW/cm2 at 600 °C) set the ground for further optimization of the anode supported LSC|Ce0.9Gd0.1O2-δ (GDC10)|Ni-GDC20 cells

Low-Cost Synthesis of the Scintillator Compound, Eu- and Dy-Doped SrAl12O19 (SA6), as a Model Material for Electronic Structure Characterization.

Crystalline inorganic scintillator materials, such as rare earth -doped strontium aluminate compounds, offer a cost-effective alternative to the widely used single crystal materials in radiation detection. The overall goal of our work is to develop a model for the effect of dopants in such materials on mechanisms of extended afterglow. To this end, the requirements for characterizing the crystal field impose demands for single phase, crystalline powders. We would like to present a solution polymerization process for synthesizing SA6 doped with Eu and Dy. When reduced, these phosphoresce in the green spectral range, and some control over the length of persistence has already been reported. To obtain single phase strontium aluminate compounds, the Pechini process was modified, in order to enable the use of nitrate precursors to form the desired inorganic solid lattices. The key mechanism is based on using a carboxylic acid group and an alcohol to trap metallic cations inside an organic environment, a resin, and igniting the mixture at relatively low temperatures to form the ceramic crystal structures. In contrast to the more commonly used solid state diffusion process (typically at 1900 °C), our modified process allows synthesis at 1100 °C and yields the single phase, crystalline structural properties necessary for characterization. We would present the modified solution polymerization process, which was developed via XRD, STA, and FT-IR, photoluminescence, and electron energy loss spectroscopy analyses, that yielded the model systems for further study of the crystal field in these scintillator materials. The materials characterization techniques implemented would also be broadly applicable in the study of other scintillator materials

Synthesis and characterization of nanoparticulate La0.6Sr0.4CoO3−δ cathodes for thin-film solid oxide fuel cells

Nanocrystalline La0.6Sr0.4CoO3−δ (LSC) powder with an ultrafine microstructure is synthesized via salt-assisted spray pyrolysis and subsequently stabilized in water-based dispersions. Nanoparticulate cathode thin films of LSC and LSC–GDC (gadolinium doped ceria) nanocomposites (with 10–40 wt% of GDC) are prepared via single step spin coating on yttria stabilized zirconia (YSZ) substrates. In order to prevent the chemical reaction between the cathode and the electrolyte, a thin buffer layer of GDC is deposited using spin coating on the YSZ substrates. The electrochemical performance of the thin film cathodes is measured by impedance spectroscopy on symmetrical cells in the temperature range of 450–650 °C. LSC cathode thin films (250 nm thick) with 30 wt% GDC content exhibit the lowest area specific resistance (ASR) values of 0.32, 0.78 and 2.04 Ω cm2 in ambient air at 650, 600 and 550 °C, respectively

Nebulized spray pyrolysis of Al-doped Li7La3Zr2O12 solid electrolyte for battery applications

Nebulized spray pyrolysis followed by consolidation and sintering was used for the first time to prepare Al-doped garnet-based Li7−3xLa3Zr2AlxO12 (x = 0–0.25) (LLZO) ultra-fine grained ceramics. The structural changes from the tetragonal (x = 0), via a mixture of the cubic and the tetragonal (x = 0.07, 0.10) to the cubic modification (x = 0.15–0.25) were observed. 27Al NMR study showed that aluminum occupy the tetrahedral 24d lithium sites. Despite their low relative density (47–56%), preliminary ionic conductivities of the LLZO ceramics, were found to be 1.2 · 10− 6 S cm− 1 and 4.4 · 10− 6 S cm− 1 for tetragonal and cubic LLZO at room temperature, with activation energies of 0.55 eV and 0.49 eV, respectively

Near-field effects and energy transfer in hybrid metal-oxide nanostructures

One of the big challenges of the 21st century is the utilization of nanotechnology for energy technology. Nanoscale structures may provide novel functionality, which has been demonstrated most convincingly by successful applications such as dye-sensitized solar cells introduced by M. Grätzel. Applications in energy technology are based on the transfer and conversion of energy. Following the example of photosynthesis, this requires a combination of light harvesting, transfer of energy to a reaction center, and conversion to other forms of energy by charge separation and transfer. This may be achieved by utilizing hybrid nanostructures, which combine metallic and nonmetallic components. Metallic nanostructures can interact strongly with light. Plasmonic excitations of such structures can cause local enhancement of the electrical field, which has been utilized in spectroscopy for many years. On the other hand, the excited states in metallic structures decay over very short lifetimes. Longer lifetimes of excited states occur in nonmetallic nanostructures, which makes them attractive for further energy transfer before recombination or relaxation sets in. Therefore, the combination of metallic nanostructures with nonmetallic materials is of great interest. We report investigations of hybrid nanostructured model systems that consist of a combination of metallic nanoantennas (fabricated by nanosphere lithography, NSL) and oxide nanoparticles. The oxide particles were doped with rare-earth (RE) ions, which show a large shift between absorption and emission wavelengths, allowing us to investigate the energy-transfer processes in detail. The main focus is on TiO2 nanoparticles doped with Eu3+, since the material is interesting for applications such as the generation of hydrogen by photocatalytic splitting of water molecules. We use high-resolution techniques such as confocal fluorescence microscopy for the investigation of energy-transfer processes. The experiments are supported by simulations of the electromagnetic field enhancement in the vicinity of well-defined nanoantennas. The results show that the presence of the nanoparticle layer can modify the field enhancement significantly. In addition, we find that the fluorescent intensities observed in the experiments are affected by agglomeration of the nanoparticles. In order to further elucidate the possible influence of agglomeration and quenching effects in the vicinity of the nanoantennas, we have used a commercial organic pigment containing Eu, which exhibits an extremely narrow particle size distribution and no significant agglomeration. We demonstrate that quenching of the Eu fluorescence can be suppressed by covering the nanoantennas with a 10 nm thick SiOx layer