Deposition and characterization of BiVO4 thin films and evaluation as photoanodes for methylene blue degradation

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Intense visible photoluminescence in Ba(Zr0.25Ti0.75)O-3 thin films

Photoluminescence at room temperature in Ba(Zr0.25Ti0.75)O-3 thin films was explained by the degree of structural order-disorder. Ultraviolet-visible absorption spectroscopy, photoluminescence, and first principles quantum mechanical measurements were performed. The film annealed at 400 degrees C for 4 h presents intense visible photoluminescence behavior at room temperature. The increase of temperature and annealing time creates [ZrO6]-[TiO6] clusters in the lattice leading to the trapping of electrons and holes. Thus, [ZrO5]-[TiO6]/[ZrO6]-[TiO6] clusters were the main reason for the photoluminescence behavior.

Plasmonic Coupling in Er3+:Au Tellurite Glass

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Structural Investigations of Glass Ceramics in the Ga2S3-GeS2-CsCl System

Transparent glass ceramics have been prepared in the Ga2S3-GeS2-CsCI pseudoternary system appropriate heat treatment time and temperature. In situ X-ray diffraction at the heat treatment temperature and Cs-133 and Ga-71 solid-state nuclear magnetic resonance have been performed in function of annealing time to understand the crystallization process. Both techniques have evidenced the nucleating agent role played by gallium with the formation of Ga2S3 nanocrystals. on the other hand, cesium is incorporated very much later into the crystallites during the ceramization. Moreover, the addition of CsCl, which is readily integrated into the glassy network, permits us to shift the optical band gap toward shorter wavelength. Thus, new glass ceramics transmitting in the whole visible range up to 11.5 mu m have been Successfully synthesized from the (Ga2S3)(35)-(GeS2)(25)-CsCl40 base glass composition.

Intense and broad photoluminescence at room temperature in structurally disordered Ba[Zr0.25Ti0.75]O-3 powders: An experimental/theoretical correlation

Intense and broad photoluminescence (PL) emission at room temperature was observed on structurally disordered Ba[Zr0.25Ti0.75]O-3 (BZT) powders synthesized by the polymeric precursor method. BZT powders were annealed at 573 K for different times and at 973 K for 2 h in oxygen atmosphere. The single-phase cubic perovskite structure of the powder annealed at 973 K for 2 It was identified by X-ray diffraction and Fourier transform Raman techniques. PL emission increased with the increase of annealing time, which reached its maximum value in the powder annealed at 573 K for 192 h. First principles quantum mechanical calculations based on density functional theory (B3LYP level) were employed to study the electronic structure of ordered and disordered models. The theoretical calculations and experimental measurements of Ultraviolet-visible absorption spectroscopy indicate that the presence of intermediary energy levels in the band gap is favorable for the intense and broad PL emission at room temperature in disordered BZT powders. The PL behavior is probably due the existence of a charge gradient on the disordered structure, denoted by means of a charge transfer process from [TiO5]-[ZrO6] or [TiO6]-[ZrO5] clusters to [TiO6]-[ZrO6] clusters. (C) 2008 Elsevier Ltd. All rights reserved.

Growth of silver nano-particle embedded in tellurite glass: Interaction between localized surface plasmon resonance and Er3+ ions

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Luminescence of Tb(3+) doped TeO(2)-ZnO-Na(2)O-PbO glasses containing silver nanoparticles

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Deposition of Al2O3 by resistive evaporation and thermal oxidation of Al to be applied as a transparent FET insulating layer

Alumina thin films have been obtained by resistive evaporation of Al layer, followed by thermal oxidation by means of annealing in appropriate atmosphere (air or O2-rich), with variation of annealing time and temperature. Optical and structural properties of the investigated films reveal that the temperature of 550 °C is responsible for reasonable oxidation, which is accelerated up to 8 times for O2-rich atmosphere. Results of surface electrical resistivity and Raman spectroscopy are in good agreement with these findings. Surprisingly, X-ray and Raman data suggest also the crystallization of Si nuclei at glass substrate-alumina interface, which would come from the soda-lime glass used as substrate. © 2013 Elsevier Ltd and Techna Group S.r.l.

Rietveld refinement and optical properties of SrWO4:Eu3+ powders prepared by the non-hydrolytic sol-gel method

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Al2O3 obtained through resistive evaporation for use as insulating layer in transparent field effect transistor

Alumina thin films have been obtained by resistive evaporation of Al layer, followed by thermal oxidation achieved by annealing in appropriate atmosphere (air or O-2-rich), with variation of annealing time and temperature. Optical and structural properties of the investigated films reveal that the temperature of 550 degrees C is responsible for fair oxidation. Results of surface electrical resistivity, Raman and infrared spectroscopies are in good agreement with this finding. X-ray and Raman data also suggest the crystallization of Si nuclei at glass substrate-alumina interface, which would come from the soda-lime glass used as substrate. The main goal in this work is the deposition of alumina on top of SnO2 to build a transparent field-effect transistor. Some microscopy results of the assembled SnO2/Al2O3 heterostructure are also shown.

Al2O3 Obtained through resistive evaporation for use as insulating layer in transparent field effect transistor

Alumina thin films have been obtained by resistive evaporation of Al layer, followed by thermal oxidation achieved by annealing in appropriate atmosphere (air or O2-rich), with variation of annealing time and temperature. Optical and structural properties of the investigated films reveal that the temperature of 550°C is responsible for fair oxidation. Results of surface electrical resistivity, Raman and infrared spectroscopies are in good agreement with this finding. X-ray and Raman data also suggest the crystallization of Si nuclei at glass substrate-alumina interface, which would come from the soda-lime glass used as substrate. The main goal in this work is the deposition of alumina on top of SnO2 to build a transparent field-effect transistor. Some microscopy results of the assembled SnO2/Al2O3 heterostructure are also shown.

Structural and Magnetic Properties of Neodymium - Iron - Boron Clusters

Using inert gas condensation techniques the properties of sputtered neodymium-iron-born clusters were investigated. A D.C. magnetron sputtering source created vaporous Nd-Fe-B which was then condensed into clusters and deposited onto silicon substrates. A composite target of Nd-Fe-B discs on an iron plate and a composite target of Nd-(Fe-Co)-B were utilized to create clusters. The clusters were coated with a carbon layer through R.F. sputtering to prevent oxidation. Samples were investigated in the TEM and showed a size distribution with an average particle diameter of 8.11 nm. The clusters, upon deposition, were amorphous as indicated by diffuse diffraction patterns obtained through SAD. The EDS showed compositionally a direct correlation in the ratio of rare-earth to transition metals between the target and deposited samples. The magnetic properties of the as-deposited clusters showed superparamagnetic properties at high temperatures and ferromagnetic properties at low temperatures; these properties are indicative of rare-earth transition metal amorphous clusters. Annealing of samples showed an initial increase in the coercivity. Samples were annealed in an inert gas atmosphere at 600o C for increasing amounts of time. The samples showed an initial increase in coercivity, but showed no additional increases with additional annealing time. SAD of annealed cluster samples showed the presence of Nd2Fe17 and a bcc-Nd phase. The bcc-Nd is the result of oxidation at high temperatures created during annealing and surface interface energy. The magnetic properties of the annealed samples showed weak coercivity and a saturation magnetization equivalent to that of Nd2Fe17. The annealed clusters showed a slight increase in coercivity at low temperatures. These results indicate a loss of boron during the sputtering process.

Plasmonic Coupling in Er3+:Au Tellurite Glass

In this paper, we report on luminescence and absorbance effects of Er+3:Au-doped tellurite glasses synthesized by a melting-quenching and heat treatment technique. After annealing times of 2.5, 5.0, 7.5, and 10.0 h, at 300 A degrees C, the gold nanoparticles (GNP) effects on the Er+3 are verified from luminescence spectra and the corresponding levels lifetime. The localized surface plasmon resonance around 800 nm produced a maximum fluorescence enhancement for the band ranging from 800 to 840 nm, corresponding to the transitions H-4(11/2) -> aEuro parts per thousand I-4(13/2) (805 nm) and S-4(3/2) -> aEuro parts per thousand I-4(13/2) (840 nm), with annealing time till 7.5 h. The measured lifetime of the levels H-4(11/2) and S-4(3/2) confirmed the lifetime reduction due to the energy transfer from the GNP to Er+3, causing an enhanced photon emission rate in these levels.

Thermoelectric properties in phase-separated half-Heusler materials

The conversion of dissipated heat into electricity is the basic principle of thermoelectricity. In this context, half-Heusler (HH) compounds are promising thermoelectric (TE) materials for waste heat recovery. They meet all the requirements for commercial TE applications, ranging from good efficiencies via environmentally friendliness to being low cost materials. This work focused on the TE properties of Ti0.3Zr0.35Hf0.35NiSn-based HH materials. This compound undergoes an intrinsic phase separation into a Ti-poor and Ti-rich HH phase during a rapid solidification process. The resulting dendritic microstructure causes a drastic reduction of the thermal conductivity, leading to higher TE efficiencies in these materials. The TE properties and temperature dependence of the phase-separated Ti0.3Zr0.35Hf0.35NiSn compound were investigated. The TE properties can be adjusted depending on the annealing treatment. The extension of annealing time for 21 days at 1000 °C revealed a reduction of the thermal conductivity and thus an enhancement of the TE performance in this sample. An increase of annealing temperature caused a change of the phase fraction ratio in favor of the Ti-rich phase, leading to an improvement of the electronic properties. rnInspired by the TE properties of the Ti0.3Zr0.35Hf0.35NiSn HH compound, the performance of different n- and p-type materials, realized via site substitution with donor and acceptor elements was examined. The fabrication of a TE n- and p-type material pair based on one starting compound can guarantee similar TE and mechanical properties and is enormous beneficial for device engineering. As donor dopants V, Nb and Sb were tested. Depending on the lattice position small doping levels were sufficient to attain distinct improvement in their TE efficiency. Acceptor-induced doping with Sc, Y and Co caused a change in the transport behavior from n- to p- type conduction, revealing the highest Seebeck coefficients obtained in the MNiSn system. rnThen, the long-term stability of an exemplary n- and p-type HH compound was proven. Surprisingly, the dendritic microstructure can be maintained even after 500 cycles (1700 h) from 373 to 873 K. The TE performance of both n- and p-type materials showed no significant change under the long-term treatment, indicating the extraordinary temperature stability of these compounds. Furthermore both HH materials revealed similar temperature-dependence of their mechanical properties. This work demonstrates the excellent suitability of phase-separated HH materials for future TE applications in the moderate temperature range.rn

Recrystallization of amorphous nano-tracks and uniform layers generated by swift-ion-beam irradiation in lithium niobate.

The thermal annealing of amorphous tracks of nanometer-size diameter generated in lithium niobate (LiNbO3) by Bromine ions at 45 MeV, i.e., in the electronic stopping regime, has been investigated by RBS/C spectrometry in the temperature range from 250°C to 350°C. Relatively low fluences have been used (<1012 cm−2) to produce isolated tracks. However, the possible effect of track overlapping has been investigated by varying the fluence between 3×1011 cm−2 and 1012 cm−2. The annealing process follows a two-step kinetics. In a first stage (I) the track radius decreases linearly with the annealing time. It obeys an Arrhenius-type dependence on annealing temperature with activation energy around 1.5 eV. The second stage (II) operates after the track radius has decreased down to around 2.5 nm and shows a much lower radial velocity. The data for stage I appear consistent with a solid-phase epitaxial process that yields a constant recrystallization rate at the amorphous-crystalline boundary. HRTEM has been used to monitor the existence and the size of the annealed isolated tracks in the second stage. On the other hand, the thermal annealing of homogeneous (buried) amorphous layers has been investigated within the same temperature range, on samples irradiated with Fluorine at 20 MeV and fluences of ∼1014 cm−2. Optical techniques are very suitable for this case and have been used to monitor the recrystallization of the layers. The annealing process induces a displacement of the crystalline-amorphous boundary that is also linear with annealing time, and the recrystallization rates are consistent with those measured for tracks. The comparison of these data with those previously obtained for the heavily damaged (amorphous) layers produced by elastic nuclear collisions is summarily discussed.