E. R. Leite

Universidade Federal de São Carlos, São Carlos do Pinhal, São Paulo, Brazil

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Publications (348)472.67 Total impact

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    ABSTRACT: a b s t r a c t This paper investigates the near-infrared emission and structural properties of Er 3+ -doped zirconium oxide thin films modified with a fixed content of zinc oxide. The films were obtained by electron beam deposition on Si(1 0 0) substrates, followed by a thermal treatment with or without a controlled oxygen flow. The samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDX). Scanning electron microscopy (SEM) was used to eval-uate the surface morphology, distributions and size of the grains in the films. The results confirmed sig-nificant changes in these films from thermal treatment with or without oxygen flow. Fourier transform infrared spectroscopy (FTIR) was used to analyze the absorption bands of the films. The photolumines-cence (PL) measurement and 4 I 13/2 ? 4 I 15/2 lifetime was measured under 980 nm near-infrared excitation. The effects of thermal treatment as well as the concentration of Er 2 O 3 on the PL emission intensity and lifetime in the near-infrared region (from the 4 I 13/2 ? 4 I 15/2 radiative transition) were studied. Thermal treatment under a controlled atmosphere increased the PL emission intensity due to a diminution of the residual OH groups, as confirmed by the XPS and analysis and FTIR spectroscopy. The film modified with 3 mol% of Er 2 O 3 content annealed in oxygen flow shows an emission intensity of two orders of mag-nitude greater than the annealed film without oxygen flow at 1550 nm, nevertheless, the bandwidth was practically the same (7.6 nm) in both cases. Published by Elsevier B.V.
    Journal of Alloys and Compounds 01/2015; 619:800-806. · 2.73 Impact Factor
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    ABSTRACT: Multiferroic laminated ceramic composites consisting of piezoelectric (BaTiO3, phase B)-magnetostrictive (La0.7Ba0.3MnO3, phase L) materials were synthesized by the Pechini method. The composites were sintered separately and in the form of L–B–L, in order to compare the properties of the separate phases and the laminated material. X-ray diffraction analysis of the separate phases revealed a tetragonal structure with the P4/mm space group for the B phase, and an orthorhombic structure with the R-3cH space group for the L phase. The dielectric and magnetic properties, as well as the magnetoelectric coupling coefficients (αMEαME), were measured as a function of frequency. The dielectric constants at 1 kHz were 1560 for the separate B phase and 2970 for the L–B–L sample. Magnetization measurement of the L–B–L pellet showed that the ferromagnetic transition temperature (TCTC) was around 304 K. Transverse (α31ME) and longitudinal (α33ME) magnetoelectric coupling coefficients were measured for the L–B–L sample at room temperature, and the maximum values obtained were 0.55 and 0.52 mV cm−1 Oe−1, respectively.
    Journal of Magnetism and Magnetic Materials 09/2014; 364:18–23. · 2.00 Impact Factor
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    ABSTRACT: We have studied the experimental conditions needed to produce LaNiO3 (LNO) nanostructures using a template-assisted method. In this route, a mesoporous anodic aluminum oxide template was filled with a chemical solution that had been prepared with polymeric precursors route. The precursor solutions and synthesized samples were characterized by X-ray diffraction (XRD), thermogravimetric analysis, infrared spectroscopy and high-resolution scanning electron microscopy (HRSEM). The XRD results for the samples that were heat-treated at 700 degrees C revealed that these samples crystallize in a perovskite-like LaNiO3 structure. HRSEM images revealed that the samples prepared with different deposition times (0.5, 1 and 2 h) promoted the formation of LaNiO3 nanotubes with different wall thicknesses.
    Journal of Nanoscience and Nanotechnology 06/2014; 14(6):4431-6. · 1.15 Impact Factor
  • Cerâmica 01/2014; 60(353):154-159.
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    ABSTRACT: Single crystalline Zn3P2 nanowires were synthesized on Si substrates via vapour phase deposition catalysed by In-Au seeds. Single nanowire devices were fabricated and the metal-Zn3P2 nanowire contacts were studied using a model based on two Schottky barriers as a function of temperature. As far we know, these are the first reported values of Schottky barriers of Ti/Zn3P2 nanowire contacts. The obtained values showed no significant dependence on the temperature, indicating that the defects at the nanowire's surfaces did not affect the device characteristics. We found evidence of an acceptor level at 49 meV, also indicating that the dominant transport mechanism is the thermal activation of carriers as is found in the bulk Zn3P2. It seems that the p-type behaviour is independent of the dimensionality of the Zn3P2 samples and primarily associated with the phosphorous interstitial atoms.
    Semiconductor Science and Technology 01/2014; 29(1):5001-. · 1.92 Impact Factor
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    ABSTRACT: Cerium oxide (ceria) has attracted attention because of its important applications such as solid oxide fuel cells, catalysts for automobile exhaust gas, catalysts to obtain hydrogen, UV blockers, biomaterials, etc.. Control methods for synthesis of ceria are of great importance to explain or predict these properties. Thus, the objective of this work was to study the growth of cerium oxide nanobelts in a microwave-assisted hydrothermal system, where in 8 min 330 nm nanobelts were obtained at 130 ºC and 3 atm. The results collaborate to the research on reformers for ethanol and/or solid oxide fuel cells anode.
    Cerâmica 09/2013; 59(351):426-430.
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    ABSTRACT: Close-packed arrays of ZrO2 nanocrystals (NCs) have been self-assembled from a colloidal solution in a withdrawal dip coating process. A benzyl alcohol route was used to obtain NCs of narrowly controlled size, and then the capping layer was replaced by oleate using solvothermal treatment. The oleate solubility was explored in chloroform, hexane and toluene to prepare thin films of NCs using a dip coating process. From TEM images, the final structures show that increasing the solvent polarity improved self-assembly to prepare mono- and multi-layer superlattices, during solvent evaporation in a short time. The entangled organic chain in the NC surface offsets the limitations of the faceted NCs, improving the assembly quality, allowing the NC assembly to approach the formation of a hard sphere model, resulting in a FCC close-packed structure. Furthermore, the low interaction of chloroform with the capping layer reduces the shrinkage effect during the solvent evaporation preserving the array in the final self-assembled structure. Molecular dynamics simulations with soft potentials supported the conclusion that hexane interacts with the organic capping ligand, increasing the apparent radius of each NC and stabilizing the colloidal suspension, whereas chloroform is partially removed from the capping layer during the aggregation process, forming an array of nanoparticles.
    Nanoscale 05/2013; · 6.73 Impact Factor
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    ABSTRACT: In this Chapter we review some of our latest results regarding the growth, characterization and magnetic properties of bulk samples (composite fibers) of the optimally doped La 1-x Ce x MnO 3 manganites by using the Laser Heated Pedestal Growth technique. It has been widely recognized that, in comparison with the hole doped manganite (like, e.g., La 1-x Ca x MnO 3), its electron doped counterpart La 1-x Ce x MnO 3 is a metastable phase. That is why, before optimizing the growth conditions, we were able to grow polycrystalline multiphase fibers. Their composition and granularity were verified through Scanning Electron Microcopy with Energy Dispersive X-ray analysis. The magnetic behavior of the fibers was probed by AC susceptibility and magnetization measurements as a function of temperature. Several ferromagnetic transitions were identified. In addition to a weak transition at T C0 =45K (due to MnO 2 impurities), three more transitions with Curie temperatures T C1 =126K, T C2 =180K, and T C,max =300K were observed and linked to fiber regions with cerium concentration of x=0.063, x=0.13, and x=0.3,respectively.
    Doping: Properties, Mechanisms and Applications, Edited by Lixin Yu, 05/2013: chapter 3: pages 71-80; Nova Science., ISBN: 978-1-62618-097-0
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    ABSTRACT: It has been demonstrated that the presence of oxide monolayers in semiconductor surfaces alters the electronic potential at surfaces and, consequently, can drastically affect the electronic transport features of a practical device such as a field effect transistor. In this work experimental and theoretical approaches to characterize Al/germanium nanowire Schottky devices by using samples covered with a thin oxide layer (2 nm width) were explored. It was also demonstrated that the oxide layer on Ge causes a weak dependence of the metal work function on Schottky barrier heights indicating the presence of Fermi level pinning. From theoretical calculations the pinning factor S was estimated to range between 0.52 and 0.89, indicating a weak Fermi level pinning which is induced by the presence of charge localization at all nanowires' surface coming from interface states.
    Journal of Applied Physics 01/2013; 114(24):243705-243705-6. · 2.21 Impact Factor
  • Roman Alvarez Roca, Edson Roberto Leite, P. Gouma
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    ABSTRACT: A simple solvothermal low‐temperature synthesis process of TiO2 nanoparticles was investigated in different solvents [Octanol (Oc), Ethanolamine (Am) and Terathane (Tr)] with titanium (IV) chloride (TiCl4) as precursor. The samples were characterized by X‐Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). XRD showed the crystallite size ranging from 4 to 12 nm, which were calculated using Debye–Scherrer's equation. The existence of poor or high crystalline anatase phases and high crystalline anatase/rutile mixture was also shown. TEM images displayed variations in the morphological behavior depending on the synthesis condition. Particles of irregular morphology with high irregular agglomeration up to well‐defined particles can be observed, which are self‐assembled by oriented attachment (OA). This self‐assembly led to TiO2 microparticles with 3‐D Wulff shape for anatase and 1‐D shape for rutile. The results showed that the TiO2 nanopowder could be easily engineered and adapted by the solvent type, the TiCl4 concentration and the synthesis time.
    Journal of the American Ceramic Society 01/2013; 96(1). · 2.43 Impact Factor
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    ABSTRACT: a b s t r a c t Zinc selenide is a semiconductor material that has been synthesized in aqueous media. However, this synthesis can yield some byproducts, which has been little exploited in literature of this area; one of these byproducts is amorphous selenium. As this amorphous species is unable to be detected through X-ray diffraction, Raman spectroscopy plays an important role in order to track this byproduct. Additionally, the crystallization process from amorphous to trigonal selenium, due to aging at room temperature, was tracked through Raman spectroscopy and transmission electron microscopy. It was observed that, within a period of 5 months, the amorphous selenium was in great part converted to trigonal selenium, which could be deleterious to the properties of the ZnSe quantum dots. & 2012 Elsevier B.V. All rights reserved.
    Materials Letters 07/2012; 87:62. · 2.27 Impact Factor
  • Cleocir Jose Dalmaschio, Edson Roberto Leite
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    ABSTRACT: The comprehension of the physical-chemistry processes related to the nanocrystals growth mechanism is fundamental in controlling the shape and assembly of inorganic nanoparticles. In this paper, we describe TiO2 nanocrystal synthesis by a colloidal process where the final shape and size of the nanocrystal is influenced by a phenomenon similar to the Rayleigh-instability of freestanding TiO2 nanorods in solution. In this process, a larger structure (the nanorod) is divided into smaller units (nanocrystals), by a kind of detachment process. A detailed high-resolution transmission electron microscopy (HRTEM) characterization facilitates the identification of a morphological feature, which characterizes a surface diffusion process. Through a classical thermodynamic analysis, energetic and geometrics parameters, which lead to fragmentations of TiO2 nanorods, were established.
    Crystal Growth & Design 06/2012; 12(7):3668–3674. · 4.69 Impact Factor
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    ABSTRACT: In this work we report on the transition from metal to insulator conduction of individual single crystalline In2 O3 wires induced by different oxygen concentration during their growth. The transport measurements revealed that the metallic conduction was mainly governed by the acoustic phonon scattering and the insulating character was addressed by the variable range hopping mechanism, which in turn can be considered as a first evidence of the occurrence of an Anderson-like metal-insulator-transition (MIT). The experimental data provided the critical carrier density to be 8×1018 cm-3 corresponding to a critical impurities spacing of 2.5 nm, which was found to be in agreement with previous reported data on polycrystalline indium oxide samples and with our recent finding on In2 O3 semiconducting samples. The approach presented here can be used to grow other metal oxide systems in which oxygen vacancies play a fundamental role for the electron transport features.
    Journal of Applied Physics 01/2012; 111(1). · 2.21 Impact Factor
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    ABSTRACT: The use of nanotechnology to enhance endosseous implant surfaces may improve the clinical control of interfacial osteoblast biology. This study investigated the influence of a nanostructure-coated implant surface on osteoblast differentiation and its effects on bone-to-implant contact (BIC) and removal torque values. Titanium disks were machined (M) or machined and subsequently treated by acid etching (Ac) or by dipping in an aluminum oxide solution (Al2O3). Surfaces were characterized by scanning electron microscopy, atomic force microscopy, and x-ray microanalysis. For the in vitro experiment, rat mesenchymal stem cells (rMSCs) were grown in osteogenic supplements on the disk surfaces for 3 days. Real-time polymerase chain reaction (PCR) was used to measure mRNA levels of several gene products (bone sialoprotein, osteocalcin, osteopontin, and RUNX-2). For the in vivo experiment, titanium implants were placed in rat tibiae and harvested after 3 to 21 days for measurement of bone-specific mRNA levels by real-time PCR. Removal torque and BIC were measured 3 to 56 days after placement. Average height deviation (Sa, in nm) values for M, Ac, and Al2O3 implants were 86.5, 388.4, and 61.2, respectively. Nanostructured Al2O3 topographic features applied to machined implants promoted MSC commitment to the osteoblast phenotype. Greater bone-specific gene expression was observed in tissues adjacent to Al2O3 implants, and associated increases in BIC and torque removal were noted. Nanostructured alumina may directly influence cell behavior to enhance osseointegration.
    The International journal of oral & maxillofacial implants 12/2011; 24(2):205-15. · 1.91 Impact Factor
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    ABSTRACT: By the joint use of experimental techniques such as field emission scanning electron microscopy (FEG-SEM), transmission electron microscopy (TEM), and high resolution transmission electron microscopy (HR-TEM) and ab initio theoretical calculations on the slabs surface energy with application of the Wulff construction was performed to study the shape of CaWO4 nanocrystals obtained by a microwave assisted hydrothermal (MAN) method. Under equilibrium conditions, the shape is a slightly truncated tetragonal bipyramid enclosed with eight isosceles trapezoidal surfaces of (101) (Ca-terminated) and two top squares of (001) (O-terminated). Calculated band structures and densities of states are analyzed to find the electronic structures of the different surfaces. The more pronounced elongation of the (001) facet of the experimental FIG with respect to the theoretical prediction results from the favorable interaction between hydroxyl anions and Ca exposed atoms of this surface.
    The Journal of Physical Chemistry C 10/2011; 115(41):20113-20119. · 4.84 Impact Factor
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    ABSTRACT: PbZr0.3Ti0.7O3 (PZT) films were produced by polymeric precursor route and deposited by spin-coater technique on Pt(111)/Ti/SiO2/Si(100) substrates. The films were heat-treated using different furnaces: (a) a conventional furnace, at 700°C; and (b) a domestic microwave oven, at 600°C. The X-ray patterns revealed that both films are single phase and reflections were identified as belongs to the PZT phase. The intensity of these reflections showed a (111), (001) and (100) preferred orientation. Morphological and electrical characterizations showed that all samples present a rather different microstructure and both with high spontaneous polarization.
    Ferroelectrics 10/2011; 335(2006):211-218. · 0.42 Impact Factor
  • Microscopy and Microanalysis 07/2011; 17:1458-1459. · 2.50 Impact Factor
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    ABSTRACT: We report on the growth of bulk samples (composite fibers) of the nominal composition La0.7Ce0.3MnO3 (LCMO) manganites (with Curie temperature TC,max = 300 K) by using the laser heated pedestal growth (LHPG) technique. Samples composition was verified through scanning electron microscopy with energy dispersive X-ray (EDX) analysis. The magnetic behavior of the fibers was probed by magnetization measurements. In addition to a weak ferromagnetic transition at TC0 = 45 K (due to MnO2 impurities), two more transitions with TC1 = 126 K and TC2 = 180 K were identified and linked to regions with cerium concentration of x = 0.063 and 0.13, respectively.
    Physica Status Solidi (A) Applications and Materials 06/2011; 208(7):1704 - 1707. · 1.53 Impact Factor
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    Boletín de la Sociedad Española de Cerámica y Vidrio, ISSN 0366-3175, Vol. 43, Nº. 3, 2004 (Ejemplar dedicado a: Electrocerámica, VI Reunión Nacional (Castellón, 19-21 junio 2003)), pags. 644-648. 06/2011;

Publication Stats

2k Citations
472.67 Total Impact Points

Institutions

  • 1997–2014
    • Universidade Federal de São Carlos
      • • Department of Chemistry
      • • Departamento de Química (DQ)
      São Carlos do Pinhal, São Paulo, Brazil
  • 1997–2009
    • São Paulo State University
      • • Department of Physical Chemistry
      • • Departamento de Química
      • • Instituto de Química - Araraquara
      San Paulo, São Paulo, Brazil
  • 2008
    • Laboratório Nacional de Luz Síncrotron
      Conceição de Campinas, São Paulo, Brazil
    • University of Campinas
      Conceição de Campinas, São Paulo, Brazil
    • Universidade Federal do Ceará
      Ceará, Ceará, Brazil
  • 2004–2008
    • Universidade Federal de São Paulo
      San Paulo, São Paulo, Brazil
    • Universidade São Francisco
      San Paulo, São Paulo, Brazil
    • Universidade Federal da Paraíba
      • Departamento de Química
      João Pessoa, Estado da Paraiba, Brazil
  • 2001–2008
    • CEP America
      Emeryville, California, United States
  • 2003–2004
    • University of São Paulo
      • Instituto de Física (IF) (São Paulo)
      San Paulo, São Paulo, Brazil
  • 2000
    • State University of Ponta Grossa
      Ponta Grossa, Paraná, Brazil
  • 1999
    • Universitat Jaume I
      • Departament de Química Física i Analítica
      Castelló de la Plana, Valencia, Spain