Search

Made available in DSpace on 2018-12-11T17:31:18Z (GMT). No. of bitstreams: 0 Previous issue date: 2017-01-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Combined experimental and first-principles studies have been conducted to obtain a fundamental understanding of the effect of A-site chemical doping on the electronic structure and ferroelectric behavior of Pb(Ca,Ba)TiO3, Pb(Sr,Ba)TiO3, and Pb(Sr,Ca)TiO3perovskite complex solid solutions. Rietveld refinement of powder X-ray diffraction data shows that the crystal structure of all the three compounds is distorted from the ideal cubic perovskite structure. At the nanoscale, piezoresponse force microscopy (PFM) studies show low-performance ferroelectric properties of Pb(Sr,Ca)TiO3thin films when compared to Pb(Ca,Ba)TiO3and Pb(Sr,Ba)TiO3films. Theoretical analysis of the electronic band structure performed on the basis of density functional theory (DFT) allows to elucidate the origin of the different ferroelectric behaviors observed in Pb(Ca,Ba)TiO3, Pb(Sr,Ba)TiO3, and Pb(Sr,Ca)TiO3thin films. DFT-based computational calculations reveal that there is a strong correlation between the effects of Ti 3d non-bonding orbitals (responsible for π Ti[sbnd]O bonding) and the ferroelectric polarization behavior of A(A′A″)BO3complex perovskite solid solutions. In our study, very low Ti 3dxy,dxz, and dyznon-bonding electronic density state contributions were observed and the presence of mainly ionic Ca[sbnd]O and Sr[sbnd]O bonds. These effects are the reason for the unusually weak polarization, low tetragonality, and poor ferroelectricity of Pb(Sr,Ca)TiO3thin films. This is in contrast to the observed behaviors of Pb(Ca,Ba)TiO3and Pb(Sr,Ba)TiO3thin films. However, our first-principles calculations agree well with the PFM-based experimental results obtained in the nanometer scale. LIEC – CDMF- Department of Chemistry Universidade Federal de São Carlos, Via Washington Luiz, Km 235, P.O. Box 676 NanO LaB – Department of Physics Universidade Federal de São Carlos, Via Washington Luiz, Km 235, P.O. Box 676 Department of Chemistry Universidade Estadual Paulista - Unesp, P.O. Box 473 LIEC- CDMF-Institute of Chemistry Universidade Estadual Paulista – Unesp Department of Chemistry Universidade Estadual Paulista - Unesp, P.O. Box 473 LIEC- CDMF-Institute of Chemistry Universidade Estadual Paulista – Unesp FAPESP: 11/20536-7 FAPESP: 12/14106-2 FAPESP: 13/07296-2 CNPq: 470147/2012-1

Made available in DSpace on 2020-12-12T01:42:52Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-11-15 This paper presents a portable laboratory platform (PLP) with electrochemical amperometric biosensors for the detection of hepatitis C virus (HCV). This PLP is composed by a controller unit, a Bluetooth module to provide communication with mobile devices, and a potentiostat circuit to perform cyclic voltammetry. The Bluetooth communication allows the mobile devices to set up the parameters, e.g., a cycling voltage in the range ±1.5 V, a scan rate in the range 5-1000 mV-1 with a step potential of 2.318 mV, and up to 4000 number of scan cycles. The electrochemical sensors were functionalized with cystamine (C4H12N2S2) and glutaraldehyde (C5H8O2) to make the covalent binding with the recombinant core-HCV protein. The experimental results have revealed a positive detection of HCV, using a redox solution of 5 mmol.L-1 of potassium ferrocyanide (K3 Fe(CN)6) on 0.1 mol.L-1 of phosphate-buffered saline (PBS). The sensitivity of the immunosensor was established at the concentration of 1 ng. μ L-1 of the anti-core-HCV IgG class antibody. This PLP has a plug-and-play connection for the biosensors, and at the same time, it offers good ergonomy with easy operation due to its low dimensions (115 mm × 75 mm × 30 mm). This PLP presents a power consumption of 280.5 mW when supplied with a 3.3-V voltage source. This consumption was measured in the worst operation case, e.g., with the Bluetooth working, resulting in an average battery life of 195 min. Department of Electrical Engineering (SEL) University of São Paulo (USP) Department of Chemistry INCTMN-CDMF Federal University of São Carlos (UFSCar) Department of Clinical Analysis School of Pharmaceutical Sciences Laboratory of Clinical Immunology and Molecular Biology (LICBM) São Paulo State University (UNESP) Institute of Chemistry São Paulo State University (UNESP) Department of Clinical Analysis School of Pharmaceutical Sciences Laboratory of Clinical Immunology and Molecular Biology (LICBM) São Paulo State University (UNESP) Institute of Chemistry São Paulo State University (UNESP)

Made available in DSpace on 2018-12-11T17:28:40Z (GMT). No. of bitstreams: 0 Previous issue date: 2016-09-01 In this article, we report a comparative study of the influence of pressure-assisted (1.72 MPa) versus ambient pressure thermal annealing on both ZnO thin films treated at 330 °C for 32 h. The effects of pressure on the structural, morphological, optical, and gas sensor properties of these thin films were investigated. The results show that partial preferential orientation of the wurtzite-structure ZnO thin films in the [002] or [101] planes is induced based on the thermal annealing conditions used (i.e., pressure assisted or ambient pressure). UV–vis absorption measurements revealed a negligible variation in the optical -band gap values for the both ZnO thin films. Consequently, it is deduced that the ZnO thin films exhibit different distortions of the tetrahedral [ZnO4] clusters, corresponding to different concentrations of deep and shallow level defects in both samples. This difference induced a variation of the interface/bulk-surface, which might be responsible for the enhanced optical and gas sensor properties of the pressure-assisted thermally annealed film. Additionally, pressure-assisted thermal annealing of the ZnO films improved the H2 sensitivity by a factor of two. UNESP Instituto de Química UTFPR Departamento de Química UFSCar Departamento de Química USP Instituto de Física de São Carlos UTFPR Departamento de Engenharia de Produção UNESP Instituto de Química

Made available in DSpace on 2018-11-26T17:54:16Z (GMT). No. of bitstreams: 0 Previous issue date: 2018-08-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) In this study, undoped-(Pb,Sr)TiO3 and Fe3+, La3+ co-doped (Pb,Sr)TiO3 thin films were investigated at the nanoscale level by piezoresponse force microscopy (PFM), in order to evaluate the impact of doping induced damages on the ferroelectric and piezoelectric properties. Detailed investigations with nano scale resolution have revealed occurrence of abnormal domains in writing pattern under forward and reverse bias for (Pb,Sr,La)(Ti,Fe)O-3 thin films. Further piezoresponse hysteresis loop measurements show that fully switchable loops were observed under high voltage mediated by defect dipoles and by ferroelectric-like polar defects clusters. They have been discussed taking into account charged defect formation with both local changes in the dipole moment and local symmetry breaking effects. In addition, the domain writing and its retention behavior of the undoped-PST and (Pb,Sr,La)(Ti,Fe)O-3 thin films were investigated. Undoped-PST films exhibited better stability for both positive and negative domains for a relatively long time in comparison to that observed for (Pb,Sr,La)(Ti,Fe)O-3 films. (C) 2018 Elsevier B.V. All rights reserved. Univ Fed Sao Carlos, Dept Chem, LIEC, Via Washington Luiz,Km 235,POB 676, BR-13565905 Sao Carlos, SP, Brazil Univ Fed Sao Carlos, Dept Phys, NanO LaB, Via Washington Luiz,Km 235,POB 676, BR-13565905 Sao Carlos, SP, Brazil Univ Estadual Paulista Unesp, Dept Chem, POB 473, BR-17033360 Bauru, SP, Brazil Univ Estadual Paulista Unesp, Dept Chem, POB 473, BR-17033360 Bauru, SP, Brazil FAPESP: 11/20536-7 FAPESP: 12/14106-2 FAPESP: 13/07296-2 FAPESP: 17/10819-8

Top-down and bottom-up are two kinds of processes employed to obtain ferroelectric nanostructures. Top-down processes are physical methods involving the use of a bulk ferroelectric material to create coherently and continuously ordered nanosized structures (such as focused ion beam milling, nanoimprint lithography). On the other hand, bottom-up synthesis methods involve solution-based routes such as sol-gel, molten salt synthesis, solution-phase decomposition, and hydro/solvothermal synthesis, which lead to the production of different nanostructures (i.e., nanorings, nanowires, nanotubes) beginning at the atomic or molecular level.

Made available in DSpace on 2018-12-11T17:31:46Z (GMT). No. of bitstreams: 0 Previous issue date: 2017-06-01 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Single phase polycrystalline and strong textured Pb0.76Ca0.24TiO3 (PCT24) thin films have been grown on platinum coated silicon and LaAlO3(1 0 0) (LAO) substrates using LaNiO3 (LNO) as a buffer layer by chemical solution deposition. X-ray diffraction measurements showed that the PCT24 thin films crystallize in a highly a-oriented single phase on LNO/LAO(1 0 0). The effects of the LNO buffer layer, nature of the substrate, and film orientation on the ferroelectric and piezoelectric properties were investigated in the nanoscale range using piezoresponse force microscopy (PFM). Local piezoelectric hysteresis loops for PCT24/LNO/LAO(1 0 0) oriented films and PCT24/Pt/Si polycrystalline films were measured on selected grains. From these piezoloops, PCT24/LNO/LAO(1 0 0) oriented films show a higher response (maximum relative d33 value) than PCT24/Pt/Si polycrystalline films. Furthermore, the comparison of simultaneously acquired surface morphology and piezoresponse images of the PCT24/Pt/Si films revealed the presence of inactive grain regions. In contrast, highly a-oriented films showed a higher presence of active grains. Our observations suggest that the improvement of ferro/piezoelectric properties is greatly associated with the use of LNO buffer layers and the growth of highly a-oriented films. Department of Chemistry Universidade Estadual Paulista – Unesp, P.O. Box 473 LIEC – Department of Chemistry Universidade Federal de São Carlos, Via Washington Luiz, Km 235, P.O. Box 676 NanO LaB – Department of Physics Universidade Federal de São Carlos, Via Washington Luiz, Km 235, P.O. Box 676 Institute of Physics of São Carlos USP UNICEP Institute of Chemistry Universidade Estadual Paulista – Unesp Department of Chemistry Universidade Estadual Paulista – Unesp, P.O. Box 473 Institute of Chemistry Universidade Estadual Paulista – Unesp FAPESP: 11/20536-7 FAPESP: 12/14106-2 FAPESP: 13/07296-2 CNPq: 470147/2012-1

Made available in DSpace on 2018-12-11T17:30:56Z (GMT). No. of bitstreams: 0 Previous issue date: 2017-04-15 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) In this work, we have systematically investigated the piezo/ferroelectric response of (Pb, Ca)TiO3 thin films prepared by polymeric precursor method using simultaneously topography, piezoresponse force microscopy (PFM) and local piezoelectric hysteresis loop measurements. The thin films were grown on Pt/Ti/SiO2/Si substrates and annealed at 400, 500 and 600 °C and subjected to structural characterization using x-ray diffraction, infrared and micro-Raman spectroscopy. The ferroelectric domains structure and the piezoelectric response evolved as a function of thermal annealing temperature as well as the density of active grains (number of switchable domains) progressively increased. Another important characteristic of these films is the onset of large area showing the coexistence of active (stronger piezoresponse signal) and inactive (weak or non piezoresponse signal) grains embedded in the polycrystalline perovskite matrix. A combination of out-of-plane (OP) and in-plane (IP) PFM images revealed local features of polarization component magnitudes in samples surface. Well-defined local piezoelectric hysteresis loop was achieved on top of individual nanometer-scale grains in both samples annealed at 500 and 600 °C, and the switching behavior is evident. Department of Chemistry Universidade Estadual Paulista - Unesp, P.O. Box 473 LIEC – Department of Chemistry Universidade Federal de São Carlos, Via Washington Luiz, Km 235, P.O. Box 676 NanO LaB – Department of Physics Universidade Federal de São Carlos, Via Washington Luiz, Km 235, P.O. Box 676 Institute of Physics of São Carlos USP UNICEP Institute of Chemistry Universidade Estadual Paulista – Unesp Department of Chemistry Universidade Estadual Paulista - Unesp, P.O. Box 473 Institute of Chemistry Universidade Estadual Paulista – Unesp FAPESP: 08/57150-6 FAPESP: 11/20536-7 FAPESP: 12/14106-2 FAPESP: 13/07296-2 CNPq: 470147/2012-1 CNPq: 573636/2008-7

Made available in DSpace on 2018-12-11T17:28:37Z (GMT). No. of bitstreams: 0 Previous issue date: 2016-11-01 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) We demonstrate manifestation of some rather unusual size effects in granular thin films prepared by a pulsed laser deposition technique. We observed that the temperature dependence of resistivity ρ(T) notably depends on the relation between the grain size Rg and the film thickness d. Namely, more granular LaNiO3 thin films (with small values of Rg) grown on LaAlO3 substrate are found to follow a universal ρ(T)∝T3/2 law for all the measured temperatures. While less granular thin films (with larger values of Rg), exhibit a more complicated behavior accompanied by a clear-cut crossover (around Tcr=200K), from ρ(T)∝T3/2 (for 20K

Single-phase Pb0.50Ba0.50Ti1−xFexO3 (PBTF) polycrystalline thin films with different Fe doping contents were prepared on Pt/Ti/SiO2/Si substrates using a chemical solution deposition method. The effects of doping on their structural, optical, magnetic, and electrical properties were studied via a multi-technique approach on different scales. A structural phase transition from tetragonal to pseudocubic was observed when the Fe content increased, resulting in tetragonality reduction of the thin films. Another consequence of the Fe content increase was the decrease in the optical band gap energy, probably induced by localized states within the forbidden gap of the PBTF thin films associated with structural disorder. The Fe addition also resulted in a gradual modification of the domain structure, as clearly observed by piezoresponse force microscopy. Two processes, a weakened distortion of the TiO6 sublattice and a decreased ferroelectric and piezoelectric response, were identified. At the macroscopic level, the ferroelectric properties of the films decreased with increasing Fe content, in good agreement with the nanoscale piezoresponse force microscopy data. Finally, a long-range magnetic order to ferromagnetism evolved by increasing the Fe doping content from x = 0.0 to 0.10.