Effect of thickness on the electrical and optical properties of Sb doped SnO2 (ATO) thin films

This work reports the preparation and characterization of (SnO2) thin films doped with 7 mol% Sb2O3. The films were prepared by the polymeric precursor method, and deposited by spin-coating, all of them were deposited on amorphous silica substrate. Then, we have studied the thickness effect on the microstrutural, optical and electric properties of these samples. The microstructural characterization was carried out by X-ray diffraction (XRD) and scanning tunneling microscopy (STM). The electrical resistivity measurements were obtained by the van der Pauw four-probe method. UV-visible spectroscopy and ellipsometry were carried out for the optical characterization. The films present nanometric grains in the order of 13 nm, and low roughness. The electrical resistivity decreased with the increase of the film thickness and the smallest measured value was 6.5 x 10(-3) Omega cm for the 988 nm thick film. The samples displayed a high transmittance value of 80% in the visible region. The obtained results show that the polymeric precursor method is effective for the TCOs manufacturing.

Electrical conductivity of soybean seed and correlation with seed coat lignin content

The effects of soybean genotype and seed coat lignin content on bulk electrical conductivity were investigated. Seeds of nine soybean cultivars were hand harvested at R8 maturation stage in Londrina, PR., Brazil in 1995/96. Seeds were electrical conductivity tested using four replicates of 50 seeds per cultivar soaked in 75 mi of deionized water at 25 degrees C for 24 hours. Seed coat lignin content was determined using the potassium permanganate method. There was a significant relationship (R-2 = 0.84**) between electrical conductivity and seed coat lignin content, the latter being a characteristic that varies among soybean genotypes; the higher the amount of lignin in the seed coat, the lower the levels of seed exudates to the soaking solution and consequently the lower the electrical conductivity. It was concluded that seed soaking electrical conductivity is influenced by the seed coat lignin content, which is a characteristic that varies among soybean genotypes. Additionally, the EC test can be used as a valuable tool in the screening process for this characteristic, which is desirable for genetically improving soybean seed quality.

Microstructure and electrical properties of perovskite (Pb, La)TiO3 thin film deposited at low temperature by the polymeric precursor method

High-quality (Pb, La)TiO3 ferroelectric thin films were successfully prepared on a Pt(111)/Ti/SiO2/Si(100) substrate for the first time by spin coating, using the polymeric precursor method. The X-ray diffraction patterns show that the films are polycrystalline in nature. This method allows for low temperature (500 degrees C) synthesis, a high quality microstructure and superior dielectric properties. The effects on the microstructure and electrical properties were studied by changing the La content. The films annealed at 500 degreesC have a single perovskite phase with only a tetragonal or pseudocubic structure. As the La content is increased, the dielectric constant of PLT thin films increases from 570 up to 1138 at room temperature. The C-V and P-E characteristics of perovskite thin films prepared at a low temperature show normal ferroelectric behavior, representing the ferroelectric switching property. The remanent polarization and coercive field of the films deposited decreased due to the transformation from the ferroelectric to the paraelectric phase with an increased La content. (C) 2001 Kluwer Academic Publishers.

Temperature dependence on the electrical properties of Ba(Ti0.90Zr0.10)O-3:2V ceramics

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Effect of atmosphere on the electrical properties of TiO2-SnO2 varistor systems

This work illustrates the advancement of research on TiO2-based electroceramics. In this work will be presented that the addition of different dopants, as well as thermal treatments at oxidizing and inert atmosphere, influences of the densification, the mean grain size and the electrical properties of the TiO2-based varistor ceramics. Dopants like Ta2O5, Nb2O5, and Cr2O3 have an especial role in the barrier formation at the grain boundary in the TiO2 varistors, increasing the nonlinear coefficient and decreasing the breakdown electric field. The influence of Cr'(Ti) is to increase the O' and O'(2) adsorption at the grain boundary interface and to promote a decrease in the conductivity by donating electrons to O-2 adsorbed at the grain boundary. In this paper, TiO2 and (Sn,Ti)O-2-based studies of polycrystalline ceramics, which show a non-linear I-V electrical response typical of low voltage varistor systems are also presented. All these systems are potentially promising for varistor applications. (C) 2004 Kluwer Academic Publishers.

Optical and electrical diagnostics of a spark-plug discharge in air

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

Electrical Properties of Textured Niobium-Doped Bismuth Titanate Ceramics

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

Analog Modeling of Human Cognitive Functions with Tripartite Synapses

Searching for an understanding of how the brain supports conscious processes, cognitive scientists have proposed two main classes of theory: Global Workspace and Information Integration theories. These theories seem to be complementary, but both still lack grounding in terms of brain mechanisms responsible for the production of coherent and unitary conscious states. Here we propose following James Robertson's "Astrocentric Hypothesis" - that conscious processing is based on analog computing in astrocytes. The "hardware" for these computations is calcium waves mediated by adenosine triphosphate signaling. Besides presenting our version of this hypothesis, we also review recent findings on astrocyte morphology that lend support to their functioning as Local Hubs (composed of protoplasmic astrocytes) that integrate synaptic activity, and as a Master Hub (composed, in the human brain, by a combination of interlaminar, fibrous, polarized and varicose projection astrocytes) that integrates whole-brain activity.

Electrical relaxation in proton conductor composites based on (NH4)H2PO4/TiO2

We report on electrical relaxation measurements of (1-x)NH4H2PO4-xTiO(2) (x = 0.1) composites by admittance spectroscopy, in the 40-Hz-5-MHz frequency range and at temperatures between 303 and 563 K. Simultaneous thermal and electrical measurements on the composites identify a stable crystalline phase between 373 and 463 K. The real part of the conductivity, sigma', shows a power-law frequency dependence below 523 K, which is well described by Jonscher's expression sigma' = sigma(0)(1 + (omega/omega(p))(n)), where sigma(0) is the dc conductivity, omega(p)/2 pi = f(p) is a characteristic relaxation frequency, and n is a fractional exponent between 0 and 1. Both sigma(0) and f(p) are thermally activated with nearly the same activation energy in the II region, indicating that the dispersive conductivity originates from the migration of protons. However, activation energies decrease from 0.55 to 0.35 eV and n increases toward 1.0, as the concentration of TiO2 nanoparticles increases, thus, enhancing cooperative correlation among moving ions. The highest dc conductivity is obtained for the composite x = 0.05 concentration, with values above room temperature about three orders of magnitude higher than that of crystalline NH4H2PO4 (ADP), reaching values on the order of 0.1 (Omega cm)(-1) above 543 K.

Optical, electrical, and thermochromic properties of polyazothiophene Langmuir-Blodgett films

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

From tin oxalate to (Fe, Co, Nb)-doped SnO(2): Sintering behavior, microstructural and electrical features

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

Congenic strains reveal the effect of the renin gene on skeletal muscle angiogenesis induced by electrical stimulation

Previous studies have indicated the importance of angiotensin II (ANG II) in skeletal muscle angiogenesis. The present study explored the effect of regulation of the renin gene on angiogenesis induced by electrical stimulation with the use of physiological, pharmacological, and genetic manipulations of the renin-angiotensin system (RAS). Transfer of the entire chromosome 13, containing the physiologically regulated renin gene, from the normotensive inbred Brown Norway (BN) rat into the background of an inbred substrain of the Dahl salt-sensitive (SS/Mcwi) rat restored renin levels and the angiogenic response after electrical stimulation. This restored response was significantly attenuated when SS-13BN/Mcwi consomic rats were treated with lisinopril or high-salt diet. The role of ANG II on this effect was confirmed by the complete restoration of skeletal muscle angiogenesis in SS/Mcwi rats infused with subpressor doses of ANG II. Congenic strains derived from the SS-13BN/Mcwi consomic were used to further verify the role of the renin gene in this response. Microvessel density was markedly increased after stimulation in congenic strains that contained the renin gene from the BN rat (congenic lines A and D). This angiogenic response was suppressed in control strains that carried regions of the BN genome just above (congenic line C) or just below (congenic line B) the renin gene. The present study emphasizes the importance of maintaining normal renin regulation as well as ANG II levels during the angiogenesis process with a combination of physiological, genetic, and pharmacological manipulation of the RAS.

Electrical and Magnetic Characterization of BSCCO and YBCO HTS Tapes for Fault Current Limiter Application

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

Structural and electrical properties of SrBi2(Ta0.5Nb0.5)(2)O-9 thin films

SrBi2(Ta0.5Nb0.5)(2)O-9 (SBTN) thin films were obtained by polymeric precursor method on Pt/Ti/SiO2/Si(1 0 0) substrates. The film is dense and crack-free after annealing at 700 degrees C for 2 h in static air. Crystallinity and morphological characteristic were examined by X-ray diffraction (XRD), field emission scanning electron microscopy (FEG-SEM) and atomic force microscopy (AFM). The films displayed rounded grains with a superficial roughness of 3.5 nm. The dielectric permittivity was 122 with loss tangent of 0.040. The remanent polarization (P-r) and coercive field (E-c) were 5.1 mu C/cm(2) and 96 kV/cm, respectively. (C) 2007 Published by Elsevier B.V.

Nanostructured films from phthalocyanine and carbon nanotubes: Surface morphology and electrical characterization

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)