Estrutura eletrônica de derivados de C60 para aplicações em células solares orgânicas

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Photo-Induced Conductivity of Heterojunction GaAs/Rare-Earth Doped SnO2

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Molecular design of new P3HT derivatives: Adjusting electronic energy levels for blends with PCBM

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

Stretching of BDT-gold molecular junctions: thiol or thiolate termination?

It is often assumed that the hydrogen atoms in the thiol groups of a benzene-1,4-dithiol dissociate when Au-benzene-1,4-dithiol-Au junctions are formed. We demonstrate, by stability and transport property calculations, that this assumption cannot be made. We show that the dissociative adsorption of methanethiol and benzene-1,4-dithiol molecules on a flat Au(111) surface is energetically unfavorable and that the activation barrier for this reaction is as high as 1 eV. For the molecule in the junction, our results show, for all electrode geometries studied, that the thiol junctions are energetically more stable than their thiolate counterparts. Due to the fact that density functional theory (DFT) within the local density approximation (LDA) underestimates the energy difference between the lowest unoccupied molecular orbital and the highest occupied molecular orbital by several electron-volts, and that it does not capture the renormalization of the energy levels due to the image charge effect, the conductance of the Au-benzene-1,4-dithiol-Au junctions is overestimated. After taking into account corrections due to image charge effects by means of constrained-DFT calculations and electrostatic classical models, we apply a scissor operator to correct the DFT energy level positions, and calculate the transport properties of the thiol and thiolate molecular junctions as a function of the electrode separation. For the thiol junctions, we show that the conductance decreases as the electrode separation increases, whereas the opposite trend is found for the thiolate junctions. Both behaviors have been observed in experiments, therefore pointing to the possible coexistence of both thiol and thiolate junctions. Moreover, the corrected conductance values, for both thiol and thiolate, are up to two orders of magnitude smaller than those calculated with DFT-LDA. This brings the theoretical results in quantitatively good agreement with experimental data.

Capacitive DNA detection driven by electronic charge fluctuations in a graphene nanopore

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

Physicochemical aspects involved in methotrexate release kinetics from biodegradable spray-dried chitosan microparticles

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Future e(+)e(-) colliders' sensitivity to Hb(b)over-bar coupling and CP violation

A complete analysis of the sensitivity to new Hbb̄ couplings from the process e+e- → bb̄vv̄ at the next generation of linear colliders was performed. These new couplings were predicted by many extensions of the Standard Model. The results are comparable to the study performed previously where a global fit analysis for L=500 fb-1 and √s=500 GeV resulted in a relative accuracy of 2.2% in the gHbb Yukawa coupling.

Crescimento epitaxial e caracterização de filmes finos: óxidos condutores e ferroelétricos preparados por deposição de solução química

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

Transport and sensors properties of nanostructured antimony-doped tin oxide films

Tin oxide thin films doped with 7 mol% antimony oxide multilayer were prepared by the polymeric precursor method. Morphological characterization revealed films with round-shaped grains, nanometric size (similar to 13 nm), and low roughness. These films display high transmittance (similar to 80%) in the visible range of transmittance spectra, which is desirable for transparent conductive oxide films. Analysis on electrical resistivity versus temperature data showed two different conduction mechanisms toward the temperature range. The gas sensor properties measurement of the thicker thin film revealed good sensibility for the NOx. (c) 2006 Elsevier B.V. All rights reserved.

Electrical properties of polymer/metal interface in polymer light-emitting devices: electron injection barrier suppression

The electrical characterization of a high efficient multilayer polymer light emitting diode using poly[(2-methoxy-5-hexyloxy)-p-phenylenevinylene] as the emissive layer and an anionic fluorinated surfactant as the electron transport layer was performed. For the sake of comparison, a conventional single layer device was fabricated. The density current vs. voltage measurements revealed that the conventional device has a higher threshold voltage and lower current compared to the surfactant modified device. The effective barrier height for electron injection was suppressed. The influence of the interfaces and bulk contributions to the dc and high frequencies conductivities of the devices was also discussed. (c) 2006 Springer Science + Business Media, Inc.

Study of charge transport in blends of natural rubber and poly(o-methoxyaniline) based on a resistor network statistical model

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

Seasonal changes in blood oxygen transport and acid-base status in the tegu lizard, Tupinambis merianae

Oxygen-binding properties, blood gases, and acid-base parameters were studied in tegu lizards, Tupinambis merianae, at different seasons and temperatures. Independent of temperature and pH, blood oxygen affinity was higher in dormant lizards than in those active during the summer. Haematocrit (Hct) and hemoglobin content ([Hb]) were greater in active lizards resulting in a higher oxygen-carrying capacity. Nucleoside triphosphate content ([NTP]) was reduced during dormancy, but the ratio between [NTP] and [Hb] remained unchanged. Dormancy was accompanied by an increase in plasma bicarbonate ([HCO(3)(-)]PI) and an elevation of arterial CO(2) partial pressure (P(aCO2)) and CO(2) content in the plasma (C(PlCO2)). These changes in acid-base parameters persist over a broad range of body temperatures. In vivo, arterial O(2) partial pressure (Pa(O2)) and O(2) content (Ca(O2)) were not affected by season and tended to increase with temperature. Arterial pH (pH(a)) of dormant animals is reduced compared to active lizards at body temperatures below 15 degreesC, while no significant difference was noticed at higher temperatures. (C) 2003 Elsevier B.V. All rights reserved.

Escape and transport for an open bouncer: Stretched exponential decays

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Aspects of solid state formation and properties of Sn(0.9)Ti(0.1)O(2) system doped with CoO and Nb(2)O(5)

The effect of calcination temperature during the formation of the solid solution Sn(0.9)Ti(0.1)O(2) doped with 1.00 mol % CoO and 0.05 mol % Nb(2)O(5) is presented. The structural characteristics of this system were studied using X-ray diffraction, and the changes in phase formation were analyzed using the Rietveld method. With an increase in calcination temperature, there is increasing miscibility of Ti into the (Ti,Sn)O(2) phase and near 1000 degrees C, and the remaining TiO(2) (anatase) was transformed into the rutile phase. The sintering process, monitored using dilatometry, suggests two mass transport mechanisms, one activated close to 900 degrees C associated with the presence of TiO(2) (anatase) and the second mechanism, occurring between 1200 and 1300 degrees C, is attributed to a faster grain boundary diffusion caused by oxygen vacancies. (C) 2008 International Centre for Diffraction Data.

Electrical properties of YSZ/NiO composites prepared by a liquid mixture technique

We report the preparation and characterization of yttria-stabilized zirconia/nickel oxide composites (YSZ/NiO). This composite is the precursor material of the cermet YSZ/Ni, which is used as solid oxide fuel cell anode material. The performance of the anode is strongly dependent on the microstructural properties of the cermet. Therefore, the control of the microstructure of the YSZ/NiO composite is a key step for the fabrication of high-performance anodes. In this study, the composites were prepared by a modified liquid mixture technique. Scanning electron microscopy analysis evidenced the good dispersion of the phases and that NiO nanoparticles are spread over the YSZ surface. Sintered pellets were studied by X-ray diffraction and impedance spectroscopy. The main results show that the composite is comprised of a well-dispersed mixture of the two phases. The electrical conductivity data show that there is a strong dependence of the transport mechanism on the relative composition of phases. (c) 2005 Elsevier Ltd. All rights reserved.