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Dive into the research topics where Roberto M. Faria is active.

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Featured researches published by Roberto M. Faria.


Journal of Applied Physics | 1981

Radiation‐induced conductivity in Teflon irradiated by x rays

B. Gross; Roberto M. Faria; G. F. Leal Ferreira

This paper reports results of measurements of radiation‐induced conductivity of Teflon (Teflon is a registered trademark of the E. J. du Pont de Nemours and Co.). FEP (polyfluorethylene propylene) foils irradiated by x rays at atmospheric pressure. The current induced by irradiation of the poled dielectric at exposure rates of the order of 102 R/s, initially increases with time for 10–20 s, reaches a maximum, and subsequently decreases. After an irradiation time of about 1 h, a steady‐state value is attained which is of the order of 25% of the maximum current. Measurements are reported of the dependence of the current amplitudes on exposure rate, of the delayed component of induced conductivity, and of the behavior of samples which had been irradiated in short‐circuit before poling. Radiation‐induced polarization effects or space‐charge formation could not be detected. The behavior of the current‐time curves is interpreted in terms of a theory of unipolar (hole) conduction.


International Journal of Gynecology & Obstetrics | 1983

Frozen section biopsy of ovarian neoplasms

Alvaro da Cunha Bastos; Carlos Alberto Salvatore; Roberto M. Faria

In a study of the frozen section biopsy of 120 ovarian neoplasms, correct results were obtained in 94.16%, incorrect in 4.16%, and inconclusive in 1.66% of the 120 cases. The “incorrect” results were all “false‐negative.” No inverse “false‐positive” results were recorded, and the “incorrect” results occurred in cases of encapsulated neoplasms of a macroscopically benign appearance with small areas of malignant changes detected only by paraffin block technique. The authors conclude that frozen section biopsy of ovarian neoplasm is plausible so long as a pathologist is available who can be provided with the proper equipment during the surgery and that the technique is more indicated in patients up to the age of 40 because of the necessity of conservative management in this age group.


Journal of Applied Physics | 1984

dc conduction and dielectric absorption in PVF2

Roberto M. Faria; B. Gross; G. F. Leal Ferreira

Charging and discharging currents in PVF2 are found to depend on the nature of the gas (argon or air) in which the samples are kept during measuring and on the pressure and humidity of the air.


IEEE Transactions on Electrical Insulation | 1986

Induced Conductivity of Mylar and Kapton Irradiated by X-Rays

R. Gregorio Filho; B. Gross; Roberto M. Faria

This paper presents a wide range of experimental results of prompt and delayed components of the conductivity induced by x-rays in Mylar (PET) and Kapton (Polyimide). Measurements were carried out under a vacuum at room temperature. They were made for a large range of parameters: electric field E (104 to 4.8X105 V/ cm); exposure rate X (85 to 550 R/ s); and thickness d of the sample (6 to 75 ¿m). Electrodes were made of evaporated aluminum, but in some measurements gold was used. Gold increased the exposure rate, due to its high er atomic number. Finally, a study of the recovery of the irradiated samples was made.


Journal of Applied Physics | 1987

Radiation‐induced conductivity of polymers in different gases

Roberto M. Faria; B. Gross; R. Gregorio Filho

The conductivity induced in various polymers by continuous irradiation with x rays was measured under a vacuum and in different gases. Oxygen, nitrogen, and air increased the induced conductivity in polyvinylidene fluoride (PVDF), while argon left it almost unchanged. Argon and air decreased it in Kapton, and air decreased it in Mylar. The saturation current is that stationary value of the current that is obtained if all radiation‐generated carriers are removed by the applied field. The measured current amplitude for PVDF in an atmosphere of air of 100% humidity reached almost 50% of that current, while in the other materials it did not exceed 1% of the saturation value. Therefore, carrier removal by the applied field played a negligible role in Kapton and Mylar.


Polymer Degradation and Stability | 1998

Structural modifications of vinylidene fluoride-trifluoroethylene (70-30) copolymer induced by X-ray irradiation

Hector A.C. Gil; Roberto M. Faria; Yoshio Kawano

X-ray radiation-induced structural changes in the semicrystalline random copolymer poly(vinylidene fluoride-co-trifluoroethylene) (70-30) film were studied by X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis, ultraviolet/visible and infrared absorption spectroscopies and Raman scattering. The X-ray diffraction shows a decreasing degree of crystallinity with increasing X-ray irradiation times. The differential scanning calorimetry experiments show that the ferroelectric transition temperature Tc and the melting temperature Tm are lowered under X-ray irradiation. Thermogravimetric analysis shows one step weight loss with a decreasing decomposition temperature and increasing amount of residue with increasing irradiation times. The UV/vis spectra of irradiated copolymer film show the appearance of absorptions at ~192, 222, 272, 342 and 364 nm related to CC<, diene, triene and chromophores of radical ion species, respectively. Infrared spectra show a small high wavenumber shift for bands associated to CH stretching vibrations, decreasing intensities at 1293 and 852cm−1 and the appearance of new bands at 1847, 1750 and 1717cm−1, that increase in intensity with irradiation times. Raman spectra show an increasing fluorescence contribution with increase of irradiation time. A decreasing intensity of bands at 847 and 884cm−1 could be related to decreasing degree of crystallinity of the copolymer film. The X-ray irradiated P(VDF-TrFE) (70-30) films show physical and chemical change consisting in diminished degree of crystallinity, loss of ferroelectric property and the formation of new chemical structures (CC<, diene, triene and chromophores of radical ion species).


Journal of Applied Physics | 2003

Enhanced optical and electrical properties of layer-by-layer luminescent films

A. Marletta; Erick Piovesan; N.O. Dantas; N.C. de Souza; C. A. Olivati; Débora T. Balogh; Roberto M. Faria; Osvaldo N. Oliveira

The electrical and optical properties of luminescent films from poly(p-phenylene vinylene) (PPV) and poly(o-methoxyaniline) (POMA) produced via the layer-by-layer technique are reported. POMA layers were obtained in a nonself-limiting process from its emeraldine salt. PPV was thermally converted from the precursor poly(xylylidene tetrahydrothiophenium chloride) with sodium dodecylbenzenesulfonate (DBS) at low temperatures of ∼110 °C and short times (∼30 min). The line shape of absorbance and photoluminescence (PL) is not affected with the PPV conversion reaction. High thermal stability of PPV was observed, with the integrated PL decreasing only 10% when the temperature was increased from 10 to 300 K. This decrease was accompanied by a small blue shift of 5 nm in the zero-phonon peak and a low electron–phonon coupling with a Huang–Rhys factor S<1 in the vibration spectral region. The combination of POMA and indium–tin–oxide (ITO) as transparent electrode and PPV+DBS as active layer (ITO/POMA/PPV+DBS/Al) le...


Journal of Polymer Research | 2013

Synthesis and photovoltaic performance of a fluorene-bithiophene copolymer

Isabel R. Grova; Douglas José Coutinho; Roberto M. Faria; Leni Akcelrud

We present the synthesis of a copolymer structure, poly(9,9′-n-di-hexyl-2,7-fluorene-alt-2,5-bithiophene), referred to herein as LaPPS43, and its physico-chemical characterization. Thin films of this polymer mixed with phenyl-C61-butyric acid methyl ester (PCBM) were used as the active layer in photovoltaic devices using the ITO/PEDOT:PSS/LaPPS43:PCBM/Ca/Al bulk heterojunction structure. The devices of different active layer thicknesses were electrically studied using J-V curves and the Photo-Celiv technique. The obtained results show that LaPPS43 combined with PCBM is a promising system for photovoltaic devices. Device performance is discussed in terms of the mean drift distance x for charge carriers. Photophysical data showed that the excitonic species are all localized in the aggregated forms. The mechanism of exciton formation and dissociation is also discussed.


ChemPhysChem | 2011

Probing the functionalization of gold surfaces and protein adsorption by PM-IRRAS.

Rodrigo Marques de Oliveira; Jacqueline Ferreira; Marcos J. L. Santos; Roberto M. Faria; Osvaldo N. Oliveira

The control of morphology and coating of metal surfaces is essential for a number of organic electronic devices including photovoltaic cells and sensors. In this study, we monitor the functionalization of gold surfaces with 11-mercaptoundecanoic acid (MUA, HS(CH(2) )(10) CO(2) H) and cysteamine, aiming at passivating the surfaces for application in surface plasmon resonance (SPR) biosensors. Using polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS), cyclic voltammetry, atomic force microscopy and quartz crystal microbalance, we observed a time-dependent organization process of the adsorbed MUA monolayer with alkyl chains perpendicular to the gold surface. Such optimized condition for surface passivation was obtained with a systematic search for experimental parameters leading to the lowest electrochemical signal of the functionalized gold electrode. The ability to build supramolecular architectures was also confirmed by detecting with PM-IRRAS the adsorption of streptavidin on the MUA-functionalized gold. As the approaches used for surface functionalization and its verification with PM-IRRAS are generic, one may now envisage monitoring the fabrication of tailored electrodes for a variety of applications.


Journal of Polymer Research | 2012

Photophysical and photovoltaic properties of a PPV type copolymer containing alternated fluorene and thiophene units

Paula C. Rodrigues; Isabel R. Grova; Douglas José Coutinho; Raquel Aparecida Domingues; Heong Sub Oh; Jangwon Seo; Roberto M. Faria; Teresa Dib Zambon Atvars; Paras N. Prasad; Leni Akcelrud

The synthesis and photophysical characterization of a PPV-type copolymer containing a fluorene derivative alternated with thiophene units is presented: poly(9,9’-dioctylfluorene-thiophene) (LAPPS29). Photophysical studies demonstrated that in the solid state only preformed ground state aggregates are responsible for exciton formation. These aggregates are formed with a wide range of size distribution. The emission from isolated segments is quenched either by resonant energy transfer, or by migration processes. Also, the main photovoltaic parameters are discussed in connection with the photophysical behavior.

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Leni Akcelrud

Federal University of Paraná

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A. Marletta

University of São Paulo

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Alexandre Marletta

Federal University of Uberlandia

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