FabricaÃÃo e caracterizaÃÃo elÃtrica de heterojunÃÃes de polianilina-silÃcio para aplicaÃÃo em dosimetria de radiaÃÃo gama

AUTOR(ES)
DATA DE PUBLICAÇÃO

2004

RESUMO

In this work a technique has been developed to fabricate high quality polyanilinesilicon heterojunction diodes for use as gas and/or ionizing radiation sensors. Polyaniline thin films (40 nm thick) produced by spin-coating on silicon substrates, were the active part of the junction structure. The devices presented excellent reproducibility of their electrical characteristics with high rectification ratio, 60,000 at Â1.0 V, and typical reverse current at - 1.0 V of 3 nA at 295K. A G/I x G plot has been used to analyze the currentâvoltage characteristics, yielding typical series resistance of 4 kΩ Â 5% and ideality factor in a range of 1,9 Â 0.5%. The heterojunction diode presents high sensitivity to gamma radiation in the dose range of 3 x 10-2 to 7 kGy with a linear response in the forward and reverse bias. The excellent electrical characteristics together with the linear response with the dose, strongly suggest the application of this device for spectrometry or dosimetry of high doses of gamma radiation. These devices presented high sensitivity to gas moistures such as ammonia, nitric acid and trichloroethylen. In both cases the sensitivity was observed through shifts of the current-voltage curves, which can be easily monitored to provide a calibration curve of the sensor either as a radiation dosimeter or as a gas sensor for use in applications for gas monitoring or radiation dosimetry. Several aspects of the reliability physics of siliconâpolyaniline heterojunction, such as degradation effects induced by local heating, charge trapping and temperature changes, have been discussed. These results further confirm the quality of the devices electrical characteristics and their suitability for radiation and gas sensors applications. Another interesting results presented in this work was the use of polyemeraldine nanofilms (thickness in the range 30-50 nm) deposited by âspin coatingâ on glass substrates as an optical dosimeter for gamma radiation based on the color change of the polymer. The nanofilms devices were characterized by UVvisible absorption spectroscopy. The deep blue color, characteristic of undoped polyaniline films before irradiation, becomes subsequently green as the film is being irradiated, and the film absorption coefficient exhibits a linear dependence with the logarithm of the irradiation dose from 1 to 10 kGy

ASSUNTO(S)

engenharia nuclear dosimetria de radiaÃÃo gama polianilina-silÃco heterojunÃÃes

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