Análise dos efeitos de diferentes atmosferas sobre a fotocondutividade do Co3O4

Abstract

In this monograph, the effects of different atmospheres on the photoconductivity of Co3O4 were analyzed. For this purpose, with a Co3O4 sample set inside a cryostat filled with the selected atmosphere, its photoresponse was measured, comparing the current flowing through it without any illumination with the current after the increase in electrical conductivity caused by the incidence of light. The atmospheres of atmospheric air, synthetic air, argon, nitrogen, oxygen and vacuum were chosen for this analysis. Considering the fact that Co3O4 has a double bandgap configuration, for each atmosphere two lasers of different wavelengths were used to illuminate the sample, aiming to excite the electrons from the valence band to the bands related to each bandgap separately. Comparing the photoresponse measurements for each atmosphere, a clear influence on the photoconductivity of the sample was noticed. For illumination with the two different wavelengths, considerably lower photoresponses and longer response times were obtained for atmospheres with oxygen and nitrogen gases when compared to argon and vacuum atmospheres. This is explained by the fact that oxygen and nitrogen react with Co3O4, adsorbing to its surface, capturing the free electrons and thus reducing the photoconductivity of the sample, while this does not happen for vacuum and argon atmospheres, as they are not reactive. The different photoresponses and response times obtained for different atmospheres indicate the possibility of using Co3O4 in applications such as gas sensors.