Charge transport under illumination in mesoporous continuous films

Recent developments in the preparation of surfactant-templated mesostructured sol-gel silica materials have extended the morphology from the originally discovered powders, with particle sizes on the order of microns, to mesoporous continuous thin films. These films could find applications in membrane-based separations, selective catalysis and sensors. Particularly, sodium dodecyl sulfate (SDS)templated sol-gel films formed by the rapid dip-coating sol-gel method possess highly ordered lamellar phase structure. The interest in the potential applications of these films and the introduction of new properties lead to the research of their chemical modifications. The improvement of their photorefractive response requires a knowledge of the microscopic processes as the charge transport mechanism. The photoconductivity technique provides information about that mechanism, and it allows measuring the transport parameters. Mesoporous continuous films were prepared by the dip-coating method on glass substrates. The films were doped with SDS, carbazole (SiK) and dispersed red one (DR1) at 1:20:20 molar concentration. Photoconductivity studies were done on them at different illumination wavelengths in order to know the transport mechanism and surfactant influence. The electric field versus current density plot shows a linear behavior, i.e. an ohmic response. The conductivity slope dependence with the polarization time shows a gaussian behavior. And there is an exponential decay from the absorption coefficient with the accumulated polarization time. Interpretation of these results is presented and the obtained charge transport parameters are reported. Key word: Mesoporous films, thin films, photoconductivity, sol-gel., dip-coating.