Conduction and TSC Properties of LB Films Adsorbing Cyanine Dyes

Abstract

The electric properties were investigated for phosphatidic acid (PA) LB films adsorbing cyanine dyes (NK-3) with sandwich electrodes. PA LB monolayers adsorbing the dyes and the monolayers of Cd salt without the dyes are deposited using subphases, containing various concentrations of the dyes and cotaining CdCl2 instead of the dyes, respectively. Conduction currents are measured at room temperature for the PA LB film devices. Increases in the conduction currents are observed in the LB films containing the dyes. Furthermore, the conduction currents remarkably increase using the Au upper electrode. The current (I) vs. voltage (V) properties nearly follow the Poole conduction, log(I)-V. Therefore, the conduction currents are very complicated and are thought to be due to composite mechanisms in the film and at the interface. TSC measurements are used to examine the dipolar polarizations in the PA LB films, in the temperature region between 150K and 300K. Remarkable increase of TSCs are observed above 260K for the devices containing the dyes. The TSCs are caused by the dipolar polarizations, and increase with the quantity of the dyes contained in the LB devices and/or aggregations of the dyes. The results are useful for applications of ultrathin film devices in the future.