Ionic conduction currents and TSCs in self-assembled monolayers

Ultrathin films were formed from two non-conjugated polyelectrolytes, polyallylamine (PAH) and polystyrenesulfonate (PSS), using a self-assembly process. It was found that these self-assembled monolayers (SAMs) have excellent layered structure from their optical absorption spectra. The films were deposited in solutions with various polymer concentrations and the condition for stable deposition was obtained. Current vs. electric field properties of the devices showed hopping conduction. The conduction was considered to be due to migration of mobile ions in the sample; this was supported by the temperature dependence of transient currents. Furthermore, thermally stimulated currents (TSCs) also suggested ionic space charge polarization. Although the origin of the mobile ions is not clear, the existence of sodium in the films is observed in electron spectroscopy for chemical analysis (ESCA). The humidity, i.e. the water in the devices, also has a great influence on the electrical properties.