Time dependent conductive behavior of the layer-by-layer self-assembled SnO2 nanoparticle thin film

The understanding of the electrical conductivity properties of polyion/nanoparticle thin film assemblies has long-term impact for exploring the unique electrical properties in applications such as sensor, actuator and conductive coating. This paper reports on the observations of the time dependent conducting behavior of the SnO2 thin film produced by layer-by-layer self-assembly. The thin film consists of 5 layers of polyion matrix and 12 nm SnO2 nanoparticles that are adsorbed in an alternating sequence. The electrical current flowing through such thin film is not stabilized immediately, but instead increases with time until saturation. We further find a threshold current that is required to trigger the current self-enhancing process. It is hypothesized that the self-heating of the semiconductive nanoparticle explains this phenomenon. Based on this hypothesis, a hybrid channel is designed to completely eliminate this effect. This fundamental study may find applications in different gas and biomedical sensors and transparent electronics.