Electrical and morphological study of carbon nanotubes/polyaniline composite films: A model to explain different tunneling regimes induced by a vertical electric field

The way carbon nanotubes can modify the charge transport of organic materials may open opportunities for new uses. However, the understandings of many intrinsic physical properties associated to those changes are still poor. Here, we report our investigation on the properties of (PAni) and PAni/carbon nanotubes (CNTs) composites obtained by innovative interfacial polymerization method at room temperature. We have used spectroscopic methods (XPS, Raman) and microscopy (SEM) to obtain relevant parameters to combine with our electrical modeling and describe properly the transport characteristics of neat polymer and its composites with carbon nanotubes in different ratios. The devices were prepared in planar field effect transistor (FET) geometry to study the tunneling injection of charge carriers under the influence of the vertical component of a crossed electric field. We found that the tunneling injection is significantly improved using the PAni/CNT composite. This effect is related to morphological changes of the PAni film synthesized in the presence of CNTs, where the PAni polymerization on CNT's surface produces tubular structures covering them. Due to the CNT's high aspect-ratio, there is electric field amplification near to their tips that enhances the tunneling injection from the metallic contacts under the influence of the vertical field. We propose a theoretical model that can predict the electric field intensity of the transition. The number of tube's tips with different amplification factors (β) produces different regimes of tunneling injection in samples with moderate CNT concentration. We then propose a theoretical model that can predict the electric field intensity of the transition between those regimes: essentially it happens when the tunneling current produced by a few junctions with strong β is greater than the current produced by the higher number of junctions with low β. However, as the CNT density increases, the enhancement of the tunneling injection decreases due to electric field screening.