Electrical properties of various single-wall carbon nanotube networks

Abstract

This thesis investigates conduction mechanisms of covalently and non covalently functionalised single wall carbon nanotube (SWCNT) networks. Unlike previous strategies where diamines were used, a novel route to covalently bridge SWCNTs by organic molecular linkers is proposed. The bridging relies on using modified Sonogashira and Ullmann couplings, which have the advantage of using spectroscopic evidence to ascertain the success of the bridging. Platinum-enriched SWCNTs were produced by coordinating Pt to pyridine ligands grafted on SWCNTs. Networks of covalently bridged SWCNTs, Pt-enriched SWCNTs and their SWCNT precursors were fabricated by vacuum filtration. In addition to these networks, networks of non covalent ly functionalised SWCNTs were built up using layer-bylayer (LbL) deposition. This second approach required the wrapping up of SWCNTs by ionic surfactants to exploit their electrostatic interactions.
Electrical properties, such as current- voltage and the current dependence on temperature and electrode separation are discussed for both filtered SWCNT and SWCNT LbL networks. Combined analyses of these characteristics were carried out to identify dominant conduction mechanisms. In this study, a modified quantum tunnelling model was proposed to best describe the in-plane electrical behaviour of the filtered SWCNT networks. As for SWCNT LbL networks, the in-plane conduction was shown to be governed by the Poole-Frenkel mechanisms while direct tunnelling dominates the out-of-plane conduction. Furthermore, the charge storage capacity of cut-SWCNT LbL networks integrated into metal- insulator-semiconductor devices are discussed in view of organic memory device applications.