Tuning the electronic properties of carbon nanotube thin films through hybrid networks [electronic resource]

Single-walled carbon nanotubes (SWNT), is a well known material which has been continuously investigated for its exceptionally unique optical, mechanical and electrical properties. The nanotubes, which can be semiconducting, metallic or semi-metallic offers a wide range of practical applications for electronics. Recent breakthroughs in studies focusing on the use of SWNT films for large area and cost effective macroelectronics represents the most realistic near-term goal of integrating SW\NT into real world devices. The focus of this study continues to build upon the use of SWNT for such devices while simultaneously investigating the effect of hybrid networks in hopes of fine tuning the electronic behavior. It has been known that the transport within SWNT is largely affected by its surrounding environment and doping can be achieved by means of charge transfer through adsorption of atoms or molecules. Recent investigations have demonstrated that polymer coating of the device may influence the electronic properties of SWNT such as the ability to control the polarity of the device. Further investigation of this phenomenon and practical utilization of hybrid networks may offer new breakthroughs for transistor and transparent conductors. We report an interesting case of photoresponsive organic transistors based on carbon nanotube fullerene composites, where a sparse, solution deposited single walled carbon nanotube network is intimately coated with fullerene molecules. Under correct network formation a reduction in drain current was observed under illumination. Transistors operated in the on-state resulted in drain currents on an order of magnitude of 10^-9 A, under illumination the on-state may be reversed, rendering these devices insulating with drain currents of 10^-12 A. It is believed that the fundamental mechanism for this phenomenon is heavily influenced by the selective formation of fullerene molecules along the carbon nanotube surface/junctions. This results in a two-fold process of exciton splitting and annihilation of free carriers upon recombination followed by subsequent charge trapping which effectively screens the gate voltage. The negative photoresponsivity can be observed even under low voltage operations. High junction resistances which continue to plague the development of highly conductive transparent carbon nanotube networks can be overcome through fine tuning of electronic behavior. Using highly electronegative fluorofullerenes, semiconducting nanotubes can be heavily doped, improving charge transport along the tube while reducing the junction resistance in contact with metallic tubes. Sheet resistances at high transparencies surpassing some of the best reported literature values can be obtained. Combining the largely solution processable approach and the effective tuning of carbon nanotube films through hybrid networks, one may gain additional insight in the field of nanoscaled science and of carbon nanotubes while opening new possibilities in the field of carbon nanotube electronics.

Keywords: Materials Science and Engineering
Advisor: Bao Zhenan advisor. Thesis advisor
Salleo Alberto