Carbon based conductive thin film : fabrication, properties and application

Abstract

Transparent conductors are increasingly becoming important components in electronic devices due to the growing demand for devices such as LED, LCD, and touch screens. In particular, the common transparent conductor, Indium tin oxide (ITO), has become increasingly expensive due to limited supplies of the raw material, thus creating the need for an alternative to this material. Carbon nanotubes (CNT) were thoroughly studied in this research to determine if they could be the replacement material for ITO.

In this research, two types of sample were used: CNT solution and CNT thin films. Three kinds of material property were investigated from the samples: electrical (conductivity), optical (raman spectra or UV-vis absorption spectra) and physical properties (morphology). The first investigation was dedicated to optimization of transparent conductive

film fabrication method. The focus of the first investigation were on feedstock quality,

composition formula, deposition methods and solutions properties. Afterwards, a study of the correlation between electrical property and optical property was carried out. Out of several reported mathematical models that could describe the correlation between conductivity and transmittance of conductive films, one model, namely the thin metallic film model was verified to be a suitable mathematical model for CNT films. That model could describe the behavior of CNT films well except in certain conditions where semiconducting nanotubes content in solution exceeds 90 %. Apart from that, a study on the effects of different metallic and semiconducting nanotube mixture was also presented, as it was believed previously that metallic semiconducting junctions are the crucial factor in CNT films, although our results proved otherwise.

The next topic of investigation was on how to improve carbon nanotube films conductivity through doping, as the present state of carbon nanotube film conductivity is still far inferior compared to Indium Tin Oxide (ITO). A new doping mechanism and new doping agents were presented in this research. Acid treatment of

carbon nanotubes, which was previously thought to be a chemical attachment or surfactant removal, proved to be a proton attachment instead. With that argument, a new dopant, the piranha mixture, was found to be a stronger dopant.

Finally, after studying the film fabrication, investigating the film physics, improving the conductivity of CNT films by doping, and obtaining a highly conductive carbon nanotube films, these films were tested by some simple devices.