Abstract
Carbon nanotubes (CNTs) are of great interests for a wide range of applications because of their unique structural,
mechanical, electrical, optical, thermal, and chemical properties. Particularly, CNT thin films can be used as
mechanically flexible, electrically conductive, and broadband optically transparent electrodes in various optoelectronic
devices. However, one crucial obstacle to implementing CNT-based applications has been the unavailability of pure
CNTs suitable for direct industrial use. The as-produced CNTs are very fluffy soot, and thus extremely difficult to be
handled in the device fabrication process. Although CNTs can be grown directly on a substrate from the catalyst
deposited on the substrate surface, the growing temperature is very high, typically > 900°C, which represents a big
challenge to device fabrication and integration. Another issue is that the catalyst on the substrate surface must be
removed without affecting the grown CNTs. In the raw CNT soot, there is always a considerable amount of impurities,
including metallic particles from the catalyst and carbonaceous impurities from the chemical reaction by-products. Such
impurities can greatly degrade the properties of CNT thin films. The production of electronic-grade CNT aqueous
solutions, which contain only individually suspended pure CNTs without any kind of surfactant, is a critical milestone
for implementing CNT-based applications. By using such solutions, pure CNT thin films of various densities can be
formed through common solution-casting processes, such as spin coating, spray coating, micro-dispensing, and ink-jet
printing. The properties of these pure CNT thin films will be discussed in this paper.
