Wafer-scale films of aligned single-wall carbon nanotubes: preparation, characterization, and optoelectronic applications
Doctor of Philosophy
Single-wall carbon nanotubes (SWCNTs) are one-dimensional materials defined by a cylindrical and hollow structure with aspect ratios of up to 10^7:1. Individual SWCNTs have been shown to possess excellent electric, optical, thermal, and mechanical properties that are promising for electronic and optoelectronic device applications. However, when they are assembled into macroscopic objects such as films and fibers, these unique properties tend to vanish, primarily due to disorder. Hence, methods are being sought for fabricating ordered SWCNT assemblies for the development of high-performance devices based on SWCNTs. In this dissertation, we present two methods for preparing highly aligned SWCNT films with excellent optoelectronic properties. The first method is based on vertically aligned SWCNT arrays grown by water-assisted chemical vapor deposition. We transferred these arrays to desired substrates to form horizontally aligned SWCNT films and created p-n junction devices that worked as flexible, room-temperature-operating, and polarization-sensitive infrared and terahertz photodetectors. The second method is based on our discovery of spontaneous global alignment of SWCNTs that occurs during vacuum filtration of SWCNT suspensions. By carefully controlling critical factors during vacuum filtration, we obtained wafer-scale, monodomain films of strongly aligned SWCNTs. By measuring polarization-dependent terahertz transmittance, we demonstrated ideal polarizer performance with large extinction ratios. The universality of this method was confirmed by applying it to diverse types of SWCNTs, all of which showed exceptionally high degrees of alignment. Furthermore, we successfully fabricated aligned SWCNT films enriched in one specific chirality by combining our new method with an advanced nanotube sorting technique: aqueous two-phase extraction. Transistors fabricated using such films showed very high conductivity anisotropies and excellent on-off ratios.
aligned carbon nanotubes; self-assembly; vacuum filtration; photodetectors; FET