Monodisperse carbon nanomaterials for thin film electronics.

摘要

Carbon nanomaterials such as carbon nanotubes and graphene are being explored for a number of applications that exploit their outstanding electronic, optical, mechanical, and chemical properties. These nanomaterials possess characteristic dimensions of approximately 1 nm and have properties that can differ dramatically based on changes in their physical structure that occur on a fraction of this length scale. Consequently, small variations, or polydispersity, in the structure of carbon nanomaterials cause their behavior to be unpredictable and have precluded their widespread use in electronic and optical applications. In this thesis, I employ density gradient ultracentrifugation to address the polydispersity problem for carbon nanotubes and graphene. This technique uses amphiphilic surfactants to establish differences in the buoyant density of carbon nanomaterials as a function of their physical and electronic structure. These minute differences in the buoyant density of the nanomaterials lead to variations in their equilibrium positions inside a density gradient following ultracentrifugation. By employing different surfactant chemistries, carbon nanotubes can be produced that are monodisperse in a number of structural parameters, such as diameter, chiral handedness, electronic type (metallic or semiconducting), and wall number. In addition, graphene with well-defined atomic layer thickness can also be isolated using density differentiation. To demonstrate the utility of these unique materials, I incorporate monodisperse carbon nanomaterials into thin film networks that exploit their enhanced electronic and optical properties. Transparent conductors consisting of highly conductive metallic carbon nanotubes, long double-walled carbon nanotubes, or density-refined graphene exhibit lower sheet resistances at higher optical transmittance levels than polydisperse carbon nanomaterial films. Moreover, thin film field-effect transistors composed of semiconducting carbon nanotube networks are shown to offer performance parameters that exceed those of conventional organic electronic materials. These results demonstrate that monodisperse carbon nanomaterials are promising candidates for future applications in thin film electronics.