1. Length-Dependent Dielectric Polarization in Metallic
Single-Walled Carbon Nanotubes
Liwei Chen, Department of Chemistry and Biochemistry, Ohio University
Carbon nanotubes (CNTs) are potentially ideal materials for nanoelectronics and alternative energy devices due to their fast charge carrier transport, ultra-high surface area, and great chemical and thermal stabilities. It is known that these properties are dependent on the chirality and diameter of the tubes — some nanotubes show metallic behavior, while others are semiconducting. A bottleneck that currently limits the realization of CNT’s full potential in these applications is the fact that as-synthesized CNTs are mixtures of metallic and semiconducting species. These two types of nanotubes are usually separated based on differences in dielectric properties — the capacity to repel electric fields — because metallic nanotubes show a stronger response than semiconducting carbon nanotubes of comparable diameter. An in-depth investigation on CNT dielectrics is critically important to understand the CNT responses to external fields and external charge perturbations, which will help us to to efficient separation of metallic from semiconducting tubes and ultimately improve alternative energy devices.
We found that the dielectric response of metallic nanotubes decreases with decreasing length, and becomes indistinguishable from that of semiconducting nanotubes below 200 nm. The results demonstrate that length also needs to be taken into consideration when separating carbon nanotubes. The implications of these results go beyond separation.
We developed a new method to study the electric properties of nanomaterials contactlessly.
We overcome the difficulty to measure very short nanotubes and obtain statistically meaningful data.
We found that defects at the ends of the nanotubes will affect the electric properties of short tube.