Analysis of carbon nanotube fibers for use as field emission cathodes

摘要

There has been a recent resurgence of interest in the development of high power microwave and terahertz (THz) sources and amplifiers. High power microwave and THz amplifiers have the potential to vastly improve a number of applications: high data rate communications, concealed weapon and threat detection, remote high resolution imaging spectroscopy of airborne chemicals, and biomedical diagnostics. Recent field emission (FE) studies of carbon nanotube fibers composed of carbon nanotubes (CNTs), have exhibited significantly higher currents at lower applied electric fields than previously studied materials. A number of methods for the growth, densification and improvements to the morphology of the CNT fibers have been studied and these efforts have exhibited improvements in the FE current, current densities, and consistency in performance over time at different applied biases and gap distances. Current-voltage characteristics measured from the CNT fibers have been successfully fit with the Fowler-Nordheim equation. However, field enhancement factors determined by fitting current-voltage characteristics have been shown to be inconsistent with theory and electrostatic simulations. SEM and optical images of the fiber tips have shown damage sites due to plasma formation near the cathode tip. Analysis of the resulting plasma has begun in order to determine the exact processes involved in damaging the CNT fibers.