Ab initio study of field emission from carbon nanotubes

An ab initio computational method has been developed to simulate the field emission from nanostructures based on the time-dependent Schrodinger equation. Electronic structures of realistic systems are calculated within the ab initio pseudopotential formalism and emission currents are obtained through a direct integration of the electron dynamics under external field for both singlewall and multiwall carbon nanotubes. In each nanotube, three distinct states are identified to contribute to the current: pi, pi*, and localized states. For most conventional metallic tips, extended states (like pi or pi* states) are the main source of the current. For carbon nanotubes, however, our quantum-mechanical calculation indicates that the currents associated with the localized state account for most of the total emission current.