End potential barriers of single-walled carbon nanotubes and their role in field emission

Very short single-walled carbon nanotube (SWNT) models carrying a net negative charge are employed to simulate tube tips in field emission situations and then, density-functional theory calculations are carried out on these models to obtain their potential barrier shapes and electric-field distributions. These results, incorporated with the SWNT band structures, are used to analyze field emission properties of SWNTs. It is shown that theoretically, low applied voltage (about ten and several volts) might generate emission current as large as 100 nanoamperes from a single SWNT, and closed end geometries lead to a better emission effect, due to their higher electron energy. In addition, limitations of the adopted theoretical approach are discussed, along with its possible improvement.