Carbon nanotube bundle-based cold cathodes for THz tube sources

We have developed high-current density field emission sources using arrays of multi-walled carbon nanotube bundles as electron sources required for THz vacuum tube sources. We have found that the arrays of 1-/spl mu/m and 2-/spl mu/m diameter nanotube bundles spaced 5 /spl mu/m apart (edge-to-edge spacing) form the most optimum combination, routinely producing 1.5 to 1.8 A/cm/sup 2/ at low electric fields of approximately 4 V//spl mu/m, rising to > 6 A/cm/sup 2/ at 20 V//spl mu/m over a /spl sim/ 100-/spl mu/m-diameter area. We have found that the field emission performance depends strongly on the bundle diameter and interbundle spacing and such arrays perform significantly better in field emission than other arrangements of nanotubes previously reported in literature.