Brightness of electron beam emitted from a single pentagon on a multiwall carbon nanotube tip

A capped multiwall carbon nanotube with a clean surface gives field emission patterns consisting of six pentagonal rings corresponding to pentagons located at the tip. To evaluate the optical properties of a single pentagon as an electron source, the I-V characteristics and angular current densities for a single clean pentagon have been measured by probe-hole-type field emission microscopy. Reduced brightness estimated from the angular current density and the geometrical size of the pentagon reached ∼5.6 × 10 9 A m -2 sr -1 V -1 at an emission current of 53 nA. This value is one order of magnitude or more higher than that of an individual multiwall carbon nanotube field emitter reported by Jonge et al.