A new mechanism responsible for the enhancement of local electric field onthe surface of emitting carbon nanotubes

Aligned carbon nanotube (CNT) films exhibit excellent electron emission pro perties at very low fields. This has been attributed to the high aspect rat io of CNTs, i.e. their emitting surface can have high local field due to ge ometrical enhancement. It is found that a new mechanism can be responsible for the enhancement of the local field on the emitting surface of CNTs. Thi s results from the space charge in the vacuum gap, which is readily generat ed due to the high emission current density, of CNTs. Details are given of both experimental and theoretical studies of this effect. The mechanism als o accounts for the distinct nonlinearity in Fowler-Nordheim plots often obs erved with CNTs. The implication of the technical application of our findin gs is also included.