Comparison of Field Emissions from Side Wall and Tip of an Individual Carbon Nanotube

Electrons are generally emitted from the tip of a carbon nanotube (CNT) when the CNT stands on a substrate, but it is not clear where electrons are emitted when a CNT is bent or lies down on a substrate. We have investigated the field emission properties of the side wall of a multi-walled carbon nanotube (MWNT) compared with that of the tip of a MWNT. We also calculated electric field intensities at the side wall and the tip of a MWNT using the finite element method. The turn-on voltage is 150 V for the tip and 570 V for the side wall of the MWNT, which is consistent with calculations indicating that the intensity of the electric field concentrated on the tip of a CNT is 2.8 times larger than that on the side wall of a CNT shaped like a loop. This suggests that the field emission is predominantly from the tips of CNTs in a field emitter. However, the emission current from the side wall is larger than that from the tip of MWNTs.