Effect of evaporation on the field emission of a carbon nanotube cathode

Evaporation of carbon nanotubes (CNT) cathodes and the degradation of its field emission are reported in this paper. After 100h at 1323K the emission current density decreases from 6.50 to 0.20mA/cm
²
at 7.50V/µm field strength, while the turn-on field increases from 1.92 to 2.45V/µm at a current density of 0.1µ/cm
²
. The C+-ion current in a mass spectrometer has also been measured to compare the CNT evaporation at different cathode temperatures between 1173K and1373K. The results indicate that the CNT evaporation rate increases greatly at temperatures above 1100K. Scanning electron microscopy (SEM) images show that the emission degradation can be mainly attributed to the decreased value of field enhancement factor β, which is caused by CNT evaporation.