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 100 h at 1323 K the emission current density decreases from 6.50 to 0.20 mA/cm² at 7.50 V/mum field strength, while the turn-on field increases from 1.92 to 2.45 V/mum at a current density of 0.1 muA/cm². The C+-ion current in a mass spectrometer has also been measured to compare the CNT evaporation at different cathode temperatures between 1173 K and 1373 K. The results indicate that the CNT evaporation rate increases greatly at temperatures above 1100 K. Scanning electron microscopy (SEM) images show that the emission degradation can be mainly attributed to the decreased value of field enhancement factor beta, which is caused by CNT evaporation.