Abstract
The emission currents of zinc oxide (ZnO) and carbon nanotube (CNT) cold cathodes show continuous degradation in sealed field emission (FE) devices when the anode voltages are maintained at a constant value; more stable currents are observed when the same cathodes are operated under ultra-high vacuum (UHV) conditions. This shows that ambient gases in the devices play an important role in degrading the emission currents of ZnO and CNT cathodes. To investigate the gas conditions in sealed FE devices, a vacuum system with a quadrupole mass spectrometer (QMS) was employed here. QMS data obtained before and after the gases in the FE devices were removed showed that the residual gases in the CNT-FE panels were H2, CH4, CO, and Ar, while in the ZnO-FE panels the residual gases were H2, CH4, CO, Ar, and CO2. It was clear that the residual gases in the two kinds of FE devices were slightly different; this was mainly due to the different cathode materials used in the FE devices. The residual gases affected the emission current of the CNT and ZnO FE devices by changing the work function at the cathode surface; this was confirmed by the F-N curves measured when the same cathodes were tested in the devices and in the UHV chamber.
