Transition of Electron Field Emission to Normal Glow Discharge

The field emission (FE) properties of single walled carbon nanotube (SWCNT)/graphene hybrid samples were investigated for high currents in dc mode and pulsed mode with pulse-ON times between 0.2 and 400 ms and duty cycles between 1% and 80% with stainless steel anodes. Our dc measurements showed a transition to glow discharge (GD) already at currents larger than 10 mA. The pulsed I-V characteristics with up to 400-mA maximum current were limited by the cathode resistance, consisting of the emitting layer resistance and the contact resistance, which was found to be between 1.1 and 1.4 kQ. A constant-voltage behavior arises after subtracting the cathode resistance. This constant-voltage behavior, the observed glowing during FE, and time-resolved measurements give evidence for the transition of Fowler-Nordheim-type FE to FE enhanced GD. FE enables a soft transition to normal GD without the need of an ignition voltage. The buildup dynamic and the time constants of the transition to GD were evaluated and discussed. The FE and GD behaviors were also compared using copper and molybdenum anodes.