Field emission from a nanocrystalline graphite/carbon nanotube emitter from room temperature to 1000 °C

Summary form only given. Field emitters, either in metallic or carbon-based form are of great interest for displays, sensors, microwave, terahertz and free electron laser applications amongst others. Since at high current densities, the individual emission sites, which are only of nm² dimensions can heat significantly above room temperature, we performed a systematic evaluation of nanocrystalline graphite/carbon nanotube emitters ranging from room temperature to 1000°C. The emitter material, which was deposited on a 1 cm × 1 cm silicon chip was placed on a custom made heater. The anode, consisting of a 1.625 mm diameter copper rod was placed 250 μm above the emitter material. Current measurements were taken from 10 μA to 500 μA at 20, 200, 400, 600, 800 and 1000°C. Short-term current fluctuations were also recorded. The maximum current density obtained is 35 mA/cm². For this experiment, we did not test at higher current densities to avoid potential damage of the emitter. At a current of 10 μA, the extraction field is 8 V/μm and increased to about 13 V/μm at 500 μA. The measurements were performed at an initial pressure of 1 × 10^-6 Torr which increased by an order of magnitude at temperatures exceeding 600°C due to out-gassing of the heater. From the Fowler-Nordheim plots we conclude that emission is strictly field emission over the entire temperature range without any indication of thermally assisted field emission at elevated temperatures. The short-term current fluctuations ΔI/I recorded were 20 % and 0.8 % for I=10 μA and 500 μA at 20°C, respectively and decreased to 5 % and 0.4 % at I=10 μA and 500 μA at 800°C, respectively, even though the pressure increased by an order of magnitude. (Current fluctuations increase with pressure). An interesting observation was made during these - easurements. A bluish glow was observed right above the emitter surface for currents above 200 μA. This glow was not observed at the higher temperatures but could have been masked by the reddish glow of the emitter chip and the heater. In the talk, the data mentioned above and additional data will be reviewed in detail and we hope that we will be able to present the spectrum of this glow and be able to offer an explanation of its origin. Current fluctuations will also be presented as a function of pressure.