Characterization of carbon nanotube field emitters in pulsed operation mode

Carbon nanotubes (CNTs) are promising candidates as electron sources for novel x-ray tubes. Short pulses, high emission currents, and long-term stability are prerequisites for practical applications in medical x-ray imaging. Here, the authors present field emission from CNTs in pulsed operation mode exhibiting very high stability for 200 cumulative hours and a maximum current of 126 mA corresponding to 202 mA/cm² at an applied field of 9.3 V/μm. They investigated the correlation of classical emitter characteristics such as threshold field and field enhancement factor to the long-term stability and maximum emission current. This correlation was found to be rather poor. Instead, they observed a steady voltage increase for a fixed current during lifetime experiments. This observation allowed to derive a degradation parameter which determines the emitter quality for pulsed applications. Detailed investigations of the degradation in dependency of pressure, duty cycle, and pulse-on time were performed to predict the stability and lifetime of CNT-based field emitters.