Miniature X-ray Tubes Utilizing Carbon-nanotube-based Cold Cathodes

The electron field-emission properties of carbon nanotubes enable the fabrication of cold cathodes for a variety of vacuum device applications. The utilization of these cathodes is an attractive alternative for the replacement of thermionic or hot cathodes for generating X-rays. Miniature X-ray tubes have been fabricated using triode-style carbon nanotubebased cathodes. In this paper we report the results of characterization studies, such as beam current dependence on the control gate voltage. Also, results on focal spot measurements and electron-beam modeling allow the possibility of reducing focused spot sizes. Driving gate voltages below 1000 volts for easy pulsing has been achieved, and the extended lifetime data suggests that a regulated power supply would be ideal for a constant AC operation mode. The 1mm focal spot size achieved so far is suitable for most XRF applications.