Department of Physics
North Carolina State
University
Raleigh, NC 27695-8202
Thermionic
emission sources that operate at temperatures less than 800C may prove
appropriate for many applications such as thermionic energy converters,
microwave amplifiers, CRTs and even light sources. While there has been substantial study of cold cathode emission from
diamond/carbon surfaces, the properties that will lead to thermionic emission
may be quite distinct. In this study,
we employ a high resolution electron emission microscope that has the
capability to image the emission from a film surface at temperatures up to
1200C. The results show fundamentally
different character for thermionic emission from high quality diamond films and
films with substantial nanocrystalline diamond. The electron emission of B-doped diamond, N-doped diamond and
highly disordered nanocrystalline diamond are imaged at temperatures up to
1000C. For only the N-doped films, the
results show a large increase in emission at temperatures of ~600 C. The temperature where emission is observed
is dependent on the N-doping and the film growth conditions. In all cases the
emission is uniform over the entire surface, which is characteristic of
conduction band emission. The emission
stability is also dependent on the surface termination. We discuss approaches to optimize the
material properties to affect the device performance.
Keywords:
electron emission, thermionic emission, nanocrystalline, N-doped