9.1: Negative electron affinity ultra-nano crystalline diamond based thermionic electron emitters for low to moderate temperature operation

Diamond based electron sources utilize two key materials properties presenting a method of efficient electron emission. Negative electron affinity (NEA) characteristics of diamond surfaces, where the vacuum level is positioned below the conduction band minimum eliminates the surface emission barrier. With suitable dopants, an electronic band configuration can be achieved resulting in a low effective work function. We have prepared nitrogen-doped diamond emitter structures by plasma assisted chemical vapor deposition. These materials exhibit a low effective work function of about 1.3 eV with detectable thermionic electron emission at temperatures lower than 250°C.