Dissociative thermal-electron attachment at a surface: CN− emission from nitrogen ion irradiated graphite

We report an observation of strong thermal-emission of CN− ions from nitrogen ion irradiated graphite surface. Careful monitoring of thermal desorption of both neutral and charged species demonstrates that the desorbed nitrogen-containing species is dominated by N2 and C2N2 molecules and emission of CN− occurs as a consequence of dissociative thermal-electron attachment to C2N2 molecules at the surface. An activation energy of 5.0±0.2 eV for ionization is derived from the temperature dependence of the CN− yield which is related to the surface work function governing the surface thermal-electron emission.