Features and mechanism of H- anion emission from 12 CaO x 7 Al2O3 surface.

The hydrogen anion (H-) and other anionic species (O-, OH-, e-) in the gas phase, emitted from the synthesized crystal surface of 12CaO·7Al2O3−H- (C12A7−H-), have been observed. The emission intensity of all the anionic species strongly depends on the sample surface temperature and the extraction field. H- has the highest emission branch ratio, and the extraction field can reduce its apparent activation energy. H- emission current at a μA/cm2-level has been achieved, which is about 4 orders of magnitude higher than that obtained from the thermal desorption process of CaH2. The observed anions of H- and OH- are attributed to their migration from the C12A7−H- cages onto the surface [i.e., Y-(cages) → Y-(surface) → Y-(gas phase) (Y = H, OH)]. The weak O- and electron emission would both arise from the dissociation of O2-:  O2-(surface) → O-(surface) + e-(surface) → O-(gas phase) + e-(space).