Ejection of Electrons from Barium Oxide by Noble Gas Ions

Electron ejection from BaO by accelerated singly charged ions of noble gases (except Kr) is investigated experimentally. BaO crystals used for the measurements are of two kinds: those annealed at 850°C and those activated by glow discharge in a noble gas. Measurements of the total yield, γ, and of the energy distribution of ejected electrons are made for ions in the kinetic energy range from 30 to 600 ev. For each kind of the ion, γ increases remarkably with increasing kinetic energy of the ions, and at the same time the electron energy distribution spreads greatly. γ also depends on the state of the BaO surface and this occurs through a change in population of low energy part of the ejected electrons. Reflection of primary ions as ions at the BaO surface is very small (<0.5%) for ionic energies less than 100 ev. A part of electrons ejected by slow ions can be accounted for by the theory of Auger electron ejection from the valence band of BaO. The enlargement of the electron energy distribution with ion kinetic energy is explained by an increase in repulsive potential between O - and the incoming ion.