DOUBLY-CHARGED ION EMISSION IN SPUTTERING OF LANTHANUM TRIFLUORIDE

Sputtering of LaF3 surface by singly charged rare gas ions (Ar+, He+) and Cs+ ions with impact energies between 100 and 5500 eV has been per formed. The emission of La+, La2+ and F+ was measured by quadrupole ma ss spectrometry. Whereas the energy distribution of F+ resembles an E- 2 dependence, the energy distributions of both singly charged and doub ly charged lanthanum ions resemble E-2 distribution multiplied by the term exp(-const./v(perpendicular-to)). At the same time, no threshold of the primary projectile energy characterizing the kinetic emission m odel has been found. We explain the production of singly and doubly ch arged lanthanum ions by a partial neutralization of their +3 lattice v alency through the electron tunneling mechanism. For He+ bombardment t he emission of lanthanum ions gives similar qualitative results. Howev er, the yield of F+ is substantially enhanced by an interatomic Auger neutralization process between lattice F- ion and the primary projecti le [1].