Negative secondary ion emission from NaBF4: Comparison of atomic and polyatomic projectiles at different impact energies
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(CsI)(n)Cs+ (n = 0-2) and C60+ projectiles were used to bombard a sodium tetrafluoroborate (NaBF4) target at energies ranging from 18 to 28 keV. The objective of these experiments was to monitor the emission of two series of secondary ions following atomic and polyatomic projectile impacts. One series is based on BF4- and its incorporation into larger polyatomic ions that reflect the stoichiometry of the original solid. The other series is based on repeating (NaF) units, and presumably represents artifact ions created by primary ion impact induced recombination/rearrangement reactions. The relative yields of several secondary ions representing both types of ion formation were measured as a function of the primary ion velocity (velocity is proportional to the kinetic energy per mass unit). When normalized to the number of projectile constituents, the secondary ion yields follow distinct trends. The non-linear increase in the yield of (NaF)F- demonstrates greater sensitivity to the number of projectile constituents than intact, analytically useful ions such as BF4- and(NaBF4)BF4-.
