KILOELECTRON VOLT CLUSTER IMPACTS - PROSPECTS FOR CLUSTER-SIMS

This paper describes part of our continuing efforts in examining the a bility of polyatomic or 'cluster' projectiles to improve secondary ion yields in SIMS. Negative secondary ion yields resulting from keV bomb ardment of lanthanum and bismuth oxide projectiles (composition (M2O3) (m)MO+) were measured and compared for both organic and inorganic targ ets. Each metal oxide projectile produces an increase in secondary ion yield when compared to the same number of Cs+ projectiles at similar energies. In addition, the nonlinear increase in secondary ion yield p er number of constituent atoms in the primary ion is compared for poly atomic projectiles within a given metal oxide series. The high seconda ry ion yields combined with efficient time-of-flight mass analysis tra nslate into prospects for SIMS under 'superstatic' conditions, which s hould be particularly attractive for the detection of organics. In con sidering analytical applications it must be recognized that when a pro jectile becomes more efficient at ejecting molecular or quasimolecular ions (intact emission), it may also become more efficient at 'manufac turing' ions (recombination processes). Moreover, the number of molecu les destroyed per analyte-specific secondary ions detected varies with projectile characteristics. The challenge for the practice of 'cluste r-SIMS' is to optimize the projectiles for maximizing sensitivity and eventually limit-of-detection. (C) 1998 Elsevier Science B.V.