AVS 46th International Symposium
    Applied Surface Science Division Monday Sessions
       Session AS1-MoA

Paper AS1-MoA8
Static SIMS with Polyatomic Primary Ions

Monday, October 25, 1999, 4:20 pm, Room 610

Session: Molecular Mass Spectrometry including Interpretation
Presenter: A. Benninghoven, Universität Münster, Germany
Authors: A. Benninghoven, Universität Münster, Germany
D. Stapel, Universität Münster, Germany
O. Brox, Universität Münster, Germany
B. Burkhardt, Universität Münster, Germany
H.F. Arlinghaus, Universität Münster, Germany
C. Crone, Universität Münster, Germany
M. Thiemann, Universität Münster, Germany
Correspondent: Click to Email
Polyatomic primary ion bombardment results in an increase in secondary ion yields Y and damage cross sections @sigma@ in such a way that the ion formation efficiency E = Y/@sigma@ increases. Investigated samples include metal and semiconductor surfaces (Ag, Si, GaAs) in different oxidation states, bulk and spin coated polymers with additives (PET, PC, PI, PP, PTFE, PMMA, PEG), SA- and LB - mono and - multilayers (thioles, arachidic acid on Au, PMA on Ag), hydrocarbon contamination layers on Si and GaAs, monolayers of biomolecules on Ag and other substrates, and biopolymers, technical polymers and pharmaceuticals isolated in an organic matrix. They have been bombarded by a variety of primary ions in the keV range O, Ne, Ar, Xe, O@sub 2@, CO@sub 2@, SF@sub 5@, C@sub 7@H@sub 7@, C@sub 10@H@sub 8@, C@sub 6@F@sub 6@ and C@sub 10@F@sub 8@. For atomic primary ions we found an increase in secondary ion yields with increasing mass of the primary ion, but only relatively small increases in efficiency. Compared with atomic ion bombardment, molecular primary ion bombardment always results in a yield and efficiency enhancements. No significant influence of the chemical composition of the primary ions on secondary ion yields has been observed, as long as static SIMS conditions were met. Yield and efficiency enhancements show saturation behaviour for primary ions composed of more than 6 (heavy) atoms. We found a strong dependence of the enhancement effects on the considered secondary ion species and a smaller averaged secondary ion emission depth for molecular primary ion bombardment. We will summarize our experimental results and will discuss them in the frame of a simple model. Whereas yield and damage cross section enhancements can be explained - at least partially - by an increase in sputter yields, the observed increase in ion formation efficiencies for molecular primary ions indicates a more efficient ionization process for polyatomic primary ion impact.