AVS 45th International Symposium
    Applied Surface Science Division Thursday Sessions
       Session AS-ThA

Paper AS-ThA9
Secondary Ion Emission from Molecular Surfaces and Overlayers under Noble Gas and Molecular Primary Ion Bombardment

Thursday, November 5, 1998, 4:40 pm, Room 307

Session: SIMS - Depth Profiling and Molecular Surface Analysis
Presenter: D. Stapel, Universität Münster, Germany
Authors: D. Stapel, Universität Münster, Germany
A. Benninghoven, Universität Münster, Germany
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By changing from atomic to molecular primary ions, considerable increases in secondary ion yields Y(X@sub i@@super q@) are achieved, in particular for molecular surfaces and overlayers. In an earlier paper@footnote 1@ we report on yield increases up to a factor of 1000 for polymer surfaces under 10 keV SF@sub 5@@super +@ bombardment. The corresponding increase of damage cross sections @sigma@(X@sub i@@super q@) is relatively small, so that the increase in ionization efficiencies E(X@sub i@@super q@) = Y(X@sub i@@super q@)/@sigma@(X@sub i@@super q@) remains high. This has important consequences for the analytical application of molecular SIMS - for spectroscopy as well as for imaging and microarea analysis. For further yield optimization and for a better understanding of this yield enhancement by the use of molecular primary ions, we carried out systematic investigations for different polymers, metals and semiconductor materials, covered by a variety of molecular overlayers as biomolecules, additives, LB- and SA-layers, etc. Comparing molecular (SF@sub 5@@super +@ , C@sub 7@H@sub 7@@super +@, C@sub 10@H@sub 10@@super +@, ...) and atomic (Ar@super +@, Kr@super +@, Xe@super +@) primary ion bombardment we found for nearly all of the investigated molecular surfaces and overlayers a strong increase in molecular ion yields, a much smaller increase in the corresponding damage cross sections, and smaller secondary ion emission depths. Experimental results will be presented and will be compared with model calculations. @FootnoteText@ @footnote 1@ F. Kötter, A. Benninghoven, Appl. Surf. Sci., in press