AVS 47th International Symposium
    Material Characterization Tuesday Sessions
       Session MC-TuP

Paper MC-TuP2
Secondary Ion Emission from Well Defined Molecular Overlayers Under Molecular Primary Ion Bombardment

Tuesday, October 3, 2000, 5:30 pm, Room Exhibit Hall C & D

Session: Poster Session
Presenter: D. Stapel, University of Muenster, Germany
Authors: D. Stapel, University of Muenster, Germany
A. Benninghoven, University of Muenster, Germany
Correspondent: Click to Email
Molecular primary ions have been shown to enhance the yield Y(X@sub i@@super q@) of organic secondary ions considerably. The simultaneous increase in the corresponding damage cross section @sigma@(X@sub i@@super q@) is much smaller. This holds in particular for thick molecular samples like LB multilayers or polymers. For LB multilayers we found yield increases up to a factor of 1000, when changing from Ar@super +@ to SF@sub 5@@super +@ bombardment. This phenomenon is important for practical analytical applications of TOF-SIMS, because yields, damage cross sections, and the resulting ion formation efficiencies E=Y/@sigma@ determine the achievable sensitivity as well as the achievable lateral resolution. In recent years we have investigated in some detail this secondary ion emission behavior for a variety of LB layers under atomic and molecular primary ion bombardment. Basic studies were performed with three series of LB layers (n = 1, 3, 5, 7, 9; n : number of monolayers) under 0.5 - 11 keV Ne@super +@, Ar@super +@, Xe@super +@, O@sub 2@@super +@, CO@sub 2@@super +@, SF@sub 5@@super +@, C@sub 7@H@sub 7@@super +@, C@sub 10@H@sub 8@@super +@, C@sub 6@F@sub 6@@super +@ and C@sub 10@F@sub 8@@super +@ bombardment. Y(X@sub i@@super q@) as well as @sigma@(X@sub i@@super q@) were determined. We found a more pronounced Y and E enhancement for multilayers (n>1). Y, @sigma@ and E increases with increasing mass of atomic primary ions and with growing number of constituents up to 6 heavy atoms. Y, @sigma@ and E features a saturation behaviour for molecular primary ion species containing more than 6 atoms. We could not find an influence of the chemical composition of the primary ion on this enhancement under static SIMS conditions. We found that the molecular secondary ions are emitted from the 1@super st@ and 2@super nd@ layer and a pronounced decrease in Y and E was determined for 1 keV SF@sub 5@@super +@ bombardment.