AVS 46th International Symposium
    Applied Surface Science Division Friday Sessions
       Session AS-FrM

Paper AS-FrM1
LEIS Measurement of Target Mass in the Presence of Inelastic Energy Losses@footnote 1@

Friday, October 29, 1999, 8:20 am, Room 6A

Session: New or Improved Surface Related Analytical Techniques
Presenter: R. Bastasz, Sandia National Laboratories
Authors: R. Bastasz, Sandia National Laboratories
J.A. Whaley, Sandia National Laboratories
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Low-energy ion scattering (LEIS) is often used to identify the elements present on a surface. Peaks observed in the energy spectrum of scattered ions can be assigned to specific target masses. However, the usual kinematic expression that relates the energy of a scattered projectile to a target atom mass does not account for inelastic losses, such as ion neutralization/reionization and excited state formation, which can significantly affect the scattered-ion energy. We have developed a simple method for unambiguously determining target atom mass from LEIS measurements regardless of the amount of inelasticity in the collision. Analysis of the scattering kinematics with an included inelastic loss term shows that the scattered particle velocities form a circle in the polar coordinate system (v@sub n@,@theta@), where v@sub n@ is the normalized scattered-ion final velocity and @theta@ is the laboratory scattering angle. While the circle radius changes with the degree of inelasticity, the circle center depends only on the target-to-projectile mass ratio. So, by measuring ion energy spectra at three or more scattering angles, it is possible to construct the appropriate scattering circle, find its center, and deduce the target mass. The only assumption in the method is that inelastic losses are not a function of the impact parameter. This assumption appears reasonable at typical observation angles, as can be illustrated with several examples of inert-gas scattering from low-Z metal surfaces. @FootnoteText@ @footnote 1@ This work was supported by the US Department of Energy under contract DE-AC04-94AL85000.