Abstract
A well-characterized Sn(100) sample was examined with monoenergetic positrons before and after exposure to oxygen. The positronium formation at the surface was measured as a function of sample temperature, incident positron energy, and oxygen exposure. The positronium fraction increased both with sample temperature and oxygen exposure, but decreased with increasing incident positron energy. Positronium formation from thermally activated detrapping of the positron from the surface state is observed providing an estimate of the positron binding energy to this surface state. No change was found in the positronium fraction when the Sn(100) crystal was exposed to hydrogen suggesting a lack of interaction between hydrogen and Sn. In all of the above cases positronium was emitted but no positron re-emission was observed; this result suggests a negative positronium work function but a positive positron work function.
Published Version
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