Observation of Surface Traps and Vacancy Trapping with Slow Positrons

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Abstract
A beam of monoenergetic positrons incident on clean metallic surfaces has been employed to measure positronium yield as a function of sample temperature and positron energy. These results show an increase in the positronium fraction as a function of temperature which is identified as thermally activated detrapping of positrons from a surface trap. Estimates are made of the depths of these traps. Positrons are observed to trap at vacancies and a monovacancy formation enthalpy is extracted from the data utilizing a simple model.