Temperature dependence of positron and positronium emission from metal surfaces

Abstract

Positron and positronium emission are measured as a function of temperature at negative and positive positron work function surfaces. At negative work function surfaces, the reflection of the thermal positron from the attrative surface potential barrier is demonstrated. The transition rate of 103 ms−1 was estimated for the capture into the surface state and, at room temperature, also for e+ and PS emission. A clear difference in the temperature dependence of Ps formation is found between Ag(100) and Ag(111) surfaces, both having a positive work function. This can be explained by invoking a new mechanism of capture into the surface state. Phonon‐assisted capture into the excited, Rydberg‐like precursor states is proposed.