Method for the measurement of positron affinities and positron work functions suitable for both positive and negative work function materials

The positron affinity A+, defined by A+ + Φ− + Φ+ = 0, where Φ− (Φ+) refer to the electron (positron) work functions, is a fundamental property of solids which is useful for the determination of the behavior of positrons in multicomponent systems. For systems with a negative positron work function it is often possible to estimate the positron work function and affinity by measuring the energy of positrons re-emitted from the surface. However, this method will not work in those cases for which the positron work function is positive. While the positron affinity may, in principle, be determined in these cases from positronium time-of-flight measurements, such measurements are technically difficult. In this paper, a new method for the determination of positron affinities and positron work functions will be outlined. This method, which is based upon measurements of the cut-off energy in positron-induced secondary electron spectra, is of particular interest in that it may be used in cases where the positron work function is positive.