Large hysteresis effect in surface ionization of Cs due to bulk diffusion

Abstract

The flux from a Cs Rydberg source, with a carbon covered Ir foil as the emitter of Cs∗, is investigated using surface ionization detection. The surface ionization detector has a Re ribbon as the detecting part. The temperature hysteresis is investigated, and a novel high temperature hysteresis effect is observed. The hysteresis at low temperature is not well described by the standard theory. Both effects are explained if diffusion of Cs into the Re surface is taken into account. With the detector at short distance from the source, the hysteresis is large and the threshold temperatures are low, which is at variance with the standard theory. This behaviour is due to the very rapid in-diffusion of Rydberg states, as is demonstrated by using the source at comparable densities without the Ir foil. The desorption energy for Cs from polycrystalline Re is reported to be around 3.3 eV.