Structural transformation of CsI thin film photocathodes under exposure toair and UV irradiation

Transmission electron microscopy has been employed to study the structure o f polycrystalline CsI thin films and its transformation under exposure to h umid air and UV irradiation. The catastrophic degradation of CsI thin film photocathode performance is shown to be associated with the film dissolving followed by its re-crystallization. This results in the formation of large lumps of CsI crystal on the substrate surface, so that the film becomes di scontinuous and Its performance as a photocathode is permanently degraded. No change in the surface morphology and the film crystalline structure was observed after the samples were UV irradiated. (C) 2000 Elsevier Science B. V, All rights reserved.