Photoemission from CsILiF and CsINaF films, enhanced by exposure to water vapour

We report here on the UV-induced photoemission from CsI photocathodes coated with LiF or NaF films. A considerable enhancement of the quantum efficiency was found after contact with water vapour. We interpret this effect as a decrease of the electron affinity of LiF and NaF, induced by adsorption of polarized H2O molecules.