Pulsed laser deposited ZnS bare and SnO2 coated ultra thin films were subjected to prolonged electron beam bombardment with 2 keV energy and a steady 44 mA/cm(2) current density, in I X 10(-6) Torr 02 pressure backfilled from a base pressure of 3 x 10(-9) Torr at room temperature. Auger electron spectroscopy (AES) was used to monitor changes of the surface chemical composition of both the bare and coated phosphor films during electron bombardment. Degradation was manifested by the decrease of sulphur and accumulation of oxygen on the surface of the bare phosphor. However, with the SnO2 coating this phenomenon was delayed until the protective SnO2, was depleted on the surface through dissociation and reduction. (c) 2007 Elsevier B.V. All rights reserved.