We report studies on thin films of a salt doped polymer electrolyte model system. Films of poly(ethylene oxide) with thickness near 1400 Angstrom, doped with lithium triflate salt at salt concentrations ranging from 0 to 40% by weight, were characterised. The high surface to volume ratio of the thin film samples makes them ideal for the study of interfacial effects on the physical properties. The lateral morphology of the system was studied with optical and atomic force microscopy, revealing strong similarities to the bulk system. The composition depth profiles of the ionic species were measured directly using dynamic secondary ion mass spectroscopy (d-SIMS) as well as X-ray photo-electron spectroscopy (XPS) accompanied with ion sputtering. The results are discussed in terms of the possible implications of interfacial effects on practical ionically conducting systems. (C) 2000 Elsevier Science Ltd. All rights reserved.