A critical thickness of similar to 64 nm is observed in epitaxial CeO2 films grown at 750 degrees C on yttrium-stabilized zirconia substrates where optimum ion channeling can be correlated with overall strain relaxation and low surface roughness. Saturation in backscattering yield, enhanced surface roughness, and strain relaxation is clearly evident in thicker films beyond this critical thickness. Despite excellent smoothness with epitaxial growth, films grown at 650 degrees C did not show low backscattering due to high misfit-dislocation density. The results are discussed from the viewpoint of the need for an optimum thickness to develop multilayers with smooth interfaces, low backscattering with overall relaxation. (c) 2006 The Electrochemical Society.