The photo-stimulated interdiffusion within chalcogenide based nano-layered structures (NLS) produces large changes in properties, which have potential application in optical pattern recording. The mechanism of these changes is investigated for two NLS consisting of 100 alternate layers of antimony and As2S3, but of different relative thicknesses, by high-resolution X-ray photoelectron spectroscopy. The results suggest the formation of Sb-S bonds at the expense of As-S bonds, with a consequent increase in the refractive index but minimal change in thickness. The role of oxygen in photoinduced transformations, especially in the top layers, is characterized and discussed. (C) 2011 Elsevier B.V. All rights reserved.