In the processing of materials, notably for nanostructures for functional properties, processing induces strains resulting in accommodation by mechanical relaxation processes (elastic, plastic, transformations, fracture) which modify the properties. Examples are given here for magnetic thin films (media, heads) and diffusion-induced defects in doped silicon, with emphasis on their microstructures using transmission electron microscopy (TEM). The characterization of these materials and their mechanical properties are essential if their functional properties are to be understood and optimized. (C) 2003 Elsevier Ltd. All rights reserved.