Epitaxially stabilized iron monosilicide films wit the CsCl structure (B2-FeSi) have been investigated by conversion electron Mossbauer spectroscopy and x-ray diffraction. A detailed investigation of the elastic strain in these metastable layers is presented. Using hyperfine interaction information the tetragonal distortion of the silicide lattice could be quantified for layers as thin as 14 Angstrom. A general tendency for strain relaxation with increasing layer thickness is observed. (C) 2004 American Institute of Physics.