This article reports on the formation of iron nitrides during nitrogen ion irradiation of Fe/Si bilayers at room temperature. The 30 nm Fe-57/Si bilayers were prepared by pulsed laser ablation and irradiated with 22 keV N2+ ions at fluences of (0.6-2)x 10(17) ions/cm(2). The structural changes and phases formed by irradiation were analyzed by Rutherford backscattering spectroscopy (RBS), X-ray diffraction analysis (XRD) and conversion electron Mossbauer spectroscopy (CEMS). The results clearly show the formation of several iron nitrides. At the lower fluences, the samples contain a mixture of epsilon-Fe2+x N and alpha-Fe with nitrogen interstitials. For the highest fluence, the paramagnetic epsilon-Fe-2 N (61%) phase predominated. It can be concluded that the elemental iron almost fully transforms to an iron-nitride layer, but that no iron silicides are formed. (C) 2003 Elsevier B.V. All rights reserved.