This article reports on the formation of iron nitrides during nitrogen ion irradiation of Fe/Si bilayers at room temperature. The 30 nm 57 Fe/Si bilayers were prepared by pulsed laser ablation and irradiated with 22 keV N 2+ ions at fluences of (0.6-2)×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 Mössbauer spectroscopy (CEMS). The results clearly show the formation of several iron nitrides. At the lower fluences, the samples contain a mixture of ε-Fe 2+x N and α-Fe with nitrogen interstitials. For the highest fluence, the paramagnetic ε-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. © 2003 Elsevier B.V. All rights reserved.