Stainless steel films doped with various amounts of nitrogen were deposited on (100) silicon wafers by radio frequency magnetron sputtering of an austenitic stainless steel target in argon and nitrogen gas mixtures, containing a range of nitrogen compositions. The evolution of phases as a function of nitrogen doping was studied by X-ray diffraction and transmission electron microscopy. It was found that with increasing nitrogen composition in the gas mixture, the crystalline structure of the films changed from bcc ferrite (alpha), to expanded fcc austenite (gamma(N)) supersaturated with nitrogen, and finally to the MN type nitride (Fe0.69Cr0.2Ni0.1Mo0.01)N phase with ideal cubic symmetry and further enlarged lattice. This MN type phase has a fee structure with a lattice parameter about 0.433 nm and possibly possesses the zinc blende type lattice structure. The morphological features of the single MN phase films produced are also discussed in this paper. (C) 2004 Elsevier B.V. All rights reserved.