STRUCTURE AND GROWTH OF ULTRATHIN IRON FILMS ON NI CU(001)/

The structure and growth of ultrathin iron films on pseudomorphic Ni/C u(100) was investigated by low and medium energy electron diffraction (LEED and MEED), respectively. A similar sequence of superstructures a s previously found for Fe/Cu(100) was observed. With growing film thic kness a (4x1)-, a (2x1)- and a pseudo ''(3x1)''-phase are found. Our f ull-dynamical LEED analysis of the (2x1) phase reveals a structure tha t very closely resembles the unusual (2x1)-phase on Fe/Cu(100). We fin d a considerable expansion to 1.880 Angstrom for the first interlayer spacing, while deeper layers have an interlayer spacing of 1.78 Angstr om, characteristic for cubic fee iron. This implies that magnetic live surface layers should also exist for fee iron on Ni/Cu(100). Small de viations in the structure and growth of Fe on Ni/Cu(100) as compared w ith Fe on Cu(100) can be attributed to the roughness of the underlying nickel films. (C) 1998 Elsevier Science B.V.