ATOMIC AND ELECTRONIC-STRUCTURE OF FE FILMS GROWN ON PD(001)

The atomic and electronic structure of Fe films grown on Pd{001} is investigated by means of low-energy electron diffraction and angle-resolved photoemission spectroscopy (ARPES). The films grow pseudomorphically, probably by way of nucleation and growth of flat islands, which ultimately coalesce to form continuous Fe{001} films. The structure of these continuous films, if grown at slow rates (of the order of 0.1 angstrom/min), is body-centered tetragonal and is shown to be a distortion from the stable bcc structure of Fe: the in-plane lattice constant is 2.75 angstrom, as dictated by the Pd{001} substrate, and the bulk interlayer spacing is 1.50-1.53 angstrom. In 10-12-layer films the first interlayer spacing is expanded by 3.6% above bulk, but with increasing thickness that spacing contracts progressively to about 6.3% below the bulk value in 40-50-layer films. Films as thick as 60-70 layers can be grown pseudomorphically at slow rates despite the large misfit (4.2%) between bcc Fe{001} and fcc Pd{001}. ARPES data indicate that these films are electronically indistinguishable from bulk bcc Fe. Thick (about 200-layer) films grown at fast rates are essentially bcc, with in-plane lattice constants of 2.87 angstrom, but with slightly expanded (3%) interlayer spacing, attributed to the presence of carbon impurities.