Dresden 2006 – scientific programme
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O: Oberflächenphysik
O 11: Epitaxy and growth I
O 11.5: Talk
Monday, March 27, 2006, 16:00–16:15, WIL A317
Growth and structure of ultrathin Ni-films on Ir(100)-(1×1) — •W. Meyer1, B. Gumler1, A. Klein1, A. Schmidt1, L. Hammer1, S. Müller1, K. Heinz1, and J. Redinger2 — 1Festkörperphysik, Universität Erlangen-Nürnberg, Staudtstr. 7, D-91058 Erlangen — 2Center for Computational Material Science, Vienna University of Technology, Gumpendorferstr. 1A, A-1060 Vienna
We report on the growth and atomic structure of epitaxial Ni-films on the metastable (1×1)-phase of Ir(100) in the coverage regime 1 - 4 ML using STM, quantitative LEED and first principle calculations. The lateral misfit for Ni on the Ir(100) substrate is +8.8% so that layer-by-layer growth should not be expected. The STM studies reveal flat growth of the first Ni-layer whilst the second film layer does not close completely but third layer islands start to grow. It comes as a surprise that the films return to an almost ideal layer-by-layer growth for the 3 and 4 ML coverages. Quantitative LEED was applied to determine the atomic structure of the surfaces. The Ni-films are heavily tetragonally distorted with an average contraction of 12.3% of the inner film layers and 14.4% for the top layer spacing relative to the Ni bulk value. The experimental observation can be understood in combination with the DFT calculations: The surface formation enthalpy for the 2 ML film is less favourable than a combination of 1 ML and 3 ML islands. For higher film thickness surface roughening does not yield a sizable energy gain. Hence, only formation of a 2 ML film is energetically hindered. The relaxed film structure calculated by DFT agrees well with the LEED results apart from the top layer spacing for which DFT predicts an enhanced contraction.