Berlin 2005 – scientific programme
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O: Oberflächenphysik
O 40: Adsorption an Oberfl
ächen IV
O 40.3: Talk
Tuesday, March 8, 2005, 11:15–11:30, TU EB202
Hydrogen-induced relaxations in epitaxial Ni-films on Cu(001) — •W. Meyer1, M. Krause1, A. Klein1, S. Müller1, L. Hammer1, K. Heinz1, D. Sander2, and J. Kirschner2 — 1Lehrstuhl für Festkörperphysik, Universität Erlangen-Nürnberg, Staudtstr. 7, D-91058 Erlangen — 2Max-Planck-Institut für Mikrostrukturphysik, Weinberg 2, D-06120 Halle/Saale
We have investigated the atomic structure and morphology of epitaxial Ni-films on Cu(001) in the coverage regime 2-12 monolayers (ML) as well as their changes upon hydrogen adsorption. Quantitative Low-Energy Electron Diffraction (LEED) and Scanning Tunnelling Microscopy (STM) were applied in-situ. The STM studies show layer-by-layer growth in the coverage range up to 5 ML while thicker films exhibit an increased roughness. The LEED structure determinations reveal a tetragonal distortion (-3.1% on average) of the hydrogen-free Ni-films very close to the predictions of elastic theory (-3.2%). For all coverage values the first layer spacing is reduced even further (by -4.5%). Yet, by adsorption of 1 ML of hydrogen it increases to a value larger than that of deeper spacings whereas the latter are rather unaffected, i.e. the films subsurface tetragonal distortion remains.
The LEED fit allows to detect also the hydrogen atoms. They reside in the 4-fold hollow sites at 0.3 Å above the top Ni layer. It has been proposed that these H-induced changes are also decisive for the accompanied spin reorientation-transition from in- to out-of-plane [1].
[1] D. Sander, W. Pan, S. Quazi, J. Kirschner, W. Meyer, M. Krause, S. Müller, L. Hammer, K. Heinz, Phys. Rev. Lett., in press