AVS 50th International Symposium
    Magnetic Interfaces and Nanostructures Wednesday Sessions
       Session MI+TF-WeA

Paper MI+TF-WeA5
Adsorption-induced Giant Stress and Surface Relaxation in Ni/W(110)

Wednesday, November 5, 2003, 3:20 pm, Room 316

Session: Magnetic Thin Films
Presenter: H.L. Meyerheim, Max-Planck-Institut f. Mikrostrukturphysik, Germany
Authors: H.L. Meyerheim, Max-Planck-Institut f. Mikrostrukturphysik, Germany
D. Sander, Max-Planck-Institut f. Mikrostrukturphysik, Germany
R. Popescu, Max-Planck-Institut f. Mikrostrukturphysik, Germany
O. Robach, ESRF, France
S. Ferrer, ESRF, France
J. Kirschner, Max-Planck-Institut f. Mikrostrukturphysik, Germany
Correspondent: Click to Email
Surface stress has been recognized as a decisive factor, which determines a variety of phenomena like self-assembled pattern formation on the nano-scale, shape evolution of nano-objects and surface reconstruction. Our work reveals an important aspect of adsorbate-induced stress which might be of key importance for the general understanding of stress-strain relations in the monolayer range. We identify an intimate correlation between structure and stress from an in-situ combination of surface x-ray diffraction and stress measurements. We show that one atomic layer of Ni induces substantial lateral shifts of the top W-atoms of up to 0.5 Å. At this coverage we measure an anisotropic change of the surface stress induced by Ni. The experiments were carried out at the ESRF in Grenoble (France). Surface stress was measured by the crystal curvature technique.@footnote 1@ From earlier experiments@footnote 2@ it is known that Ni forms a c(1x7) superstructure on W(110) at a coverage above 0.8 monolayers (ML, 1ML=1.41x10@super15@ atoms/cm@super2@). Up to 0.8 ML the stress measurements indicate compressive stress along [001] and tensile stress along [1-10]. The emergence of the c(1x7)-structure coincides with the formation of compressive stress along [1-10]. The x-ray analysis shows that the Ni-atoms form a distorted densely packed hexagonal adlayer. However, the most important and astonishing aspect is the pronounced shifts (up to 0.5 Å) of the first layer W-atoms out of their bulk positions along [1-10]. The structure consists of alternating Ni-W-Ni-chains running along [1-11]. In conclusion we have measured a substantial adsorbate-induced relaxation in a system, which is generally considered to be structurally inert upon adsorbate deposition. There is a striking correlation between the onset of lateral shifts of atomic positions and compressive surface stress. @FootnoteText@@footnote 1@D. Sander et al. Rev. Sci. Instr. 66, 4734 (1995); @footnote 2@D. Sander et al. Phys. Rev. B57, 1406 (1998).