Berlin 2008 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 32: Oxides and Insulators: Clean Surfaces

O 32.9: Vortrag

Dienstag, 26. Februar 2008, 15:00–15:15, MA 042

Stress of CoO(111) on Ir(100) — •Zhen Tian, Dirk Sander, and Juergen Kirschner — Max-Plank Institute of Microsctructure Physics

An important aspect of epitaxial oxide films is that the growth of (111) oriented films with rock salt structure leads to polar surfaces, where adjacent layers are composed of either anions or cations only. Considerable repulsive Coulomb interaction within the oxide (111) layers are therefore expected [1]. We measured the stress change during the formation of CoO(111) on Ir(100) by post-oxidation of Co films [2]. Combined structural investigations by LEED and stress measurements by the crystal curvature technique are performed. The formation of the CoO(111)-c(10×2) structure by post-oxidation of 2 monolayers Co induces a compressive surface stress change of −0.5 N/m. The epitaxial Co film prior to oxidation is under a tensile stress of +16 GPa, which is induced by the lattice misfit between fcc-Co and Ir. The formation of the CoO(111) film induces a tensile stress change of +2.1 N/m, as compared to the clean Ir(100) surface. This stress change is quantitatively ascribed to the anisotropic misfit between the c(10×2) structure of CoO(111) and Ir(100) of +0.22 % and +4.2 % along Ir[110] and Ir[110], respectively. Our stress measurements indicate that charge depolarization effects [3] might be operative on the CoO(111)-c(10×2) film.

[1] C. Noguera, J. Phys.: Condens. Matter 12 (2000) R367-R410.

[2] C. Giovanardi, L. Hammer, and K. Heinz, Phys. Rev. B 74, 125429 (2006).

[3]C. Tusche, H. L. Meyerheim, and J. Kirschner, Phys. Rev. Lett. 99 (2007) 026102.