Dresden 2009 – scientific programme

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O: Fachverband Oberflächenphysik

O 3: Oxides and insulators I

O 3.1: Talk

Monday, March 23, 2009, 11:15–11:30, SCH A01

(√3×√3)R30^∘ Superstructure in CoO(111) Surfaces — •Wolfgang Meyer, Kerstin Biedermann, Matthias Gubo, Lutz Hammer, and Klaus Heinz — Lehrstuhl für Festkörperphysik, Universität Erlangen-Nürnberg, Staudtstr. 7, 91058 Erlangen

CoO(111) films of thicknesses 10-150 Å were prepared by using a Ir(100)-(1×1) surface as a support. At all thicknesses they exhibit a (√3×√3)R30^∘ superstructure with respect to the hexagonal unit cell of CoO(111). The latter is slightly distorted below the thickness of about 15 Å (due to the films’ accommodation to the quadratic unit cell of the Ir substrate) but relaxes to ideal hexagonal symmetry at larger thickness. Thereby, however, the in-plane lattice parameter only gradually approaches that of bulk CoO (3.012 Å) – at a thickness of about 150 Å it is still (but only) 0.6% above that.

Though the (√3×√3)R30^∘ structure reversibly transforms to a (1×1) phase with temperature increasing beyond 50^∘C it must be considered as the CoO films’ ground state structure. As the thick films exhibit a lattice parameter rather close to that of bulk CoO(111) one can assume that the (√3×√3)R30^∘ termination is intrinsic to CoO(111). This makes the crystallography of the surface even more interesting and, in the light of that, we have investigated it by quantitative LEED and atomically resolved STM. It turns out that the CoO(111) surface is metallic and terminated by a wurtzite-type stacking of layers (as retrieved earlier [1]), whereby the atoms within the unit cell undergo a layer dependent buckling or trimerization.

[1] W. Meyer et al., Phys. Rev. Lett. 101 (2008) 016103