Phys. Rev. B, 79 121403 (R) (4pp) (2009)

## Superstructure in the termination of CoO(111) surfaces: Low-energy electron diffraction and scanning tunneling microscopy

W. Meyer, K. Biedermann, M. Gubo, L. Hammer, K. Heinz

Lehrstuhl für Festkörperphysik, Universität Erlangen-Nürnberg Staudtstr. 7, D-91058 Erlangen, Germany

Abstract
The surface structures of CoO(111) films epitaxially grown on Ir(100)-(1x1) are investigated by means of quantitative low-energy electron diffraction and scanning tunneling microscopy. A ($\sqrt{3}\times\sqrt{3})R30^\circ$ superstructure is revealed for the films' ground states. It appears for film thicknesses > 10\$\,\AA\ both for strained and unstrained films and so most likely applies also to the (111) surface of a bulk CoO crystal. The superstructure is interpreted as a stress-relieving reaction to the switch from rocksalt-type to wurtzite-type stacking below the surface which has been detected earlier.