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

Abstract

The surface structures of CoO(111) films epitaxially grown on $\text{Ir}(100)\ensuremath{-}(1\ifmmode\times\else\texttimes\fi{}1)$ are investigated by means of quantitative low-energy electron diffraction and scanning tunneling microscopy. A $(\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3})R30\ifmmode^\circ\else\textdegree\fi{}$ superstructure is revealed for the films' ground states. It appears for film thicknesses $\ensuremath{\ge}10\text{ }\text{\AA{}}$ 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.