Structural elements in the oxidation process of a single cobalt layer on Ir(100)-(1×1)

Abstract

The ordered phases developing in sequence by oxidation of a single monolayer of cobalt deposited on Ir(100)-$(1\ifmmode\times\else\texttimes\fi{}1)$ were investigated by low-energy electron diffraction (LEED), scanning tunneling microscopy, and thermal desorption spectroscopy. It turns out that the structural elements of the different phases observed for increasing oxygen content and analyzed by quantitative LEED are pyramids based on squares or triangles made up by cobalt species and oxygen on top. The Co-O bond lengths are smaller than in the bulk of cobalt oxide owing to the reduced coordination of oxygen. For O:Co ratios of $r=1/4$, 1/2, and 5/8, the bonding of the oxide to the iridium substrate is merely by the cobalt species, and at $r=1$ it is via both Co and O.