Cobalt oxide nanolayers on Pd(100): The thickness-dependent structural evolution

The growth of interface-stabilized cobalt oxide (CoO_x) nanolayers on Pd(100) has been investigated and their structures are reported as a function of coverage. Several different phases have been observed by LEED and STM experiments, and they have been characterized spectroscopically by photoemission and X-ray absorption. The data indicate that in the low coverage regime (up to Θ_Co ≈ 2–3 ML) rock-salt CoO type phases are formed (defective in the single layer regime, and stoichiometric in multilayers) with (100) or (111) termination. At higher coverage (Θ_Co ≈ 10–20 ML) spinel Co₃O₄(111) and CoO(100) layers have been detected, in ratios dependent on the preparation conditions. The observed structures are discussed in relation to similar structures reported recently for CoO_x films on Ir(100) [W. Meyer et al., J. Phys.: Condens. Matter 20 (2008) 265011].