Growth mode and oxidation state analysis of individual cerium oxide islands on Ru(0001)

• Cerium oxide is grown on ruthenium inside a low-energy electron microscope (LEEM).
• The identified carpet growth mode is shown to determine the oxide island shape.
• Intensity-voltage LEEM is demonstrated to be sensitive to oxidation state changes.
• The oxidation state is found to be laterally homogeneous on the nanometer scale.
• Ceria islands of the same oxidation state may have different substrate registries.

The growth of cerium oxide on Ru(0001) by reactive molecular beam epitaxy has been investigated using low-energy electron microscopy (LEEM) and diffraction as well as local valence band photoemission. The oxide islands are found to adopt a carpet-like growth mode, which depending on the local substrate morphology and misorientation leads to deviations from the otherwise almost perfect equilateral shape at a growth temperature of 850 °C. Furthermore, although even at this high growth temperature the micron-sized CeO2(111) islands are found to exhibit different lattice registries with respect to the hexagonal substrate, the combination of dark-field LEEM and local intensity-voltage analysis reveals that the oxidation state of the islands is homogeneous down to the 10 nm scale.