Eu oxides on Ni(100): Polar surfaces, magic clusters and structures with large lattice dilation

Sub-monolayers of Eu oxide were grown on Ni(100) and analysed by means of in-situ scanning tunnelling microscopy and low energy electron diffraction. For changes of the O2 pressure not more than a factor of two, four different surface phases were found which consist of EuO(111), ‘magic’ clusters and two 2-dimensional nano-layers without a counterpart in bulk Eu oxides. A structural model for one of the latter phases suggests an O–O nearest neighbour (NN) distance of 4.4 Å — considerably larger than the 3.64 Å for bulk EuO.