Structural analysis of the oxidized Cu bilayer on Ru(0 0 0 1) by tensor LEED

A tensor LEED analysis confirms the previously proposed model of a modified Cu2O surface layer forming a (3×2√3)-O/Cu structure on Ru(0 0 0 1). The hexagonal sandwich structure of Cu2O(1 1 1) is modified to wave-like O–Cu–O chains arranged along [1 1 2] directions. The oxidized surface layer exhibits a Ru/Cu–O–O–Cu–O stacking containing half a monolayer of O. The atoms of the interface Cu plane continue the hcp stacking sequence of the Ru substrate, whereas those of the next Cu plane occupy fcc lattice sites. Both Cu planes are buckled with a buckling amplitude of 0.26 Å in each case and the glide-plane symmetry saved. This distortion within the oxidized Cu film leads to a considerable variation of the O–Cu bond lengths compared to the ideal value of 1.85 Å in Cu2O, whereas the spacings between O layers and between center of mass planes of buckled Cu layers exhibit values typical for Cu2O. However, there is a considerable asymmetry of the O–Cu interlayer spacings involved. The best-fit Pendry R-factor (RP=0.45) appears to be acceptable in view of the complexity of the structure and of the restricted quality of the experimental conditions.