Oxygen adsorption and ordering onRu(101¯0)

The dissociative oxygen chemisorption on the $\mathrm{Ru}\left(101\mathrm{}¯0\right)$ surface has been studied by monitoring the changes of the $\mathrm{O}1s$ and $\mathrm{Ru}{3d}_{5/2}$ core levels and by measuring the evolution of the diffraction pattern during oxygen exposure at 270 K. The sensitivity of core level binding energies to different geometrical configurations, together with the measurements of the oxygen-induced diffraction spot profile along the [0001] and $\left[12¯10\right]$ directions, permit us to follow the details of formation of the $c(2\mathrm{}\times 4)$ and the $(2\mathrm{}\times 1)p2mg$ ordered structures.