Roles of deformation and interaction: Formation of 1 ML subsurface oxygen occupation under Ru(0 0 0 1)

Abstract

Oxygen incorporation into subsurface until the formation of 1ML subsurface oxygen occupation in Ru(0001) surface is investigated by density-functional theory. Changes in deformation energy of substrate and interaction energies among various parts within adsorption system during oxygen penetration into subsurface are discussed as a function of subsurface oxygen coverage. Results show that oxygen adsorption and diffusion on surface contribute to the penetration process, and the preferred on-surface coverage for oxygen penetration is close to 1.0ML. With increasing pre-occupied subsurface oxygen coverage, both diffusion barrier and penetration barrier decrease before the last oxygen incorporation on (2×2) Ru(0001) slab, which makes subsequent oxygen incorporation easier than the first one. In the case of penetration process, deformation energy and interaction energy between penetrating atomic oxygen and the topmost Ru layer, two incompatible items in penetration barrier, play decisive roles only for the first oxygen penetration but not for subsequent ones. The amplitude in height fluctuation of the topmost Ru layer regulates the penetration barrier strictly by enhancing the validity of substrate deformation, which could indicate the important role of steps or defects for oxygen incorporation and CO oxidation as proposed by experiments.