The onset of sub-surface oxidation induced by defects in a chemisorbed oxygen layer

We investigate the onset of internal oxidation of a Cu(110) surface induced by oxygen subsurface adsorption via defects in the Cu(110)-(2 × 1)-O chemisorbed layer. The presence of a boundary formed by merged add-row structure domains due to a mismatch of half unit-cell leads to preferred oxygen adsorption at the subsurface tetrahedral sites. The resulting distorted Cu-O tetrahedra along the domain boundary have comparable bond length and angles to those of the bulk oxide phase of Cu2O. Our results indicate that the presence of defects in the oxygen-chemisorbed adlayer can lead to the internal oxidation via the formation of Cu2O-like tetrahedra in between the topmost and second outermost atomic layers at the oxygen coverage θ = 0.53 and the second and third outermost atomic layers at θ = 0.56. These results show that the internal oxidation of a metal surface can occur in the very beginning of the oxygen chemisorption process enabled by the presence of defects in the oxygen chemisorbed layer.