  Combination of neutron and X-ray reflectometry was used to study the vertical
structure of 100 nm-thin copper films with implanted oxygen ions of energy E =
[10-30] keV and doses D=[0.2-5.4]x$10^{16}$ $cm^{-2}$. The study shows that
oxygen ion implantation with an energy of E = 30 keV leads to the formation of
a 3 nm thick layer on the surface. Density and copper/oxygen stoichiometry of
the observed surface layer are close to $Cu_2O$ oxide. We attribute the $Cu_2O$
oxide formation to highly mobilized copper atoms generated by stimulated ion
implantation.
