The low energy ion assisted control of interfacial structure: ion incident angle effects

It is difficult to maintain smooth unmixed interfaces during the vapor deposition of giant magnetoresistive multilayers, especially as the number of layers is increased. Recent atomistic modeling of normal incident angle ion impacts with model Ni/Cu/Ni multilayer surfaces have indicated that low energy (3 eV) inert gas ion bombardment significantly reduced the roughness of Cu on Ni interfaces without causing interlayer mixing. Higher ion energies (12 eV or above) were necessary to achieve similar smoothing of the Ni on Cu interface, but this was accompanied by extensive mixing between the surface Ni atoms and the underlying Cu atoms by an impact ion induced exchange mechanism. Here, molecular dynamics simulations have been used to explore the effect of varying the incident ion angle during 12 eV Ar+ and Xe+ ion bombardment of a model Ni on Cu surface. The results indicate that increasing the incident ion angle up to 70° reduced the probability of intermixing while retaining most of the surface flattening effect seen in the previous study. A low combination of interfacial roughness and intermixing was obtained for an incident ion angle of approximately 60°. The heavier Xe+ ions were found to transfer more momentum to the surface atoms than the lighter Ar+ ions, and resulted in significantly more mixing at all angles of incidence.