Mixing and corrosion in Ni implanted with Pt through a sacrificial layer of alumina

Sputtering is a significant problem in the high-dose implantation of heavy ions, limiting the achievable peak concentration. To increase the retained dose, a target can be coated with a thin sacrificial layer of low sputtering yield, which slowly erodes while protecting the target during an implant. Metal oxides have low sputtering yields, making them prime candidates for use as sacrificial layers. The focus of this work was the assessment of the performance of Al2O3 as a sacrificial layer when Pt is implanted into Ni targets. Also investigated were the ion-beam mixing and corrosion behaviour of the samples. The mixing of sacrificial layer material into Ni is significantly reduced for Al2O3 compared with Al; the difference between Al and Al2O3 mixing can be explained in terms of the differences between their thermodynamic parameters. Corrosion resistance measurements show a substantial difference between Pt-implanted and unimplanted samples; at the lowest implant doses of (0.1-0.2) x 10(17) Pt ions cm(-2), the corrosion rate is reduced by about a factor of ten relative to that of unimplanted Ni. At higher Pt doses, less corrosion protection is observed. It is proposed that, at higher doses, ion-beam mixing causes Ni to be bound into intermetallic compounds; with less elemental Ni available to form an NiO passive layer, the corrosion rate increases.