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 h eavy ions, limiting the achievable peak concentration. To increase the retained dose, a target can be coated with a thin sacrificial layer o f low sputtering yield, which slowly erodes while protecting the targe t during an implant. Metal oxides have low sputtering yields, making t hem prime candidates for use as sacrificial layers. The focus of this work was the assessment of the performance of Al2O3 as a sacrificial l ayer 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 ex plained in terms of the differences between their thermodynamic parame ters. Corrosion resistance measurements show a substantial difference between Pt-implanted and unimplanted samples; at the lowest implant do ses of (0.1-0.2) x 10(17) Pt ions cm(-2), the corrosion rate is reduce d by about a factor of ten relative to that of unimplanted Ni. At high er Pt doses, less corrosion protection is observed. It is proposed tha t, at higher doses, ion-beam mixing causes Ni to be bound into interme tallic compounds; with less elemental Ni available to form an NiO pass ive layer, the corrosion rate increases.