High dose implantation of yttrium and barium ions into copper: the use of a sacrificial carbon layer for enhanced retention

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High dose implantation of heavy ions is highly problematical, since these ions may have sputtering yields ( S y) in excess of 30, with high doses leading to significant target erosion and a resultant loss of the implanted species. Although the S y of heavy ions into metals can be very high, the S y of those same ions into lighter materials is often quite low. We have been investigating a technique involving the use of thin (< 1000 Å) C coatings on metal targets, to act as slowly sputtering “sacrificial layers” during heavy ion implants. Uncoated Cu samples were implanted with high doses (>1.5×10 17 ions/cm 2) of 400 or 600 keV Y and Ba ions. The retention in these samples was ∼ 80% for the Y implantation but only ∼ 10% for the Ba implantation. The Ba implants were then repeated into Cu targets coated with a thin (750 Å) layer of C. This yielded excellent results, with Ba retentions close to 100%. Results of a SIMS study (to examine C mixing) and X-ray diffraction to investigate phase formation will also be discussed.