Helium plasma induced nanostructure formation in copper and nickel

Abstract

Copper and nickel samples were exposed to helium plasma to investigate surface nanostructure formation and associated helium nano-bubble growth. Plasma fluences from 3.9 × 1023 He m−2 to 3.1 × 1024 He m−2 were used for this study. For copper with an unpolished surface finish 50–100 nm wide nanoscale pillars were formed, with more complex structures observed at higher plasma fluences. This is due to the uneven topography providing nucleation sites that stabilises the growth of these features. For polished copper surfaces nano-scale pillars formed on some crystal grains but not others, indicating strong crystal orientation effects on nano-structure formation. The formation of nano-scale islands and pillars was also observed in both polished and unpolished nickel samples, with nano-structure formation occurring across all crystal grains.Nanostructures that formed on nickel samples exposed to helium plasma at controlled temperatures from 200 °C to 325 °C showed significant sensitivity to the sample temperature. Dense fields of 50 nm diameter nanostructures formed at 300 °C, larger but sparse nanostructures formed at 325 °C, and little change was observed at and below 250 °C.Sub-surface helium bubbles were measured and displayed similar sizes for bubbles formed in both copper and nickel samples.