Sputtering and secondary ion emission from Cu/Ni(1 0 0)

The growth and sputtering of Cu/Ni(1 0 0) in the Cu coverage range 0–2 monolayers (ML) have been studied using secondary ion mass spectrometry. Relative secondary ion (SI) yield data derived from these measurements have been compared with ballistic sputter yields predicted by molecular dynamics computer simulations. From the comparison, it is suggested that ionisation probabilities for atoms and dimers sputtered from Cu/Ni(1 0 0) are attenuated by a factor of 2–3 with respect to clean Ni(1 0 0), probably due to the work function shift accompanying Cu deposition. Two simple models of the ionisation process for sputtered atoms have been implemented. The electron tunnelling model proved to be more successful at predicting the variation of relative SI yields with Cu coverage than the thermalisation model. The mean information depth for atomic secondary ions (Ni+, Cu+) is found to be 0.39±0.15 ML beneath the surface layer of a 1 ML Cu/Ni(1 0 0) target. The surface layer of Cu/Ni(1 0 0) contributes ∼69% of atomic secondary ions, and ∼81% of the atomic constituents of dimer secondary ions (Ni2+, NiCu+, Cu2+).