A three-dimensional atom-probe study of preferential sputtering of a Ni91Pt9 alloy

A three-dimensional optical atom probe (OAP) has been used to investigate local ordering and segregation phenomena, in a Ni91Pt9 alloy after sputtering and annealing. For the sputtering procedure, a separate preparation chamber, with a scannable Ar-sputter-gun is connected to the OAP vessel. The specimen tips for this study were prepared from single-crystal samples. In thermal equilibrium, the surface of a (111)-oriented, specimen is enriched in platinum by a factor of two with respect to the bulk. The atom-probe results are in close agreement to complementary surface sensitive results obtained from ion scattering spectroscopy (ISS) and Auger electron spectroscopy (AES). Uniform sputtering of the tip leads to a decisive depletion of Pt on the surface and the next subatomic layer.