PHYSICAL SPUTTERING OF CU-NI ALLOYS - A MOLECULAR-DYNAMICS STUDY

Several important aspects of physical sputtering of Cu-Ni alloys by Ar+ ions were simulated in the present work, using molecular dynamics and embedded-atom potentials. The total sputtering yields obtained for 0.5, 1, and 3 keV bombardments are closer to the experimental values for pure Cu than for Ni, and depend only slightly on alloy composition and temperature (up to 600 K). Sputtering of Cu atoms is slightly preferential, with the partial (or component) sputtering yield ratio Y(Cu)/Y(Ni) congruent-to 1.2, weakly dependent on ion energy and composition. The sputter fraction from the first atom layer decreases from 0.98 to 0.86 when the ion energy increases from 0.5 to 3 keV. Practically, however, all the sputtered atoms originate from the two outermost atom layers. From the energy spectra obtained for Cu and Ni atoms sputtered from a Cu0.5Ni0.5 alloy, the surface binding energies of the alloying elements are found to be U(Cu)(Cu-Ni) = 3.28+/-0.13 eV and U(Ni)(Cu-Ni) = 3.97+/-0.17 eV. The power-law parameter derived for 1 keV Ar+ sputtering is m = 0.05. After the collisional phase, the alloy surface is no longer atomically smooth, and noticeable compositional alteration occurs in the outer few atom layers.