Surface damage of Cu/Ni alloys by low energy noble gas ion bombardment

Compositional changes of the surface and near-surface layers in Cu/Ni alloys during noble gas ion bombardment from room temperature to 873K have been studied by means of microprobe Auger spectroscopy (μ-AES), X-ray microanalysis (XMA) and scanning electron microscopy (SEM). After sputtering at room temperature, the surface is enriched with nickel by the selective sputtering of copper. With the increase in the specimen temperature sputtering at a high dose rate results in further nickel enrichment. On the other hand copper segregation is observed at a low dose rate. A long range depletion of copper in the order of 100 nm in thickness is observed depending on the sputtering time, specimen temperature and ion beam density. From the depth profile of the copper depleted region, the enhanced diffusion coefficients of copper in the ion-damaged layer are measured. The enhancements of diffusion coefficients of copper for a 40at% Ni-Cu specimen are 3.6 x 108, 1.3 x 104 and 19 at 573, 723 and 873K, respectively. The apparent activation energy calculated, assuming an Arrhenius type equation, is 5 to 6kcal/mol. It is suggested that an interstitial type diffusion mechanism is predominant in the damage layer. The depletion of copper is of the order of a few μm along the grain boundary for the sputtering at 873K. SEM observation has revealed a large difference in the topographical feature of each grain surface and grain boundary for sputtering at both room and elevated temperatures. (author)