Study of preferential sputtering and segregation effects on the surface composition of Al-Pd- Mn quasi-crystals

Using 2 keV He⁺ and Ne⁺ low-energy ion scattering (LEIS), it was found that the Al/Pd concentration ratio at the surface of a nominally Al_69.9Pd_20.5Mn_9.6 quasi-crystal decreases to a steady-state value under bombardment as a result of preferential sputtering. Sputtering of an annealed surface results in a significant increase in Mn concentration on the surface which remained at annealing temperatures below 575 K. Variations of the Mn/Pd and Al/Pd ratios have been measured by LEIS as a function of temperature in the range 295-975 K for clean-annealed and sputtered surfaces. The results show that Al/Pd ratio does not significantly change from 295 to 575 K for both He⁺ and Ne⁺ but increases with sample temperatures up to 875 K.