YIELDS AND COMPOSITION CHANGES IN LOW-ENERGY SPUTTERING OF BINARY-ALLOYS - EXPERIMENTS AND COMPUTER-SIMULATIONS

Emission-angle-integrated yields of neutral atoms and molecules ejecte d from binary alloys (Cu0.63Zn0.37,Ni0.8W0.2, Cu0.28W0.72) due to Arand Xe+ impact in the energy range from 30 to 1000 eV were determined by means of sputtered-neutral mass spectrometry using a hemispherical specimen arrangement. The yields of small homo- and heteronuclear mole cules exhibit a dependence on the respective atom yields, which is cha racteristic of a statistical formation mechanism and is valid down to very low energies (approximately 100 eV). Compositional changes of the near-surface concentration and the fluence-dependent evolution of par tial atomic yields were investigated for Ni0.8W0.2 by means of the bin ary-collision computer code T-DYN. The same projectiles and a similar energy range as in the experiments were used. The simulations produce a pronounced surface enrichment of W with steady-state concentrations ranging from > 0.9 at 50-eV impact energy to approximately 0.4 for 200 0 eV, while the yields of Ni and W exhibit a decrease and increase, re spectively, with bombarding fluence. For both atomic species, the stea dy-state yields obtained from the simulations show a good agreement wi th the respective experimental data with the possible exception of ver y low energies. Also, transients in the yield evolution towards steady -state conditions have been monitored for selected impact energies and agree very well with corresponding simulation runs.