LOW-ENERGY SPUTTERING OF SMALL NEUTRAL CLUSTERS FROM ALLOYS

Emission-angle integrated yields of small neutral clusters ejected from binary alloys (Ni0.8W0.2, Cu0.63Zn0.37, and Cu0.28W0.72) due to Ar+ and Xe+ impact in the energy range from 30 to 1000 eV are compared with the respective yields from pure Cu and Ni. Detection is done by sputtered-neutral mass spectrometry and hemispherical specimens are used. Compared to elemental samples the relative dimer and trimer yields are enhanced for the alloys. This enhancement is more pronounced for Xe+ projectiles and for low bombarding energies. At energies of about 1 keV the relative yield data from alloys and pure samples appear to merge. This observation is ascribed to the presence of an element (W in this case) whose mass matches more favorably that of the projectile and thus facilitates the ejection of small clusters. While for Ar+ bombardment the yields of dimers and trimers exhibit a dependence which is in accordance with a statistical formation mechanism and which is valid down to very low energies (about 100 eV), such a correlation is not observed for Xe+ ion sputtering of the alloys.