LOW-ENERGY SPUTTERING OF SMALL NEUTRAL CLUSTERS FROM ALLOYS

Emission-angle integrated yields of small neutral clusters ejected fro m binary alloys (Ni0.8W0.2, Cu0.63Zn0.37, and Cu0.28W0.72) due to Arand Xe+ impact in the energy range from 30 to 1000 eV are compared wit h the respective yields from pure Cu and Ni. Detection is done by sput tered-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 Xeprojectiles and for low bombarding energies. At energies of about 1 ke V the relative yield data from alloys and pure samples appear to merge . This observation is ascribed to the presence of an element (W in thi s case) whose mass matches more favorably that of the projectile and t hus facilitates the ejection of small clusters. While for Ar+ bombardm ent the yields of dimers and trimers exhibit a dependence which is in accordance with a statistical formation mechanism and which is valid d own to very low energies (about 100 eV), such a correlation is not obs erved for Xe+ ion sputtering of the alloys.