ANGLE-INTEGRATED YIELDS OF NEUTRAL CLUSTERS IN LOW-ENERGY SPUTTERING OF NICKEL AND COPPER

Spherical samples of nickel and copper were subjected to normal-incidence Ar+ ion bombardment at energies ranging from 30 to 1000 eV. Emission-angle integrated yields of neutral dimers and trimers were determined by means of sputtered-neutral mass spectrometry; they were found to scale with the atomic yields squared and cubed, respectively. Such a dependence is evidence for a cluster formation mechanism which proceeds via the agglomeration of sputtered atoms, ejected independently albeit from the same collision cascade. For near-threshold energies drastic differences were observed between cluster yields integrated over all emission angles and those detected along the surface normal; these appear to be due to different emission distributions of atoms and multimers at very low energies.