Yields and kinetic energy distributions of sputtered neutral copper clusters

Abstract Neutral copper clusters up to Cu 15 were observed from the sputtering of polycrystalline copper by normally incident 3.6 keV Ar + . This is the first observation of sputtered neutral clusters larger than Cu 5 . The sputtered neutral species were detected by laser post-ionization time-of-flight mass spectrometry. The absolute sputtering yield of Cu 2 was determined to be 0.05 Cu 2 /Ar + . Sputtering yields of the larger clusters relative to the atom were estimated from their postionized concentrations and found to range from 10 −4 for Cu 3 to 10 −9 for Cu 11 . The kinetic energy distributions of Cu, Cu 2 and Cu 3 were also measured. The energ distribution of the atoms agreed very well with the expected distribution from the Sigmund-Thompson model. The maxima in the energy distributions were in the order Cu 3 > Cu 2 > Cu. All three distributions had approximately the same high-energy dependence. Neither the single nor the multiple collision models that have been proposed to describe the cluster energy distributions appear to agree with our measurements.