YIELDS AND KINETIC-ENERGY DISTRIBUTIONS OF SPUTTERED NEUTRAL COPPER CLUSTERS

Neutral copper clusters up to Cu15 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 Cu5. The sputtered neutral species were detected by laser post-ionization time-of-flight mass spectrometry. The absolute sputtering yield of Cu2 was determined to be 0.05 Cu2/Ar+. Sputtering yields of the larger clusters relative to the atom were estimated from their positionized concentrations and found to range from 10(-4) for Cu3 to 10(-9) for Cu11. The kinetic energy distributions of Cu, Cu2 and Cu3 were also measured. The energy 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 Cu3 > Cu2 > 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.