Sputtering of tin and gallium-tin clusters

摘要

Tin and gallium-tin clusters have been produced by 4 keV Ar(sup +) ion bombardment of polycrystalline tin and the gallium-tin eutectic alloy and analyzed by time-of-flight mass spectrometry. The sputtered neutral species were photoionized with 193 nm (6.4 eV) excimer laser light. Neutral tin clusters containing up to 10 atoms and mixed gallium-tin clusters Ga(sub (n-m))Sn(sub m) with n (<=) 4 for the neutrals and N (<=) 3 for the sputtered ionic species have been detected. Laser power density dependent intensity measurements, relative yields, and kinetic energy distributions have been measured. The abundance distributions of the mixed clusters have been found to be nonstatistical due to significant differences in the ionization efficiencies for clusters with equal nuclearity but different number of tin atoms. The results indicate that Ga(sub 2)Sn and Ga(sub 3)Sn like the all-gallium clusters have ionization potentials below 6.4 eV. In the case of Sn(sub 5), Sn(sub 6), GaSn and Ga(sub (n-m))Sn(sub m) clusters with n=2 to 4 and m>1, the authors detect species that have sufficient internal energy to be one photon ionized despite ionization potentials that are higher 6.4 eV. The tin atom signal that is detected can be attributed to photofragmentation of dimers for both sputtering from polycrystalline tin and from the gallium-tin eutectic alloy.