Magic Numbers and Critical Sizes of Tin Clusters Emitted from a Liquid Metal Ion Source

Sn cluster ions from a liquid metal ion source have been analyzed by mass spectrometry. Discontinuous variations in ion intensity as a function of the cluster size were found at n=4 and 6 (magic numbers) for singly charged clusters, where n is the number of atoms contained in the cluster. By comparing this with other studies for Si, Gee, and Sn clusters, it is concluded that the presently found magic numbers can be attributed to cluster stability. The critical size, above which multiply charged clusters are observed, was n=3 and 4 for doubly and triply charged states, respectively. The critical sizes are also discussed using the Rayleigh limit for charged droplets.