Size Distribution and Dissociation Patterns of Iron-Sulfur Binary Cluster Ions from Sputter Ion Source

Abstract

The size distribution of iron-sulfur binary cluster ions, Fe_nS_m⁺ (n=1-36, m=1-23), was investigated using secondary ion mass spectrometry (SIMS). The dissociation patterns, n=2-26, m=1-17, were also investigated by varying the acceleration voltage of secondary ions step by step. Iron-sulfur binary cluster ions were produced by 10 keV Xe ion bombardment on a pyrite (FeS₂) sheet and were mass-analyzed by a sector type mass spectrometer. Judging from the size distribution observed in mass spectra, the composition ratio n/m of the cluster ions gradually tended to increase as the cluster size became larger. The dissociation patterns of small size tended to yield the Fe_nS_n⁺ (n=2, 4, 6) and Fe_nS_n-1⁺ (n=7, 8, 9) which might be more stable structure. As the cluster size became larger, the dissociation mainly occurred by emitting Fe or S₂. Dissociation patterns of Fe_nS_m⁺ suddenly changed at Fe_nS_M⁺ which had maximum peak intensity in the series of Fe_nS_m⁺ for the fixed n. In case of m≤M, Fe emission occurred and S₂ emission for m>M