Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
5368279 | Applied Surface Science | 2010 | 8 Pages |
The secondary ion mass spectrum of silicon sputtered by high energy C60+ ions in sputter equilibrium is found to be dominated by Si clusters and we report the relative yields of Sim+ (1 â¤Â m â¤Â 15) and various SimCn+ clusters (1 â¤Â m â¤Â 11 for n = 1; 1 â¤Â m â¤Â 6 for n = 2; 1 â¤Â m â¤Â 4 for n = 3). The yields of Sim+ clusters up to Si7+ are significant (between 0.1 and 0.6 of the Si+ yield) with even numbered clusters Si4+ and Si6+ having the highest probability of formation. The abundances of cluster ions between Si8+ and Si11+ are still significant (>1% relative to Si+) but drop by a factor of â¼100 between Si11+ and Si13+. The probability of formation of clusters Si13+-Si15+ is approximately constant at â¼5 Ã 10â4 relative to Si+ and rising a little for Si15+, but clusters beyond Si15 are not detected (Simâ¥16+/Si+ < 1 Ã 10â4). The probability of formation of Sim+ and SimCn+ clusters depends only very weakly on the C60+ primary ion energy between 13.5 keV and 37.5 keV. The behaviour of Sim+ and SimCn+ cluster ions was also investigated for impacts onto a fresh Si surface to study the effects that saturation of the surface with C60+ in reaching sputter equilibrium may have had on the measured abundances. By comparison, there are very minor amounts of pure Sim+ clusters produced during C60+ sputtering of silica (SiO2) and various silicate minerals. The abundances for clusters heavier than Si2+ are very small compared to the case where Si is the target.The data reported here suggest that Sim+ and SimCn+ cluster abundances may be consistent in a qualitative way with theoretical modelling by others which predicts each carbon atom to bind with 3-4 Si atoms in the sample. This experimental data may now be used to improve theoretical modelling.