Paper AS-TuM11
Molecular Depth Profile of Sugar Films: A Comparison Study of C60 Ions and Traditional Cs+ and O2+ Ions

Tuesday, October 21, 2008, 11:20 am, Room 207

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is a powerful surface analysis technique because it supplies both molecular information and element information with a reasonable high spatial resolution (~100nm). Furthermore, 3-dimensinal imaging is also feasible. Normally, dual beam analysis strategy I used , in which a second ion beam is applied for sputtering to realize layer-by-layer analysis. Traditionally, low energy Cs+ and O2+ ions are used. However, they are reactive species and organic molecules are easy to be damaged during sputtering process so that only elemental information is collected. Recent years, a new sputtering species, C60 ions were introduced. They are relatively soft and they can sputter materials away with very limited damage so that molecular depth profile can be realized. 3-dimensional imaging of cells and tissues by ToF-SIMS has been of great interest for more than ten years. However, cells and tissues contain a lot of water and they are not compatible with high vacuum environment at room temperature. Immobilizing cells in a sugar matrix has proven to be a good way to resolve this problem. The sugar matrix is stable in vacuum environment. Therefore, the behavior of sugar molecules during ion sputtering is of great important. In this work, we did a comparison study of molecular depth prolife of sugar film on a silicon wafer with C60+, C60++, C60+++, Cs+ and O2+ species. C60n+ species show very exciting molecular depth profile behavior, but Cs+ and O2+ ions seems to damage most of sugar molecules in a short time. X-ray photoelectron spectrometry (XPS) was used to characterize the sputtering craters. The XPS results are well consistent with our ToF-SIMS data.