Direct Comparison of Au₃⁺ and C₆₀⁺ Cluster Projectiles in SIMS Molecular Depth Profiling

The sputtering properties of two representative cluster ion beams in secondary ion mass spectrometry (SIMS), C₆₀⁺ and Au₃⁺, have been directly compared. Organic thin films consisting of trehalose and dipalmitoylphosphatidylcholine (DPPC) are employed as prototypical targets. The strategy is to make direct comparison of the response of a molecular solid to each type of the bombarding cluster by overlapping the two ion beams onto the same area of the sample surface. The ion beams alternately erode the sample while keeping the same projectile for spectral acquisition. The results from these experiments are important to further optimize the use of cluster projectiles for SIMS molecular depth profiling experiments. For example, Au₃⁺ bombardment is found to induce more chemical damage as well as Au implantation when compared with C₆₀⁺. Moreover, C₆₀⁺ is found to be able to remove the damage and the implanted Au effectively. Discussions are also presented on strategies of enhancing sensitivity for imaging applications with cluster SIMS.