ToF-SIMS analysis of an organic layer using toluene and its cluster ion beam projectiles generated by multiphoton ionization

Study Summary

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is becoming an essential tool in the molecular and imaging analysis fields of mass spectrometry owing to its sensitivity and ability to monitor the distribution of elements or molecules.

Fig. 1. General schematic diagram of ToF-SIMS with the organic molecular cluster ion beam apparatus.

In this study, we developed a home-built time-of-flight (ToF)-SIMS instrument and generated organic molecular cluster ion beams ionized by multiphoton ionization (MPI) as a primary ion beam. Further, the sample stage loaded with rhodamine 6G was bombarded with size-controlled toluene cluster ions to produce secondary ions. Mass spectra of rhodamine 6G were acquired as a function of the size of toluene cluster ions. We plotted the fragments-to-parent ion ratio against each size of cluster ion, and we found that an intact rhodamine 6G signal would be observed with less fragmentations using (Tol)_n>18⁺.

Fig. 2. Sum of fragments-to parent ion ratio as a function of the energy per nucleon

We expect this combination of the organic molecular cluster ion beam generated by MPI and ToF-SIMS to greatly expand the field of surface analysis. Given the advantage of organic molecular cluster ion beams for ToF-SIMS analysis, the present work provides new insight into primary cluster ion beams produced by photoionization.