Secondary Ion Mass Spectrometric Analysis of soft materials - Current challenges and future applications

1. Quantum Science and Engineering Center, Kyoto University, Uji, 611-0011 Kyoto, Japan.
2. SENTAN, Japan Science and Technology Agency (JST), Chiyoda, 102-0075 Tokyo, Japan.

Secondary particle emission under ion irradiation provides unique opportunities for material analysis. Secondary ion mass spectrometry (SIMS) is now widely used in elemental analysis of semiconductors and metals. Chemical analysis of soft materials such as polymers, organic semiconductors and biological materials, is now in strong demand because of the increasing importance of these materials in emerging technologies. Newly developed ion beams, such as cluster and swift heavy ions, are used for organic- and bio-SIMS [1, 2]. These beams have higher secondary molecular ion emission yields than conventional monomer ion beams in the keV energy in range, because of their dense excitation during ion impact. In the last decade, molecular imaging and molecular depth profiling techniques have been developed for organic materials, and beams of small metal cluster ions or large Ar clusters ions with energy in the keV range are now widely used in commercial SIMS instruments.

We have demonstrated the technique of molecular imaging with swift heavy ion beams (MeV-SIMS) in biological material analysis. In this method, a high-energy ion accelerator is combined with an orthogonal acceleration time-of-flight mass spectrometer (oa-ToF-MS) that uses quasi-continuous beams, enabling high mass (>10,000) and high lateral resolution (~1 m) with a finely focused beam. Furthermore, swift heavy ion beams (>MeV) have a high transmission capability in matter, which allows their use for analysis of volatile samples such as liquids, solid–liquid interfaces and wet biological samples under ambient pressure (100,000 Pa). This technique creates new possibilities of ion beam analysis.
Current challenges and future applications of the SIMS technique with these new ion beams will be discussed.
[1] J. Matsuo, S. Torii, K. Yamauchi, K. Wakamoto, M. Kusakari, S. Nakagawa, M. Fujii, T. Aoki and T. Seki, Applied Physics Express 7, 56602 (2014)
[2] J. Matsuo, S. Ninomiya, H. Yamada, K. Ichiki, Y. Wakamatsu, M. Hada, T. Seki, T. Aoki, Surf. Interface Anal., 42, 1612 (2010)