Makiko FUJII oral presentation (PB2-Thu3-2-5)
Secondary Molecular Ion Emissions under Cluster Ion Bombardments on Large Molecules with Various Molecular Weight
1 Quantum Science and Engineering Center, Kyoto University, Gokasho, 611-001 Uji, Japan
2 SENTAN, Japan Science and Technology Agency (JST), Chiyoda, 102-0075 Tokyo, Japan
3 University of Namur, 61 rue de Bruxelles, 5000 Namur, Belgium
4 Technische Universität Kaiserslautern - Fachbereich Physik, , 67663 Kaiserslautern, Germany
5 JEOL Ltd., Akishima, 196-8558 Tokyo, Japan
6 Yokohama National University - Graduate School of Environment and Information Sciences, 79-5 Tokiwadai, Hodogaya-ku, 240-0085 Yokohama, Japan
Secondary ion mass spectrometry (SIMS) is now widely used for chemical analysis of polymers and biomaterials, with various primary ion beams, such as Aun, Bin, C60 and Arn. Much attention has been given to sensitivity improvements, especially for large molecules. We have developed a finely focused large cluster ion beam (~1 μm) for the primary ion beam used in SIMS . The latest SIMS equipment combined with this ion beam uses mass spectrometers of the quadrupole time-of-flight (Q-TOF) type equipped with MS/MS capability. This new SIMS equipment allows us to determine the structure of the secondary ion by using the collision-induced dissociation (CID) technique.
A typical SIMS spectrum of polyethylene glycol (PEG) and the chemical structure of the PEG molecule are shown in Fig. 1. A PEG mixture of PEG 1000, 2000, 3000 (ratio 1:1:2) were spin-coated on Si wafers. Strong peaks were assigned as [M+Na]+ and the molecular weight distribution of PEG was clearly revealed, but the sensitivity was strongly dependent on molecular weight of PEG. The intensity of fragmented ions, such as [M+Na-H2O]+, was one order of magnitude lower than that of [M+Na]+. Although secondary ion yields around 1000 Da were independent on the primary beam, the secondary ion yields around 3000 Da were strongly dependent on the primary beam. This result indicated that especial care is required in measuring large molecules with SIMS.
 J. Matsuo, S. Torii, K. Yamauchi, K. Wakamoto, M. Kusakari, S. Nakagawa,
M. Fujii, T. Aoki, and T. Seki, Appl. Phys. Express 7, 2014, 056602