Analytical techniques for soft-materials have been remarkably advanced. Among those techniques, static secondary ions mass spectrometry (SSIMS) with high sensitivity and high spatial resolution is attracted attention as one of the most useful methods for macromolecules on solid surface. It has been reported that damage cross-section by projectiles of cluster ions has not increased so much or rather sometimes decreased in comparison to that of monomer ions. In addition, imaging analysis of organic materials by Bi cluster TOF-SIMS which is one of the conventional SSIMS has been performed in the last ten years. Therefore, it is important to establish the analysis conditions in the SSIMS imaging ions are found.

In this study, 1, 2-distearoyl-sn-glycero-3-phosphocholine (DSPC) which is one of the typical lipids in human living body, and N,N'-Di(1-naphthyl)-N,N'-diphenylbenzidine (C₄₄H₃₂N₂, NPD) and 4,4’,4’’-Tri[2-naphthyl (phenyl)amino] triphenylamine (C₆₆H₄₈N₄, 2-TNATA) which are one of organic electro-luminescence, were analyzed by TOF-SIMS. In the analysis, we focused influences of the species of the primary Bi ions on the yields of secondary ions, damage cross-section and spatial resolution.

Samples were thin films of DSPC, NPD and 2-TNATA spin-coated onto the surfaces of a clean Si wafer to acquire the mass spectra for evaluating yield of secondary ions and damage cross-section. Also, the pattered samples to obtain the mass images for evaluating spatial resolution were prepared. TOF-SIMS measurements were performed in a TOF.SIMS 5 instrument (ION-TOF GmbH). The pulsed primary Bi₁⁺, Bi₃⁺ and Bi₃²⁺ ion beams accelerated 25 kV was bombarded to the samples and the positively charged secondary ions were analyzed. These thin films were analyzed in the high-current bunched mode. Secondary ion images of patterning samples were collected in the non-bunched burst alignment mode.

The present results show that the incidence of large cluster ions increases yields of secondary ions, and yields of secondary ions strongly depend on the molecule species. High resolution imaging is achieved using Bi₃²⁺ ions due to high-sensitive detection of the secondary ions, and the spatial resolution depends generally on yields of the secondary ions. It is remarked that the primary ion species for the highest yields of secondary ions depend on primary ions dose density because damage cross-section of Bi₃²⁺ ions is higher than that of Bi₁⁺ and Bi₃⁺ ions. Consequently, it is concluded that selection of the primary ion species is crucial to SSIMS analysis of macromolecules by Bi cluster ions.