Effects of polymer crystallization on the molecular sensitivity in TOF-SIMS measurements using Bi1+ and Bi32+ ions

Abstract

Bi cluster ions are among the most utilized primary sources for time-of-flight secondary ion mass spectrometry (TOF-SIMS). Although Bi clusters have advantages over larger clusters, such as C60+ and Arn+, TOF-SIMS is less sensitive for macromolecules when Bi clusters are used as primary ions. Matrix-enhanced SIMS is a more sensitive technique for large molecules, because the matrix limits fragmentation. The matrix is thought to reduce molecular crystallinity and cohesiveness, which facilitate the extraction of large molecules from the sample surface. In this study, the authors investigate the effects of polyethylene glycol structure on the molecular sensitivity of TOF-SIMS using different primary Bi ion species. The results indicate that amorphous PEG enables the detection of larger molecules than crystalline PEG by TOF-SIMS when either Bi1+ or Bi32+ ions are used for irradiation. This suggests that the structures of organic molecules affect the propagation of kinetic energy from the primary ions. This phenomenon reduces damage to polymer chains and enhances the sensitivity of TOF-SIMS for intact molecular ions.