The Static Limit in MeV Secondary Ion Mass Spectrometry.

Static limit in secondary ion mass spectrometry (SIMS) is defined as a threshold beam fluence, where secondary ions are desorbed only from the virgin surface. For the common SIMS technique, the static SIMS limit is set to approximately 10¹² ions/cm². Within the present paper, we investigated the applicability of the static limit for a mass spectrometry imaging technique known as MeV-SIMS, where the target surface is bombarded by primary ions within the MeV energy range domain. Here, desorption of secondary ions relies mainly on electronic excitations instead of collision cascades, as is the case for the lower energy primary ion beams. We have measured the disappearance cross sections of several organic targets for three different chlorine primary ion beam energies. Results show how the disappearance cross section depends on the primary ion beam energy. Generally, the static SIMS regime applies for a range of primary ion beam fluences similar to that for the common SIMS technique; however, the dependence of the disappearance cross section within the lower MeV energy domain (up to 10 MeV) exhibits somewhat unexpected characteristics. Further, we thoroughly investigated the dynamics of the secondary ion mass spectra after prolonged primary ion bombardment. Secondary ion yields of various peaks were monitored during analysis, and the corresponding data can be used to identify specific peaks and also to determine fragmentation patterns of analyzed organic molecules.