Investigating the difficulty of eliminating flood gun damage in TOF-SIMS

A study is presented of the damage caused by low energy electrons from a flood gun used for charge neutralisation in static SIMS. It is found that, in a typical time-of-flight (TOF)-SIMS instrument, the electron fluence during spectrum acquisition would be around 1.9x1020 electrons/m2. Analysis of the molecular fragmentation for PS, PVC, PMMA and PTFE shows that an upper limit of 6x1018 electrons/m2 can be defined to retain intensities at 1% of their true levels. At a fluence of 7.5x1020 electrons/m2 the relative signal intensities, for some materials, have changed by over a factor of four. Recommendations for flood gun currents and fluence are provided to ensure that no significant electron damage occurs but that charge neutralisation is maintained