Electron flood gun damage in the analysis of polymers and organics in time-of-flight 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 SIMS instrument, the electron fluence during spectrum acquisition would be around 1.9×1020 electrons/m2. Analysis of the molecular fragmentation for PS, PVC, PMMA and PTFE shows that an upper limit of 6×1018 electrons/m2 can be defined before significant electron-induced damage is observed. After a fluence of 7.5×1020 electrons/m2, the secondary ion intensities for some materials have changed by over a factor of 2. The effect of flood gun electron energies between 10 and 20 eV is investigated and the precise energy is found not to be critical. Recommendations for flood gun currents and fluence are provided to ensure that no significant electron damage occurs but charge neutralisation is maintained. This is necessary to obtain a good level of repeatability and reproducibility for static SIMS spectra and is critical to obtain effective G-SIMS spectra.