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 1.9 x 10(20) electrons/m(2). Analysis of the molecular fragmentation for PS, PVC, PMMA and PTFE shows that an upper limit of 6 x 10(18) electrons/m(2) can be defined to retain intensities at 1% of their true levels. At a fluence of 7.5 x 10(20) electrons/m(2) 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. Crown Copyright (C) 2002 Published by Elsevier Science B.V. All rights reserved.