Isotopic Ratio Measurements by Time-of-Flight Secondary Ion Mass Spectrometry
Albert J. Fahey, S R. Messenger
Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) is often considered synonymous with SIMS in the static limit where the ion fluence on the sample surface is so low that damage is negligible. For this same reason its use in measuring isotopic ratios has generally been ruled out. However, the high spatial resolution Ga+ ion beams typically used in ToF-SIMS make it a potentially attractive technique for the isotopic characterization of small features such as particles. We have developed a technique to measure isotopic ratios by Tof-SIMS with a spatial resolution of < 1 υm. Peak fitting and interference stripping algorithms have been developed and are presented in this work. The precision of the measurements is close to counting statistical limits and the variability in mass bias is comparable to dynamic SIMS.