secondary ion mass spectrometry time-of-flight secondary ion mass spectrometry time-of-flight secondary ion mass spectroscopy TOF-SIMS CHMO:0000565 ToF-SIMS Mass spectrometry where the sample is bombarded with a stream of primary mass-selected particles and the secondary ions ejected from the sample are detected by accelerating them to the same (known) kinetic energy and measuring the time taken for each ion to reach a detector at a known distance. This time is dependent on the mass-to-charge ratio of the ion.