Time of flight secondary ion mass spectroscopy (Tof-SIMS)

Tof-SIMS is a material surface analytical technique. It can provide detailed elemental and molecular information about surfaces, full layers, interfaces and even 3D analysis of a sample. It is a very sensitive technique that requires a very high vacuum (10-9~10-11 mbar). As schematically shown in Figure 1, a pulsed beam of primary ions (usually Cs or Ga) is used to excite and remove molecules from the very outermost surface of the test sample. These molecules are excited to be dissociated ions which could be either positive or negative depending on the measurement settings. After being etched away from the sample surface, these ions are extracted and accelerated by a field with a known strength and subsequently reach the detector via a long field-free drift path. As the velocity of ion depends on the mass-to-charge ratio that is unique to every ion, all ions with a different mass will reach the detector at different times. The detector measures the “time of flight” of the various ions being etched from the sample and in this way an atomic mass survey can be obtained with a remarkable high mass resolution. In this way, the composition of the various ions can be identified.

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Figure 1: Schematic illustration of a Tof-SIMS measurement. Adapted from [1].

[1] https://www.ru.ac.za/media/rhodesuniversity/content/nanotechnology/documents/TOF-SIMS%20MUTHUMUNI.pdf