Secondary ion ionization

Secondary ion mass spectrometry (SIMS) is to measure the secondary ions, ionized clusters, atoms and atomic clusters, which are emitted from the surface of particles, when it is bombarded with a primary beam of ions, such as He", Ne", or Ar", with energies in the range of hundreds of eV to keV scale. The emitted ions and ionized clusters are analyzed directly by using a mass spectrometer. Therefore, chemical composition of the surface can be analyzed with the obtained accordingly. SIMS has two modes of analysis (i) static and (ii) dynamic. Static SIMS uses an ion beam with low current density, so as to confine the analysis to the outermost layers. Dynamic SIMS uses beams of high current density, so that successive atomic layers can be eroded at a relatively high rate. Comparatively, the analytical conditions of dynamic SIMS are less suitable for surface analysis. 

These relations, however, extend only over a limited range, with the range depending on the respective secondary ion ionization potential or electron affinity relative to that of the substrates Fermi edge at the time of emission as discussed below. 

---