The Effect of Energetic Electrons on the Secondary Ion Emission

There have been two main mechanisms proposed for ionization processes in SIMS; they are the electronic excitation by atomic collisions [1] and the atom-surface resonant electron tunneling [2,3]. A direct evidence of the electron tunneling has recently been reported [4], and its delicate experiment was a rather academic task, adjusting the relative position between the Fermi-level and vacuum level (or changing the work function of sample surface). In the present work, we have tried to perform the experiments under conventional conditions which could meet the requirement for traditional utilities of SIMS.