Investigation of the ion ejection mechanism of gallium liquid metal ion sources

A gallium liquid metal ion source and an ion energy analysis system were constructed in order to study the ion ejection mechanism. We have performed measurements of the energy distribution of 69Ga⁺ at elevated source temperatures up to 500 -C at a fixed ion current of 2 ¡ik using a 127° electrostatic energy analyser. Results on the emitted ion energy distribution indicate that a notable secondary peak and a low energy tail are formed in addition to the main peak at source temperatures above 300 cC, The field evaporation, field ionization and charge transfer collision are discussed in detail as the ionization mechanisms of the emitted ion. The experimental evidence is presented for the field ionization process as one of the formation mechanisms of69Ga⁺. A comparison between the experimental and theoretical distributions is also carried out.