Rate of decrease in the intensity ratio of doubly charged ions to singly charged ions in liquid-metal ion source with gold-based alloy

We have investigated the intensity ratio of doubly charged ions to singly charged ions (R21) of Au82Si18 and Au66Sb34 ion sources. R21 was measured as a function of emission current, in order to establish the empirical relation between the electric field at the ionization point and the emission current. The rate of decrease in R21 was represented by the slope of a logarithmic plot of R21 with respect to the emission current. As a result, it was shown that Au and Si ions had similar rates of decrease, namely 0.3 for Au82Si18 ion source. Au and Sb ions had low rates of decrease, of less than 0.05 for Au66Sb34 ion source. These results showed that the alloy ion source exhibited a lower rate of decrease in R21, in accordance with the surface tension of the constituent.