A UNIFIED DESCRIPTION OF LIQUID METAL ION SOURCE ENERGY DISTRIBUTIONS

Abstract
Energy distributions for liquid metal ion sources (LMIS) operated close to the melting point of the feedstock are well known. Despite this, reasons for the shift in voltage deficit with current have remained unclear. The change in characteristics when LMIS are operated at elevated temperatures has hitherto been treated as a separate effect and has lacked adequate explanation. Angular-resolved results presented here for a gallium LMIS confirm that a secondary peak is formed in the energy distribution diagram at temperatures above 250°C. It is argued that a distribution based on a spectrum of energies can correlate both high and low temperature data. From comparisons between angular resolved results in these two regimes, it is concluded that LMIS behaviour with current and with temperature derives from fundamentally the same effect. It is proposed that emission is by a single ionisation mechanism but that the final distribution is distorted by additional processes. A model based on a peak splitting effect due to longitudinal movements of the LMIS apical jet is discussed. This model is shown to predict observed LMIS distribution shapes in the high and low temperature regimes and to account for the off-axis variation.