“…Their performance strongly depends on the quality of their electron sources [1]. Currently, the Schottky emitter [2,3] and Cold-field emitter [4][5][6] have been used as point electron sources with high brightness, high stability, and low energy spread. The zirconiacoated-tungsten (Zr/O/W) Schottky emitter, developed by Swanson et al [7,8], provides us with a particularly good balance of brightness (about 5× 10 7 A/cm 2 /sr at 5 kV), lifetime (in excess of 15,000 hours), and energy spread (about 0.4 eV) [3].…”