Fig. 1. Electric lens model in SIMION simulation

Fig. 2. Effect of grid position on focusing results

Fig. 3. Effect of electrode distance on focusing results

Fig. 4. Effect of initial potential on focusing results

Fig. 5. Effect of electrode 2 potential on focusing efficiency

Fig. 6. Effect of electrode potential on electron beam focusing efficiency at different positions of electron guns

Fig. 7. Morphology of beam spots recorded by CCD

Fig. 8. Beam spot distribution of different guns while adjusting potential of electrode 1 (a) and electrode 2 (b)

Fig. 9. Variation of distance between two beam spots when adjusting electrode potential