An asymmetric electrostatic lens for field-emission microprobe applications
- 1 April 1979
- journal article
- conference paper
- Published by AIP Publishing in Journal of Applied Physics
- Vol. 50 (4) , 2494-2501
- https://doi.org/10.1063/1.326260
Abstract
The properties of a physically asymmetric three‐element electrostatic lens have been calculated numerically for voltage‐symmetric and voltage‐asymmetric cases. The lens has low chromatic aberration, Cc∞/f < 0.5, when operated in the voltage‐asymmetric mode with voltage ratios Vfinal/Vinitial as low as 2. Calculations of beam diameter versus current with realistic field electron emission parameters of dI/dΩ=1 mA sr−1 and ΔE=2 eV at 5 kV emitter voltage show that at 30‐kV final‐beam voltage 250 nA current could be focused into a 0.25‐μm spot at 5 cm working distance, with an emitter‐lens separation of 1.5 cm. It is shown that while the two‐element immersion lens is inappropriate for high‐current microprobe applications, the three‐element asymmetric lens is well suited for this work.This publication has 16 references indexed in Scilit:
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