Analysis of magnetic electron lens with secant hyperbolic field distribution

TL;DR

This paper evaluates a secant-hyperbolic magnetic field model for electron lenses used in electron microscopes, comparing it with existing models and finite element simulations to improve focal property calculations.

Contribution

It introduces and assesses a secant-hyperbolic magnetic field model for electron lenses, enhancing the accuracy of focal property estimations in electron-optical instruments.

Findings

The secant-hyperbolic model closely matches finite element simulation results.

Compared to existing models, it offers improved accuracy in magnetic field representation.

The model facilitates better prediction of lens focal characteristics.

Abstract

Electron-optical imaging instruments like Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) use specially designed solenoid electromagnets for focusing of electron beam probe. Indicators of imaging performance of these instruments, like spatial resolution, have strong correlation with focal characteristics of the magnetic lenses which in turn have been shown to be functions of the spatial distribution of axial magnetic field generated by them. Owing to complicated design of practical lenses, empirical mathematical expressions are deemed convenient for use in physics based calculations of their focal properties. So, degree of closeness of such models to the actual field distribution determines accuracy of the calculations. Mathematical models proposed by Glaser[1] and Ramberg[1] have historically been put into extensive use. In this paper the authors discuss one such model with secant-hyperbolic type magnetic field distribution function, and present a comparison among these models, with results from finite element based field simulations as reference.