Design of an Objective Magnetic Lens and Study of its Magnetic and Optical Properties in the Scanning Electron Microscope

Abstract

The study's objective is to investigate the optical properties of the objective magnetic lens, which is considered as the most crucial part of the electron microscope. Three models of objective lenses (Snorkel, Pinhole, Gemini), equal in geometric dimensions were taken, and their optical properties, as well as their magnetic properties. It was found that the lens (P) achieved the best results, which were studied at a continuous excitation (NI=2000 A-t) and different acceleration voltages ranging from (8-16 kV), in addition to different values for the aperture angle (α). Then, we conducted an improvement on the selected lens by changing the width of the air gap between the poles (S) and studying the properties of the lens. We obtained better results for spherical (Cs=1.62 mm) and chromatic (Cc=1.84 mm) aberrations, focal length (fₒ=2.92 mm), as well as the highest value of the magnetic field (Bz=0.38 T) at an acceleration voltage (Vr=10000 V), excitation (NI=2000 A-t), and air gap width (S=5 mm), and the diameter of the electron probe (dp=11.25 nm) at an aperture angle (α=2 mrad).