تصميم الشكل الهندسي للذراع الحديدي في العدسة الكهرومغناطيسية المكثفة-الشيئية

Abstract EN

The optimization of the main polepiece structure and the geometrical shape of iron shroud in the asymmetric double polepiece magnetic lens for the condenser-objective mode led to the possibility of the higher resolution lens design for the electron microscope.

This work is handled by three steps, the designed lens having optimum properties through the construction of a fine geometrical shape of the iron shroud which results the highest flux density peak of the magnetic field with a lowest spherical aberration coefficient, at (Vr =200 kV) and excitation of (NI=10.5 kA-t).

In the first step the thickness of the iron shroud was studied whereas the optical properties of the lens were studied, by putting west point in the iron shroud in the second step.

Moreover, the effect of the height of the west point position on the optical performance was studied in the third step.

The Calculation has been made for the axial magnetic field distribution, the magnetic flux lines trajectories and the optical properties to limit the defects in the lens and consequently improve the geometrical shape of the iron shroud.

It was found that the focal length inversely proportional to the thickness of the iron shroud and the best depth for the west point equals (dpw=13 mm), beside that the west point position was (h=35 mm) which gave the best resolving power (δ= 0.2 nm).

The obtained results of the preferred properties in the present work have been compared with those of the published results, and it was found that both results are in a good agreement with each other.