An electrostatic-electromagnetic alignment section for the electron microscope

Abstract

A high resolution electron microscope must be equipped with a double condenser lens system, and should have a pumping tube into the gun. With fine beam illumination, the mechanical stability of the column becomes important; it is desirable to avoid mechanical alignment of the illuminating system, and to rely on electrical methods. If provision is to be made for reflection electron microscopy, electrical or magnetic alignment of the illuminating system has many advantages. It is not possible to design a compact system with purely magnetic deflectors, but since the large deflection of the electron beam required for reflection microscopy is in one plane only, it is possible to obtain the small deflection in the plane at right angles by insulating the pole pieces of the magnetic deflectors and using them as electrostatic deflector plates. They may be quite closely spaced, thus reducing the excitation required both for magnetic and electrostatic deflections.