Transmission electron microscope with a mirror objective free of spherical and axial chromatic aberrations.

The basic scheme of a transmission electron microscope (TEM) with a mirror objective free of spherical and axial chromatic aberrations, which are the main factors limiting the resolution of electron microscopes, is considered. As an objective, an axisymmetric electrostatic mirror (ASEM), the electrodes of which are coaxial cylinders of equal diameter, separated by gaps of finite width, is considered. Based on previously developed aberration concepts, taking into account relativistic effects, the families of three-electrode ASEM are calculated that satisfy the condition of eliminating spherical and axial chromatic aberrations simultaneously at a fixed focal length and a finite width of the interelectrode gaps.

The objective lens of the electron microscope with correction of spherical and axial chromatic aberrations.

The paper describes the principle of operation of a relatively simple aberration corrector for the transmission electron microscope objective lens. The electron-optical system of the aberration corrector consists of the two main elements: an electrostatic mirror with rotational symmetry and a magnetic deflector formed by the round-shaped magnetic poles. The corrector operation is demonstrated by calculations on the example of correction of basic aberrations of the well-known objective lens with a bell-shaped distribution of the axial magnetic field.

Electrostatic mirror objective with eliminated spherical and axial chromatic aberrations.

Computational formulae for the coefficients of the third-order spherical aberration and the second-order axial chromatic aberration are presented for an axially symmetric electrostatic electron mirror. A technique for eliminating the high-order derivatives of the potential axial distribution in mirror systems from the integrands is described. Conditions for elimination of spherical and axial chromatic aberrations, either separately or simultaneously, are found for a three-electrode axially symmetric mirror composed of coaxial cylinders of the same diameter.