We present a numerical method for iterative computation of electron optical systems influenced by space charge with an improved accuracy in the same calculation time. We replace the common algorithm for evaluating the space charge distribution with a new one based on the calculation of the current density distribution from an aberration polynomial. We introduce a re-meshing algorithm which adapts the mesh used for the field calculation by the finite element method in each iteration to the actual space charge distribution to keep it sufficiently fine in all areas with non-zero space charge.

The model of thermionic electron gun was developed. The Dirichlet problem for the cylinder (the Wehnelt electrode) restricted by two bottoms, one of them imitates a plane cathode and another imitates the equipotential surface, was solved analytically. It allows to study electron optical properties of the gun and its behaviour in dependence on Wehnelt potential for different cylinder depths. When the focal distance and the crossover size have the minimal value, this mode is called a work one. The crossover size and the beam half-angle values in this mode were approximated and the analytical method for electron gun calculation was developed.

This paper presents computed dependencies of the detected electron energy distribution on the water vapour pressure in an environmental scanning electron microscope obtained using the EOD software with a Monte Carlo plug-in for the electron-gas interactions. The software GEANT was used for the Monte Carlo simulations of the beam-sample interactions and the signal electron emission from the sample into the gaseous environment. The simulations were carried out for selected energies of the signal electrons collected by two electrodes with two different diameters with the voltages of +350 V and 0, respectively, and then 0 and +350 V, respectively, and for the distance of 2 mm between the sample and the detection electrodes of the ionization detector. The simulated results are verified by experimental measurements. Consequences of the simulated and experimental dependencies on the acquisition of the topographical or material contrasts using our ionization detector equipped with segmented detection electrode are described and discussed.

We explore the benefits of using novel electrode shapes in electrostatic lenses. Two representative types of lenses are considered and significant improvements are obtained in their spherical aberrations.