INNER SHELL SPECTROSCOPY AND RELATIVISTIC ATOM IONIZATION CROSS SECTION BY ELECTRON IMPACT

Abstract

The elemental composition of materials in the Transmission Electron Microscope is probed by inner shell ionization of atoms by a high energetic electron beam. Proper elemental quantification of the material requires detailed knowledge of the electron-atom differential ionization cross section (DCS). In the current work, the cross section is calculated in the context of relativistic quantum mechanics. Relativistic effects become important due to the high energy of the electron beam. The atomic dynamics is calculated in a fully relativistic setting, using Dirac-Hartree-Fock (DHF) solutions for the atomic bound and continuum wavefunctions. The relaxation of the atom due to the ionization by the beam needs to be taken into account. To address this, a continuum wave is computed in a self-consistent field of an ion. Non-orthogonality between atomic and ionic wavefunctions leads to additional corrections. They are shown to be important at low energy of the ionized electron which is particularly interesting for materials with elements which have close ionization energies