Day 1 - Principles of Electron Optics and Aberration Correction in STEM - Duscher

This lecture by Professor Gerd Duscher introduces the fundamental principles of electron optics and aberration correction in scanning transmission electron microscopy (STEM). It begins with an overview of electron-matter interactions, emphasizing the strong interaction of electrons with matter and the various signals generated. The lecture explains the basic components of an electron microscope, including the electron gun, condenser lenses, objective lens, and projector lenses, and how they are used to form images and diffraction patterns. The concept of resolution is discussed, with the Rayleigh criterion and the difference between point resolution and information limit. The main focus is on aberrations, particularly spherical aberration, and how they limit resolution. The lecture introduces the aberration function and its expansion in terms of aberration coefficients, including defocus, astigmatism, coma, and higher-order terms. It explains how aberrations can be measured and corrected using Zemlin tableaus and Ronchigrams, and concludes with a live demonstration of tuning an instrument and correcting aberrations.