This week, we will see how to build the microscope from its individual components: lenses and aperture. Then we will have a review of the operating modes of the microscope.

In this week on the basics of electron diffraction we discuss the case of 2-beam diffraction at the Bragg angle in TEM and then show how it can be represented by the Ewald sphere/reciprocal lattice construction.

In this week we finish on the basics of electron diffraction, by first taking a look at zone axis or multi-beam diffraction where we have scattering from many different crystal planes at the same time. Next, we explain this by a relaxation of the Bragg condition in the Ewald sphere/reciprocal lattice construction resulting from the TEM sample size and shape. We then see how this affects diffraction spot intensity when slightly deviated from the perfect Bragg condition in the 2-beam case.

In this week we will tackle the subject of dynamical scattering in TEM. Dynamical scattering is multiple elastic scattering; it effectively involves the diffraction and rediffraction of electrons as they transmit through a sample. In the first lecture, we look at the basic theory of dynamical scattering in the 2-beam case and use the theoretical expressions to calculate plots of beam intensity versus excitation error for different specimen conditions. In the next lecture, we use this theory to explain the dynamical scattering phenomenon of thickness fringes.

This week we look at more effects of dynamical scattering, on both TEM images and diffraction pattern formation. First we look at how dynamical scattering produces bend contours in bright-field and dark-field images when the crystal lattice is bent across an imaged region of TEM sample. Secondly, a special case of dynamical scattering called double diffraction is introduced, in which multiple elastic scattering leads to the formation of diffraction spots for crystal planes which are systematic absences.

In this first week about phase contrast, we will define the contrast transfer function of the objective lens. In a second part we will consider an object that affects only weakly the phase of the electron wave and not its amplitude. This will lead us to the definition of the phase contrast transfer function.

In this week we will analyse more in details the Phase Contrast Transfer Function, and see how it can be used to understand the contrast in the image of a thin amorphous film. In a second part, we will address the high resolution images of crystalline specimens.