Image Formation

Abstract

The starting point for this chapter is the wave function of the electron at the object exit surface. Here we follow the electron wave from the object to the image and describe the nonlinear process of image formation. We start with the imaging process assuming an ideal microscope. The description is then refined by taking into account wave aberrations induced by the objective lens. In the next step, we consider effects of incoherence caused by fluctuations of the lens currents and of the high tension, and by electron energy loss. The interpretation of TEM images is further complicated by the loss of the phase of the electron wave because only the image intensity can be recorded in the image plane. Two methods will be briefly outlined that may be able to (approximately) solve this inverse problem of phase retrieval, namely off-axis electron holography and focal-variation reconstruction. For further information, see [1, 2, 3, 4, 5, 6].