Electron microscope image contrast formed by electrons from elastic–inelastic and inelastic–elastic scattering processes

Abstract

The contribution of inelastically scattered electrons to the electron microscope images is investigated by putting a very small aperture at various positions in the back focal plane of the objective lens between the central and the diffraction spots and taking the corresponding electron microscope images. In the images of wedge shaped bent aluminum crystal, two kinds of bend contours from a crystal lattice plane are observed. They are the images formed by electrons due to inelastic–elastic and elastic‐inelastic scattering processes, which are named as Kikuchi and anti‐Kikuchi electrons. The separation of these two kinds of bend contours in the image becomes large with increasing distance of the aperture position from the central and diffraction spots. Observed images have a nature similar to normal bend contours in bright‐field and dark‐field images when the aperture is placed close to the central and diffraction spots, respectively. When the aperture is placed close to the diffraction spots, two bend contours with bamboo‐shoot shape are partly overlapping. In this area a kind of contrast anomaly is observed. This anomaly is attributed to the interference between Kikuchi and anti‐Kikuchi electron waves and an explanation is given using dynamical theory of inelastic Bloch wave scattering.

The Fresnel effect of a defocused biprism on the fringes in inelastic holography

“…This approach, however, fails completely to describe the outcome of experiments involving the direct measurement of coherence using an electron biprism [1,2]. Recently there have been several experiments, mostly based on holography, to test the effects of partial coherence in combination with inelastic scattering [3][4][5][6][7][8]. The outcome of these experiments has proven to be difficult to understand in simple terms of either coherent or incoherent imaging and it was shown that partial coherence has to be taken into account properly [9][10][11][12][13][14][15][16][17][18][19][20][21][22], to be able to understand the obtained contrast.…”

Fringe contrast in inelastic LACBED holography

“…After first claims that single atoms could be seen in energy filtered HR images [12] it became soon clear that coupling between elastic and inelastic scattering plays a dominant role in image formation, hampering a straightforward interpretation. There were a few attempts to demonstrate inelastic coherence in diffraction using a biprism [13,14] or a double crystal interferometer [15].…”