Imaging properties of bright-field and annular-dark-field scanning confocal electron microscopy

Imaging properties of scanning confocal electron microscopy (SCEM) were studied by calculating simple model systems using the multislice method. A simple geometrical explanation was given, particularly for the difference between bright field (BF) and annular dark field (ADF) SCEM. It is demonstrated that the BF-SCEM image contrast consists of two features. One gradually changes over a wide defocus range and depends on the lateral size of the object. Another appears only near the focus and is independent of sample size. On the contrary, ADF-SCEM image contrast does not depend on the lateral size of the object. Therefore, the ADF-SCEM will provide more readily interpretable image contrast.

Research highlights
► Multislice based SCEM simulations demonstrate that BF-SCEM images have strong dependence on the lateral size of the object.
► The contrast dependence of BF-SCEM on the lateral size of the object is explained by a simple relation between w and the illumination angle.
► In contrast to BF-SCEM, ADF-SCEM does not show much dependence on the lateral size because of the effect of ADF aperture in combination with the collector lens and detector aperture.