Phase-contrast imaging in aberration-corrected scanning transmission electron microscopy

• Published in: Micron (Oxford, England : 1993) Vol. 49; pp. 1 - 14
• Main Authors: Krumeich, F., Müller, E., Wepf, R.A.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01-06-2013
• Subjects: Aberration; Aberration-correction; Bright field; Computer programs; computer software; Illumination; image analysis; Image transmission; Imaging; lighting; nanoparticles; Phase contrast; Reciprocity theorem; Scanning electron microscopy; Scanning transmission electron microscopy; Simulation; STEM; transmission electron microscopes; transmission electron microscopy; Aberration-correction; Phase contrast; Reciprocity theorem; Bright field; STEM
• ISSN: 0968-4328; 1878-4291
• DOI: 10.1016/j.micron.2013.03.006

•Cs-corrected STEM is a flexible alternative to HRTEM.•Phase-contrast STEM imaging can be qualitatively understood on the basis of the principle of reciprocity.•Projected crystal potentials are reflected in the images.•Phase-contrast STEM imaging depends on defocus and specimen thickness.
Although the presence of phase-contrast information in bright field images recorded with a scanning transmission electron microscope (STEM) has been known for a long time, its systematic exploitation for the structural characterization of materials began only with the availability of aberration-corrected microscopes that allow sufficiently large illumination angles. Today, phase-contrast STEM (PC-STEM) imaging represents an increasingly important alternative to the well-established HRTEM method. In both methods, the image contrast is coherently generated and thus depends not only on illumination and collection angles but on defocus and specimen thickness as well. By PC-STEM, a projection of the crystal potential is obtained in thin areas, with the scattering sites being represented either with dark or bright contrast at two different defocus values which are both close to Gaussian defocus. This imaging behavior can be further investigated by image simulations performed with standard HRTEM simulation software based on the principle of reciprocity. As examples for the application of this method, PC-STEM results obtained on metal nanoparticles and dodecagonal quasicrystals dd-(Ta,V)1.6Te are discussed.