Extended Depth of Field for High-Resolution Scanning Transmission Electron Microscopy

摘要

Aberration-corrected scanning transmission electron microscopes (STEM)provide sub-angstrom lateral resolution; however, the large convergence anglegreatly reduces the depth of field. For microscopes with a small depth offield, information outside of the focal plane quickly becomes blurred and lessdefined. It may not be possible to image some samples entirely in focus.Extended depth-of-field techniques, however, allow a single image, with allareas in-focus, to be extracted from a series of images focused at a range ofdepths. In recent years, a variety of algorithmic approaches have been employedfor bright field optical microscopy. Here, we demonstrate that some establishedoptical microscopy methods can also be applied to extend the ~6 nm depth offocus of a 100 kV 5th-order aberration-corrected STEM (alpha_max = 33 mrad) toimage Pt-Co nanoparticles on a thick vulcanized carbon support. Thesetechniques allow us to automatically obtain a single image with all theparticles in focus as well as a complimentary topography map.