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