Microscopy and Microanalysis

TEM and STEM Materials Applications

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

Robert Hovdena1 c1, Huolin L. Xina2 and David A. Mullera1a3

a1 School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14853, USA

a2 Department of Physics, Cornell University, Ithaca, NY 14853, USA

a3 Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY 14853, USA

Abstract

Aberration-corrected scanning transmission electron microscopes (STEMs) 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 (αmax = 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.

(Received September 03 2010)

(Accepted September 13 2010)

(Online publication December 02 2010)

Correspondence:

c1 Corresponding author. E-mail: rmh244@cornell.edu