Low Voltage Electron Microscopy: Principles and Applications

Chapter 6

Gentle STEM of Single Atoms: Low keV Imaging and Analysis at Ultimate Detection Limits

Ondrej L. Krivanek¹, Wu Zhou^2,3, Matthew F. Chisholm³, Juan Carlos Idrobo^2,3, Tracy C. Lovejoy¹, Quentin M. Ramasse⁴ and Niklas Dellby¹

¹Nion Co., USA

²Department of Physics and Astronomy, Vanderbilt University, USA

³Materials Science and Technology Division, Oak Ridge National Laboratory, USA

⁴SuperSTEM Laboratory, STFC Daresbury, UK

6.1 Introduction

Scanning transmission electron microscopy (STEM), introduced in its modern form by Crewe and coworkers over 40 years ago [1–4], has made important advances in the last few years. Chief among these was the successful implementation of working aberration correctors, which has improved the available spatial resolution significantly: 1 Å is now routine and 0.5 Å is attainable. Single atoms as light as boron have been imaged using annular dark field modes and as light as hydrogen using annular bright field modes. Electron energy loss spectroscopy (EELS) and energy-dispersive X-ray spectroscopy (EDXS) have become standard techniques for analyzing the chemical composition of individual atomic columns in crystals, and EELS and EDXS data from single atoms have been acquired. Most of these developments have been reviewed in a recent 760-page book on STEM that comprises 18 chapters on topics ranging from the history of STEM to new STEM techniques such as fluctuation imaging [5]. More recent developments such as single atom EDXS and fine structure ...