title: Fast Atomic-Scale Elemental Mapping of Crystalline Materials by STEM Energy-Dispersive X-Ray Spectroscopy Achieved with Thin Specimens.
abstract: Elemental mapping at the atomic-scale by scanning transmission electron microscopy (STEM) using energy-dispersive X-ray spectroscopy (EDS) provides a powerful real-space approach to chemical characterization of crystal structures. However, applications of this powerful technique have been limited by inefficient X-ray emission and collection, which require long acquisition times. Recently, using a lattice-vector translation method, we have shown that rapid atomic-scale elemental mapping using STEM-EDS can be achieved. This method provides atomic-scale elemental maps averaged over crystal areas of ~few 10 nm2 with the acquisition time of ~2 s or less. Here we report the details of this method, and, in particular, investigate the experimental conditions necessary for achieving it. It shows, that in addition to usual conditions required for atomic-scale imaging, a thin specimen is essential for the technique to be successful. Phenomenological modeling shows that the localization of X-ray signals to atomic columns is a key reason. The effect of specimen thickness on the signal delocalization is studied by multislice image simulations. The results show that the X-ray localization can be achieved by choosing a thin specimen, and the thickness of less than about 22 nm is preferred for SrTiO3 in [001] projection for 200 keV electrons.
authors.affiliation: 1Sandia National Laboratories,Albuquerque,NM 87185,USA.
authors.forename: Ping
authors.initials: P
authors.lastname: Lu
authors.affiliation: 2Department of Materials Science and Engineering,University of Illinois at Urbana-Champaign,1304 W Green St,Urbana,IL 61801,USA.
authors.forename: Renliang
authors.initials: R
authors.lastname: Yuan
authors.affiliation: 2Department of Materials Science and Engineering,University of Illinois at Urbana-Champaign,1304 W Green St,Urbana,IL 61801,USA.
authors.forename: Jian Min
authors.initials: JM
authors.lastname: Zuo
keywords: STEM-EDS; atomic-scale; elemental mapping; fast chemical imaging; thin specimen