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Atomic-resolution chemical mapping of ordered precipitates in Al alloys using energy-dispersive X-ray spectroscopy

Abstract

Scanning transmission electron microscopy (STEM) coupled with energy-dispersive X-ray spectroscopy (EDS) is a common technique for chemical mapping in thin samples. Obtaining high-resolution elemental maps in the STEM is jointly dependent on stepping the sharply focused electron probe in a precise raster, on collecting a significant number of characteristic X-rays over time, and on avoiding damage to the sample. In this work, 80 kV aberration-corrected STEM-EDS mapping was performed on ordered precipitates in aluminium alloys. Probe and sample instability problems are handled by acquiring series of annular dark-field (ADF) images and simultaneous EDS volumes, which are aligned and non-rigidly registered after acquisition. The summed EDS volumes yield elemental maps of Al, Mg, Si, and Cu, with sufficient resolution and signal-to-noise ratio to determine the elemental species of each atomic column in a periodic structure, and in some cases the species of single atomic columns. Within the uncertainty of the technique, S and β” phases were found to have pure elemental atomic columns with compositions Al2CuMg and Al2Mg5Si4, respectively. The Q’ phase showed some variation in chemistry across a single precipitate, although the majority of unit cells had a composition Al6Mg6Si7.2Cu2.

Category

Academic article

Client

  • Research Council of Norway (RCN) / 221714
  • NORTEM / 197405

Language

English

Author(s)

Affiliation

  • Norwegian University of Science and Technology
  • University of Oxford
  • SINTEF Industry / Materials and Nanotechnology

Year

2017

Published in

Micron

ISSN

0968-4328

Volume

96

Page(s)

103 - 111

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