title: 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, 80kV 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.
authors.affiliation: Department of Physics, NTNU - Trondheim, NO-7491 Trondheim, Norway. Electronic address: sigurd.wenner@ntnu.no.
authors.forename: Sigurd
authors.initials: S
authors.lastname: Wenner
authors.affiliation: Department of Materials, University of Oxford, Parks Road, OX1 3PH Oxford, UK.
authors.forename: Lewys
authors.initials: L
authors.lastname: Jones
authors.affiliation: Materials and Chemistry, SINTEF, NO-7491 Trondheim, Norway.
authors.forename: Calin D
authors.initials: CD
authors.lastname: Marioara
authors.affiliation: Department of Physics, NTNU - Trondheim, NO-7491 Trondheim, Norway.
authors.forename: Randi
authors.initials: R
authors.lastname: Holmestad
keywords: Aluminium alloys; Energy-dispersive X-ray spectroscopy; Precipitation; Scanning transmission electron microscopy