Work-Package 21

WP21 is a multi-institution joint research activity focussed on the development and application of atomic resolution electron imaging to study a broad range of structural problems across materials science, engineering, chemistry and physics. Within the past decade or so, the development of hardware correctors for the spherical and, more recently, chromatic aberrations of the main objective lens have revolutionized imaging capabilities at the atomic level. The result of these developments has been the development of a number of new modes of imaging, including negative spherical aberration (Cs) imaging (NCSI) in the conventional high-resolution transmission electron microscope (HRTEM) and annular bright-field (ABF) imaging in the scanning transmission electron microscope (STEM).

Alongside these instrumental developments have come improvements in computational power and methods for simulating images. The result has been an increasing emphasis on the quantitative analysis of atomic-resolution electron microscope images to physical measurements from samples. Now exists the opportunity to obtain information about atomic column positions, local variations in strain, changes in composition and bonding, and vacancy and impurity concentrations. Despite the recent technical improvements, fundamental changes in image analysis and acquisition methods are required to maximise the potential and applicability of atomic resolution imaging. This WP involves the development of methods for quantification and interpretation of TEM images acquired using state-of-the-art instrumentation and techniques.
One particular focus of the WP is to compare methods for quantitative comparisons between experimental measurements and simulations with the use of advanced statistical parameter estimation methods applied to high resolution TEM or STEM images to determine unknown structure parameters accurately and precisely.

JRA2 - image 1 JRA2 - image 2 

The figure above left shows work from the University of Antwerp where an image of a gold nanorod has been quantified in terms of the number of atoms in each column using the statistical distribution of column intensities. In contrast, the figure above right show collaborative work between the University of Antwerp and the University of Oxford where a platinum catalyst nanoparticle has been quantified by accurate image calibration, calculation of absolute scattering cross-sections and comparison to numerical simulations.

Another focus of the WP is the optimisation of imaging conditions to detect light elements. The image below shows a simulation of a twin boundary in an MgAl2O4 spinel, and shows that beryllium should be detectable if segregated to the grain boundary when using the annular bright-field mode of STEM. One advantage of this approach is that it can be performed pixel-by-pixel simultaneously with other imaging modes such as annular dark-field which provides atomic-number sensitive imaging of the cation locations.

JRA2 - image 3

Partners involved:

University of Oxford (Work-Package leader); ER-C Jülich (WP co-leader); CNRS/LPS Orsay; Universiteit Antwerpen; TU Graz; Universidad de Zaragoza; Jozef Stefan Institute Ljubljana; TU Dresden; CEOS GmbH


Peter Nellist (University of Oxford)
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Rafal Dunin-Borkowski (FZ Jülich)
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