Advanced volume reconstruction and data mining methods in atom probe tomography
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The dream of an atomic-scale tomographic analytic microscope Breakthroughs in materials science are often concomitant to advances in characterization methods. At the nanometer scale, new functionalities or properties of devices or materials have been discovered by designing the matter in three dimensions, making the need for three-dimensional (3D) characterization microscopes mandatory. Quantum dots, quantum wells, and quantum wires in photonic materials, and the downscaling of modern transistors, are striking examples of this phenomenon. To fully understand the relationship between the structure of materials and their properties, an ultimate microscope should be able to provide the 3D position as well as elemental identity of each atom accurately in a material system, which means with subnanometer resolution. Knowing the reality of matter at this scale helps materials scientists model the physical mechanisms of interest, such as mechanical properties, photon emission properties, and electronic conduction properties. Currently, at this scale, very few analytical 3D microscopes exist.1–4 The resolutions of x-ray tomography and focused ion beam slicing approaches are far too low at present. Only
scanning transmission electron microscope (STEM) tomography and atom probe tomography (APT) are well placed in this race. Both techniques produce comparable images in terms of field of view and resolution, as seen in Figure 1, which shows an example of an alloy composed of Ag particles in an Al matrix. For the same sample, both microscopy techniques reveal similar atomic-scale distributions of the Ag atoms in the Al matrix, where the spherical particles are a few nm in size.3,5 Although significant leaps forward have been made in STEM tomography (recently achieving atomic resolution),6,7 APT is currently more suited to the routine production of analytic tomographic images with subnanometer spatial resolution. APT instruments are used in more than 50 labs around the world, in both academia and industry, with the fields of applications ranging from metals to biological materials, yielding exciting results across many fields.4,8,9 New users of the technique face two pitfalls when exploiting the power of the technique. The first is data generation.10,11 APT performance is related to the physical principles involved in the instrument. Though these basic principles are relatively simple, the images are not free from artifacts. Artificial features or biased images may be misinterpreted by beginners in the field.
F. Vurpillot, Groupe de Physique des Matériaux, UMR CNRS 6634, Université et INSA de Rouen, France; [email protected] W. Lefebvre, Groupe de Physique des Matériaux, UMR CNRS 6634, Université et INSA de Rouen, France; [email protected] J.M. Cairney, School of Aerospace Mechanical and Mechatronic Engineering, and Australian Centre for Microscopy & Microanalysis, The University of Sydney, Australia; julie. [email protected] C. Oberdorfer, Institute of Materials Science, University of Stuttgart, Germa
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