Correlative Scanning Precession Electron Diffraction and Atom Probe Tomography to access the 3D polycrystalline grain microstructure of nanomaterials

• Applicant: Dr. Xuyang Zhou, since 9/2022
• Subject Area: Physical Chemistry of Solids and Surfaces, Material Characterisation ; Experimental Condensed Matter Physics
• Term: from 2019 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 431450858

In transmission electron microscopy acquiring a stack of diffraction patterns by moving a collimated beam in a two-dimensional scan produces a four-dimensional dataset. This dataset contains the information on local grain orientations, phase distributions, and grain and phase boundary locations. In case of nanomaterials overlapping grains often compromize the data analysis as this leads to superimposed diffraction patterns. Even if it is possible to index these, it is not possible to tell which grain is situated on the upside/downside of the TEM specimen from a measurement along a single perspective. Here we propose to develop a 3D Scanning Precession Electron Diffraction (SPED) method based on a series of 2D-SPED measurements at different tilt angles to overcome these limitations. Tomographic post-processing routines adopted from the synchrotron community will enable to reconstruct grain orientation and grain boundary maps in 3D. The additional use of APT on the same sample will simplify this development and will provide complementary information on the 3D distribution of elements. This combination of techniques will be used in this project to study grain boundary segregation. However, this development gives access to the 3D investigation of coupled chemical and crystallographic materials science phenomena with nanometer resolution in general.In this project existing data processing toolboxes and acquisition routines from 2D-SPED will be further developed to give access to the 3D case. A dedicated approach is used to extract a signal that by-passes the intensity modulations due to dynamic effects and fulfills the projection requirement. The orientation dependence of the diffraction signal will be handled by a curative algorithm and implemented in the tomographic reconstruction tools. After the development, the correlative approach will be applied to investigate grain boundary segregation in the nanocrystalline Fe-C system where APT crystallography is not applicable. This topic is of high importance as C is known to stabilize ferritic nanostructures and to increase grain boundary cohesion. The correlative 3D-SPED/APT approach will help to understand the related phenomena, as a large number of randomly oriented grain boundaries will be characterized in terms of both, their five crystallographic interface parameters, and their atomic-scale chemical composition. For this challenging tasks we unite the expertise of four method developers from complementary fields: 2D-SPED (Edgar Rauch, Grenoble), 3D synchrotron diffraction contrast tomography (Wolfgang Ludwig, Grenoble), correlative TEM/APT and grain boundary segregation (Michael Herbig, Düsseldorf) and APT crystallography (Andrew Breen, Düsseldorf).

• DFG Programme: Research Grants
• International Connection: France
• Co-Investigator: Dr. Andrew Breen
• Cooperation Partners: Professorin Dr. Sophie Cazotte; Professor Pierre Lhuissier, Ph.D.; Privatdozent Dr. Wolfgang Ludwig; Privatdozent Dr. Edgar Rauch; Professorin Dr. Muriel Veron
• Ehemaliger Antragsteller: Dr. Michael Herbig, until 8/2022