Correlative orientation (TEM) and compositional mapping (APT) in 3-dimensions with high spatial and chemical resolution
In collaboration with Dr. Edgar Rauch, SIMAP laboratory, Grenoble, and Dr. Wolfgang Ludwig, MATEIS, INSA Lyon, we are developing a correlative scanning precession electron diffraction and atom probe tomography method to access the three-dimensional (3D) crystallographic character and compositional information of nanomaterials with unprecedented spatial and chemical resolution.
We are developing a nanobeam scanning precession electron diffraction (SPED) tomography technique to perform orientation mapping in 3D at the nanometer scale. While scanning the nanometer sized electron beam in two dimensions across a specimen, a complementary metal oxide semiconductor (CMOS)-based camera records high quality diffraction patterns at each probe position. This generates a complex 4D dataset containing information on local crystal symmetries, lattice strains and crystal orientations of potentially overlapping grains as well as embedded secondary phases along the beam direction. Figure 1a schematically shows the 4D-SPED data acquisition on a needle shaped specimen for atom probe tomography (APT). The data processing (Fig. 1b) is a vital step in the technique development and is performed using the ASTAR software package (NanoMEGAS SPRL) in combination with Python codes to extracts information from overlapping grains to generate virtual dark field (VDF) images. These VDF images are used in the tomographic reconstruction routines (Fig. 1c) to obtain a full 3D view of the nanograins and phases as well as their 3D crystallographic orientation.
The key objective of this project is to correlate the 3D orientation mapping data on the exact same specimen with atom probe tomography (APT). Using needle-shaped APT specimens for the 4D-SPED data acquisition enables to correlate the 3D crystallographic information of materials with the corresponding 3D compositional data obtained from APT measurements. This correlative approach facilitates, for example, the 3D characterization of grain orientation and grain boundaries with their associated five macroscopic degrees of freedom as well as their 3D atomic-scale chemical composition in nanocrystalline materials.