Nanoscale elemental sensitivity study of Nd₂Fe₁₄B using absorption correlation tomography.

Transmission X-ray microscopy (TXM) is a rapidly developing technique with the capability of nanoscale three dimensional (3D) real-space imaging. Combined with the wide range in energy tunability from synchrotron sources, TXM enables the retrieval of 3D microstructural information with elemental/chemical sensitivity that would otherwise be inaccessible. The differential absorption contrast above and below absorption edges has been used to reconstruct the distributions of different elements, assuming the absorption edges of the interested elements are fairly well separated. Here we present an "Absorption Correlation Tomography" (ACT) method based on the correlation of the material absorption across multiple edges. ACT overcomes the significant limitation caused by overlapping absorption edges, significantly expands the capabilities of TXM, and makes it possible for fully quantitative nano-scale 3D structural investigation with chemical/elemental sensitivity. The capability and robustness of this new methodology is demonstrated in a case study of an important type of rare earth magnet (Nd₂Fe₁₄B).