A bimodal tomographic reconstruction technique combining EDS-STEM and HAADF-STEM

Abstract

A three-dimensional (3D) chemical characterization of nanomaterials can be obtained using tomography based on high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) or energy dispersive X-ray spectroscopy (EDS) STEM. These two complementary techniques have both advantages and disadvantages. The Z-contrast images have good image quality but lack robustness in the compositional analysis, while the elemental maps give more element-specific information, but at a low signal-to-noise ratio and a longer exposure time. Our aim is to combine these two types of complementary information in one single tomographic reconstruction process. Therefore, an imaging model is proposed combining both HAADF-STEM and EDS-STEM. Based on this model, the elemental distributions can be reconstructed using both types of information simultaneously during the reconstruction process. The performance of the new technique is evaluated using simulated data and real experimental data. The results demonstrate that combining two imaging modalities leads to tomographic reconstructions with suppressed noise and enhanced contrast.

Automatic correction of nonlinear damping effects in HAADF–STEM tomography for nanomaterials of discrete compositions

“…The second sample is a hetero-nanoparticle, which is an Ag nanoparticle with a diameter of approximately 110 nm with an embedded Au octahedron [7] . It is studied as a case where the cupping artifacts reduce the image contrast between different chemical compositions.…”

“…This dataset has been used to investigate HAADF-EDS bimodal tomography (HEBT) in [7] . In that study, the authors have no- iced that the raw data had strong intensity damping which not only limited straightforward segmentation of the HAADF reconstructions but also undermined the validity of HEBT based on linear models.…”

“…In that study, the authors have no- iced that the raw data had strong intensity damping which not only limited straightforward segmentation of the HAADF reconstructions but also undermined the validity of HEBT based on linear models. Therefore, in [7] the data has been linearized in the data preprocessing as mentioned in Section 3.2 of [7] . Fig.…”

“…1 (a), an example of the cupping artifact is given. It is a 2D cross section of an Au-Ag core-shell nanoparticle [7] , reconstructed using the SIRT algorithm [8] . If we look at the line-profile of the 2D image ( Fig.…”

Quantitative Aspects of 3D Chemical Tomography in the Scanning Transmission Electron Microscope

“…In ET, the 3-D structure of a specimen is mathematically calculated from a series of 2-D projections acquired over a range of specimen orientations. Recent advances in specimen preparation, automation of data collection, and improved reconstruction methods have also made it feasible to couple tomographic data acquisition with X-ray energy dispersive and electron energy-loss spectroscopies (XEDS and EELS, respectively) in order to carry out 3-D elemental and chemical analysis at similar length scales [1][2][3][4][5][6][7].…”