A phantom-based forward projection approach in support of model-based iterative reconstructions for HAADF-STEM tomography.

We introduce a forward model for the computation of high angle annular dark field (HAADF) images of nano-crystalline spherical particles and apply it to image simulations for assemblies of nano-spheres of Al, Cu, and Au with a range of sizes, as well as an artificial bi-sphere, consisting of solid hemispheres of Al and Cu or Al and Au. Comparison of computed intensity profiles with experimental observations on Al spheres at different microscope accelerating voltages provides confidence in the forward model. Simulated tomographic tilt series for both HAADF and bright field (BF) images are then used to illustrate that the model-based iterative reconstruction (MBIR) approach is capable of reconstructing sphere configurations of mixed atomic number, with the correct relative reconstructed intensity ratio proportional to the square of the atomic number ratio.