A Model Based Method for Tomographic Reconstructions of Nanoparticle Assemblies

Small angle X-ray scattering is a primary tool for resolving the crystal structures of self-assembled nanoparticle superlattices [1]. However, it is not quite informative when periodic lattices are broken into clusters due to their inhomogeneity. Therefore, it is desirable to develop a method to rapidly reconstruct the three-dimensional architecture of cluster ensembles in real space. Conventional tilt-series electron tomography is well poised for this task; it is, yet, limited by its low throughput. For instance, a reasonable reconstruction generally requires 70-140 tilt images, which would need 40 minutes or 2-4 hours to record a BF-TEM or an ADF-STEM tilt series, respectively. In addition, the intensity of BF-TEM images is not a linear or any simple monotonic function of the sample thickness particularly when gold nanoparticles are imaged; this could dramatically lower the resolution and interpretability of the reconstructed tomograms. Here, we present a model based tomographic method that only relies on the projected centroids of the nanoparticles and bypasses the image intensity. This method only requires 5-10 tilt images and it is useful for calibrating a TEM goniometer and field/scan distortions.