Atomic Lattice Resolved Electron Tomography of a 3D Self Assembled Mesocrystal

Complex 3D architectures of nanoscale building blocks can be created by self-assembly, but characterization of the atomic to mesoscale structure of such materials is limited by the difficulty of visualizing atoms across multiple length scales. Here, scanning transmission electron microscopy (STEM) and full-tilt tomographic reconstruction are used to image a single-crystalline region of a 3D epitaxially-fused PbSe quantum dot (QD) superlattice containing 633 QDs at a spatial resolution of 2.16 Å. The combined real-space and reciprocal-space analysis enables 3D mesoscale correlations of atomic lattice and superlattice order across hundreds of nanocrystals in 3D for the first time. Inhomogeneity in QD positional and orientational order reveals that the QD surface layers template the superlattice and that orientational entropy is higher in the interior layers than the surface layers. The measurement and analysis techniques presented here are applicable to a broad range of 3D nanostructured materials.