This is a copy of the slides presented at the meeting but not formally written up for the volume.

To address the needs of a wide variety of potential application domains, the sophistication and structural complexity of engineered nanoparticle systems has been steadily increasing. Often the unique functionality of these systems depends on the 3-dimensional distribution of multiple phases, ranging from simple coatings to core-shell morphologies to multifunctionalizations for drug delivery. This need for controlled 3-dimensional chemical heterogeneity at the nanoscale presents significant challenges both for the nanomanufacturing of these materials and their metrology and characterization. Even when the nanoparticles have relatively simple structures, the demands of modern process control methodologies and the specifications of end users frequently require increased metrology precision and decreased measurement bias for critical measurands such as coating thicknesses or particle size distributions. Recent advances in electron microscopy and focused ion beam (FIB) technology provide powerful tools for the 3-dimensional structural and elemental characterization of nanomaterials. Dimensional metrology using phase contrast high-resolution transmission electron microscopy (HRTEM) and scanning transmission electron microscopy (STEM) can measure the physical dimensions of nanostructures at the single nanometer level. Elemental mapping using energy-filtered TEM (EFTEM) can be used to map the spatial distribution of different stoichiometries, while electron tomography can reconstruct the 3-dimensional morphology of nanoparticle assemblies. Examples of the above techniques will be presented along with recent NIST efforts to fuse these techniques into a methodology for 3-dimensional chemical imaging of engineered nanostructures.