Due to projection effects, analytical transmission electron microscopy (AEM) of thinned or sectioned samples has traditionally been limited to essentially two-dimensional imaging and analysis. Current nanometer scale devices are too small and complex for current sectioning capabilities and two-dimensional analysis since the electron beams pass through more than one device component. Moreover, existing approaches to acquire spectral images are too time-consuming and impractical. For example, a one second collection time taken at each nanometer-sized pixel of a 1,000 by 1,000 pixel image requires about 12 days.
Our approach produces 3D elemental maps using chemical tomography, based on tilt series of spectroscopic data in the AEM. The practicality of this approach has been demonstrated recently by the successful generation of experimental 3D elemental maps from nanometer-scale sample data acquired in the laboratory. Significant challenges of diffraction contrast and automating the AEM acquisition of spectral datasets have been addressed by a NIST team of scientists from MML, PML, and ITL.