Spatial resolution in EFTEM elemental maps

Imaging filters developed over the last few years permit rapid elemental mapping by energy-filtering transmission electron microscopy (EFTEM), with resolution and sensitivity limited primarily by the sample and by the TEM. We explore the attainable spatial resolution in the elemental maps theoretically and experimentally, and suggest optimized set-up procedures for maximizing the resolution. The chromatic aberration of the objective lens of the microscope is shown to be a major limit. Its influence can be minimized by using small energy intervals and limited collection angles, but this is done at the cost of decreased collection efficiency. Resolution of better than 1 nm and sensitivities to less than a monolayer of elements with favourable edges are readily attainable in elemental maps obtained with acquisition times of 40s total and less, Resolution better than 0.5 nm should be attainable with further optimization of the acquisition parameters.