Energy-filtered transmission electron microscopy based on inner-shell ionization

We demonstrate that energy-filtered transmission electron microscopy (EFTEM) based on inner-shell ionization can contain atomic resolution information. We present a comparison between experimental data and simulation for the EFTEM image of the _N4,5${\mathrm{N}}_{4,5}$ edge (threshold energy 99 eV) of lanthanum in _LaB6${\mathrm{LaB}}_6$ in which direct interpretation of the location of the lanthanum columns is possible. Our first principles approach is based on calculating transition potentials for inelastic scattering. For our case study, the localization of the transition potentials is such that elastic contrast is only weakly preserved in the EFTEM image. This is not always the case, but we show how the approach based on calculating the elastic wave function and the transition potentials can provide insight about when direct interpretation may and may not be possible. In our test specimen, the direct interpretation fails for thicker specimens when the long tails of the transition potential from multiple adjacent sites leads to significant image features other than at the sites of the element of interest. We can thus anticipate instances where direct interpretation may be more reliable, such as looking for a single impurity in an otherwise well known sample.