Anisotropic atomic contrast by final-state selection in electron energy-loss spectroscopy

Understanding individual electronic orbitals involved in chemical bonding through scanning transmission electron microscopy and electron energy loss spectroscopy is essential for advancing materials science. Although previous theoretical and experimental results show the anisotropic image contrast of the corresponding particular final-state, the interpretation of these contrasts remain unclear. Here, we demonstrate the experimental anisotropic atomic contrast in the mapping of the fine structure of the O $K$- and Ti ${L}_{2,3}$-edges of rutile $\mathrm{Ti}{\mathrm{O}}_{2}$, and propose a qualitative theoretical explanation. Our results revealed that the contrast does not directly reflect the electron density of the final state orbital, but rather the direction in which the selected transition matrix element is reflected. And its direction sometimes corresponds to that of selected orbital but not always so. The proposed interpretation method would be used for the analysis of future experimental data.