The visualization of electron orbitals in real space is expected as a next-generation technique that has been evolved from high spatial resolution electron microscopy. Core excitation electron energy-loss spectra with a high signal-to-noise ratio were recorded in a scanning transmission electron microscope with high spatial resolution to directly observe the electron orbitals in real space. We experimentally demonstrate that anisotropic distributions of oxygen 2p orbitals in SrTiO3 were observed in real space and were dependent on the difference in the chemical bonds between Ti and O atoms. The results open the door to the visualization of electronic orbitals with electron microscopes.
High-angle annular dark-field (HAADF) imaging and elemental mapping at the atomic scale by scanning transmission electron microscopy (STEM) combined with electron energy-loss spectroscopy (EELS) are widely used for material characterization, in which quantitative understanding of the contrast of the image is required. Here, we report an unexpected image contrast in the elemental mapping of rutile TiO2, where the Ti L2,3 map shows an anisotropic elliptical shape that extends along the long axis in the octahedral structure, while the atomic contrast of Ti columns in the HAADF image is almost circular. Multi-slice simulation reveals that unique electron channeling related to the rutile structure and the difference of the potentials between HAADF and EELS cause the different atomic contrasts in the two images.
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