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electronic orbitals

While we know that all matter is composed of atoms, our understanding of the electron orbitals that are fundamental to the properties of these atoms has historically been limited to theory and indirect evidence rather than direct experimental measurements of electron density. Work in x-ray diffraction, electron diffraction, and transmission electron microscopy have produced maps of electron densities in near-defect-free crystals. Additionally, atomic force microscopy and scanning tunneling microscopy have been used to characterize bonding electron orbitals of individual molecules and surface atoms. Our work has focused on directly characterizing core-level electron orbitals using spatially resolved energy-dispersive x-ray spectroscopy (EDX) in a scanning transmission electron microscope (STEM).

 


Figure:(a) HAADF-STEM image of strontium titanate viewed along the [001] zone axis with a model of the atomic positions overlaid at the top. (b) STEM/EDX map showing superimposed Sr (purple), Ti (green), and O (yellow) maps. (c-d) Individual Sr Kα and Sr L STEM/EDX maps. The scale bar is 2 Å. (e-h) Experimentally observed projected excitation potentials of the 1s and 2p orbitals for Sr and Ti including atomic thermal vibrations and excitation broadening, derived from (a-d). Figure and text adapted from [1]

Recommended Reading

  1. "Atomic bonding effects in annular dark field scanning transmission electron microscopy. II. Experiments"
    M. L. Odlyzko, J. T. Held, K. A. Mkhoyan
    - J. Vac. Sci. Technol. A 34, 041603 (2016).   [Ed. Pick]

  2. "Atomic bonding effects in annular dark field scanning transmission electron microscopy. I. Computational predictions"
    M. L. Odlyzko, B. Himmetoglu, M. Cococcioni, K. A. Mkhoyan
    - J. Vac. Sci. Technol. A 34, 041602 (2016).   [Ed. Pick]

  3. "Probing core-electron orbitals by scanning transmission electron microscopy and measuring the delocalization of core-level excitations"
    J. S. Jeong, M. L. Odlyzko, P. Xu, B. Jalan, and K. A. Mkhoyan
    - Phys. Rev. B 93, 165140 (2016)

  4. "Improving Signal-to-Noise Ratio in Scanning Transmission Electron Microscopy Energy-Dispersive X-Ray (STEM-EDX) Spectrum Images Using Single-Atomic-Column Cross-Correlation Averaging"
    J. S. Jeong, K. A. Mkhoyan
    - Microsc. Microanal. 22, 536 (2016)
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