Electron microscopy measurements of electron orbitals

Quantitative characterization and real-space mapping of the electron orbital are highly desirable as it’s a basic orderparameter linking microscopic electronic structure and macroscopic properties in material science. Here we brieflyre-view the recent progress in the measurements of orbital populations via electron microscopic methods, includingquant-itative convergent-beam electron diffraction (QCBED), electron energy-loss spectroscopy (EELS) and others. Combingwith the rapid development of four-dimensional scanning transmission electron microscopy (4D-STEM), we propose thefuture potential directions and discuss possible solutions towards real-space orbital mapping at atomic scale.