Phase contrast imaging in transmission electron microscopy, e.g., off-axis electron holography, is able to be used to measure functional (electric/magnetic) properties in materials; in combinations with in situ capabilities, to further study the responses in the presence of the external stimuli, including temperature, magnetic field or current/voltage.

Quantitative measurement of electromagnetic signals is based on the Aharonov-Bohn effect, i.e., the electron phase difference measured by electron holography could be quantitatively related to the surrouding electric potential and magnetic vector potetiatial:

Other electromagnetic imaging techniques include Fresnel imaging, differential phase contrast and electron pytychography in scanning transmission electron microscopy.

Current research fields include:

• Electric potential and charges in two-dimensional projections;

• Electron-beam-induced charging and secondary electrons;

• Magnetic fields/inductions;

• Electron holograhpic tomographyof electromagnetic fields, sources and potentials.

References：

1. Aharonov, Y. & Bohm, D. Significance of electromagnetic potentials in the quantum theory. Phys. Rev. 115, 485-491 (1959).

2. Hawkes, P. W. & Spence, J. C. H. Eds. Springer Handbook of Microscopy. Springer Cham. 2019.

3. Carter, C. B. & Williams, D. B. Eds. Transmission Electron Microscopy: Diffraction, Imaging, and Spectrometry. Springer Cham. 2016.

4. Volkl, E., Allard, L. F. & Joy, D. C. Eds. Introduction to Electron Holography. Springer. 1999.

5. Tonomura, A. The Quantum World Uneviled by Electron Waves. World Scientific. 1998.