Phase Contrast in Scanning Transmission Electron Microscopy with Nanostructured Phase Gratings*

Off-axis electron holography, which uses an electrostatic biprisim to interfere electrons transmitted through a specimen with a reference wave, has for many years been the premier technique for retrieving the phase of electrons. With holography, one can both reconstruct long-range electric and magnetic fields [1], and map the charge distribution in a nanowire [2]. However, the resolution of off-axis electron holography is fundamentally limited because interference fringes are recorded in real space; standard reconstruction of the phase has a resolution on the order of the fringe spacing.

A similar technique is possible in scanning transmission electron microscopy, where the transmitted beam and reference beam are focused, and holograms are recorded in diffraction as the beams are scanned. Resolution is limited only by the size of the focused beams at the specimen. We show that phase retrieval is straightforward and intuitive and present a proof-of-principle demonstration.

[1] O. Matteucci et al., Adv. in Imaging & Elect. Phys. 99, 171 (1997).
[2] Z. Ghan et al., Nano Lett. 16, 3748 (2016).