Abstract

To achieve higher resolution and improved interpretability in electron microscopy, indirect restoration of the specimen exit plane wavefunction is currently widely used. There are a few methods available, and the major difference between these methods is the assumptions on the coherence effects. I will focus on two of the methods: Wiener filter and the Maximum Likelihood (MAL) algorithm. The former applies linear imaging approximation (strong central beam), whereas the latter is more general. Both algorithms on the simulated and experimental data will be discussed and compared.

On the other hand, exit wave restoration can be achieved by using a series of images at either different defoci or beam tilts. Focal series restoration is a much more popular method as the acquisition of images at different defocus is easier in a conventional electron microscope. However, with the aberration-corrected electron microscope, tilt series acquisition is equally straightforward as focus series, and the tilt series has an advantage of better resolution over the focus series. Examples of exit wave restoration on the two material systems will be shown to demonstrate the power of the technique. The restorations of the peapod structure of Sc3N@C68@SWNT and catalytic Pt nanoparticles will be discussed.

Finally, the interpretation, and extension of the exit wave restoration and its limit will be discussed.