How to Select the Items for the Shopping List of Future High Resolution Electron Microscopists?

Instrumental developments continue to push the resolution of electron microscopes beyond 1 Å. Apart from the continuous improvement in resolution of the classical high resolution electron microscopes (HREM), new possibilities emerge, such as, correction of the spherical aberration both in transmission and scanning transmission electron microscopy (TEM and STEM, respectively), combination of TEM with high angle annular dark field (HAADF) STEM, monochromators, and offaxis holography. Furthermore, in our view, the new electron microscope will show a large versatility in experimental settings under computer control, such as, TEM or STEM, imaging or diffraction techniques (such as convergent beam electron diffraction, precession, and ptychography), focus, voltage, spherical aberration, beam tilt, and crystal tilt. The main limiting factors in the experiment will be the incident electron dose, that is, the amount of electrons that interact with the object during the experiment, and the recording time, because of the radiation sensitivity of the object and the specimen drift, respectively. The question then arises which instrument and which experimental settings are optimal given the incident electron dose or the recording time available. To answer this question, an optimality criterion that meets the purpose of future HREM is needed.