Advanced computing for ultra-high-resolution in TEM
1. Introduction Attempts to push the resolution of electron microscopes towards 1 Å follow presently two different strategies. One approach takes advantage of the short electron wavelength provided by high-voltage instruments (E > 1 MeV) resulting in an "interpretable" point resolution close to the information limit. An alternative strategy is based on the idea to extend the information limit of conventional medium-voltage instruments (E ≈ 200 - 300 keV) by taking advantage of the excellent coherence properties of field-emission guns (FEG). In the latter approach, however, the gain of extra information beyond the "interpretable" point resolution is of no direct use for structure interpretation. Generally, the interpretability of single highresolution images suffers from a loss of phase information and from contrast-delocalization effects, the latter being caused by the spherical aberration and the defocussing of the objective lens. These derealization effects become drastically apparent when aiming at the ultra-high resolution regime (d < 1.5 Å) which is routinely accessible with medium-voltage FEG-TEMs.