Moiré patterns in electron microscopy with atomic focuser crystals.

The periodic array of very fine cross-overs formed at the exit face of a thin 'atomic focuser' crystal, illuminated by a parallel electron beam, may be used to form moiré patterns with a specimen crystal such that the structure of the specimen crystal may be derived with a resolution of better than 0.5 Å. Computer simulations of the moiré pattern formation have been made for the simple idealized case of two parallel gold-like lattices having a 10% difference in lattice constant. Moiré images are shown for the case of a small objective aperture in the viewing electron microscope such that the individual crystal lattices are not resolved and for a larger objective aperture for which the individual crystal lattices are resolved and the intensity is measured at the positions of the atoms of the atomic focuser crystal. The latter case confirms the viability of the scheme for ultra-high-resolution imaging of general specimens by use of a thin-crystal periodic atomic focuser, as previously proposed.