Atomic-focuser Imaging by Graphite Crystals in Carbon Nanoshells

One of the atomic-focuser modes for ultra-high resolution electron microscopy is described theoretically and illustrated by the observation of images formed within the diffraction spots of nanodiffraction patterns of carbon nanoshells. In this mode, the specimen is illuminated by the focused probe of a scanning transmission electron microscope and is followed by a thin crystal at a Fourier-image distance. The theory shows that each diffraction spot of the crystal contains a magnified image of the illuminated area of the specimen, having a resolution depending on the width of the intensity peak of electrons channeled along atomic rows in the crystal. A thin graphite crystal, contained within one wall of a carbon nanoshell, can act as an atomic focuser to image part of the other wall of the nanoshell, or tungsten atoms deposited on this wall. Simulations of the transmission of electrons through graphite crystals show that the images formed should have a resolution of about 0.06 nm. Experimental images suggest that this resolution has been attained in the imaging of tungsten atoms or clusters of tungsten atoms.