Atomic-focuser imaging by graphite crystals in carbon nanoshells

One of the atomic-focuser modes for ultra-high resolution electron microsco py is described theoretically and illustrated by the observation of images formed within the diffraction spots of nanodiffraction patterns of carbon n anoshells. In this mode, the specimen is illuminated by the focused probe o f a scanning transmission electron microscope and is followed by a thin cry stal at a Fourier image distance. The theory shows that each diffraction sp ot 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 c rystal, contained within one wall of a carbon nanoshell, can act as an atom ic focuser to image part of the other wall of the nanoshell, or tungsten at oms deposited on this wall. Simulations of the transmission of electrons th rough graphite crystals show that the images formed should have a resolutio n of abo ut 0.06 nm. Experimental images suggest that this resolution has b een attained in the imaging of tungsten atoms or clusters of tungsten atoms .