THE ULTRA-HIGH-RESOLUTION IMAGING OF SINGLE ADATOMS OF GOLD BY CRYSTAL APERTURE FE-STEM

The method of crystal aperture scanning transmission electron microsco py (STEM) was proposed in an earlier paper [1] and tested experimental ly in an electron microscope system utilizing a lanthanum hexaboride s ource. In the present work a dedicated STEM, fitted with a cold field- emission (FE) electron-source was utilized in the imaging, in bright f ield, of gold atoms on a {110} surface of copper. The STEM beam was ac curately parallel to the [110] zone axis of the copper foil. According ly, for the beam centred in zone axis tunnels, it is argued that ray o ptical principles, which according to the earlier postulate forms the basis of the method, would control the image formation. In the present experiments, it is shown that the configuration of groups of atoms im aged, is uniquely consistent with that of atoms adsorbed in stacking f ault positions on the {110} surface. Thus, such atoms would be positio ned symmetrically at the exit mouths of [110] zone axis tunnels where the proposed method would produce the highest resolution. The experime ntal results further indicate that a probe diameter of less than 0.05 nm was obtained. This is interpreted as strong supporting evidence for the validity of the ray optical model in the present method.