Sub-ångström resolution of atomistic structures below 0.8 Å

Microcharacterization of defects is greatly facilitated with improvement in resolution. By improving temporal coherence (chromatic aberration) and compensating spatial incoherence, we have achieved the goal of the 1 Å microscope (OÅM) project at the US Department of Energy's National Center for Electron Microscopy by extending the limits of high-resolution transmission electron microscopy to sub-ångström levels. The OÅM combines focal-series image-processing software with a modified 300 keV electron microscope equipped with a highly coherent field emission electron gun. By operating at an ‘α-null’ value of underfocus in order to minimize the effects of spatial incoherence, and by reducing the OÅM's electron-gun extraction voltage to improve temporal coherence, we are able to transfer information below 0.8 Å. In a test specimen of silicon viewed in the [112] orientation in the OÅM we are able to ‘see’ atoms separated by only 0.78 Å. Sub-ångström resolution at this level offers the materials researcher an effective tool for the characterization of defects with unprecedented precision.