Using a monochromator to improve the resolution in TEM to below 0.5Â Ã . Part I: Creating highly coherent monochromated illumination

► A monochromator is used to minimize the effect of chromatic aberration. ► We use a prototype gun of which the brightness is one order more than that of a standard Schottky-FEG. ► Brightness after monochromation is comparable to that of a standard S-FEG without monochromator. ► Highly coherent illumination can be obtained by focusing the dispersed source on the specimen. ► We demonstrate improvement of information transfer in TEM to 0.5 Å.