Robust point source: Field emission from an iridium tip

In this article, iridium tips produced by electrochemical etching are evaluated for use as field emitters in electron sources for electron microscopy. They prove to have a much larger radius of curvature than predicted by Fowler–Nordheim curves for field emission. The source’s brightness is estimated at B > 1012 A m−2 sr−1 by projection microscopy. The position of the emitting region appears stable, although the current itself may be affected when pressure exceeds 10−9 mbar. The robustness of iridium tips is demonstrated by their ability to withstand such high pressures without significant optical or electrical changes.