This report demonstrates the most spatially-coherent electron source ever reported. A coherence angle of 14.3 +/- 0.5 degrees was measured, indicating a virtual source size of 1.7 +/-0.6 Angstrom using an extraction voltage of 89.5 V. The nanotips under study were crafted using a spatially-confined, field-assisted nitrogen etch which removes material from the periphery of the tip apex resulting in a sharp, tungsten-nitride stabilized, high-aspect ratio source. The coherence properties are deduced from holographic measurements in a low-energy electron point source microscope with a carbon nanotube bundle as sample. Using the virtual source size and emission current the brightness normalized to 100 kV is found to be 7.9x10^8 A/sr cm^2.
@article{arxiv.1208.2994,
title = {Nanoscale structuring of tungsten tip yields most coherent electron point-source},
author = {Josh Y. Mutus and Lucian Livadaru and Radovan Urban and Jason Pitters and A. Peter Legg and Robert A. Wolkow},
journal= {arXiv preprint arXiv:1208.2994},
year = {2013}
}