Reducing virtual source size by using facetless electron source for high brightness

Brightness of an electron source is key for the high spatial resolution of electron microscopy and analysis. A small source size is essential for high brightness, and it has been achieved by using small crystal facets; however, the emission current is reduced when the facet area is decreased. To achieve a small source size while maintaining a large emission current, we conceived of the novel idea of a facetless electron source with a curved emission surface. Computational simulations of electron trajectories revealed that the virtual source, which is the spot at which back-projected trajectories are focused, of a facetless source was smaller than that of the conventional source with a facet and that the brightness of the facetless source was approximately four times larger. To achieve electron emission from a curved surface, we fabricated a facetless source by coating amorphous carbon on a metallic electron source. Electron emission from the coated surface showed a homogeneous pattern, which is clear evidence for emission from the curved surface of the facetless source.