Aberrations of emission cathodes: Nanometer diameter field-emission electron sources

The electron optical properties of nanometer sized field-emission cathodes are examined for suitability as electron sources for low-voltage scanning electron microscopy, low-voltage transmission point projection microscopy, and low-voltage transmission and reflection electron holography. First-order electron optical properties, aperture and chromatic aberrations, and source coherence are computed using an all-orders numerical method, and compared with analytically computed properties where possible. The electron optical properties of planar emitters, conventional field-emission tips, and new nanotip structures are compared in the absence of space-charge effects. It is found that the spherical and chromatic aberrations of nanotips are dominated by their base structures and that beams produced by nanotips can be considered as totally coherent.