Theoretical calculation of probe size of low‐voltage scanning electron microscopes

Detailed investigating into the effects of spherical and chromatic aberrations, diffraction and the probe current allows the more general formulae for the optimized aperture and the minimum probe radius in low‐voltage scanning electron microscopes (LVSEMs) to be derived using both wave optics and geometric optics. The probe sizes for a diversity of electron sources in LVSEMs have been estimated, which may be useful for practical applications. The computed results indicate the possibility of achieving 1·5–2·0‐nm resolution at low voltages. 1993 Blackwell Science Ltd