Estimate of minimum measurable voltage in the SEM

The minimum measurable voltage in the SEM is estimated for a voltage contrast linearization scheme with restricted- and unrestricted-aperture analysers, using approximations for the shapes of the energy distribution curves and assuming that the only significant source of noise is on the collected electrons. A similar estimate is also made for Auger electron voltage measurement schemes. A numerical example shows that the hemispherical retarding-potential analyser system (unrestricted aperture) provides the lowest measurable voltage.