THEORETICAL CALCULATION OF PROBE SIZE OF LOW-VOLTAGE SCANNING ELECTRON-MICROSCOPES

Detailed investigating into the effects of spherical and chromatic abe rrations, diffraction and the probe current allows the more general fo rmulae for the optimized aperture and the minimum probe radius in low- voltage scanning electron microscopes (LVSEMs) to be derived using bot h wave optics and geometric optics. The probe sizes for a diversity of electron sources in LVSEMs have been estimated, which may be useful f or practical applications. The computed results indicate the possibili ty of achieving 1.5-2.0-nm resolution at low voltages.