Monochromators in electron microscopy

Abstract

Monochromators used in electron microscopes have been reviewed. There are three steps in its progress. At the first step, monochromator is used in retarding mode. Wien filter monochromator and analyzer are floating on the high voltage connected to the gun high voltage. It provides very high energy resolution of about 10meV at 60kV accelerating voltage. In the second step, various gun monochromators; the Wien filter (fringe field monochromator, single focus monochromator and double focus monochromator) and electrostatic omega type are proposed and some of which are commercialized. The double Wien filter and the electrostatic omega monochromators have functions of astigmatic focus on the slit plane and the compensation of the dispersion at the last focus.As the third step, the earth potential monochromator is proposed. Only highly stabilized beam can go through the earth potential monochromator slit, whose magnetic field is stabilized around the 10−8, even if the beam stability from the gun is not so high. This function will be useful in the future high spatial resolution electron microscopy.