Practical Electron Microscopy and Database

In order to improve the energy spread of the electron sources in EMs, monochromators have recently been introduced. In the best cases, the energy spread with a monochromator for any source can be reduced to < ~100 meV. There are two basic setups: the Wien filter with crossed electric and magnetic fields and the electrostatic Omega filter. It is very common that both types improve the energy width to about 0.2 eV at an acceptable beam current of several 100 pA. The single Wien filter limits the probe size to about 2 nm, whereas there is no such limitation in the case of the Omega filter. This spatial aberration of the Wien filter can be improved by using double Wien filters [1]. However, Wien filter is not suitable for routine use and has not been duplicated by any manufacturer.

[1] Martínez G, Tsuno K. 2004. Design of Wien filters with high resolution. Ultramicroscopy 100:105–14