High-energy resolution electron spectrometer for 1-nm spatial analysis

A Wien Filter electron spectrometer has been successfully combined with a dedicated scanning transmission electron microscope (STEM) to obtain an energy resolution of 140 meV with a specimen collection semiangle of 25 mR at 100 keV. A cold-field emission electron source is used to produce a 0.35-10-nm-size electron beam which has a spread in energy of about 0.25 eV. Because this energy spread is much larger than the spectrometer energy resolution, deconvolution techniques may be applied under appropriate conditions to yield a spectroscopic energy resolution of about 70 meV at a 12.5-mR collection semiangle. The Wien Filter is a conventional design, but is immersed in a high-voltage electrode of asymmetric design to facilitate control of prespectrometer electron trajectories. A doublet quadrupole lens is used to match the spectrometer angular acceptance range with that of scattered electrons at the specimen. A weak sextupole lens is used to reduce the second-order angular aberrations.