Novel electron monochromator for high resolution imaging and spectroscopy

A mirror electron monochromator has been developed for reducing the energy spread of commonly used high brightness electron sources from the characteristic range of 0.3–1 eV to values below 100 meV. The monochromator utilizes mirror optics and thereby exploits the symmetry inherent in reversing the electron trajectory to monochromatize the primary beam with a knife edge instead of a conventional slit. The performance of the key electron-optical components of the monochromator has been simulated. These components include the combination of an electron mirror with a magnetic prism array. In initial testing, the monochromator has demonstrated the ability to reduce the energy spread of a 5 keV electron beam that was generated by a Schottky electron emitter from its initial value of 0.65–0.75 eV to 180 meV with an exit beam current exceeding 1 nA and to 100 meV with an exit beam current of 50 pA. Here, the attainable energy resolution was found to be limited by the noise on the power supply. The monochromator is designed to attach to scanning and transmission electron microscopes thus making them suitable for enhancing the study of the structure, composition, and bonding states of new materials at the nanoscale. For scanning electron microscopy, the monochromator will increase the spatial resolution of the acquired images of specimens, in particular, at low landing energies where the chromatic aberrations become dominant. For transmission electron microscopy, the monochromator will refine the spectra extracted from electron spectrometers, where the energy spread of the electron source limits the achievable energy resolution.