High Energy/Spatial Resolution Electron Microscopy from LaB₆ Nanostructured Electron Source

In recent years, tremendous advancement in S(TEM)-EELS has enabled milli-eV energy resolution and sub-angstrom spatial resolution. New instrumentation has led to new microscopy methodology for extracting material information richer than ever before. In a modern EELS-STEM system, the energy resolution is determined by the energy spread of electron beam coming out of the monochromated electron gun; and spatial resolution, on the other hand, is limited by the geometric aberration generated in the gun due to such monochromation processes. To achieve improvement in both resolution pursuits, though conflicting in nature, it is vital to find an electron source with both brightness and monochromaticity as high as possible. Conventionally available electron sources, including thermionic electron source, Schottky electron source and W(310) cold field emission electron source, with their respective limitations, are insufficient to help overcome current technology barrier. In this talk, we will introduce a new type of ultrahigh brightness cold field electron source made of low work function LaB₆ single crystalline nanowire. We will first go over how nanostructured electron source surpasses conventional counterparts as a mechanistic discussion of basic emission properties. Then application examples in commercial S(TEM), SEM and semiconductor inspection instruments will be demonstrated. Finally, we will discuss several new future development schemes for next generation STEM-EELS that is enabled by the unique features of the LaB6 nanostructured electron source.