KEYWORDS: Scanning electron microscopy, Scanning transmission electron microscopy, Sensors, Electron beams, Contamination, Monochromators, Chromatic aberrations, Crystals, Electron microscopes, Image resolution
For decades, high resolution scanning electron microscopes (SEM) have strived to offer improved performance in the
high and low energy regimes. High energies have always been attractive, because they lead to sub-nanometer resolution
without complex electron optics, especially when using a scanning transmission electron microscopy (STEM) mode in
the SEM. Lower energies have caught the attention of microscopists, due to their increased surface sensitivity,
minimized charging effects or reduced depth of radiation damage. While going to very low beam landing energies was
demonstrated more than 20 years ago, keeping a nanometric spot-size below 1 keV proved to be a technological
challenge. Only a few years ago did the first commercial SEM succeed in delivering sub-nanometer resolution at 1 kV,
but with some restrictions. Recently, the introduction of the extreme high resolution (XHR) SEM has demonstrated subnanometer
resolution in the entire 1 to 30 kV range, thanks to a monochromatized Schottky electron source that reduces
the effects of chromatic aberrations at lower energies. Of at least equal interest is the fact that the same XHR SEM can
take advantage of its optics, modularity, platform stability and cleanliness developments to explore new avenues, such as
high resolution imaging at very low beam energies or up to 30 kV STEM-in-SEM. For the first time, complementary
information from the very surface and internal structure at the true nanometer level is obtained in the same SEM.
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