Scientific Background
It has long been known that the best achievable spatial resolution of an optical microscope, that is the smallest feature it can observe, is of the order of the wavelength of the light λ, which is about 550 nm for green light. One route to improve this resolution is to use particles with smaller λ, such as high-energy electrons. Practical limitations set a convenient electron energy to 100–300 keV that corresponds to λ = 3.7–2.0 pm. Unfortunately, the resolution of electron microscopes is limited not by the electron wavelength, but by intrinsic imperfections of electron lenses. These are referred to as spherical and chromatic aberrations because of their similarity to aberrations in optical lenses. Those aberrations are reduced by installing in a microscope a set of specially designed auxiliary "lenses" which are called aberration correctors.
Read more about this topic: Transmission Electron Aberration-Corrected Microscope
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