Sub-Angstom Resolution Using Aberration Corrected Electron Optics

Since the invention of electron optics during the 1930’s, lens aberrations have
limited the achievable spatial resolution to about 50 times the wavelength of the
imaging electrons. This situation is similar to that faced by Leeuwenhoek in the
17th century, whose work to improve the quality of glass lenses led directly to his
discovery of the ubiquitous "animalicules" in canal water, the first hints of the
cellular basis of life. Although the electron optical aberration problem was well
understood, more than 60 years elapsed before a practical correction scheme for
electron microscopy was demonstrated, and even then the remaining chromatic
aberrations still limited the obtained improvement. We report here successful
aberration correction in a Scanning Transmission Electron Microscope, which is
less sensitive to chromatic aberration, achieving an electron probe smaller than
1 Å for the first time. This performance, about 20 times the electron wavelength
at 120 KeV energy, allows dynamic imaging of single atoms, clusters of a few
atoms, and single atomic layer "rafts" of atoms coexisting with Au islands on
a carbon substrate. Atomic column imaging of semiconductors is now possible
using a beam energy which is below the damage threshold for silicon.