  Nearly twenty years ago, following a sixty year struggle, scientists
succeeded in correcting the bane of electron lenses, spherical aberration,
using electromagnetic aberration correction. However, such correctors
necessitate re-engineering of the electron column, additional space, a power
supply, water cooling, and other requirements. Here, we show how modern
nanofabrication techniques can be used to surpass the resolution of an
uncorrected scanning transmission electron microscope more simply by sculpting
a foil of material into a refractive corrector that negates spherical
aberration. This corrector can be fabricated at low cost using a simple process
and installed on existing electron microscopes without changing their hardware,
thereby providing an immediate upgrade to spatial resolution. Using our
corrector, we reveal features of Si and Cu samples that cannot be resolved in
the uncorrected microscope.
