It has been dogma for more than a hundred years that the light microscope cannot resolve structures that are much closer together than the length of the wavelength of light. This limit is on the order of a few hundred nanometers. This rule was “broken” by using the electron beam as the illumination source. The shorter wavelength of the electron beam gave correspondingly better resolution, down in the nanometer range. The rule was “broken” again when non-optical scanning probe microscopes (such as the scanning tunneling and atomic force microscopes) were developed. This technology gave us resolution in the sub-nanometer range, imaging individual atoms and molecules. However, scanning probe microscopes scan the surface of the specimen, excluding what's underneath from our view.