He went on to develop serial block - face electron microscopy, whereby detailed 3D imagery of minute structures within tissue are generated by the repeated removal of thin slices and scanning of the remaining cut surface of samples. (kavlifoundation.org)
Four years later, Max Knoll discovered a means to sweep an electron beam over the surface of a sample, creating the first scanning electron microscope (SEM) images. (sciencemag.org)
It consists of a tiny metal finger with a tip only a few atoms wide that moves back and forth just above the surface of a sample. (sciencemag.org)