While at Argonne Crewe became interested in electron microscopy, an interest stimulated by the major biology program there. Crewe saw ways in which it would be possible to improve the images important to that work. He came up with a design for a scanning electron microscope and set up a group at Argonne to build it, getting it to function in 1963. This work became so interesting to Crewe that in 1967 he decided to leave Argonne and return to the university's physics faculty, which had granted him a full professorship in 1963. In 1964 Crewe developed the first
field emission electron gun in collaboration with Hitachi, a new type of electron source that enabled much higher optical quality than had previously been possible. This gun, combined with inventions in electron lenses and detection, led to the development of the highest resolution microscope at that time. In 1970 his field emission
scanning transmission electron microscope succeeded in taking images individual atom (though not the first, this achievement usually being credited to
Erwin Muller). In 1975 he was successful in obtaining the first motion pictures of atoms, providing new insight into atomic interaction and material formation. There followed, during the 1980s, a series of important refining techniques. In 1980 he invented a method for the correction of spherical aberration in electron optical systems using sextupoles and, in 1996, Crewe invented a new type of focusing lens for low voltage scanning microscopes. He held 19 patents for his inventions, and had more than 275 publications, most of them concerned with electron optics and electron microscopes. Beginning in the 1970s and continuing to the present day commercial electron microscopes were developed based on Crewe's innovations. These systems enabled significant advances in the biomedical, pharmaceutical, and semiconductor industries. Hitachi Corporation produced the first successful commercial version of the field emission scanning electron microscope in 1970 which received an IEEE Milestone award in 2012. Crewe was a consultant to Hitachi in this effort. Since that time Hitachi has produced over 5300 cold field emission
scanning electron microscopes and over 4000 (Schottky) thermal field emission scanning electron microscopes. They are considered the highest resolution instruments available and cost over one million USD each to build. Today there are over 5000 field emission microscopes operational in semiconductor fabrication facilities worldwide, enabling companies like Intel and IBM to produce the latest and fastest microprocessors. Crewe served as Dean of Physical Sciences at the University of Chicago from 1971 to 1981. In 1977 was named the William E. Wrather Distinguished Service Professor, and from 2002 he was the Wrather Distinguished Service Professor Emeritus. He continued to explore new methods of obtaining high resolution, and in 2003 developed a low voltage electron microscope using a
dipole permanent magnet as a lens. ==Honors==