Scanning Electron Microscope (SEM)
The Early History and Development of The Scanning Electron Microscope The earliest known work describing the concept of a Scanning Electron Microscope was by M. Knoll (1935) who, along with other pioneers in the field of electron optics, was working in Germany. Subsequently M. von Ardenne (1938) constructed a scanning transmission electron microscope (STEM) by adding scan coils to a transmission electron microscope. The first STEM micrograph was of a ZnO crystal imaged at an operating voltage of 23 kV at a magnification of 8000 times, and a spatial resolution between 50 and 100 nm. The micrograph contained 400 x 400 scan lines and took 20 min to record, because the film was mechanically scanned in synch with the beam. The instrument had two electrostatic lenses, with the scan coils placed between them. The instrument also had a viewing CRT, but it was not used to record the image The first SEM used to examine the surface of a solid specimen was described by Zworykin et al. (194...