Ardenne applied scanning of the electron beam in an attempt to surpass the resolution of the transmission electron microscope (TEM), as well as to mitigate substantial problems with chromatic aberration inherent to real imaging in the TEM. Although Max Knoll produced a photo with a 50 mm object-field-width showing channeling contrast by the use of an electron beam scanner, it was Manfred von Ardenne who in 1937 invented a microscope with high resolution by scanning a very small raster with a demagnified and finely focused electron beam. History Īn account of the early history of scanning electron microscopy has been presented by McMullan. Specimens are observed in high vacuum in a conventional SEM, or in low vacuum or wet conditions in a variable pressure or environmental SEM, and at a wide range of cryogenic or elevated temperatures with specialized instruments. Some SEMs can achieve resolutions better than 1 nanometer. The number of secondary electrons that can be detected, and thus the signal intensity, depends, among other things, on specimen topography.
In the most common SEM mode, secondary electrons emitted by atoms excited by the electron beam are detected using a secondary electron detector ( Everhart–Thornley detector). The electron beam is scanned in a raster scan pattern, and the position of the beam is combined with the intensity of the detected signal to produce an image.
The electrons interact with atoms in the sample, producing various signals that contain information about the surface topography and composition of the sample. von Ardenne's first SEM Operating principle of a Scanning Electron Microscope (SEM) SEM with opened sample chamber Analog type SEMĪ scanning electron microscope ( SEM) is a type of electron microscope that produces images of a sample by scanning the surface with a focused beam of electrons. Image of pollen grains taken on a SEM shows the characteristic depth of field of SEM micrographs M. Not to be confused with Scanning tunneling microscope.
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