![]() The device, a replicate of which is shown in the figure, used two magnetic lenses to achieve higher magnifications, the first electron microscope. ![]() In 1931, Max Knoll and Ernst Ruska successfully generated magnified images of mesh grids placed over an anode aperture. The team consisted of several PhD students including Ernst Ruska. In 1928, at the Technical University of Berlin, Adolf Matthias (Professor of High Voltage Technology and Electrical Installations) appointed Max Knoll to lead a team of researchers to advance research on electron beams and cathode-ray oscilloscopes. To this day the issue of who invented the transmission electron microscope is controversial. According to Dennis Gabor, the physicist Leó Szilárd tried in 1928 to convince him to build an electron microscope, for which Szilárd had filed a patent. Others were focusing of the electrons by an axial magnetic field by Emil Wiechert in 1899, improved oxide-coated cathodes which produced more electrons by Arthur Wehnelt in 1905 and the development of the electromagnetic lens in 1926 by Hans Busch. ![]() One significant step was the work of Hertz in 1883 who made a cathode-ray tube with electrostatic and magnetic deflection, demonstrating manipulation of the direction of an electron beam. Many developments laid the groundwork of the electron optics used in microscopes. Reproduction of an early electron microscope constructed by Ernst Ruska This articles contains some general information mainly about transmission electron microscopes. Photoemission electron microscopy (PEEM) is similar to LEEM using electrons produced at surfaces by photonsĪdditional details can be found in the above.Low-energy electron microscopy (LEEM), used to image surfaces.Ultrafast scanning electron microscopy, version of SEM that can operate very fast.Electron microprobe similar to a SEM, but more for chemical analysis.Scanning electron microscope (SEM) is similar the STEM, but with thick samples.Scanning transmission electron microscopy (STEM) is similar to TEM with a scanned electron probe.Transmission electron microscopy (TEM) where swift electrons go through a thin sample.As the wavelength of an electron can be up to 100,000 times shorter than that of visible light, electron microscopes have a higher resolution of about 0.1 nm, which compares to about 200 nm for light microscopes. They use electron optics that are analogous to the glass lenses of an optical light microscope. The separated electron is called the auger electron (Figure 1).An image of an ant in a scanning electron microscopeĪn electron microscope is a microscope that uses a beam of electrons as a source of illumination. This excess energy is compensated by the separation of an electron from the outer layer of the atom or the emission of X-rays from the atom. The descent of an electron to a lower energy layer causes excess energy in the atom. The hole created in the atom is filled by electrons at a higher energy level due to the separation of the secondary electron. Each of the incident electrons can produce several secondary electrons. The electron separated from the atom that leaves the atom with very little energy (about 5 electron volts) is called a secondary electron. As a result of this energy transfer, the incident electron loses some of its energy and changes direction, and the specimen atom loses its electron and ionizes. Their path is so close to the specimen atoms that some of their energy is transferred to the electrons of the atom. A number of other electrons pass close to the atoms. ![]() These electrons are called backscattered electrons. Some of the electrons collide with the specimen atoms and return in the opposite direction by changing their direction 180 degrees. Different reactions may occur when a high-energy electron beam strikes a specimen. ![]()
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