The invention of the electron microscope Ernst August Friedrich Ruska (German: Ernst August Friedrich Ruska, born December 25, 1906 in Heidelberg, Baden, Germany - 1988 Berlin, May 27, 2011), West German physicist, inventor of the electron microscope, and winner of the Nobel Prize in Physics in 1986. The history of Ruska's development of electron microscopes can actually be traced back to the late 19th century. In the process of studying cathode rays, people found that the shadow of the anode often appears on the wall of the cathode ray tube. Braun designed and built the original oscilloscope tube in 1987. This prepared the technical conditions for the birth of the electron microscope. In 1926, H. Busch published a paper on magnetic focusing, pointing out that electron beams can be focused when passing through an axially symmetric electromagnetic field, just like light can be focused when passing through a lens, so electron imaging can be used. This provides theoretical preparation for electron microscopy. The main factor limiting the resolution of optical microscopy is the wavelength of light. Because electron beam wavelengths are much shorter than light wavelengths, electron microscopy using electron beam imaging can be expected to achieve much higher resolution than optical microscopy. Ernst Ruska was born on December 25, 1906 in Heidelberg, Baden, Germany. His father was a professor of history at the University of Berlin. From 1925 to 1927, Ernst loved engineering when he was in middle school. He studied electrical engineering at two companies in Munich. Later, he followed his father to Berlin. In the summer of 1928, he entered the Technical University of Berlin in Chalottinburg, Berlin, where he worked in a high-voltage laboratory and engaged in research on cathode ray oscilloscope tubes. Beginning in 1929, Ruska conducted electron lens experiments under the guidance of team leader M. Knoll. This is very beneficial to Ruska's growth. From 1928 to 1929, on the basis of participating in the research work on oscilloscope tube technology, Ruska conducted experimental research on using magnetic lenses and electrostatic lenses to focus electron beams for imaging, confirming that an optical cable with a diameter of 0.3 mm under electron beam irradiation can A low-magnification (1.3x) image was generated and the lens imaging formula was verified. This laid the foundation for the creation of the electron microscope. In 1931, Knorr and Ruska began to develop electron microscopes. They experimentally proved that in order to obtain the same focal length, the number of turns of the coil installed in the iron shell was much smaller than that of the coil without iron shell. . From April to June 1931, they used an electron microscope with a secondary magnetic lens to achieve a magnification of 16 times. Through calculations, they realized that according to De Broglie's matter wave theory, the wavelength of electrons is five orders of magnitude shorter than the wavelength of light waves, and it is possible for electron microscopes to achieve higher resolution. They predict that future electron microscopes will have a diffraction-limited resolution of 0.22 nanometers when the accelerating voltage is 75,000 volts and the aperture angle is 2 × 10-2 radians. Between 1932 and 1933, Ruska and his collaborator Borries further developed an electron microscope with an all-metal mirror body, using a magnetic coil wrapped in an iron shell as a magnetic lens. In order to make the magnetic field more concentrated, they inlaid non-magnetic conductor copper rings in the air gap of the iron shell of the magnetic coil, and made the ends of the inner cavity of the ferromagnetic upper and lower shells into funnel shapes (magnetic pole shoes) to reduce the pole shoe aperture and gap. Both are reduced to 2 mm, and the focal length is reduced to 3 mm. In March 1932, Boris and Ruska applied for a German patent for this magnetic lens result. In 1933, Ruska used a magnetic lens with a focal length of 3 mm to obtain a magnification of 12,000 times under an accelerating voltage of 75,000 volts. He also installed a condenser to adjust the brightness of the electron beam at high magnification. He took photos of aluminum foil and cotton filaments with a resolution better than that of an optical microscope, and experimented with using thin specimens to transmit electron beams to form electron magnified images. In 1934, Ruska obtained a doctorate in engineering from the Technical University of Berlin with a thesis entitled "Magnetic Objective Lenses for Electron Microscopes". From 1934 to 1936, Ruska continued experimental research on improving the electron microscope. He used a condenser to generate a high current density electron beam to achieve high magnification imaging, and a two-stage magnification imaging system using an objective lens and a projection mirror.
However, their invention was not immediately recognized by the academic community and relevant departments at that time. Ruska and Polis worked hard to convince people that they could develop an electron microscope with performance superior to that of an optical microscope. They made numerous trips to government and industrial research departments to secure financial support. After three years of hard work, in the spring of 1937 Siemens-Hasker finally agreed to fund the establishment of an electron optics and electron microscope laboratory. Many young scholars have come to participate in research work. Ernst Ruska began to develop commercial electron microscopes in 1937. In 1938, he built two electron microscopes with condensers, objective lenses and projection lenses with pole shoes, and devices for changing samples and films. , images with a magnification of 30,000 times can be obtained. Ernst Ruska's brother Helmut Ruska and other medical scientists immediately used it to study bacteriophages, etc., and achieved great success. In 1939, the first commercial electron microscope manufactured by Siemens finally came out. In the same year, the electron microscope was exhibited for the first time at the Leipzig International Fair, attracting widespread attention. In 1940, at the suggestion of Ernst Ruska, Siemens-Halmert Ruska became director. The laboratory is equipped with 4 electron microscopes and welcomes scholars from various countries to do research, promoting the application and development of electron microscopes in various fields such as metals, biology, and medicine. Under the influence of Ruska's work, scientists from various European countries began to research and manufacture electron microscopes. Ernst Ruska and his collaborators worked tirelessly for decades to improve electron microscopes and made important contributions to the development of modern science. Electron microscopes have opened up new ways for people to observe the microscopic world of matter. The medium and high-resolution electron microscopes produced in the mid-1950s were able to observe leaching defects and promoted the development of solid state physics, metal physics and materials science. The emergence of ultra-high-resolution electron microscopes in the 1970s enabled direct observation of atoms. This has played a huge role in promoting the development of solid state physics, solid state chemistry, solid state electronics, materials science, geology and mineralogy, and molecular biology. After him, not only the high-voltage electron microscope and the scanning electron microscope came out, but also another microscope with a completely different principle appeared, which was the scanning tunneling microscope invented in 1982. Scanning tunneling microscope is another powerful weapon to access the microscopic world. (The above is accepted under "Wonderful Inventions" in the Interesting Science Series)