The history of developing electron microscope can actually be traced back to the end of 19. In the process of studying cathode ray, it is found that anode shadow often appears on the tube wall of cathode ray tube. Braun designed and manufactured the original oscilloscope tube in 1987. This prepared the technical conditions for the birth of electron microscope. 1926, H.Busch published a paper on magnetic focusing, pointing out that an electron beam can be focused when it passes through an axisymmetric electromagnetic field, just as light can be focused when it passes through a lens, so it can be imaged by electrons. This makes theoretical preparation for electron microscope. The main factor limiting the resolution of optical microscope is the wavelength of light. Because the wavelength of electron beam is much shorter than that of light wave, it can be expected that the resolution of electron microscope using electron beam imaging will be much higher than that of optical microscope.
Ernst ruska was born in Heidelberg, Baden, Germany on February 25th. His father is a history professor at the University of Berlin. From 1925 to 1927, ruska liked engineering in middle school and studied electrical engineering in two companies in Munich. Later, he went to Berlin with his father. 1in the summer of 928, he entered Berlin Technical University in Chalotenburg, Berlin, and worked in a high-pressure laboratory to study cathode-ray oscilloscopes. Since 1929, ruska has been conducting experiments on electronic lenses under the guidance of group leader M.Knoll, which is very beneficial to the growth of ruska.
During the period of 1928 ~ 1929, on the basis of participating in the research work of oscilloscope tube technology, ruska conducted experimental research on focusing electron beams with magnetic lenses and electrostatic lenses. It is proved that the optical cable with a diameter of 0.3 mm can produce low magnification image (1.3 times) under electron beam irradiation, and the lens imaging formula is verified. This laid the foundation for the birth of electron microscope. 193 1 year, Noel and ruska began to develop the electron microscope. They proved through experiments that in order to obtain the same focal length, the number of turns of the coil with iron shell is much less than that without iron shell. 19365438+From April to June, 2000, they used a two-stage magnetic lens to enlarge the electron microscope and obtained a magnification of 16 times. Through calculation, they realized that according to de Broglie's theory of matter wave, the wavelength of electrons is five orders of magnitude shorter than that of light waves, and the electron microscope may achieve higher resolution. They predicted that in the future electron microscope, when the accelerating voltage is 75,000 volts and the aperture angle is 2× 10-2 radians, the resolution of diffraction limit will be 0.22 nm.
During the period of 1932 ~ 1933, ruska and his collaborator Borries further developed an electron microscope with an all-metal reflector, using a magnetic coil wrapped in an iron shell as a magnetic lens. In order to make the magnetic field more concentrated, they embedded a non-magnetic copper ring in the air gap of the iron shell of the magnetic coil, and made the ends of the inner cavities of the ferromagnetic upper and lower shells into funnels (pole shoes), so that the aperture and gap of the pole shoes were reduced to 2mm and the focal length was reduced to 3mm. 1932 In March, Pohris and ruska applied for a German patent for this magnetic lens achievement.
1933, ruska used a magnetic lens with a focal length of 3mm, and obtained a magnification of12,000 times at an accelerating voltage of 75,000 volts, and installed a condenser to adjust the brightness of the electron beam under high magnification. He took photos of aluminum foil and cotton silk with better resolution than optical microscope, and tried to form an electron magnified image by transmitting electron beams from thin samples.
From 65438 to 0934, ruska received his Ph.D. degree in engineering from Berlin University of Technology with his thesis entitled "Magnetic Objective of Electron Microscope". From 1934 to 1936, ruska continued the experimental research on improving the electron microscope. He used a condenser to generate a high current density electron beam to realize high magnification imaging, and adopted a two-stage magnification imaging system of objective lens and projection lens. But at that time, their inventions were not immediately recognized by academic circles and relevant departments. Ruska and Pohris tried their best to convince people that they could develop an electron microscope with better performance than an optical microscope. They went to the government and industrial research departments for financial support many times. After three years' running, in the spring of 1937, Siemens-haskell finally agreed to set up an electron optics and electron microscope laboratory. Many young scholars have come to take part in this research work.
Ernst ruska began to develop commercial electron microscope from 1937. 1938, he made two electron microscopes with condenser, objective lens and projection lens with polar shoes, and equipment for changing samples and negatives, which can obtain images with magnification of 30,000 times. Ernst ruska's younger brother Helmut ruska and other medical scientists immediately used it to study phage, and achieved great success. 1939 the first commercial electron microscope made by Siemens finally came out. In the same year, the electron microscope was exhibited for the first time in Leipzig International Expo, which attracted wide attention. 1940, at the proposal of Ernst ruska, Siemens-Haskell developed the above-mentioned laboratory into the first open electron microscope laboratory, with Helmut ruska as the director. The laboratory is equipped with four electron microscopes, inviting scholars from all over the world to do research work, which promotes the application and development of electron microscopes in various fields such as metal, biology and medicine. Under the influence of ruska's work, European scientists also began to research and manufacture electron microscopes.
Ernst ruska and his collaborators have worked tirelessly to improve the electron microscope for decades, and made important contributions to the development of modern science. Electron microscope has opened up a new way for people to observe the microscopic world of matter. The medium and high resolution electron microscope made in the mid-1950s can observe crystal defects and promote the development of solid state physics, metal physics and materials science. The ultra-high resolution electron microscope that appeared in the 1970s enabled people to observe atoms directly. This has greatly promoted the development of solid state physics, solid state chemistry, solid state electronics, material science, geological mineralogy and molecular biology.
Ernst ruska died in Berlin on May 27th, 1988, more than one year after he won the Nobel Prize in Physics. He devoted his life to the cause of electron microscope. After him, not only the high-voltage electron microscope and the scanning electron microscope appeared, but also another microscope with completely different principles, that is, the scanning tunneling microscope invented by 1982. Scanning tunneling microscope is another powerful weapon leading to the microscopic world.