To care for your eyes, young friends must first do it. When reading and studying, they should put books and papers 25 cm away from their eyes. This distance is called "apparent distance" How did the "25 cm distance" required by teachers and parents come from? It turns out that our eyes can distinguish two points of 0. 1 mm (1000000 nm) which are 25 cm away from our eyes. In this case, for the eyes, their viewing angle is about 1', and the image can just fall on the two photosensitive cells of the retina. If the distance between two points is less than 0. 1 mm, their images on the retina will all fall on a photosensitive cell, and our vision will only feel one point. Obviously, by trying to enlarge this perspective, we can see smaller things.
The birth of optical microscope The appearance of microscope began 400 years ago. 1590 or so, the optician Zhan Sen placed two convex lenses in front of each other and found that the details of the object became very clear. The optical microscope was invented by accident in this way. However, when it comes to microscopes, Levin Hooke, a Dutchman, is much more famous than Zhan Sen. Levin Hooke's contribution lies not only in making microscopes magnified 300 times, but also in their practical application. This made him an outstanding figure in the history of microscope development.
After reading the recorded text about Levin Hook, what impressed us most was his overwhelming curiosity. He is a businessman who sells linen products, but he enjoys making glass and metal products.
He polishes glasses and assembles microscopes in his spare time. Being a businessman is to make a living; Doing experiments, that's his game. Levin Hooke discovered a microscopic world with a self-made microscope, a world that people have never seen before. This made him extremely excited. We are used to the beauty of nature, and only with a microscope can we find that the microscopic nature is also very moving and beautiful! Levinhawk observed the "details" of many things with interest. Saliva, urine, leaves, cow dung, etc. Has become his observation object. He observed bacteria with a microscope for the first time, which broke people's superstitious speculation for hundreds of years and opened up a new era of conquering infectious diseases.
The history of microscope is the history of continuously improving resolution: making smaller and smaller sample details form a viewing angle above 1' on the eyes. Scientists gradually realize that the resolution of optical microscope is directly proportional to the wavelength of illumination radiation. The shorter the wavelength of the illumination radiation, the higher the resolution of the microscope. The wavelength of visible light is 400 nm to 760 nm. The maximum effective magnification of modern optical microscope can reach 2000 times, which can distinguish objects of 200 nanometers and see the smallest bacteria. Most viruses are much smaller than bacteria, so they can't be observed by optical microscope.
With the birth of electron microscope, people's understanding of light is deepening. 1864, Maxwell reduced all electromagnetic phenomena to a set of mathematical equations, deduced that there are electromagnetic waves in nature, and pointed out that light is only a special electromagnetic wave with a very small wavelength.
1878, people realized that the resolution of optical microscope is limited in theory. Scientists know that in order to improve the resolution, samples must be irradiated with "radiation" with shorter wavelength. 1905, 26-year-old Einstein published a paper entitled "Inspiring Views on the Generation and Transformation of Light", which revealed the wave-particle duality of photons for the first time. 192 1 year, Einstein won the nobel prize in physics for the achievements of this paper. 1in the summer of 923, 32-year-old de Broglie proposed that all physical particles have fluctuations; In 1924, he gave the formula for calculating the wavelength of matter wave. The greater the momentum of a physical particle, the shorter its wavelength. De Broglie won the 1929 Nobel Prize in Physics.
These revolutionary events in physics led to the revolution of microscope science and technology. German scientists ruska and Noel believe that since "all physical particles fluctuate", electron beams can be used as the "light source" of the microscope instead of light. Like photons, electrons have wave-particle duality, and the wavelength of electrons is much shorter than that of light. By irradiating the sample with an electron beam, we can distinguish the finer details of the sample. 1932, they developed the first electron microscope with a magnification of 12000, which surpassed the optical microscope. Ruska is only 26 years old this year. 1939, under the auspices of ruska, Siemens manufactured the world's first practical electron microscope. At present, the working voltage of electron microscope is as high as 654.38+0000V, and the effective magnification is as high as 654.38+00000 times. Electron microscope completed a revolution in microscope technology, so ruska won half of the Nobel Prize in Physics 1986, and the other half was shared by Bunnig and Basil who developed scanning tunneling microscope. Ruska was 80 years old when he won the Nobel Prize in Physics, only two years after his death.
The revolutionary feature of electron microscope is to use electron beam instead of optical illumination. After the electrons are accelerated by a voltage of 50 ~ 100 kV, the wavelength is 0.53 ~ 0.37 nm, which is roughly equal to L/ 1000 of the optical wavelength. According to the relationship between the two wavelengths, we can infer that the resolution of electron microscope will be much higher than that of optical microscope. Modern electron microscope can distinguish two points on an object with a distance of 0.2 nm, which is11000 of optical microscope. With the help of electron microscope, people can observe the crystal structure of metals, the structure of protein molecules, cells and viruses. The invention of electron microscope promoted the study of biology.
The birth of scanning tunneling microscope The object observed by electron microscope should be placed in vacuum, dehydrated and hit by high-speed electrons. Therefore, the samples that can be observed by electron microscope are limited, and the observation results are also affected. The development of science and technology needs a microscope based on new principles; The theoretical breakthrough of microscope must rely on the revolutionary progress of basic science. 1958, Japanese scientist Esaki Reona discovered tunneling effect while studying heavily doped PN junction, revealing the physical principle of electron tunneling effect in solid. Esaki Reona shared the 1973 Nobel Prize in Physics with Giaever and Josephson.
1978, the inspiration of the new microscope comes from a conversation. One day, Laurel, a scientist at IBM Zurich Laboratory, introduced the research plan of surface physics in their laboratory to Buennig, a German graduate student. Buennig, 3 1 year-old, suggested that tunnel effect could be used to study surface phenomena! Raul is very interested in his idea. Then, at the end of 1978, rohrer invited Buennig to Zurich to develop a microscope using tunneling effect. Buennig and Laurel overcame many difficulties and finally developed the scanning tunneling microscope in 198 1 year. It is another revolutionary progress of microscope technology, and the magnification reaches ten million times. The revolutionary performance of this new microscope is that it studies the surface of materials through tunnel effect. Therefore, it does not use a lens, is not destructive to the sample, and can obtain a three-dimensional image.
The successful development of scanning tunneling microscope shows the harmonious beauty of comprehensive results. Buennig and rohrer were not the first to study surface phenomena by tunnel effect, but American physicist Giaever. We can imagine that observing the atomic scale of the sample surface inevitably requires the instrument to have extremely high stability. Giaever failed to overcome this huge obstacle. However, in three years, Buennig and Laurel achieved a breakthrough in theory, experimental technology and mechanical technology, solved the stability problem of the instrument and achieved the final success. Without the breakthrough of mechanical technology, scanning tunneling microscope is impossible to succeed.
The resolution of scanning tunneling microscope is extremely high, reaching 0.2 nm in the horizontal direction and 0.00 1 nm in the vertical direction, which can give the information of atomic scale on the surface of the sample. As we know, the typical linearity of atoms is 0.3 nanometers. For single-atom imaging, this resolution is enough. The invention of scanning tunneling microscope promoted the research of biological science, surface physics, semiconductor materials and technology and chemical action. Scanning tunneling microscope technology continues to develop. For example, in order to make up for the defect that scanning tunneling microscope can only image and process conductors and semiconductors, an atomic force microscope which can image and process nano-scale insulators has been developed.
In the 1930s, there also appeared a microscope that used electrons to display the surface structure of objects, that is, a field emission microscope. 1937, Miao Lei invented the field emission microscope, which directly projected the image of the emitter surface onto the fluorescent screen. Because it is "direct projection", the magnification of this microscope is approximately equal to the radius of the fluorescent screen divided by the radius of the emitter, which can reach 654.38+0 million. Field emission microscope and field ion microscope are one of the most powerful microscopes so far. The resolution of field emission microscope can reach 2 nm. The resolution of field ion microscope is higher, which can reach 0.2 nm. What does a resolution of 0.2 nm mean? That is, a single atom on the surface of the sample (needle tip) can be displayed on the fluorescent screen. In field ion microscope, the tip of the sample is subjected to strong electric field force. Therefore, the field ion microscope is only used to study metal materials, not biomolecules.
From optical microscope, electron microscope to scanning tunneling microscope, microscopy and modern science have gone hand in hand for more than 400 years. Microscope accompanied Galileo, Newton, Maxwell and Einstein along the way. The development history of microscope is the history of scientific revolution, technological innovation and manufacturing technology development. Microscope is the harmonious product of human science, technology and engineering activities. The history of microscope development, like the history of science, is a mirror, which gives us a lot of profound enlightenment.
Microscopes help us to see the microscopic characteristics of objects. With the microscope, people can not only study the microstructure and discover new laws, but also discover other pleasing beauty on a smaller scale. Microscope is not only the product of the integration of truth, goodness and beauty, but also the "witness" of the integration of truth, goodness and beauty.