Why does the electron microscope's resolution differ so greatly from a light microscope?
Because electron microscopes use electron beams and optical microscopes use visible light, and the wavelength of electron beams is shorter than that of visible light, the resolution of electron microscopes is much higher than that of optical microscopes.
The resolution of the microscope is related to the incident cone angle and wavelength of the electron beam passing through the sample.
The wavelength of visible light is about 300-700 nanometers, while the wavelength of electron beams is related to the accelerating voltage. According to the principle of wave-particle duality, the wavelength of high-speed electrons is shorter than that of visible light, and the resolution of the microscope is limited by the wavelength it uses, so the resolution of the electron microscope (0.2 nanometers) is much higher than that of the optical microscope (200nm).
The application of electron microscope technology is based on the optical microscope. The resolution of the optical microscope is 0.2μm, and the resolution of the transmission electron microscope is 0.2nm. That is to say, the transmission electron microscope is magnified by 1000 on the basis of the optical microscope. times.
Although the resolution of an electron microscope is much higher than that of a light microscope, it has some disadvantages:
1. In an electron microscope, samples must be observed in a vacuum, so live samples cannot be observed. With the advancement of technology, the environmental scanning electron microscope will gradually realize the direct observation of living samples;
2. When processing the sample, it may produce a structure that the sample does not have, which exacerbates the difficulty of analyzing the image afterwards;
3. Due to the strong electron scattering ability, secondary diffraction is easy to occur;
4. Because it is a two-dimensional plane projection image of a three-dimensional object, sometimes the image is not unique;
5. Since the transmission electron microscope can only observe very thin samples, it is possible that the structure of the surface of the material is different from the structure inside the material;
6. For ultra-thin samples (less than 100 nanometers), the sample preparation process is complicated and difficult, and the sample preparation is damaged;
7. The electron beam may destroy the sample through collision and heating;
8. The purchase and maintenance prices of electron microscopes are relatively high.
