Why is the resolution of electron microscopes much higher than that of optical microscopes?
Because electron microscopes use electron beams and optical microscopes use visible light, and the wavelength of electron beams is shorter than the wavelength of visible light, the resolution of electron microscopes is much higher than that of optical microscopes.
The resolution of a 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 to 700 nanometers, and the wavelength of the electron beam is related to the accelerating voltage. According to the principle of wave-particle duality, the wavelength of high-speed electrons is shorter than the wavelength of visible light, and the resolution of the microscope is limited by the wavelength used. Therefore, the resolution of the electron microscope (0.2 nanometers) is much higher than the resolution of the optical microscope. (200 nm).
The application of electron microscopy 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 magnifies 1000 times on the basis of the optical microscope. times.
Although the resolution of electron microscopy is much higher than that of optical microscopy, it has some disadvantages:
1. In an electron microscope, the sample must be observed in a vacuum, so living samples cannot be observed. With the advancement of technology, environmental scanning electron microscopy will gradually enable direct observation of living samples;
2. When processing the sample, structures that the sample does not originally have may be produced, which makes it more difficult to analyze the image later;
3. Due to the extremely strong electron scattering ability, secondary diffraction is prone 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 transmission electron microscopes can only observe very thin samples, the structure of the surface of the substance may be different from the structure of the interior of the substance;
6. For ultra-thin samples (below 100 nanometers), the sample preparation process is complex and difficult, and the sample preparation may be damaged;
7. The electron beam may destroy the sample through collision and heating;
8. The price of purchasing and maintaining an electron microscope is relatively high.
