What is the difference between an electron microscope and an optical microscope in observing objects?
Optical microscopes are very different from electron microscopes, with different light sources, different lenses, different imaging principles, different resolutions, different depths of field, and different sample preparation methods. Optical microscope, commonly known as light microscope, is a microscope that uses visible light as the illumination source. An optical microscope is an optical instrument that uses optical principles to magnify and image tiny objects that cannot be distinguished by the human eye, so that people can extract microstructure information. It is widely used in cell biology. An optical microscope generally consists of a stage, a spotlight lighting system, an objective lens, an eyepiece, and a focusing mechanism. The stage is used to hold the object to be observed. The focus adjustment mechanism can be driven by the focus adjustment knob, and the stage can be roughly adjusted or finely adjusted to facilitate clear imaging of the observed object. The image formed by the optical microscope is an inverted image (upside down, left and right interchangeable). The electron microscope is the birth of high-end technology products. It is similar to the optical microscope we usually use, but it is very different from the optical microscope. First, optical microscopes make use of light sources. The electron microscope uses electron beams, and the results seen by the two are different. Let’s just say that the magnification is different. For example, when observing a cell, the light microscope can only see cells and some organelles, such as mitochondria and chloroplasts, but only The existence of its cells can be seen, but the specific structure of organelles cannot be seen. The electron microscope can see the fine structure of organelles in more detail, and even macromolecules like proteins. Electron microscopes include transmission electron microscopes, scanning electron microscopes, reflection electron microscopes, and emission electron microscopes. Among them, the scanning electron microscope is more widely used. Scanning electron microscopy is widely used in the analysis and research of materials. It is mainly used in material fracture analysis, micro-area component analysis, surface morphology analysis of various coatings, layer thickness measurement, microstructure morphology and nanomaterial analysis. The combination of X-ray diffractometer or electron energy spectrometer constitutes an electronic microprobe for material composition analysis, etc. Scanning Electron Microscope (SEC), abbreviated as SEC, is a new type of electron optical instrument. It consists of three parts: vacuum system, electron beam system and imaging system. It uses various physical signals excited when the finely focused electron beam scans the surface of the sample to modulate the imaging. The incident electrons cause secondary electrons to be excited from the sample surface. What the microscope observes are the electrons scattered from each point, and the scintillation crystal placed next to the sample receives these secondary electrons, modulates the electron beam intensity of the picture tube after amplification, and changes the brightness on the screen of the picture tube. The deflection coil of the kinescope keeps scanning synchronously with the electron beam on the surface of the sample, so that the fluorescent screen of the kinescope displays the topographic image of the sample surface. It has the characteristics of simple sample preparation, adjustable magnification, wide range, high image resolution, and large depth of field. Transmission electron microscope application performance: 1. Analysis of crystal defects. All structures that destroy the normal lattice period are collectively called crystal defects, such as vacancies, dislocations, grain boundaries, and precipitates. These structures that destroy the periodicity of the lattice will lead to changes in the diffraction conditions of the area where the defect is located, making the diffraction conditions of the area where the defect is located different from that of the normal area, thus showing a corresponding difference in brightness and darkness on the fluorescent screen. 2. Organization analysis. In addition to various defects that can produce different diffraction patterns, they can be used to analyze the structure and orientation of crystals while observing the morphology of the structure. 3. In situ observation. With the corresponding sample stage, in situ experiments can be performed in the TEM. For example, the deformation and fracture process can be observed by stretching the sample with strain. 4. High-resolution microscopy technology. Improving the resolution so that we can observe the microstructure of matter more deeply has been the goal that people are constantly pursuing. The high-resolution electron microscope uses the phase change of the electron beam, and coherent imaging is formed by more than two electron beams. Under the condition that the resolution of the electron microscope is high enough, the more electron beams used, the higher the resolution of the image, even It can be used to image the atomic structure of thin samples.
