What is the difference between electron microscope and light microscope in observing objects?
There are significant differences between optical microscopes and electron microscopes, including different light sources, lenses, imaging principles, resolutions, depth of field, and sample preparation methods. Optical microscope, commonly known as light mirror, is a type of 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, in order to extract information about microstructures. It has a wide range of applications in cell biology.
An optical microscope generally consists of a stage, a spotlight illumination system, an objective lens, an eyepiece, and a focusing mechanism. The stage is used to hold the observed object. The focusing knob can be used to drive the focusing mechanism, allowing for coarse or fine adjustment of the stage, facilitating clear imaging of the observed object.
The image formed by an optical microscope is inverted (upside down, left-right exchange). Electron microscopes are the birthplace of high-end technological products, which have similarities with the optical microscopes we usually use, but are greatly different from them. Firstly, optical microscopes utilize light sources. Electron microscopy, on the other hand, uses electron beams, and the results that can be seen from the two are different, let alone the magnification. For example, when observing a cell, a light microscope can only see the cell and some organelles, such as mitochondria and chloroplasts, but can only see the presence of its cells and cannot see the specific structure of organelles. Electron microscopes can provide a more detailed view of the intricate structure of organelles, and even reveal large molecules such as proteins. Electron microscopes include transmission electron microscopes, scanning electron microscopes, reflection electron microscopes, and emission electron microscopes. Among them, scanning electron microscopy is more widely used.
Scanning electron microscopy is widely used in material analysis and research, mainly for material fracture analysis, micro area composition analysis, various coating surface morphology analysis, layer thickness measurement, microstructure morphology and nano material analysis. It can also be combined with X-ray diffractometer or electron energy spectrometer to form electron microprobes for material composition analysis, etc.
Scanning Electron Microscope (SEC), abbreviated as SEC, is a new type of electron optical instrument. It consists of three main parts: vacuum system, electron beam system, and imaging system. It modulates imaging using various physical signals excited by a fine focused electron beam scanning the sample surface. The incident electrons excite secondary electrons on the surface of the sample. The microscope observes the electrons scattered from each point. The scintillation crystal placed beside the sample receives these secondary electrons, modulates the electron beam intensity of the picture tube after amplification, and changes the brightness of the picture tube screen. The deflection coil of the cathode ray tube is synchronously scanned with the electron beam on the surface of the sample, so that the fluorescent screen of the cathode ray tube displays the morphology 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.
Application performance of transmission electron microscopy:
1. Crystal defect analysis. All structures that disrupt the normal lattice period are collectively referred to as crystal defects, such as vacancies, dislocations, grain boundaries, precipitates, etc. These structures that disrupt the periodicity of the lattice will cause changes in the diffraction conditions in their respective regions, resulting in diffraction conditions in the defect area being different from those in the normal area, thus displaying corresponding differences in brightness and darkness on the fluorescent screen.
2. Organizational analysis. In addition to various defects that can generate different diffraction patterns, crystal structure and orientation analysis can be performed while observing the morphology of the tissue.
3. In situ observation. By using the corresponding sample stage, in-situ experiments can be conducted in transmission electron microscopy. For example, using strain tensile samples to observe their deformation and fracture processes.
4. High resolution microscopy technology. Improving resolution for a deeper observation of the microstructure of matter has always been a goal pursued by people. High resolution electron microscopy utilizes the phase change of electron beams to coherently image two or more electron beams. Under conditions where the resolution of the electron microscope is high enough, the more electron beams used, the higher the resolution of the image, and it can even be used for imaging the atomic structure of thin samples.
