Introduction to the characteristics and functions of transmission electron microscopes
Transmission Electron Microscope (TEM) is a large-scale microscopic analysis equipment that uses high-energy electron beams as illumination sources to perform magnified imaging. In 1933, German scientists Ruska and Knoll developed the world's first transmission electron microscope (see Figure 1). In 1939, Siemens used this electron microscope as a prototype and mass-produced it. The first batch of commercial transmission electron microscopes, about 40 units, has a resolution 20 times higher than that of optical microscopes. Since then, mankind has had more powerful weapons for scientific research on the microscopic world. Today, transmission electron microscopy has been around for more than 70 years. Electron microscopy, an interdisciplinary subject formed by the application of electron microscopy, has been increasingly perfected. The resolving power of electron microscopy has also increased by more than 100 times compared with the original time, reaching the sub-angstrom level. And it plays an increasingly important role in natural science research.
Features of transmission electron microscope
1) Due to limitations of sample preparation technology, for most biological samples, only a resolution of 2nm can generally be achieved.
2) The resolving power of electron microscope images depends not only on the resolution of the electron microscope itself, but also on the contrast of the sample structure.
3) The light source used in the electron microscope is electron waves, and the wavelength has no color reaction in the non-visible light range. The image formed is a black and white image, and the image must have a certain contrast.
4) Biological tissues and cell components are mainly composed of light elements such as C\H\O\N. Their atomic numbers are low, their electron scattering ability is weak, and the differences between them are very small. The image contrast under the electron microscope is generally relatively small. Low.
5) Due to the weak penetrating ability of the electron beam, the sample must be made into ultra-thin sections.
6) The observation surface is small, the direct grid can be 3mm, and the ultra-thin sectioning range is 0.3-0.8mm.
7) Strong irradiation of electron beams can easily damage the sample, causing deformation, sublimation, etc., or even breakdown and rupture, which may cause artifacts in the observed structure.
8) The electron microscope tube must be kept in vacuum during observation. In order to ensure that the sample is not damaged under vacuum, the sample must be free of moisture. Therefore, living biological samples cannot be observed.
9) Biological sample preparation is complex. During the multi-step sample preparation process, the sample is prone to structural changes such as shrinkage, expansion, fragmentation, and loss of content.
