Transmission Electron Microscope (TEM) can see fine structures of less than 0.2 um that are invisible under an optical microscope. These structures are called submicroscopic structures or ultrastructures. Since electrons are easily scattered or absorbed by an object, the penetrating power is low, and ultrathin sections (usually 50-100 nm) must be prepared. The imaging method is similar to that of an optical biological microscope except that an electronic lens is used instead of a glass lens. Working principle: The electrons are emitted by the tungsten cathode under heating. Under the action of the anode accelerating voltage, the condensing mirror (electromagnetic lens) converges to illuminate the sample as an electron beam. The electron beam passing through the sample carries the structural information of the sample itself through the objective lens, and the sample surface is magnified on the image plane, and then amplified twice by the intermediate mirror and the projection mirror to form a three-stage magnified image to image or The form of the diffraction spectrum (diffracting pattern) is displayed on a fluorescent screen, or recorded on a photographic film, or directly on a computer hard disk. The structure of the transmission electron microscope consists of three main parts: an electron optical system (light tube), a vacuum system, and an electronic system. The imaging principle of TEM can be divided into three cases: absorption image, diffraction image, and phase image.

Characteristics of TEM: 1) Due to the limitations of sample preparation techniques, for most biological samples, the resolution of 2 nm is generally only achieved.

2) The resolving power of an electron microscope image 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 an electron wave, and the wavelength has no color reaction in the non-visible range, and the formed image is a black and white image, and the image must have a certain contrast.

4) The biological tissues and cellular components are mainly composed of light elements such as C\H\O\N. Their atomic number is low, the electron scattering ability is weak, and the difference between them is very small. The contrast of images under electron microscope is generally smaller. low.

5) Due to the weak penetration of the electron beam, the sample must be made into ultra-thin sections.

6) The observation surface is small, the net can be directly 3mm, and the ultra-thin slice range is 0.3-0.8mm.

7) Strong irradiation of the electron beam, easy to damage the sample, deformation, sublimation, etc., or even breakdown and breakdown, may cause artifacts in the observation structure.

8) The electron microscope barrel must be kept vacuum during observation. In order to ensure that the sample is not damaged under vacuum, the sample should be free of moisture. Therefore, biological samples of living organisms cannot be observed.

9) The biological sample preparation is complicated, and the sample is prone to shrinkage, expansion, breakage and inclusion in the process of preparing a large number of steps.

Loss of structural changes such as loss.

Beijing Zhongxian Hengye Instrument & Meter Co., Ltd. is a high-tech enterprise founded by Tsinghua University's Industrial Engineering Department alumni. It is a professional provider of optical microscopes. Zhongxian Hengye adheres to the motto of Tsinghua University's “self-improvement, ethics and morality”, and provides professional, practical and cost-effective microscopic optical solutions to the users with scientific and rigorous concepts. Customers include agriculture, forestry, medical, aerospace, aviation, marine, military, machinery, metallurgy, electric power, petrochemical, geological and other industries, in universities, research institutes, medical and health, life sciences, industrial materials, agricultural systems, animal husbandry systems, The military system and other fields have considerable visibility and influence.

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