Comparative analysis of performance and characteristics of electron microscopy (including transmission electron microscopy, scanning electron microscopy) and optical microscopy
1) The imaging principle and contrast source are different. The source of the electron microscope is an electron beam, and the TEM is a transmission imaging, which can observe the shape and structure inside the sample, and is a two-dimensional image. The SEM is a secondary electron image, which mainly observes a stereoscopic image (ie, a three-dimensional image) of the surface appearance of the sample. Optical microscopy uses visible light as the light source, and the sample is an absorption image, typically a two-dimensional image in color or black.
2) The resolution power is different from the magnification. Electron microscopy is the use of short wavelengths and electromagnetic lenses to increase resolution and control the continuity of changing magnification. The TEM resolution is determined by the phase difference. The highest resolution of TEM is currently 0.1 nm. The magnification is a few hundred times lower and up to 1.5 million times. The horizontal resolution of the SEM under ultra-high vacuum conditions is 0.14 nm, and the vertical resolution has reached a level of 0.01 nm. The resolution power depends mainly on the size of the incident electron beam spot of the electron probe. The magnification is at least 10 times and the maximum is 1.5 million times. The magnification is determined by the ratio of the kinescope deflection coil current to the electron microscopy scan coil current. The magnification of the two electron microscopes can be arbitrarily changed and continuously adjustable. The optical microscope has a limiting resolution of 200 nm and a magnification of 1-2000 times.
3) The field of view, depth of field and depth of focus are different. Field of view or field of view refers to the range of samples that can be seen, depending on the resolution and magnification. Depth of field is the range of depths at which a sharp image can be obtained when an electron beam is scanned over a sample. The TEM has a small field of view of 1.0 mm to 0.1 um. The depth of field is large, and under the same separate skill, it is 1000 times larger than the optical microscope, which is convenient for focusing and stereo photography. The depth of focus can reach 100m, which is very advantageous for the textile position of the fluorescent screen and photo negative. The SEM field of view is much larger than that of the transmission electron microscope, and has a range of 10 nm to 10 μm. The depth of field is also larger than that of TEM. It can directly observe the uneven structure of various samples, and the image is full of three-dimensionality and can be used for stereo analysis. The optical microscope market is 0.1mm (1000x)-100mm (1x) with a small depth of field.
4) Sample preparation requirements are different. TEM, the electron must be able to pass through the sample to be imaged, so the sample is required to be thin and the field of view is small. The biological sample is prepared into ultra-thin sections of about 50 nm, and the sample preparation is relatively complicated. The SEM requires less stringent soils with good conductivity, as long as it is suitable for the size of the sample chamber. Conductive samples such as metals can be directly observed in an electron microscope. Non-conducting samples can be observed by treatments such as fixing, dehydration, drying and coating. The sample preparation process is easier to handle than ultra-thin sections. The optical microscope requires paraffin-embedded sections, and the slice thickness is thicker than TEM, generally 12-15 um.
5) Damage and contamination of the sample. TEM: The accelerating voltage is high, the electron energy is large, and the electron beam irradiation causes damage to the sample, which is easy to cause contamination of the sample and the lens barrel. The electron microscope must be operated under vacuum conditions, and sample preparation must be performed before the sample is placed in an electron microscope for observation. The light source of the optical microscope is visible light, and there is no problem of sample damage. However, when the dewaxing, dyeing, etc. are improperly operated, or when the appliance is not clean enough, it is likely to cause pollution.
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 moralityâ€, 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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