The characteristics and working principle of scanning electron microscope
Features of scanning electron microscope
Compared with optical microscope and transmission electron microscope, scanning electron microscope has the following characteristics: (A) can directly observe the structure of the sample surface, the sample size can be as large as 120mm × 80mm × 50mm. (2) The sample preparation process is simple, without cutting into thin slices. (3) The sample can be translated and rotated in a three-dimensional space in the sample chamber. Therefore, the sample can be observed from various angles. (4) The depth of field is large and the image is three-dimensional. The depth of field of the scanning electron microscope is several hundred times larger than that of the optical microscope and several dozen times larger than that of the transmission electron microscope. (5) The enlargement range of the image is wide and the resolution is relatively high. It can be enlarged from ten times to hundreds of thousands of times. It basically includes the magnifying range from magnifying glass, optical microscope to transmission electron microscope. The resolution is between the optical microscope and the transmission electron microscope, up to 3nm. (6) The degree of damage and contamination of the sample by the electron beam is small. (7) While observing the morphology, other signals from the sample can also be used for micro-component analysis.
The structure and working principle of scanning electron microscope
(1) Structure 1. Lens tube
The lens barrel includes an electron gun, a condenser lens, an objective lens and a scanning system. Its role is to generate a very thin electron beam (about a few nm in diameter), and make the electron beam scan on the surface of the sample, while exciting various signals.
2. Electronic signal collection and processing system
In the sample chamber, the scanning electron beam interacts with the sample to produce a variety of signals, including secondary electrons, backscattered electrons, X-rays, absorbed electrons, Auger electrons, and so on. Among the above signals, the most important is the secondary electrons, which are the outer electrons in the sample atoms excited by the incident electrons, which are generated in the region of a few nm to tens of nm below the surface of the sample, the generation rate mainly depends on Sample morphology and composition. Generally speaking, the scanning electron mirror refers to the secondary electron image, which is the most useful electronic signal to study the surface morphology of the sample. The detector for detecting secondary electrons (the probe in Figure 15 (2) is a scintillator. When the electron hits the scintillator, 1 generates light in it. This light is transmitted to the photomultiplier tube by the light pipe, and the optical signal That is, it is converted into a current signal, which is then converted into a voltage signal by pre-amplification and video amplification, and finally it is sent to the grid of the kinescope.
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