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Measurement Principle of Scanning Electron Microscope(SEM)
Column Structure
The eye lens of human and the lens of optical microscope play a role in forming images.
Differently from the way, SE uses Electron Beam.
The above picture is the example of Scanning Electron Microscope(SEM) Column.
Generally, there is Electro Gun on the top of the column, and this electro gun generates electron beam.
The electron beam generated from electro gun reaches the specimen, the object that the use intends to see by electronic inducement.
When the beam reaches the specimen, according to the amount and strength of the beam, various kinds of electrons come out.
Collecting the electrons, the amount and types are converted into the shape, structure, etc. of the specimen.
The electron microscope consists of the high tension system for generating electron beam, the vacuum system for making electrons arrive at the specimen efficiently, the lens system for electrical control of the lens, the detection systems ofr collecting the electron beam, the whole equipments and electric control, etc.
- High tension system : As the device to generate the electron beam from the electron gun, I need tens kV of acceleration voltage though there are differences in accordance with the types of electrons to be collected.
- Vacuum system : The movement process to make the electrons reach the specimen without the loss of gas, etc.
The vacuum state should be maintained.
- Lens system : In order to acquire the high magnification and clear image, the lens is used. The location and control of the lens have much effect on the contents of the image.
- Detection system : On the end of electron beam(Probe), it is converted into the signals of the movement and detection electron.
- Equipment system : For the equipment devices for high vacuum and the control of the axis of electron beam, the design and asScanning Electron Microscope(SEM)bling of equipments have an influence on the performance of the equipments.
- Electric system : controls high tension, vacuum, lens, detection, etc. electrically.
- Software : the utility to show the outcome of the detections systems(Scan) and control the electrical system of PC.
Optical Microscope VS Electronic Microscope
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Optical Microscope |
Electronic Microscope |
| Illumination medium |
Visible ray |
Electron line |
| Reflection |
Approx, ~200nm |
Approx. ~3.5nm |
| Magnification |
10~2000x |
10~1,000,000x |
| Lens |
10~2000x |
Electromagnetism |
| Contrast |
Absorption, reflection |
Absorption, diffraction, Phase |
| Data |
Color |
Gray |
| Monitor |
Naked eye, projection screen |
Braun tube |
Classifications of Scanning Electron Microscope(SEM)
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