Imaging principle of the electron microscope
The electron microscope is a large instrument that uses electron beams as the illumination source to transmit or reflect samples and is imaged on a fluorescent screen through multiple amplifications of electromagnetic lenses. The electron microscope consists of a barrel, a vacuum device, and a power cabinet. Electron microscopes can be divided into transmission electron microscopes, scanning electron microscopes, reflection electron microscopes, and emission electron microscopes according to structure and purpose. So what is the imaging principle of an electron microscope? Let's introduce it below.
Imaging principle of the electron microscope:
1. Absorption image: When electrons hit a sample with a high mass and density, the main imaging mechanism is scattering. The area of the sample with a large scattering angle to the electron, a small number of electrons pass through, and the brightness of the image is darker. Early transmission electron microscopes were based on this principle.
2. Diffraction image: After the electron beam is diffracted by the sample, the amplitude distribution of the diffraction waves at different positions of the sample corresponds to the different diffraction abilities of each part of the crystal in the sample. When crystal defects occur, the diffraction ability of the defective part is different from that of the intact area, resulting in an uneven amplitude distribution of the diffraction waves that reflects the distribution of crystal defects.
3. Phase image: When the sample is thinner than 100Å, electrons can pass through the sample, and the amplitude change of the wave can be ignored, and the imaging is based on the change in phase.
The above content is an introduction to the imaging principle of the electron microscope. The commonly used electron microscopes are transmission electron microscopes and scanning electron microscopes. Compared with optical microscopes, electron microscopes replace visible light with electron beams, replace optical lenses with electromagnetic lenses, and use fluorescent screens to image electrons that are invisible to the naked eye. Generally, the magnification of electron microscopes is much higher than that of optical microscopes.