The difference between MINI scanning electron microscope SEM and optical microscope
Electron microscope is a large instrument that uses an electron beam as the illumination source, and images the sample on a fluorescent screen through the transmission or reflection of the electron flow and the multi-level amplification of the electromagnetic lens. The electron microscope replaces visible light with electron flow and the lens with a magnetic field, allowing the movement of electrons to be replaced. It utilizes X-ray imaging with much shorter wavelengths than ordinary visible light and has high resolution. An optical microscope, on the other hand, is an optical instrument that uses visible light illumination to form magnified images of small objects. In summary, there are several main differences between electron microscopes and optical microscopes:
1. Different lighting sources. The illumination source used in electron microscopy is the electron flow emitted by the electron gun, while the illumination source of the light mirror is visible light (sunlight or light). Due to the wavelength of the electron flow being much shorter than the wavelength of the light wave, the amplification and resolution of electron microscopy are significantly higher than those of the light mirror.
2. Different lenses. The objective lens that plays a magnifying role in electron microscopy is an electromagnetic lens (a circular electromagnetic coil that can generate a magnetic field in the * area), while the objective lens of a light lens is an optical lens made of ground glass. There are three sets of electromagnetic lenses in electron microscopy, which are equivalent in function to the condenser, objective, and eyepiece in optical lenses.
3. Different imaging principles. In an electric mirror, the electron beam acting on the tested sample is amplified by an electromagnetic lens and projected onto a fluorescent screen for imaging or applied to a photosensitive film for imaging. The mechanism for the difference in electron intensity is that when the electron beam acts on the sample being tested, the incident electrons collide with the atoms of the material, resulting in scattering. Due to the different scattering degrees of electrons in different parts of the sample, the electron image of the sample is presented in intensity. The object image of the sample in the optical mirror is presented as a brightness difference, which is caused by the difference in how much light is absorbed by the different structures of the tested sample.
4. The preparation methods of the specimens used are different. The preparation process of the tissue and cell specimens used for electron microscopy observation is complex, with high technical difficulty and cost. Special reagents and operations are required in the stages of sampling, fixation, dehydration, and embedding. After embedding, the embedded tissue blocks need to be cut into ultra-thin specimen slices with a thickness of 50-100nm using an ultra-thin slicer. The specimens observed under the microscope are generally placed on a glass slide, such as ordinary tissue section specimens, cell smear specimens, tissue compression specimens, and cell drop specimens.
The resolution of an optical microscope is related to the wavelength of light waves. For objects that are close to or smaller than the wavelength of light waves, optical microscopes are powerless. The wavelength of electron motion is much longer than that of light waves, and smaller objects can be seen. An optical microscope is a magnifying imaging system composed of a set of optical lenses, while an electron microscope uses electron flow instead of visible light, a magnetic field instead of a lens, allowing the movement of electrons to replace photons, allowing for the viewing of smaller objects than those seen by an optical system.
