MINI Scanning Electron Microscope SEM vs. Optical Microscope
Electron microscope is an electron beam as a source of illumination, through the electron flow on the sample of the transmission or reflection and electromagnetic lenses of the multi-stage amplification in the fluorescent screen after the imaging of large instruments, electron microscope by the electron flow instead of visible light, by the magnetic field instead of the lens, so that the movement of electrons instead of the wavelength of X-rays than the ordinary visible light is utilized to image, with a high degree of resolution. Optical microscopes, on the other hand, are optical instruments that utilize visible light illumination to form magnified images of tiny objects. To summarize, electron microscope and optical microscope mainly have the following aspects of the difference:
1. Different illumination sources. Electron microscope used in the source of illumination is the electron gun issued by the electron flow, while the source of illumination of the light microscope is visible light (daylight or light), due to the wavelength of the electron flow is much shorter than the wavelength of light waves, so the magnification of the electron microscope and the resolution of the light microscope is significantly higher than that of the light microscope.
2. Lenses are different. Electroscope in the magnifying role of the objective lens is electromagnetic lens (can produce a magnetic field in the * part of the toroidal electromagnetic coil), while the objective lens of the optical mirror is a glass milled from the optical lens. Electromagnetic lenses in the mirror in a total of three groups, respectively, with the light mirror in the focusing lens, objective lens and eyepiece function is equivalent.
3. Different imaging principles. In the electron microscope, the role of the sample to be examined by the electromagnetic lens amplification of the electron beam to the fluorescent screen imaging or the role of the photographic film imaging. The difference between the intensity of the electron is that the mechanism is, the electron beam on the sample being examined, the incident electrons and material atoms collide to produce scattering, due to the different parts of the sample on the electrons have a different degree of scattering, so the sample electron image to the intensity of the presentation. The object image of the sample in the light microscope is presented by the brightness difference, which is caused by the different structure of the sample to be examined how much light is absorbed.
4. The specimens used in different ways of preparation, electron microscopy observation of tissue cell specimens used in the preparation of more complex procedures, technical difficulties and costs are higher, in the sampling, fixation, dehydration and embedding and other aspects of the need for special reagents and operations, zui later also need to be embedded in a good block of tissue put into the ultra-thin slicer cut into ultra-thin slices of specimens of 50 ~ 100nm thick. The specimens observed by light microscope are generally placed on slides, such as ordinary tissue section specimens, cell smear specimens, tissue compression specimens and cell drop specimens and so on.
The resolution of the light microscope is related to the wavelength of light waves. For objects close to and smaller than the wavelength of light waves, the optical microscope can do nothing. Electron motion at wavelengths much shorter than the wavelength of light waves makes it possible to see much finer objects. While an optical microscope is a magnifying imaging system consisting of a set of optical lenses, an electron microscope consists of a stream of electrons instead of visible light, a magnetic field instead of a lens, and the motion of electrons instead of photons, which makes it possible to see smaller objects than can be seen with an optical system.
