Light microscope is an optical instrument that uses optical principles to magnify and image tiny objects that cannot be distinguished by the human eye, so that people can extract microstructure information. The application of electron microscopy technology is based on the basis of optical microscopy. The resolution of the light microscope is 0.2 μm, and the resolution of the transmission electron microscope is 0.2 nm, which means that the transmission electron microscope is magnified 1000 times on the basis of the light microscope.
Electron microscopes can be divided into transmission electron microscopes, scanning electron microscopes, reflection electron microscopes and emission electron microscopes according to their structure and use. Light microscopes can be divided into trinocular microscopes and binocular microscopes according to the number of eyepieces; according to the stereoscopic image, they can be divided into stereoscopic and non-stereoscopic microscopes; according to the observation objects, they can be divided into biological and metallographic microscopes; according to optical principles It can be divided into polarized light, phase contrast and differential interference contrast microscopy.
The light microscope uses visible light as the medium, and the electron microscope uses the electron beam as the medium. Since the wavelength of the electron beam is much smaller than that of the visible light, the resolution of the electron microscope is much higher than that of the light microscope. The maximum magnification of an light microscope is only about 1500 times, and a scanning microscope can magnify more than 10,000 times.
According to the de Broglie wave theory, the wavelength of an electron is only related to the accelerating voltage:
λe=h / mv= h / (2qmV)1/2=12.2 / (V)1/2 (Å)
Under the accelerating voltage of 10 KV, the wavelength of electrons is only 0.12Å, which is much lower than 4000-7000Å of visible light, so the resolution of electron microscopes is naturally much better than that of light microscopes. However, the electron beam diameter of scanning electron microscope is mostly between 50-100Å, and the reaction volume of elastic scattering (Elastic Scattering) and inelastic scattering (Inelastic Scattering) of electrons and nuclei will be larger than the original electron beam diameter. Therefore, the resolution of the general transmission electron microscope is higher than that of the scanning electron microscope.
An important feature of scanning electron microscopes is that they have a large depth of field, which is about 300 times that of light microscopes, which makes scanning microscopes more suitable for observing samples with larger surface fluctuations than light microscopes.
For more information, please visit https://www.sputtertargets.net/.
Vacuum Evaporation Coating 