What is a Electronic microscope?

An electron microscope is a microscope that observes a sample by irradiating it with an electron beam. Because the wavelength of the electron beam is extremely short, it is possible to visualize ultrafine structures that cannot be observed with an optical microscope. There are two types: one that outputs the transmittance of the electron beam as an image, and the other that images the signal generated by the interaction between the electron beam and the sample. Many commercially available electron microscopes are optimized for viewing industrial materials and biological samples, respectively.

The main elements that make up an electron microscope include the electron source, lens, and detector. These are similar to the elements of an optical microscope, but their operating principles are very different. First, the electron beam attenuates and disappears as soon as it collides with molecules in the air. Therefore, electron beam generation and irradiation must be performed in a vacuum. Second, the glass lenses used in typical optical microscopes are transparent to electron beams. Therefore, in order to refract the electron beam, a magnetic lens is used, which uses a magnetic field to focus the electron beam. Magnetic lenses have a characteristic of having large optical aberrations, and to improve this, they are designed with small numerical apertures. This allows electron microscopes to have a deep depth of focus, making it possible to perform deep, three-dimensional observations.

Electron microscopes are mainly classified into the following two types.

Transmission Electron Microscopy (TEM)
In TEM, an electron beam is transmitted through the sample and contrast is obtained by attenuation. For this reason, the sample must be prepared very thin. The voltage that accelerates electrons is called accelerating voltage, and at an accelerating voltage of 300 kV, the wavelength of the electrons is 0.00197 nm, and the resolution reaches 0.1 nm. This translates to the highest magnification of 800,000 times, which means it has 800 times the resolution of an optical microscope. TEM observes transmitted electrons inside a sample, so it is suitable for observing the crystal structure inside the sample.

Scanning Electron Microscopy (SEM)
In SEM, when a sample is irradiated with an electron beam in a vacuum, secondary electrons, reflected electrons, characteristic X-rays, etc. are emitted. SEM scans an electron beam and detects secondary electron and backscattered electron signals to form an image. Since secondary electrons are generated near the sample surface, secondary electron images are suitable for observing minute irregularities on the sample. On the other hand, reflected electrons are electrons that collide with atoms in the sample and are bounced back, and their number depends on the composition of the sample. Backscattered electron images are suitable for evaluating the composition distribution on the sample surface.

When an electron beam hits a sample, atoms on its surface are excited and emit electrons. This emitted electron is called a secondary electron. In SEM, images are obtained by point-scanning the intensity of these secondary electrons.

Application of Electronic microscope

In the industrial field, it is used to investigate the cause by analyzing the fracture surface of damaged metal parts and to perform quality checks by observing the machined surface. Also, by observing the network of high molecular polymers, we can investigate the mechanical properties and evaluate the contamination of impurities. In the field of life science, we map the connections between nerve cells by visualizing the microstructure of intracellular small organs and observing intricately intertwined nerve cells. In addition, it was awarded the 2017 Nobel Prize in Chemistry because it became clear that it can be applied to the structural analysis of proteins by performing a simple pretreatment on the sample.

※Includes information on some trading companies