The electron microscope was invented. Digital microscopes

The electron microscope is not called so because it uses any components containing electronics - although there are more than enough of them. But the main thing is that instead of a stream of light rays that carry information about an object and which we can simply see by bringing our eyes closer to the eyepieces, an electron microscope uses a stream of electrons - exactly the same as in a conventional TV. We will be able to observe an image similar to a television one on a screen covered with a special compound that glows when a stream of electrons hits it. But how does an electron microscope magnify?

The fact is that just as the glass of an ordinary lens changes the course of light rays, magnetic and electric fields change the movement of the electron flow, which makes it possible to focus electron "beams" with the same effects as in the usual "glass" light optical system. However, due to the extremely small size of electrons and the significant "refraction" of electron beams, the image magnification is approximately a thousand times greater than that of an optical microscope. Instead of the eyepieces familiar to us in an electron microscope, the image is either projected onto a very small luminescent screen, from which the observer examines it in a familiar optical microscope with a slight increase, or using an optical-electronic converter, it is displayed on a conventional television screen, or - which is most often used on practice - fixed on a photographic plate. For an electron microscope, there is no such parameter as color accuracy, because color is a property of light rays, not electrons. There is no color in the microcosm, therefore “color” images obtained with an electron microscope are nothing more than a convention.

This was approximately the principle of operation of the first electron microscope in history, according to existing classification it belonged to OPEM microscopes - “a conventional transmission electron microscope”, outwardly it looked more like a large metal-working machine than a microscope, as people used to see it over the previous century and a half. In this device, which provides an increase of up to a million times, the sample was "shown through" by a stream of electrons moving in a constant direction. A little later, scanning electron microscopes appeared, in which an electron beam focused to subatomic dimensions "scans" the surface of the sample, and the image is observed on the monitor screen. Actually, the “magnification” of a scanning microscope is also a convention, it is the ratio of the screen size to the size of the original scanned object. It was on such a device that a person was able to see individual atoms for the first time. So far, this is the limit of technological possibilities. And in fact, the world of elementary particles is so different from ours that we are unlikely to be able to comprehend it to the end, even seeing it with our own eyes.

To study nanoobjects with the resolution of optical microscopes ( even using ultraviolet) is clearly insufficient. As a result, in the 1930s the idea arose to use electrons instead of light, the wavelength of which, as we know from quantum physics, is hundreds of times smaller than that of photons.

As you know, our vision is based on the formation of an image of an object on the retina of the eye by light waves reflected from this object. If, before entering the eye, light passes through the optical system microscope, we see an enlarged image. At the same time, the course of light rays is skillfully controlled by the lenses that make up the objective and the eyepiece of the device.

But how can you get an image of an object, and with a much higher resolution, using not light radiation, but a stream of electrons? In other words, how is it possible to see objects based on the use of particles, not waves?

The answer is very simple. It is known that the trajectory and speed of electrons are significantly affected by external electromagnetic fields, which can be used to effectively control the movement of electrons.

The science of the movement of electrons in electromagnetic fields and the calculation of devices that form the desired fields is called electronic optics.

An electronic image is formed by electric and magnetic fields in much the same way as a light image is formed by optical lenses. Therefore, in an electron microscope, devices for focusing and scattering an electron beam are called “ electronic lenses”.

electronic lens. The coil wires carrying the current focus the electron beam in the same way that a glass lens focuses a light beam.

The magnetic field of the coil acts as a converging or diverging lens. To concentrate the magnetic field, the coil is covered with a magnetic " armor» made of a special nickel-cobalt alloy, leaving only a narrow gap in the inner part. The magnetic field created in this way can be 10-100 thousand times stronger than the Earth's magnetic field!

Unfortunately, our eye cannot directly perceive electron beams. Therefore, they are used for drawing” images on fluorescent screens (which glow when electrons hit). By the way, the same principle underlies the operation of monitors and oscilloscopes.

Exists a large number of various types of electron microscopes among which the scanning electron microscope (SEM) is the most popular. We will obtain its simplified scheme if we place the object under study inside the cathode ray tube of an ordinary television between the screen and the electron source.

In such microscope a thin beam of electrons (beam diameter about 10 nm) runs around (as if scanning) the sample in horizontal lines, point by point, and synchronously transmits a signal to the kinescope. The whole process is similar to the operation of a TV in the scanning process. The source of electrons is a metal (usually tungsten), from which, when heated as a result of thermal electronic emission electrons are emitted.

Scheme of operation of a scanning electron microscope

Thermionic emission is the exit of electrons from the surface of the conductors. The number of released electrons is small at T=300K and grows exponentially with increasing temperature.

When electrons pass through a sample, some of them are scattered due to collisions with the nuclei of atoms in the sample, others due to collisions with electrons of atoms, and still others pass through it. In some cases, secondary electrons are emitted, x-rays are induced, and so on. All these processes are recorded by special detectors and in a transformed form are displayed on the screen, creating an enlarged picture of the object under study.

The magnification in this case is understood as the ratio of the size of the image on the screen to the size of the area that the beam runs around on the sample. Due to the fact that the wavelength of an electron is orders of magnitude smaller than that of a photon, in modern SEMs this increase can reach 10 million15, corresponding to a resolution of a few nanometers, which makes it possible to visualize individual atoms.

Main disadvantage electron microscopy- the need to work in a complete vacuum, because the presence of any gas inside the microscope chamber can lead to ionization of its atoms and significantly distort the results. In addition, electrons have a destructive effect on biological objects, which makes them inapplicable for research in many areas of biotechnology.

History of creation electron microscope is a remarkable example of an achievement based on an interdisciplinary approach, when independently developing fields of science and technology came together to create a new powerful tool for scientific research.

The pinnacle of classical physics was the theory of the electromagnetic field, which explained the propagation of light, electricity and magnetism as the propagation electromagnetic waves. Wave optics explained the phenomenon of diffraction, the mechanism of image formation, and the interplay of factors that determine resolution in a light microscope. good luck quantum physics we owe the discovery of the electron with its specific corpuscular-wave properties. These separate and seemingly independent developments led to the creation of electron optics, one of the most important inventions of which in the 1930s was the electron microscope.

But scientists did not rest on this either. The wavelength of an electron accelerated by an electric field is several nanometers. This is not bad if we want to see a molecule or even an atomic lattice. But how to look inside the atom? What is a chemical bond like? What does a single chemical reaction look like? For this, today different countries scientists develop neutron microscopes.

Neutrons are usually part of atomic nuclei along with protons and have almost 2000 times more mass than an electron. Those who have not forgotten de Broglie's formula from the quantum chapter will immediately realize that the wavelength of a neutron is as many times smaller, that is, it is picometers thousandths of a nanometer! Then the atom will appear to researchers not as a blurry spot, but in all its glory.

Neutron microscope has many advantages - in particular, neutrons reflect hydrogen atoms well and easily penetrate into thick layers of samples. However, it is very difficult to build it: neutrons do not have an electric charge, so they calmly ignore magnetic and electric fields and strive to elude the sensors. In addition, it is not so easy to expel large clumsy neutrons from atoms. Therefore, today the first prototypes of the neutron microscope are still very far from perfection.

ELECTRONIC MICROSCOPE- a device for observing and photographing a multiply (up to 10 6 times) enlarged image of an object, in which instead of light rays are used, accelerated to high energies(30-1000 keV and more) under deep conditions. Phys. Fundamentals of corpuscular-beam optical. devices were laid down in 1827, 1834-35 (almost a hundred years before the advent of electromagnetics) by W. R. Hamilton, who established the existence of an analogy between the passage of light rays in optically inhomogeneous media and the trajectories of particles in force fields . The expediency of creating E. m. became obvious after the nomination in 1924 of the hypothesis of de Broglie waves, and tehn. prerequisites were created by H. Busch, who in 1926 studied the focusing properties of axisymmetric fields and developed a magnetic field. electronic lens. In 1928, M. Knoll and E. Ruska set about creating the first magn. translucent E. m. (TEM) and three years later received an image of the object, formed by electron beams. In subsequent years, the first raster electron beams (SEMs) were built, operating on the principle of scanning, i.e., moving a thin electron beam (probe) over an object sequentially from point to point. K ser. 1960s REM have reached a high tech. perfection, and from that time began their widespread use in scientific. research. TEMs have the highest resolution, exceeding in this parameter the light microscopes in several thousand times. The resolution limit, which characterizes the ability of the device to display separately two as close as possible details of an object, for TEM is 0.15-0.3 HM, i.e., it reaches a level that allows one to observe the atomic and molecular structure of the studied objects. Such high resolutions are achieved due to the extremely short wavelength of electrons. The lenses of E. m. have aberrations, effective methods correction to-rykh was not found, in contrast to the light microscope (see. Electronic and ion optics). Therefore, in the TEM magn. electronic lenses(EL), for which the aberrations are an order of magnitude smaller, completely replaced the electrostatic ones. Optimum aperture (see. Diaphragm in electronic and ion optics), it is possible to reduce the spherical. lens aberration affecting

on the resolution of E. meters. TEMs in operation can be divided into three groups: high-resolution E. meters, simplified TEMs, and unique ultra-high-coarse E. meters.

high resolution TEM(0.15-0.3 nm) - universal multi-purpose devices. They are used to observe the image of objects in a bright and dark field, to study their structure by electro-nographic. method (see Electronography), carrying out local quantities. using an energy spectrometer. loss of electrons and X-ray crystals. and semiconductor and obtaining spectroscopic. images of objects using a filter that filters out electrons with energies outside the specified energy. window. The energy loss of electrons passed through the filter and forming an image is caused by the presence of a single chemical in the object. element. Therefore, the contrast of areas in which this element is present increases. By moving the window along the energetic spectrum receive distribution decomp. the elements contained in the object. The filter is also used as a monochromator to increase the resolution of electromagnetic meters in the study of thick objects, which increase the energy spread of electrons and (as a consequence) chromatic aberration.

With the help of add. devices and attachments, the object studied in TEM can be tilted in different planes at large angles to the optical. axis, heat, cool, deform. The voltage accelerating electrons in high-resolution electromagnetic meters is 100-400 kV, it is regulated in steps and is highly stable: in 1-3 minutes, its value is not allowed to change by more than (1-2) 10 -6 from the initial value. The thickness of the object, which can be "enlightened" by the electron beam, depends on the accelerating voltage. In 100-kilovolt E. m. study objects with a thickness of 1 to several. tens of nm.

Schematically, a TEM of the described type is shown in Fig. 1. In his electron-optical. system (column) with the help of a vacuum system creates a deep vacuum (pressure up to ~ 10 -5 Pa). Scheme of electron-optical. TEM system is shown in fig. 2. An electron beam, the source of which is a thermal cathode, is formed in electron gun and a high-voltage accelerator, and then it is focused twice by the first and second condensers, which create a small-sized electronic "spot" on the object (with adjustment, the spot diameter can vary from 1 to 20 μm). After passing through the object, some of the electrons are scattered and retained by the aperture diaphragm. Unscattered electrons pass through the diaphragm opening and are focused by the objective in the object plane of the intermediate electron lens. Here the first enlarged image is formed. Subsequent lenses create a second, third, etc. image. The last - projection - lens forms an image on a cathodoluminescent screen, which glows under the influence of electrons. The degree and nature of electron scattering are not the same at different points of the object, since the thickness, structure and chem. the composition of the object varies from point to point. Accordingly, the number of electrons passing through the aperture diaphragm changes, and hence the current density in the image. There is an amplitude contrast, which is converted into light contrast on the screen. In the case of thin objects prevails phase contrast, caused by a change in phases scattered in the object and interfering in the image plane. A magazine with photographic plates is located under the E. M. screen; when photographing, the screen is removed and the electrons act on the photoemulsion layer. The image is focused by an objective lens using a smooth adjustment of the current, which changes its magn. field. The currents of other electronic lenses regulate the increase in E. m., which is equal to the product of the magnifications of all lenses. At high magnifications, the brightness of the screen becomes insufficient and the image is observed using a brightness amplifier. To analyze the image, analog-to-digital conversion of the information contained in it and processing on a computer are performed. The image, enhanced and processed according to a given program, is displayed on a computer screen and, if necessary, entered into a memory device.

Rice. 1. Transmission type electron microscope (PEM): 1 - electron gun with an accelerator; 2-condenweed lenses; 3 -objective lens; 4 - projection lenses; 5 - light microscope, additionally magnifieddeciphering the image observed on the screen; b-thatbeads with viewing windows through which you can observegive an image; 7 -high voltage cable; 8 - vacuum system; 9 - Remote Control; 10 -stand; 11 - high-voltage power supply; 12 - lens power supply.

Rice. 2. Electron-optical scheme of TEM: 1 -cathode; 2 - focusing cylinder; 3 -accelerator; 4 -pervyy (short-focus) condenser, creating reduced image of the electron source; 5 - the second (long-focus) condenser, which wraps a thumbnail image of the source electrons per object; 6 -an object; 7 - aperture dialens fragment; 8 - lens; 9 , 10, 11 -system projection lenses; 12 - cathodoluminescent screen.

Simplified TEM designed for scientific studies, in which high resolution is not required. They are also used for pre- viewing objects, routine work and for educational purposes. These devices are simple in design (one condenser, 2-3 electronic lenses to magnify the image of the object), have a lower (60-100 kV) accelerating voltage and lower stability of high voltage and lens currents. Their resolution is 0.5-0.7 nm.

UHV E. m . (SVEM) - devices with an accelerating voltage of 1 to 3.5 MB - are large structures with a height of 5 to 15 m. Special equipment is equipped for them. premises or build separate buildings that are an integral part of the SVEM complex. The first SVMs were designed to study objects of large (1–10 µm) thickness, which retained the properties of a massive solid body. Due to the strong influence of chromatic aberrations, the resolution of such E. m. is reduced. However, compared with 100-kilovolt E. m., the resolution of the image of thick objects in SVEM is 10-20 times higher. Since the energy of electrons in UHEM is greater, their wavelength is shorter than in high-resolution TEM. Therefore, after solving complex technical. problems (it took more than one decade) and the implementation of high vibration resistance, reliable vibration isolation and sufficient mechanical. and electric stability, the highest resolution (0.13-0.17 nm) for translucent electromagnetic meters was achieved, which made it possible to photograph images of atomic structures. However, spherical aberration and defocusing of the lens distort the images obtained with the maximum resolution, and interfere with obtaining reliable information. This informational barrier is overcome with the help of focal series of images, to-rye obtained with decomp. lens defocus. Simultaneously, for the same defocusings, the atomic structure under study is simulated on a computer. Comparison of focal series with a series of model images helps to decipher the microphotographs of atomic structures taken with UHEM with the highest resolution. On fig. 3 shows a diagram of the SVEM located in the special. building. Main the components of the device are combined into a single complex using a platform, which is suspended from the ceiling on four chains and shock-absorbing springs. On top of the platform there are two tanks filled with electrically insulating gas at a pressure of 3-5 atm. A high-voltage generator is placed in one of them, and an electrostatic generator is placed in the other. electron accelerator with electron gun. Both tanks are connected by a branch pipe, through which the high voltage from the generator is transmitted to the accelerator. From the bottom to the tank with the accelerator adjoins the electron-optical. a column located in the lower part of the building, protected from X-ray by a ceiling. radiation generated in the accelerator. All of these nodes form a rigid structure that has the properties of physical. a pendulum with a large (up to 7 s) period of its own. , which are extinguished by liquid dampers. The pendulum suspension system provides effective isolation of the SVEM from the external. vibrations. The device is controlled from a remote control located near the column. The arrangement of lenses, columns, and other units of the device is similar to the corresponding TEM devices and differs from them in large dimensions and weight.

Rice. 3. Ultrahigh voltage electron microscope (SVEM): 1-vibration isolation platform; 2-chains, on which the platform hangs; 3 - shock-absorbing springs; 4-tanks in which the generator is locatedhigh voltage and electron accelerator with electronnoah gun; 5-electron-optical column; 6- ceiling separating the SVEM building into the upper and lower halls and protecting personnel working lower hall, from x-rays; 7 - remote control microscope control.

Raster E. m. (SEM) with a thermionic gun - the most common type of devices in electron microscopy. They use tungsten and hexaboride-lanthanum thermal cathodes. The resolution of the SEM depends on the electron brightness of the gun and in devices of the class under consideration is 5–10 nm. The accelerating voltage is adjustable from 1 to 30-50 kV. The SEM device is shown in fig. 4. Using two or three electron lenses, a narrow electron probe is focused onto the sample surface. Magn. deflection coils deploy the probe over a given area on the object. When the probe electrons interact with the object, several types of radiation arise (Fig. 5): secondary and reflected electrons; Auger electrons; x-ray bremsstrahlung and characteristic radiation (see characteristic spectrum); light radiation, etc. Any of the radiations, the currents of electrons that have passed through the object (if it is thin) and absorbed in the object, as well as the voltage induced on the object, can be recorded by the corresponding detectors that convert these radiations, currents and voltages into electric. signals, to-rye, after amplification, are fed to a cathode ray tube (CRT) and modulate its beam. The CRT beam is scanned synchronously with the scanning of the electron probe in the SEM, and an enlarged image of the object is observed on the CRT screen. The magnification is equal to the ratio of the frame size on the CRT screen to the corresponding size on the scanned surface of the object. Photograph the image directly from the CRT screen. Main The advantage of SEM is the high information content of the device, due to the ability to observe images using signals decomp. detectors. Using SEM, you can explore the microrelief, the distribution of chemical. composition by object, pn-transitions, produce x-rays. spectral analysis, etc. SEM are widely used in technol. processes (control in electronic-lithographic technologies, testing and detection of defects in microcircuits, metrology of micro-products, etc.).

Rice. 4. Diagram of a scanning electron microscope (REM): 1 - electron gun insulator; 2 -V-imagethermal cathode; 3 - focusing electrode; 4 - anode; 5 - condenser lenses; 6 -diaphragm; 7 - two-tier deflecting system; 8 -lens; 9 - aperture diaphragm of the lens; 10 -an object; 11 -detector of secondary electrons; 12 -crystalpersonal spectrometer; 13 -proportional counter; 14 - preamplifier; 15 - amplification block; 16, 17 - registration equipment x-ray radiation; 18 - amplification unit; 19 - magnification control unit; 20, 21 - burn blocksumbrella and vertical scans; 22, 23 -electhrone ray tubes.

Rice. 5. Scheme of registration of information about the object, received in SEM; 1-primary electron beam; 2-detector of secondary electrons; 3-rent detectorgene radiation; 4-detector of reflected electronsronov; 5-detector of Auger electrons; 6-light detectornew radiation; 7 - detector of passed electronew; 8 - circuit for registering the current passed through electron object; 9-circuit for current registration electrons absorbed in the object; 10-scheme for rehystration of the electrical capacity.

The high resolution of the SEM is realized in the formation of an image using secondary electrons. It is inversely related to the diameter of the zone from which these electrons are emitted. The size of the zone depends on the probe diameter, the properties of the object, the speed of the primary beam electrons, etc. At a large penetration depth of the primary electrons, secondary processes developing in all directions increase the zone diameter and the resolution decreases. The secondary electron detector consists of photomultiplier(PMT) and electron-photonic converter, osn. an element to-rogo is the scintillator. The number of scintillator flashes is proportional to the number of secondary electrons knocked out at a given point of the object. After amplification in the PMT and in the video amplifier, the signal modulates the CRT beam. The magnitude of the signal depends on the topography of the sample, the presence of local electric. and magn. microfields, the magnitude of the coefficient. secondary electron emission, to-ry, in turn, depends on the chemical. sample composition at a given point.

Reflected electrons are captured by a semiconductor detector with p - n-transition. The contrast of the image is due to the dependence of the coefficient. reflections from the angle of incidence of the primary beam at a given point of the object and from at. substance number. The resolution of the image obtained in "reflected electrons" is lower than that obtained with the help of secondary electrons (sometimes by an order of magnitude). Due to the straightness of the flight of electrons, information about the sep. areas of the object, from which there is no direct path to the detector, is lost (shadows appear). To eliminate information loss, as well as to form an image of the relief of the sample, its elemental composition does not affect the swarm and, conversely, to form a picture of the distribution of chemical. elements in the object, which is not affected by its relief, the SEM uses a detector system consisting of several. detectors placed around the object, the signals of which are subtracted from one another or added, and the resulting signal, after amplification, is fed to the CRT modulator.

X-ray characteristic radiation is recorded crystal. (wave-dispersed) or semiconductor (energy-dispersed) spectrometers, to-rye complement each other. In the first case, X-ray radiation after reflection by the crystal of the spectrometer enters the gas proportional counter, and in the second - x-ray. quanta excite signals in a semiconductor cooled (to reduce noise) detector made of silicon doped with lithium or germanium. After amplification, the signals of the spectrometers can be fed to the CRT modulator and a picture of the distribution of one or another chemical will appear on its screen. element on the surface of the object.

On a SEM equipped with X-ray. spectrometers, produce local quantities. analysis: register the number of pulses excited x-ray. quanta from the area on which the electron probe was stopped. Crystalline spectrometer using a set of analyzer crystals with decomp. interplanar distances (see Bragg-Wulf condition) discriminates with a high spectrum. characteristic resolution. wavelength spectrum, covering the range of elements from Be to U. The semiconductor spectrometer discriminates X-ray. quanta by their energies and simultaneously registers all elements from B (or C) to U. Its spectral resolution is lower than that of crystalline. spectrometer, but higher sensitivity. There are other advantages: fast delivery of information, simple design, high performance.

Raster Auger-E. m. (ROEM) devices, in which, when scanning an electron probe, Auger electrons are detected from an object depth of no more than 0.1–2 nm. At such a depth, the exit zone of Auger electrons does not increase (in contrast to secondary emission electrons) and the instrument resolution depends only on the probe diameter. The device works at ultrahigh vacuum (10 -7 -10 -8 Pa). Its accelerating voltage is approx. 10 kV. On fig. 6 shows the ROEM device. The electron gun consists of a lanthanum hexaboride or tungsten thermal cathode operating in the Schottky mode and a three-electrode electrostatic. lenses. The electron probe is focused by this lens and the magnet. a lens in the focal plane to-rogo is an object. The collection of Auger electrons is carried out using a cylindrical. a mirror energy analyzer, the inner electrode of which covers the lens body, and the outer one adjoins the object. With the help of an analyzer that discriminates Auger electrons by energy, the distribution of chem. elements in the surface layer of the object with submicron resolution. To study the deep layers, the device is equipped with an ion gun, with the help of which the upper layers of the object are removed by ion-beam etching.

Rice. b. Scheme of a scanning Auger electron microscope(ROEM): 1 - ion pump; 2- cathode; 3 - three-electrode electrostatic lens; 4-channel detector; 5-aperture lens aperture; 6-double deflecting system for sweeping the electronic probe; 7-lens; 8- outer electrode cylindrical mirror analyzer; 9-object.

SEM with field emission gun have high resolution (up to 2-3 nm). The field emission gun uses a cathode in the form of a point, at the top of which a strong electric current occurs. field pulling electrons out of the cathode ( field emission). The electronic brightness of a gun with a field emission cathode is 10 3 -10 4 times higher than the brightness of a gun with a thermionic cathode. Correspondingly, the electron probe current increases. Therefore, in a SEM with a field emission gun, along with a slow sweep, a fast sweep is carried out, and the probe diameter is reduced to increase the resolution. However, the field emission cathode operates stably only at ultrahigh vacuum (10 -7 -10 -9 Pa), which complicates the design and operation of such SEMs.

Translucent raster E. m. (STEM) have the same high resolution as TEM. These devices use field emission guns operating under conditions of ultrahigh vacuum (up to 10 -8 Pa), providing sufficient current in a probe of small diameter (0.2-0.3 nm). The probe diameter is reduced by two magn. lenses (Fig. 7). Below the object are detectors - central and ring. Unscattered electrons fall on the first one, and after conversion and amplification of the corresponding signals, a bright-field image appears on the CRT screen. Scattered electrons are collected on the ring detector, creating a dark-field image. In STEM, one can study thicker objects than in TEM, since the increase in the number of inelastically scattered electrons with thickness does not affect the resolution (there is no electron optics for imaging after the object). Using an energy analyzer, the electrons that have passed through the object are separated into elastically and inelastically scattered beams. Each beam hits its own detector, and the corresponding images containing complements are observed on the CRT. information about the elemental composition of the object. High resolution in STEM is achieved with slow sweeps, because in a probe with a diameter of only 0.2–0.3 nm, the current is small. PREM are equipped with all devices used in electron microscopy for analytical. research objects, and in particular spectrometers energetic-tich. electron loss, x-ray spectrometers, complex systems for detecting transmitted, backscattered and secondary electrons that select groups of electrons scattered on decomp. angles having different energy, etc. The devices are equipped with a computer for the complex processing of incoming information.

Rice. 7. Schematic diagram of a translucent rasterelectron microscope (PREM): 1-auto-emissionion cathode; 2-intermediate anode; 3- anode; 4- diaphragm "illuminator"; 5-magnetic lens; 6-twotiered deflection system for electron sweepleg probe; 7-magnetic lens; 8 - aperture lens aperture; 9 - object; 10 - deflecting system; 11 - ring detector of scattered electrons; 12 - detector of unscattered electrons (removed when operation of the magnetic spectrometer); 13 - magnetic spectrometer; 14-deflecting system for selection electrons with different energy losses; 15 - gap spectrometer; 16-spectrometer detector; RE-secondarynew electrons; hv- x-ray radiation.

Emission E. m. create an image of an object with electrons, to-rye emits the object itself when heated, bombarded by a primary electron beam, under the action of an e-mag. radiation and when applying a strong electric. field pulling electrons out of the object. These devices usually have a narrow purpose (see. electronic projector).

Mirror E. m. serve the arr. for visualization electrostatic. "potential reliefs" and magn. microfields on the surface of the object. Main electron-optical element of the device is electronic mirror, and one of the electrodes is the object itself, which is under a small negative. potential relative to the cathode of the gun. The electron beam is sent to electronic mirror and is reflected by the field in the immediate vicinity of the surface of the object. The mirror forms an image on the screen "in reflected beams": the microfields near the surface of the object redistribute the electrons of the reflected beams, creating a contrast in the image that visualizes these microfields.

Prospects for the development of E. m. Improvement of electromagnetic meters with the aim of increasing the amount of information obtained, which has been carried out for many years, will continue in the future, and improving the parameters of instruments, and above all increasing the resolution, will remain the main task. Work on the creation of electron-optical. systems with small aberrations have not yet led to a real increase in the resolution of E. m. This applies to non-axisymmetric aberration correction systems, cryogenic optics, and lenses with corrective spaces. in the axial region, etc. Searches and research in these areas are underway. Research work on the creation of electronic holographic features continues. systems, including those with correction of the frequency-contrast characteristics of lenses. Miniaturization of electrostatic lenses and systems using the achievements of micro- and nanotechnologies will also contribute to solving the problem of creating electronic optics with small aberrations.

Lit.: Practical scanning electron microscopy, ed. D. Gouldstein, X. Yakovitsa, trans. from English, M., 1978; Spence D., Experimental high-resolution electron microscopy, trans. from English, M., 1986; Stoyanov P. A., Electron microscope SVEM-1, "Proceedings of the Academy of Sciences of the USSR, series of physics", 1988, vol. 52, no. 7, p. 1429; Hawks P., Kasper E., Fundamentals of electronic optics, trans. from English, vol. 1-2, M., 1993; Oechsner H., Scanning auger microscopy, Le Vide, les Couches Minces, 1994, t. 50, no. 271, p. 141; McMullan D., Scanning electron microscopy 1928-1965, "Scanning", 1995, t. 17, no. 3, p. 175. P. A. Stoyanov.

ELECTRON MICROSCOPE
a device that allows you to get a greatly enlarged image of objects, using electrons to illuminate them. An electron microscope (EM) makes it possible to see details that are too small to be resolved by a light (optical) microscope. EM is one of the most important instruments for fundamental scientific research into the structure of matter, especially in such fields of science as biology and solid state physics. There are three main types of EM. In the 1930s, the conventional transmission electron microscope (CTEM) was invented, in the 1950s, the scanning (scanning) electron microscope (SEM), and in the 1980s, the scanning tunneling microscope (RTM). These three types of microscopes complement each other in the study of structures and materials of different types.
CONVENTIONAL TRANSMISSION ELECTRON MICROSCOPE
OPEM is in many ways similar to a light microscope, see MICROSCOPE, only for illuminating samples it uses not light, but an electron beam. It contains an electronic projector (see below), a series of condenser lenses, an objective lens, and a projection system that matches the eyepiece but projects the actual image onto a fluorescent screen or photographic plate. The electron source is usually a heated cathode made of tungsten or lanthanum hexaboride. The cathode is electrically isolated from the rest of the device, and the electrons are accelerated by a strong electric field. To create such a field, the cathode is maintained at a potential of the order of -100,000 V relative to other electrodes, which focus electrons into a narrow beam. This part of the device is called an electron searchlight (see ELECTRONIC GUN). Since electrons are strongly scattered by matter, there must be a vacuum in the microscope column where the electrons move. It maintains a pressure not exceeding one billionth of atmospheric pressure.
Electronic optics. An electronic image is formed by electric and magnetic fields in much the same way as a light image is formed by optical lenses. The principle of operation of a magnetic lens is illustrated by a diagram (Fig. 1). The magnetic field created by the turns of a coil carrying a current acts like a converging lens whose focal length can be changed by changing the current. Since the optical power of such a lens, i.e. the ability to focus electrons depends on the strength of the magnetic field near the axis; to increase it, it is desirable to concentrate the magnetic field in the smallest possible volume. In practice, this is achieved by the fact that the coil is almost completely covered with a magnetic "armor" made of a special nickel-cobalt alloy, leaving only a narrow gap in its inner part. The magnetic field created in this way can be 10-100 thousand times stronger than the Earth's magnetic field on the earth's surface.

The OPEM scheme is shown in fig. 2. A row of condenser lenses (only the last one shown) focuses the electron beam on the sample. Typically, the former creates a non-enlarged image of the electron source, while the latter controls the size of the illuminated area on the sample. The aperture of the last condenser lens determines the beam width in the object plane. The sample is placed in the magnetic field of a high power objective lens, the most important OPEM lens, which determines the maximum possible resolution of the instrument. The aberrations of an objective lens are limited by its aperture, just as they are in a camera or a light microscope. An objective lens gives an enlarged image of the object (usually with a magnification of the order of 100); the additional magnification introduced by the intermediate and projection lenses ranges from a little less than 10 to a little more than 1000. Thus, the magnification that can be obtained in modern OPEMs is from less than 1000 to 1,000,000 ELECTRONIC MICROSCOPE. (At a magnification of a million times grapefruit grows to the size of the Earth.) The object to be examined is usually placed on a very fine mesh placed in a special holder. The holder can be mechanically or electrically smoothly moved up and down and left and right.

Image. The contrast in OPEM is due to the scattering of electrons during the passage of an electron beam through the sample. If the sample is sufficiently thin, then the fraction of scattered electrons is small. When electrons pass through a sample, some of them scatter due to collisions with the nuclei of atoms of the sample, others due to collisions with electrons of atoms, and still others pass without undergoing scattering. The degree of scattering in any region of the sample depends on the thickness of the sample in that region, its density, and the average atomic mass (number of protons) at that point. Electrons leaving the diaphragm with an angular deviation exceeding a certain limit can no longer return to the image-bearing beam, and therefore strongly scattering areas of increased density, increased thickness, and locations of heavy atoms look like dark zones on a light background in the image. Such an image is called bright-field because the surrounding field is brighter than the object. But it is possible to make it so that the electric deflection system passes only one or another of the scattered electrons into the lens diaphragm. Then the sample looks bright in the dark field. A weakly scattering object is often more convenient to view in the dark field mode. The final enlarged electronic image is made visible by means of a fluorescent screen that glows under the influence of electron bombardment. This image, usually low contrast, is usually viewed through a binocular light microscope. With the same brightness, such a microscope with a magnification of 10 can create an image on the retina that is 10 times larger than when observed with the naked eye. Sometimes a phosphor screen with an image intensifier tube is used to increase the brightness of a weak image. In this case, the final image can be displayed on a conventional television screen, allowing it to be recorded on videotape. Video recording is used to record images that change over time, for example, due to a chemical reaction. Most often, the final image is recorded on photographic film or photographic plate. A photographic plate usually makes it possible to obtain a sharper image than that observed with the naked eye or recorded on videotape, since photographic materials, generally speaking, register electrons more efficiently. In addition, 100 times more signals can be recorded per unit area of ​​photographic film than per unit area of ​​videotape. Thanks to this, the image recorded on the film can be further enlarged by about 10 times without loss of clarity.
Permission. Electron beams have properties similar to those of light beams. In particular, each electron is characterized by a certain wavelength. The resolution of the EM is determined by the effective wavelength of the electrons. The wavelength depends on the speed of the electrons and, consequently, on the accelerating voltage; the greater the accelerating voltage, the greater the speed of the electrons and the shorter the wavelength, and hence the higher the resolution. Such a significant advantage of EM in resolving power is explained by the fact that the wavelength of electrons is much smaller than the wavelength of light. But since electronic lenses do not focus as well as optical ones (the numerical aperture of a good electronic lens is only 0.09, while for a good optical lens this value reaches 0.95), the resolution of the EM is 50-100 electron wavelengths. Even with such weak lenses in an electron microscope, a resolution limit of approx. 0.17 nm, which makes it possible to distinguish individual atoms in crystals. To achieve resolution of this order, very careful tuning of the instrument is necessary; in particular, highly stable power supplies are required, and the instrument itself (which may be approx. 2.5 m high and weigh several tons) and its accessories require vibration-free mounting.
RASTER ELECTRON MICROSCOPE
SEM, which has become the most important instrument for scientific research, serves as a good complement to OPEM. SEMs use electron lenses to focus an electron beam into a very small spot. It is possible to adjust the SEM so that the spot diameter in it does not exceed 0.2 nm, but, as a rule, it is a few or tens of nanometers. This spot continuously runs around some part of the sample, similar to a beam running around the screen of a television tube. An electrical signal that occurs when an object is bombarded by beam electrons is used to form an image on the screen of a television kinescope or cathode ray tube (CRT), the sweep of which is synchronized with the electron beam deflection system (Fig. 3). The magnification in this case is understood as the ratio of the size of the image on the screen to the size of the area that the beam runs around on the sample. This increase is from 10 to 10 million.

The interaction of focused beam electrons with sample atoms can lead not only to their scattering, which is used to obtain an image in OPEM, but also to X-ray excitation, visible light emission, and emission of secondary electrons. In addition, since the SEM has only focusing lenses in front of the sample, it makes it possible to study "thick" samples.
Reflective SEM. Reflective SEM is intended for studying massive samples. Since the contrast that occurs when registering reflected, i.e. of back-scattered and secondary electrons, is mainly related to the angle of incidence of electrons on the sample, the surface structure is revealed in the image. (The intensity of backscattering and the depth at which it occurs depend on the energy of the electrons of the incident beam. The emission of secondary electrons is determined mainly by the composition of the surface and the electrical conductivity of the sample.) Both of these signals carry information about general characteristics sample. Due to the small convergence of the electron beam, it is possible to carry out observations with a much greater depth of field than when working with a light microscope, and to obtain excellent three-dimensional micrographs of surfaces with a very developed relief. By registering the X-ray radiation emitted by the sample, it is possible, in addition to data on the relief, to obtain information about chemical composition sample in the surface layer with a depth of 0.001 mm ELECTRONIC MICROSCOPE. The composition of the material on the surface can also be judged from the measured energy with which certain electrons are emitted. All the difficulties of working with SEM are mainly due to its recording and electronic visualization systems. In a device with full range detectors, along with all the functions of the SEM, the operating mode of the electron probe microanalyzer is provided.
Scanning transmission electron microscope. A scanning transmission electron microscope (STEM) is a special type of SEM. It is designed for thin samples, the same as those studied in OPEM. The RPEM scheme differs from the scheme in Fig. 3 only because it does not have detectors located above the sample. Since the image is formed by a traveling beam (rather than a beam that illuminates the entire area of ​​the sample under study), a high-intensity electron source is required so that the image can be registered in a reasonable time. The high-resolution RTEM uses high-brightness field emitters. In such an electron source, a very strong electric field (approx. V/cm) is created near the surface of a very small diameter tungsten wire sharpened by etching. This field literally pulls billions of electrons out of the wire without any heating. The brightness of such a source is almost 10,000 times greater than that of a source with a heated tungsten wire (see above), and the emitted electrons can be focused into a beam with a diameter of less than 1 nm. Beams were even obtained, the diameter of which is close to 0.2 nm. Autoelectronic sources can only operate under ultra-high vacuum conditions (at pressures below Pa), in which there are no contaminants such as hydrocarbon and water vapors, and it becomes possible to obtain high-resolution images. Thanks to such ultrapure conditions, it is possible to study processes and phenomena that are inaccessible to EMs with conventional vacuum systems. Research in RPEM is carried out on ultrathin samples. Electrons pass through such samples almost without scattering. Electrons scattered at angles of more than a few degrees without deceleration are recorded, falling on a ring electrode located under the sample (Fig. 3). The signal taken from this electrode is highly dependent on the atomic number of the atoms in the region through which the electrons pass - heavier atoms scatter more electrons in the direction of the detector than light ones. If the electron beam is focused to a point with a diameter of less than 0.5 nm, then individual atoms can be imaged. In reality, it is possible to distinguish individual atoms with an atomic mass of iron (i.e., 26 or more) in the image obtained in the RTEM. Electrons that have not undergone scattering in the sample, as well as electrons slowed down as a result of interaction with the sample, pass into the hole of the ring detector. An energy analyzer located under this detector allows you to separate the former from the latter. By measuring the energy lost by electrons during scattering, one can obtain important information about the sample. The energy losses associated with the excitation of X-rays or the knocking out of secondary electrons from the sample make it possible to judge the chemical properties of the substance in the region through which the electron beam passes.
RASTER TUNNELING MICROSCOPE
In the EMs discussed above, magnetic lenses are used to focus electrons. This section is about EM without lenses. But before moving on to the Scanning Tunneling Microscope (RTM), it will be useful to look briefly at two older types of lensless microscopes that produce a projected shadow image.
Autoelectronic and autoionic projectors. The field electron source used in RTEM has been used in shadow projectors since the early 1950s. In a field electron projector, electrons emitted by field emission from a tip of very small diameter are accelerated towards a luminescent screen located at a distance of several centimeters from the tip. As a result, a projected image of the surface of the tip and particles located on this surface appears on the screen with an increase equal to the ratio of the screen radius to the radius of the tip (order). Higher resolution is achieved in an autoion projector, in which the image is projected by helium ions (or some other elements), the effective wavelength of which is shorter than that of electrons. This makes it possible to obtain images showing the true arrangement of atoms in the crystal lattice of the material of the tip. Therefore, field-ion projectors are used, in particular, to study the crystal structure and its defects in materials from which such tips can be made.
Scanning tunneling microscope (RTM). This microscope also uses a metal tip of small diameter, which is the source of electrons. An electric field is created in the gap between the tip and the sample surface. The number of electrons pulled out by the field from the tip per unit time (tunneling current) depends on the distance between the tip and the sample surface (in practice, this distance is less than 1 nm). As the tip moves along the surface, the current is modulated. This allows you to get an image associated with the relief of the surface of the sample. If the tip ends with a single atom, then it is possible to form an image of the surface by passing atom by atom. RTM can only work if the distance from the tip to the surface is constant, and the tip can be moved with an accuracy of atomic dimensions. Vibrations are suppressed due to the rigid structure and small dimensions of the microscope (no more than a fist), as well as the use of multilayer rubber shock absorbers. high precision provide piezoelectric materials that lengthen and contract under the action of an external electric field. By applying a voltage of the order of 10-5 V, it is possible to change the dimensions of such materials by 0.1 nm or less. This makes it possible, by fixing the tip on an element of piezoelectric material, to move it in three mutually perpendicular directions with an accuracy of the order of atomic dimensions.
ELECTRONIC MICROSCOPY TECHNIQUE
There is hardly any sector of research in the field of biology and materials science where transmission electron microscopy (TEM) has not been applied; this is due to advances in sample preparation techniques. All techniques used in electron microscopy are aimed at obtaining an extremely thin sample and providing maximum contrast between it and the substrate that it needs as a support. The basic technique is designed for samples with a thickness of 2-200 nm, supported by thin plastic or carbon films, which are placed on a grid with a cell size of approx. 0.05 mm. ( Suitable Sample, whichever way it is obtained, is processed in such a way as to increase the intensity of electron scattering on the object under study.) If the contrast is large enough, then the observer's eye can distinguish details that are at a distance of 0.1-0.2 mm from each other without strain . Therefore, in order for the image created by an electron microscope to distinguish details separated on a sample by a distance of 1 nm, a total magnification of the order of 100-200 thousand is necessary. The best of microscopes can create an image of a sample on a photographic plate with such a magnification, but Too small area shown. Usually a micrograph is taken at a lower magnification and then enlarged photographically. The photographic plate allows for a length of 10 cm approx. 10,000 lines. If each line on the sample corresponds to a certain structure with a length of 0.5 nm, then to register such a structure, an increase of at least 20,000 is required, while using SEM and STEM, in which the image is recorded by an electronic system and deployed on a television screen, only OK. 1000 lines. Thus, when using a television monitor, the minimum required magnification is about 10 times greater than when photographing.
biological preparations. Electron microscopy is widely used in biological and medical research. Techniques for fixing, embedding and obtaining thin tissue sections for examination in OPEM and RPEM and fixation methods for studying bulk samples in SEM have been developed. These techniques make it possible to study the organization of cells at the macromolecular level. Electron microscopy revealed the components of the cell and details of the structure of membranes, mitochondria, the endoplasmic reticulum, ribosomes, and many other organelles that make up the cell. The sample is first fixed with glutaraldehyde or other fixatives, and then dehydrated and embedded in plastic. Methods of cryofixation (fixation at very low - cryogenic - temperatures) allow to preserve the structure and composition without the use of chemical fixatives. In addition, cryogenic methods allow imaging of frozen biological samples without dehydration. Using ultramicrotomes with polished diamond or chipped glass blades, tissue sections can be made with a thickness of 30-40 nm. Mounted histological preparations can be stained with heavy metal compounds (lead, osmium, gold, tungsten, uranium) to enhance the contrast of individual components or structures.

Biological studies have been extended to microorganisms, especially viruses, which are not resolved by light microscopes. TEM made it possible to reveal, for example, the structures of bacteriophages and the location of subunits in the protein coats of viruses. In addition, positive and negative staining methods have been able to reveal the structure with subunits in a number of other important biological microstructures. Nucleic acid contrast enhancement techniques have made it possible to observe single- and double-stranded DNA. These long, linear molecules are spread into a layer of basic protein and applied to a thin film. The specimen is then vacuum-coated with a very thin layer heavy metal. This layer of heavy metal "shadows" the sample, due to which the latter, when observed in the OPEM or RTEM, looks like it is illuminated from the side from which the metal was deposited. If, however, the sample is rotated during deposition, then the metal accumulates around the particles from all sides evenly (like a snowball).
non-biological materials. TEM is applied in materials research to study thin crystals and boundaries between different materials. To obtain a high-resolution image of the interface, the sample is filled with plastic, the sample is cut perpendicular to the interface, and then it is thinned so that the interface is visible on the sharp edge. The crystal lattice strongly scatters electrons in certain directions, giving a diffraction pattern. The image of a crystalline sample is largely determined by this pattern; the contrast is highly dependent on the orientation, thickness, and perfection of the crystal lattice. Changes in the contrast in the image make it possible to study the crystal lattice and its imperfections on the scale of atomic sizes. The information obtained in this way supplements that provided by X-ray analysis of bulk samples, since EM makes it possible to directly see dislocations, stacking faults, and grain boundaries in all details. In addition, electron diffraction patterns can be taken in EM and diffraction patterns from selected areas of the sample can be observed. If the lens diaphragm is adjusted so that only one diffracted and unscattered central beam passes through it, then it is possible to obtain an image of a certain system of crystal planes that gives this diffracted beam. Modern instruments make it possible to resolve grating periods of 0.1 nm. Crystals can also be studied by dark-field imaging, in which the central beam is blocked so that the image is formed by one or more diffracted beams. All these methods have provided important information about the structure of very many materials and have significantly clarified the physics of crystals and their properties. For example, the analysis of TEM images of the crystal lattice of thin small-sized quasicrystals in combination with the analysis of their electron diffraction patterns made it possible in 1985 to discover materials with fifth-order symmetry.
High voltage microscopy. Currently, the industry produces high-voltage versions of OPEM and RPEM with an accelerating voltage of 300 to 400 kV. Such microscopes have a higher penetrating power than low-voltage instruments, and are almost as good as the 1 million volt microscopes that were built in the past. Modern high-voltage microscopes are quite compact and can be installed in an ordinary laboratory room. Their increased penetrating power proves to be a very valuable property in the study of defects in thicker crystals, especially those from which it is impossible to make thin specimens. In biology, their high penetrating power makes it possible to examine whole cells without cutting them. In addition, these microscopes can be used to obtain three-dimensional images of thick objects.
low voltage microscopy. There are also SEMs with an accelerating voltage of only a few hundred volts. Even at such low voltages, the electron wavelength is less than 0.1 nm, so the spatial resolution is again limited by the aberrations of the magnetic lenses. However, since electrons of such low energy penetrate shallowly below the surface of the sample, almost all of the electrons involved in imaging come from a region very close to the surface, thereby increasing the resolution of the surface relief. Using low-voltage SEM, images were obtained on solid surfaces of objects smaller than 1 nm in size.
radiation damage. Because electrons are ionizing radiation, the sample in an EM is constantly exposed to it. (As a result of this action, secondary electrons are produced, which are used in the SEM.) Therefore, the samples are always exposed to radiation damage. The typical dose of radiation absorbed by a thin sample during the recording of a microphotograph in OPEM approximately corresponds to the energy that would be sufficient to completely evaporate cold water from a pond 4 m deep with a surface area of ​​1 ha. To reduce radiation damage to the sample, it is necessary to use various methods of its preparation: staining, pouring, freezing. In addition, it is possible to register an image at electron doses that are 100-1000 times lower than by the standard method, and then improve it by computer image processing methods.
HISTORICAL REFERENCE
The history of the creation of the electron microscope is a wonderful example of how independently developing areas of science and technology can, by exchanging the information received and joining efforts, create a new powerful tool for scientific research. The pinnacle of classical physics was the theory of the electromagnetic field, which explained the propagation of light, the emergence of electric and magnetic fields, the movement of charged particles in these fields as the propagation of electromagnetic waves. Wave optics made clear the phenomenon of diffraction, the mechanism of image formation and the play of factors that determine resolution in a light microscope. We owe successes in the field of theoretical and experimental physics to the discovery of the electron with its specific properties. These separate and seemingly independent developments led to the creation of the foundations of electron optics, one of the most important applications of which was the invention of the EM in the 1930s. A direct hint of this possibility can be considered the hypothesis of the wave nature of the electron, put forward in 1924 by Louis de Broglie and experimentally confirmed in 1927 by K. Davisson and L. Germer in the USA and J. Thomson in England. Thus, an analogy was suggested, which made it possible to construct an EM according to the laws of wave optics. H. Bush discovered that electronic images can be formed using electric and magnetic fields. In the first two decades of the 20th century the necessary technical prerequisites were also created. Industrial laboratories working on the cathode-beam oscilloscope provided vacuum technology, stable sources of high voltage and current, and good electron emitters. In 1931, R. Rudenberg filed a patent application for a transmission electron microscope, and in 1932 M. Knoll and E. Ruska built the first such microscope, using magnetic lenses to focus electrons. This instrument was the forerunner of modern OPEM. (Ruska was rewarded for his work by winning the 1986 Nobel Prize in Physics.) In 1938 Ruska and B. von Borris built a prototype industrial OPEM for Siemens-Halske in Germany; this instrument eventually made it possible to achieve a resolution of 100 nm. A few years later, A. Prebus and J. Hiller built the first high-resolution OPEM at the University of Toronto (Canada). The wide possibilities of OPEM became apparent almost immediately. His industrial production It was launched simultaneously by Siemens-Halske in Germany and RCA Corporation in the USA. In the late 1940s, other companies began to produce such devices. The SEM in its current form was invented in 1952 by Charles Otley. True, preliminary versions of such a device were built by Knoll in Germany in the 1930s and by Zworykin with employees at the RCA corporation in the 1940s, but only the Otley device could serve as the basis for a number of technical improvements that culminated in the introduction of an industrial version of the SEM into production in the middle 1960s. The circle of consumers of such a rather easy-to-use device with a three-dimensional image and an electronic output signal has expanded with the speed of an explosion. Currently, there are a dozen industrial SEM manufacturers on three continents and tens of thousands of such devices used in laboratories around the world. In the 1960s, ultrahigh-voltage microscopes were developed to study thicker samples. , where a device with an accelerating voltage of 3.5 million volts was put into operation in 1970. RTM was invented by G. Binnig and G. Rohrer in Zurich in 1979. This very simple device provides atomic resolution of surfaces. For the creation of the RTM, Binnig and Rohrer (simultaneously with Ruska) received the Nobel Prize in Physics.
see also

What is a USB Microscope?

USB microscope is a kind of digital microscope. Instead of the usual eyepiece, here is installed digital camera, which captures the image from the lens and transfers it to the monitor or laptop screen. Such a microscope is connected to a computer very simply - via a regular USB cable. The microscope comes with special software that allows you to process the resulting images. You can take photos, create videos, change the contrast, brightness and size of the picture. Possibilities software manufacturer dependent.

The USB microscope is primarily a compact magnifying device. It is convenient to take it with you on trips, to meetings or out of town. Normally, a USB microscope cannot boast of high magnification, but for examining coins, small print, art objects, fabric samples or banknotes, its capabilities are quite enough. With the help of such a microscope, you can examine plants, insects and any small objects around you.

Where to buy an electron microscope?

If you have finally decided on the choice of model, you can buy an electron microscope on this page. In our online store you will find an electron microscope at the best price!

If you want to see the electron microscope with your own eyes, and then make a decision, visit the Four Eyes store closest to you.
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