ELECTRONIC MICROSCOPE- a device for observing and photographing repeatedly (up to 10 6 times) an enlarged image of an object, in which instead of light rays are used, accelerated to high energies (30-1000 keV and more) in deep conditions. Phys. fundamentals of corpuscular-beam optical instruments. instruments were laid in 1827, 1834-35 (almost a hundred years before the advent of EM) by W. P. 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 feasibility of creating EM became obvious after the hypothesis of de Broglie waves was put forward in 1924, and tech. prerequisites were created by H. Busch (H. Busch), to-ry in 1926 investigated the focusing properties of axisymmetric fields and developed a magn. electronic lens. In 1928 M. Knoll and E. Ruska began to create the first magn. transmission EM (TEM) and three years later obtained an image of the object, formed by electron beams. In subsequent years, the first raster EMs (SEMs) were built, operating on the principle of scanning, that is, sequential from point to point of movement of a thin electron beam (probe) over the object. K ser. 1960s SEM have reached a high tech. perfection, and from that time began their widespread use in scientific. research. FEM have the highest resolution, surpassing the light microscopes in several. thousand times. The solution, which characterizes the device's ability to display separately two very closely spaced details of an object, for a TEM is 0.15-0.3 HM, i.e., it reaches a level that makes it possible to observe an atomic and the molecular structure of the investigated objects. These high resolutions are achieved thanks to the extremely short electron wavelength. Lenses of E. m. Have aberrations, effective methods of correction to-rykh have not been found, in contrast to the light microscope (see. Electronic and ion optics Therefore, in the TEM magn. electronic lenses(EL), in which aberrations are an order of magnitude smaller, have completely replaced the electrostatic ones. Optimal aperture (see. Diaphragm in an elec tronic and ionic optik e) it is possible to reduce the spherical. lens aberration affecting
on the resolution of EMs. TEMs in operation can be divided into three groups: high-resolution EMs, simplified TEMs, and unique ultra-high-resolution EMs.
High resolution TEM(0.15 - 0.3 nm) - universal devices for multipurpose purposes. They are used to observe the image of objects in a light and dark field, to study their structure electro-nographic. method (see. Electronography), holding local quantities. using a spectrometer energetic. loss of electrons and x-ray crystalline. and semiconductor and receiving spectroscopic. images of objects using a filter that filters out electrons with energies outside a given energetic. window. The energy loss of electrons passed by the filter and forming an image is caused by the presence of one chemical in the object. element. Therefore, the contrast of areas in which this element is present increases. Moving the window along the energy spectrum receive distribution decomp. elements contained in the object. The filter is also used as a monochromator for increasing the resolving power of electrons in the study of objects of great thickness, which increase the spread of electrons in energy and (as a consequence) chromatic aberration.
With the help of add. devices and attachments studied in the TEM object can be tilted in different planes at large angles to the optical. axes, heat, cool, deform. The voltage accelerating electrons in high-resolution EM is 100-400 kV, it is regulated stepwise and is highly stable: for 1 - 3 minutes its value cannot be changed by more than (1-2) · 10 -6 from the initial value. The thickness of the object depends on the accelerating voltage, which can be "illuminated" by an electron beam. In 100-kilovolt emulsions, objects from 1 to several thicknesses are studied. tens of nm.
A schematic TEM of the described type is shown in Fig. 1. In his electronic optical. the system (column) with the help of a vacuum system creates a deep vacuum (pressure up to ~ 10 -5 Pa). Electron-optical circuit the FEM system is shown in Fig. 2. A beam of electrons, the source of which is a hot 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 electronic "spot" on the object (the spot diameter can vary from 1 to 20 µm upon adjustment). After passing through the object, some of the electrons are scattered and retained by the aperture diaphragm. Unscattered electrons pass through the aperture of the diaphragm and are focused by the objective in the object plane of the intermediate electron lens. The first enlarged image is formed here. Subsequent lenses create a second, third, etc. image. The latter, a projection lens, forms an image on a cathodoluminescent screen, which glows under the influence of electrons. The degree and nature of the scattering of electrons are not the same at different points of the object, since the thickness, structure and chemical. 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. An amplitude contrast arises, which is converted into light contrast on the screen. In the case of thin objects, the phase contrast caused by a change in the phases scattered in the object and interfering in the image plane. A store with photographic plates is located under the screen of the emulsion; when photographing, the screen is removed and the electrons act on the photoemulsion layer. The image is focused by an objective lens by means of a smooth current adjustment that changes its magn. field. The currents of other electronic lenses regulate the magnification of the EM, a cut 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, an analog-digital conversion of the information contained in it and processing on a computer are performed. The amplified and processed image according to a given program is displayed on the computer screen and, if necessary, entered into a memory device.
Rice. 1. Transmission electron microscope (TEM): 1
-electronic cannon with an accelerator; 2-condensateweed lenses; 3
-objective lens; 4
- projection lenses; 5
-light microscope, additionally zoomed outreading the image seen on the screen; b-thatbeads with observation 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 device; 12
- lens power supply.
Rice. 2. Electron-optical TEM scheme: 1
-cathode; 2 - focusing cylinder; 3
-accelerator; 4
-perhigh (short throw) condenser creating reduced image of the electron source; 5
- the second (long-focus) condenser, which transfers a thumbnail image of the source electrons per object; 6
-an object; 7
-aperture diafragment of the lens; 8
- lens; 9
, 10, 11
-system projection lenses; 12
-cathodoluminescent screen.
Simplified TEMs intended for scientific. studies in which high resolution is not required. They are also used for preliminaries. viewing objects, routine work and for educational purposes. These devices are simple in design (one condenser, 2-3 electronic lenses for increasing the image of an 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.
Ultrahigh-voltage E. m ... (SVEM) - devices with an accelerating voltage from 1 to 3.5 MB - are large-sized 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 SVEMs were intended for the study of objects of large (1 -10 µm) thickness, with a cut retaining the properties of a massive solid. Due to the strong influence of chromatic. aberrations, the resolving power of such emis- sions is reduced. However, in comparison with 100-kilovolt EMs, the resolution of images of thick objects in SHEM is 10-20 times higher. Since the energy of electrons in SHEM is higher, their wavelength is shorter than in high-resolution TEM. Therefore, after solving complex tech. problems (it took more than one decade) and the implementation of high vibration resistance, reliable vibration isolation and sufficient mechanical and electric. The highest (0.13-0.17 nm) resolution for translucent EMs was achieved on the SHEM, which made it possible to photograph images of atomic structures. However, spherical. lens aberration and defocusing distort images captured at ultimate resolution and prevent reliable information from being obtained. This information barrier is overcome with the help of focal series of images, to-rye are obtained when dec. defocusing the lens. In parallel, for the same defocusings, the atomic structure under study is simulated on a computer. Comparison of the focal series with the series of model images helps to decipher micrographs of atomic structures taken with the SHEM with the ultimate resolution. In fig. 3 shows a diagram of the SVEM located in the special. building. Main the units of the device are combined into a single complex using a platform, the edges are suspended from the ceiling on four chains and shock-absorbing springs. On top of the platform there are two tanks filled with insulating gas at a pressure of 3-5 atm. In one of them a high-voltage generator is placed, in the other an electrostatic one. electron accelerator with an 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 electronic-optical. a column located in the lower part of the building, protected by a ceiling from x-rays. radiation generated in the accelerator. All listed nodes form a rigid structure with physical properties. pendulum with a large (up to 7 s) period of proper. , to-rye are extinguished by liquid dampers. The pendulum suspension system provides effective isolation of the SVEM from the outside. vibrations. The device is controlled from the remote control located near the column. The arrangement of lenses, columns and other units of the device is similar to the corresponding FEM devices and differs from them in large dimensions and weight.
Rice. 3. Ultrahigh voltage electron microscope (SVEM): 1-vibration isolating platform; 2-chains, on which the platform hangs; 3 - shock-absorbing springs; 4-tanks containing the generator youhigh voltage and electron accelerator with electronnoah cannon; 5-electron-optical column; 6- the overlap dividing the SVEM building into the upper and lower halls and protective personnel working the lower hall, from x-rays; 7 - remote control microscope control.
Raster E. m... (SEM) with a thermal emission gun is the most common type of devices in electron microscopy... They use tungsten and hexaboride-lanthanum hot cathodes. The resolution of the SEM depends on the electronic brightness of the gun and in devices of this class 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 electronic lenses, a narrow electron probe is focused onto the sample surface. Magn. deflecting coils deploy the probe over a predetermined area on the object. When the probe electrons interact with the object, several types of radiation are generated (Fig. 5): secondary and reflected electrons; Auger electrons; x-ray bremsstrahlung and characteristic radiation (see. Characteristic spectrum); light radiation, etc. Any of the radiation, currents of electrons passing 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 appropriate detectors that convert these emissions, currents and voltages into electricity. signals, which, after amplification, are fed to a cathode-ray tube (CRT) and modulate its beam. The scanning of the CRT beam is performed 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. The image is photographed 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 from decomp. detectors. With the help of SEM, you can investigate the microrelief, the distribution of chemical. composition for the object, p-n-transitions, to produce x-rays. spectral analysis and other SEM are widely used in technol. processes (control in electronic lithographic technologies, verification and detection of defects in microcircuits, metrology of micro-products, etc.).
Rice. 4. Scheme of a scanning electron microscope (SEM): 1
- an insulator of an electron gun; 2
-V-imageny hot cathode; 3
- focusing electrode; 4
- anode; 5
- condenser lenses; 6
-diaphragm; 7
- two-tier deflecting system; 8
-lens; 9
-aperture lens diaphragm; 10
-an object; 11
-secondary electron detector; 12
-crystalface spectrometer; 13
-proportional counter; 14
- preamplifier; 15
- amplification unit; 16, 17
- equipment for registration X-ray radiation; 18
- amplification unit; 19
- magnification adjustment unit; 20, 21
- blocks burnzonal and vertical sweeps; 22, 23
-elekthrone-beam tubes.
Rice. 5. Scheme of registration of information about the object, received in the SEM; 1-primary electron beam; 2-secondary electron detector; 3-detector rentgene radiation; 4-detector of reflected electrons; 5-detector of Auger electrons; 6-detector lightproduct radiation; 7 - detector of past electronew; 8 - circuit for recording the current passed through object of electrons; 9-circuit for recording current electrons absorbed in the object; 10-circuit for reregistration of the electrical potential.
High resolution SEM is realized when forming 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 diameter of the probe, the properties of the object, the speed of the electrons of the primary beam, etc. With a large depth of penetration of the primary electrons, the secondary processes developing in all directions increase the diameter of the zone and the resolution decreases. The secondary electron detector consists of photomultiplier tube(Photomultiplier) and electron-photon converter, main. the element of which 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 photomultiplier 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 electrics. and magn. microfields, values of coeff. secondary electron emission, to-ry, in turn, depends on the chemical. composition of the sample at a given point.
The 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 numbers. 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, the information about the department. areas of the object, from which there is no direct path to the detector, is lost (shadows appear). To eliminate the loss of information, as well as to form an image of the relief of the sample, the cut is not affected by its elemental composition and, conversely, to form a distribution pattern of chemical. elements in an object, which is not influenced by its relief, in the SEM a detector system is used, consisting of several. detectors placed around the object, the signals of which are subtracted from one another or summed up, 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, which 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. The quanta excite signals in a semiconductor cooled (for noise reduction) 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 appears on its screen. element along the surface of the object.
On a SEM equipped with an X-ray. spectrometers produce local quantities. analysis: record the number of pulses excited by the X-ray. quanta from the site where the electronic probe is stopped. Crystallich. spectrometer using a set of crystal analyzers with dec. interplanar distances (see. Bragg-Wolfe condition) discriminates with a high spectrum. resolution characteristic spectrum in terms of wavelengths, covering the range of elements from Be to U. The semiconductor spectrometer discriminates against 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 information delivery, simple design, high performance characteristics.
Raster Auger-E. m... (ROEM) -devices, in which, when scanning an electronic probe, Auger electrons are detected from the depth of the object 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 resolution of the device depends only on the diameter of the probe. The device operates at ultra-high vacuum (10 -7 -10 -8 Pa). Its accelerating voltage is approx. 10 kV. In fig. 6 shows the ROEM device. The electron gun consists of a hexaboride-lanthanum or tungsten hot cathode operating in the Schottky mode, and a three-electrode electrostatic. lenses. The electron probe is focused by this lens and magn. lens, in the focal plane of which the object is located. The collection of Auger electrons is carried out using cylindrical. mirror energy analyzer, the inner electrode of which covers the lens body, and the outer one is adjacent to the object. With the help of an analyzer that discriminates against Auger electrons in energy, the distribution of chemical is investigated. elements in the surface layer of an object with submicron resolution. To study the deep layers, the device is equipped with an ion gun, with the help of a cut the upper layers of the object are removed by the method of ion-beam etching.
Rice. b. Schematic of a scanning Auger electron microscope(ROEM): 1 - ion pump; 2- cathode; 3 - three-electrode electrostatic lens; 4-channel detector; 5-aperture lens diaphragm; 6-bunk deflecting system for sweeping the electronic probe; 7-lens; 8- outer electrode of cylindrical mirror analyzer; 9-object.
SEM with a field emission gun have a high resolution (up to 2-3 nm). In a field emission gun, a cathode is used in the form of a point, at the top of which a strong electric shock occurs. the field that pulls out electrons from the cathode ( autoelectronic emission)... The electronic brightness of the gun with a field emission cathode is 10 3 -10 4 times higher than the brightness of the gun with a hot cathode. The current of the electron probe increases accordingly. Therefore, in an SEM with a field emission gun, along with a slow fast sweep, 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 in ultra-high vacuum (up to 10 -8 Pa), providing sufficient current in a small-diameter probe (0.2-0.3 nm). The diameter of the probe is reduced by two magn. lenses (fig. 7). Below the object there are detectors - central and circular. The first one gets unscattered electrons, and after conversion and amplification of the corresponding signals, a bright-field image appears on the CRT screen. A ring detector collects scattered electrons to create a dark-field image. In STEM, it is possible to study thicker objects than in TEM, since an increase in the number of inelastically scattered electrons with thickness does not affect the resolution (after the object, there is no electronic optics for image formation). With the help of an energy analyzer, electrons passing through the object are separated into elastically and inelastically scattered beams. Each beam hits its own detector, and the corresponding images, containing additional ones, are observed on the CRT. information about the elemental composition of the object. A high resolution in STEM is achieved at slow sweeps, since the current in a probe with a diameter of only 0.2-0.3 nm is low. PREM are equipped with all devices used in electron microscopy for analytical. research objects, and in particular spectrometers energetic. loss of electrons, roentgen. spectrometers, sophisticated systems for detecting transmitted, backscattered and secondary electrons, emitting a group of electrons scattered on the decomp. corners with diff. energy, etc. Devices are completed with computers for integrated processing of incoming information.
Rice. 7. Schematic diagram of the translucent rasterelectron microscope (PREM): 1-autoemissionic 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 scattered electron detector; 12 - detector of unscattered electrons (removed at operation of the magnetic spectrometer); 13 - magnetic spectrometer; 14-deflection sampling system electrons with different energy losses; 15 - slit spectrometer; 16-detector spectrometer; VE-secondaryelectrons; hv-X-ray radiation.
Emission E. m... create an image of the object with electrons, to-rye emits the object itself when heated, bombarded with a primary beam of electrons, under the influence of an electromagnet. radiation and the imposition of a strong electric. field that rips electrons out of the object. These devices usually have a narrow purpose (see. Electronic projector).
Mirrored E. m... serve Ch. arr. for visualization of electrostatic. "potential reliefs" and magn. microfields on the surface of the object. Main electronic 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 directed into an electron mirror and reflected by the field in the immediate vicinity of the object's surface. 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, visualizing these microfields.
Development prospects of E. m... The improvement of electronic measurements with the aim of increasing the volume of information received, which has been carried out for many years, will continue in the future, and the improvement of the parameters of instruments, and, above all, an increase in the resolving power, will remain the main task. Work on the creation of electronic optical. systems with small aberrations have not yet led to a real increase in the resolution of EM. This applies to non-axisymmetric systems for correcting aberrations, cryogenic optics, and lenses with correcting spaces. in the axial area, etc. Searches and research in the indicated directions are underway. Prospecting work continues on the creation of electronic holography. systems, including those with correction of frequency-contrast characteristics of lenses. Miniaturization electrostatic lenses and systems using the achievements of micro- and nanotechnology will also contribute to solving the problem of creating electronic optics with low aberrations.
Lit .: Practical scanning electron microscopy, ed. D. Gouldstein, H. Jacobits, trans. from English, M., 1978; Spence, D., High Resolution Experimental Electron Microscopy, trans. from English, M., 1986; Stoyanov PA, Electronic microscope SVEM-1, "Izvestiya AN SSSR, ser. Fiz.", 1988, vol. 52, no. 7, p. 1429; Hawks P., Kasper E., Fundamentals of Electronic Optics, trans. from English, t. 1-2, M., 1993; Oechsner H., Scanning auger microscopy, Le Vide, les Couches Minces, 1994, t. 50, no. 271, p. 141; McMul-lan D., Scanning electron microscopy 1928-1965, "Scanning", 1995, t. 17, no. 3, p. 175. P. A. Stoyanov.
We are starting to publish a blog of an entrepreneur, a specialist in the field information technologies and part-time amateur designer Alexei Bragin, which tells about an unusual experience - for a year now, the author of the blog has been busy restoring sophisticated scientific equipment - a scanning electron microscope - practically at home. Read about the engineering, technical and scientific challenges Alexey had to face and how he coped with them.
A friend called me once and said: found interesting thing, must be brought to you, however, weighs half a ton. This is how I got a column from a JEOL JSM-50A scanning electron microscope in my garage. She was written off from some research institute long ago and taken out for scrap metal. They lost the electronics, but managed to save the electron-optical column together with the vacuum part.
Since the main part of the equipment has been preserved, the question arose: is it possible to save the entire microscope, that is, restore and bring it into working condition? And right in the garage, with your own hands, with the help of only basic engineering and technical knowledge and improvised means? True, before I had never dealt with such scientific equipment, let alone how to use it, and had no idea how it works. But it's interesting, after all, it's not just to start an old piece of hardware into a working state - it's interesting to figure everything out on your own and check if it is possible using scientific method, to master completely new areas. So I began to restore the electron microscope in the garage.
In this blog, I will tell you what I have already done and what remains to be done. Along the way, I will introduce you to the principles of operation of electron microscopes and their main components, and also talk about the many technical obstacles that I had to overcome in the course of work. So let's get started.
To restore the microscope that turned out to be in my possession at least to the state of "drawing with an electron beam on a luminescent screen", the following was necessary:
Let's start in order. Today I will talk about how electron microscopes work. They are of two types:
Transmission electron microscope
TEM is very similar to a conventional optical microscope, except that the sample under study is irradiated not with light (photons), but with electrons. The wavelength of the electron beam is much shorter than that of the photon beam, so much higher resolution can be obtained.
The electron beam is focused and controlled using electromagnetic or electrostatic lenses. They even have the same distortions (chromatic aberrations) as optical lenses, although the nature of the physical interaction here is completely different. Incidentally, it also adds new distortions (caused by the twisting of electrons in the lens along the axis of the electron beam, which does not happen with photons in an optical microscope).
TEM has drawbacks: the samples under study must be very thin, thinner than 1 micron, which is not always convenient, especially when working at home. For example, to see your hair in the light, it must be cut lengthwise for at least 50 layers. This is due to the fact that the penetrating ability of an electron beam is much worse than a photon one. In addition, TEMs, with rare exceptions, are rather cumbersome. This device, pictured below, does not seem to be that big (although it is taller than a person and has a solid cast-iron bed), but it also comes with a power supply the size of a large cabinet - in total, almost an entire room is needed.
But the TEM has the highest resolution. With its help (if you try hard), you can see individual atoms of a substance.
University of Calgary
This resolution is especially useful for identifying the causative agent of a viral disease. All viral analytics of the twentieth century was built on the basis of TEM, and only with the advent of cheaper methods for diagnosing popular viruses (for example, polymerase chain reaction, or PCR), the routine use of TEMs for this purpose has ceased.
For example, here's what the H1N1 flu looks like "in the light":
University of Calgary
Scanning electron microscope
SEM is mainly used to study the surface of samples with a very high resolution (magnification in a million times, versus 2 thousand for optical microscopes). And this is already much more useful in the household :)
For example, this is what the individual bristle of a new toothbrush looks like:
The same should happen in the electron-optical column of the microscope, only here the sample is irradiated, and not the phosphor of the screen, and the image is formed on the basis of information from sensors that fix secondary electrons, elastically reflected electrons, and so on. This is the type of electron microscope that will be discussed in this blog.
Both the TV picture tube and the electron-optical column of the microscope work only under vacuum. But I will talk about this in detail in the next issue.
(To be continued)
To study nano-objects of resolution of optical microscopes ( even using ultra-violet) is clearly not enough. In this regard, 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 shorter 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. In this case, the course of light beams is skillfully controlled by the lenses that make up the objective and 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 influenced by external electromagnetic fields, with the help of which it is possible to effectively control the motion of electrons.
The science of the movement of electrons in electromagnetic fields and the calculation of devices that form the required 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 turns of the coil wires through which the current flows focus the electron beam in the same way that a glass lens focuses the light beam.
The coil's magnetic field acts as a converging or diffusing lens. To concentrate the magnetic field, the coil is closed with a magnetic " armor»Made of a special nickel-cobalt alloy, leaving only a narrow gap in the interior. The magnetic field created in this way can be 10-100 thousand times stronger than the magnetic field of the Earth!
Unfortunately, our eyes cannot directly perceive electron beams. Therefore, they are used for “ drawing”Images on fluorescent screens (which glow when electrons strike). By the way, the same principle underlies the operation of monitors and oscillographs.
Exists a large number of various types of electron microscopes, among which the most popular is the scanning electron microscope (SEM). We get a simplified diagram of it if we place the object under study inside the cathode-ray tube of an ordinary TV set 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 along horizontal lines, point by point, and synchronously transmits the signal to the kinescope. The whole process is similar to the operation of a TV during the sweep process. The source of electrons is a metal (usually tungsten), from which, when heated, electrons are emitted as a result of thermionic emission.
Scheme of operation of a scanning electron microscope
Thermionic emission- the exit of electrons from the surface of the conductors. The number of emitted electrons is small at T = 300 K and grows exponentially with increasing temperature.
When electrons pass through the sample, some of them are scattered due to collisions with the nuclei of the atoms of the sample, others due to collisions with the electrons of the atoms, and still others pass through it. In some cases, secondary electrons are emitted, X-rays are induced, etc. All these processes are registered by special detectors and in a transformed form are displayed on the screen, creating an enlarged picture of the object under study.
Magnification in this case is understood as the ratio of the size of the image on the screen to the size of the area covered by the beam on the sample. Due to the fact that the wavelength of an electron is orders of magnitude shorter than that of a photon, in modern SEM this increase can reach 10 million15, corresponding to a resolution of a few nanometers, which makes it possible to visualize individual atoms.
The main disadvantage electron microscopy- the need to work in full 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- a wonderful example of achievement based on an interdisciplinary approach, when independently developing fields of science and technology, united, created a powerful new tool scientific research.
The pinnacle of classical physics was theory electromagnetic field, which explained the propagation of light, electricity and magnetism as the propagation of electromagnetic waves. Wave optics explained the phenomenon of diffraction, the mechanism of imaging and the play of factors that determine the resolution in a light microscope. Success quantum physics we owe the discovery of the electron with its specific corpuscular-wave properties. These separate and seemingly independent paths of development led to the creation of electronic optics, one of the most important inventions of which in the 1930s was the electron microscope.
But the scientists did not rest on this either. The wavelength of an electron accelerated by an electric field is several nanometers. This is good 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 the process of a single chemical reaction look like? For this today in different countries scientists are developing neutron microscopes.
Neutrons are usually included in atomic nuclei along with protons and have almost 2000 times the mass of an electron. Those who have not forgotten the de Broglie formula from the quantum chapter will immediately realize that the wavelength of the neutron is as many times less, that is, it is picometers in thousandths of a nanometer! Then the atom will appear to researchers not as a vague speck, but in all its glory.
Neutron microscope has many advantages - in particular, neutrons reflect hydrogen atoms well and easily penetrate thick layers of samples. However, it is very difficult to build it: neutrons do not have an electric charge, therefore they calmly ignore magnetic and electric fields and strive to elude the sensors. Plus, it's not easy to expel large, hulking neutrons from atoms. Therefore, today the first prototypes of a neutron microscope are still very far from being perfect.
ELECTRON MICROSCOPE
a device that allows you to obtain a highly magnified 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 on the structure of matter, especially in such fields of science as biology and solid state physics. There are three main types of EVs. In the 1930s, the conventional transmission electron microscope (OPEM) was invented, the scanning (scanning) electron microscope (SEM) in the 1950s, and the scanning tunneling microscope (RTM) in the 1980s. These three types of microscopes complement each other in the study of structures and materials of different types.
CONVENTIONAL TRANSMISSION ELECTRONIC MICROSCOPE
OPEM is in many ways similar to a light microscope, see MICROSCOPE, but only to illuminate the samples it does not use light, but a beam of electrons. It contains an electron spotlight (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 tungsten or lanthanum hexaboride cathode. 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 about -100,000 V relative to the other electrodes focusing the electrons into a narrow beam. This part of the device is called an electronic spotlight (see ELECTRONIC GUN). Since electrons are highly scattered by matter, there must be a vacuum in the microscope column where the electrons move. It maintains a pressure not exceeding one billionth 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 the diagram (Fig. 1). The magnetic field created by the turns of the coil, through which the current flows, acts as a collecting lens, the focal length of which 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 magnetic field strength 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 diagram is shown in Fig. 2. A row of condenser lenses (only the last one is shown) focuses the electron beam on the sample. Usually the former creates an unmagnified 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 plane of the object. The sample is placed in the magnetic field of an objective lens with high optical power - the most important OPEM lens, which determines the maximum possible resolution of the device. The aberrations of an objective lens are limited by its aperture in the same way as in a camera or light microscope. The objective lens gives an enlarged image of the object (usually with a magnification of about 100); the additional magnification introduced by intermediate and projection lenses ranges from slightly less than 10 to slightly more than 1000. Thus, the magnification that can be obtained in modern OPEMs is from less than 1000 to ELECTRONIC MICROSCOPE1,000,000. (At a magnification of a million times the grapefruit grows to the size of the Earth.) The object under study is usually placed on a very fine mesh, inserted into a special holder. The holder can be mechanical or electrically move smoothly up and down and left and right.
Image. The contrast in the OPEM is due to the scattering of electrons as the electron beam passes through the sample. If the sample is thin enough, then the fraction of scattered electrons is small. When electrons pass through the sample, some of them are scattered due to collisions with the nuclei of the atoms of the sample, others due to collisions with the electrons of the 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 this region, its density, and the average atomic mass (number of protons) at a given point. Electrons leaving the diaphragm with an angular deviation exceeding a certain limit can no longer return to the beam carrying the image, and therefore strongly scattering areas of increased density, increased thickness, the locations of heavy atoms appear in the image as dark zones on light background... Such an image is called brightfield because the surrounding field is lighter than the object in it. But it is possible to make the electric deflecting system pass only one or another of the scattered electrons into the lens diaphragm. Then the sample looks light on dark field... A weakly scattering object is often more convenient to view in darkfield mode. The final magnified electronic image is converted into a visible one by means of a luminescent screen that glows under the influence of electron bombardment. This image, usually low-contrast, is usually viewed through a binocular light microscope. At 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 electro-optical converter is used to increase the brightness of a weak image. In this case, the final image can be displayed on a conventional television screen, which allows 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 allows a sharper image to be obtained 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 video tape. Thanks to this, the image recorded on photographic 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 has a specific wavelength. The resolution of an EM is determined by the effective wavelength of the electrons. The wavelength depends on the speed of the electrons, and therefore on the accelerating voltage; the higher the accelerating voltage, the higher the speed of the electrons and the shorter the wavelength, which means the higher the resolution. Such a significant advantage of EM in resolution is due to the fact that the wavelength of electrons is much shorter than the wavelength of light. But since electronic lenses do not focus as well as optical lenses (the numerical aperture of a good electronic lens is only 0.09, while for a good optical lens it reaches 0.95), the EM resolution 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 between individual atoms in crystals. To achieve a resolution of this order, very careful instrument tuning is required; in particular, highly stable power supplies are required, and the device itself (which can be approx. 2.5 m high and weigh several tons) and its additional equipment require vibration-free installation.
RASTER ELECTRONIC MICROSCOPE
SEM, which has become essential instrument for scientific research, serves as a good complement to the OPEM. SEM uses electronic lenses to focus the electron beam into a very small spot. You can adjust the SEM so that the spot diameter in it does not exceed 0.2 nm, but, as a rule, it is units or tens of nanometers. This spot continuously traverses a certain area of the sample, similar to a ray traversing the screen of a television tube. Electrical signal that arises when the object is bombarded with the beam electrons, is used to form an image on the screen of a television picture tube or cathode ray tube (CRT), the sweep of which is synchronized with the electron beam deflection system (Fig. 3). Magnification in this case is understood as the ratio of the size of the image on the screen to the size of the area covered by the beam on the sample. This increase is from 10 to 10 million.
The interaction of the electrons of the focused beam with the atoms of the sample can lead not only to their scattering, which is used to obtain an image in OPEM, but also to the excitation of X-ray radiation, emission of visible light, and emission of secondary electrons. In addition, since the SEM has only focusing lenses in front of the sample, it allows one to study "thick" samples.
Reflective SEM. Reflective SEM is designed for studying bulk samples. Since the contrast arising from the registration of reflected, i.e. backscattered, and secondary electrons, is associated mainly with 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 electron energy of the incident beam. The emission of secondary electrons is mainly determined by the surface composition and conductivity of the sample.) Both of these signals provide information about the general characteristics of the sample. Due to the low convergence of the electron beam, observations can be carried out with much greater depth sharpening than when working with a light microscope, and obtain excellent volumetric micrographs of surfaces with a highly developed relief. By registering the X-ray radiation emitted by the sample, it is possible, in addition to the data on the relief, to obtain information about chemical composition sample in the surface layer with a depth of ELECTRONIC MICROSCOPE 0.001 mm. The composition of the material on the surface can also be judged by the measured energy with which certain electrons are emitted. All the difficulties of working with SEM are mainly due to its registration and electronic visualization systems. In a device with a full set of detectors, along with all SEM functions, an operating mode of an electron probe microanalyzer is provided.
Scanning transmission electron microscope. A scanning transmission electron microscope (RPEM) is a special type of SEM. It is designed for thin samples, the same as those studied in the OPEM. The RPEM circuit differs from the circuit in Fig. 3 only in that there are no detectors located above the sample. Since the image is formed by a traveling beam (and not by a beam that illuminates the entire area of the sample), a high-intensity electron source is required so that the image can be recorded in a reasonable time. High-resolution RPEM uses high-brightness field emitters. In such a source of electrons, a very strong electric field (approx. V / cm) is generated near the surface of a very small diameter etched tungsten wire. 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 that of a heated tungsten wire source (see above), and the electrons emitted by it can be focused into a beam with a diameter of less than 1 nm. Even beams with a diameter close to 0.2 nm were obtained. Autoelectronic sources can only operate in ultrahigh vacuum conditions (at pressures below Pa), in which there are completely 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 with little or no 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 strongly depends on the atomic number of atoms in the region through which the electrons pass - heavier atoms scatter more electrons towards the detector than light ones. If the electron beam is focused to a point less than 0.5 nm in diameter, an image of individual atoms can be obtained. In reality, it is possible to distinguish in the image obtained in the RPEM, individual atoms with an atomic mass of iron (i.e., 26 or more). Electrons that have not undergone scattering in the sample, as well as electrons that have 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 the former to be separated from the latter. By measuring the energy lost by electrons in scattering, important information about the sample can be obtained. 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 about chemical properties matter in the region through which the electron beam passes.
RASTER TUNNEL MICROSCOPE
The EMs discussed above use magnetic lenses to focus electrons. This section is devoted to EM without lenses. But, before moving on to a scanning tunneling microscope (RTM), it will be useful to briefly dwell on two old types of lensless microscope in which a projected shadow image is formed.
Auto-electronic and auto-ion projectors. The auto-electronic source used in RPEM has been used in shadow projectors since the early 1950s. In a field projector, electrons emitted by field emission from a tip of a very small diameter are accelerated towards a luminescent screen located a few centimeters from the tip. As a result, a projected image of the surface of the tip and the particles on this surface appears on the screen with an increase equal to the ratio of the radius of the screen to the radius of the tip (about). Higher resolution is achieved in a field-ion projector, in which the projection of the image is carried out by ions of helium (or some other elements), the effective wavelength of which is shorter than that of electrons. This allows images to be obtained showing the true arrangement of atoms in the crystal lattice of the tip material. 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 small diameter metal tip that is the source of electrons. An electric field is generated in the gap between the tip and the sample surface. The number of electrons drawn 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). When the tip moves along the surface, the current is modulated. This allows you to obtain an image associated with the surface relief of the sample. If the tip ends with a single atom, then you can form an image of the surface, passing atom by atom. The RTM can work only under the condition that the distance from the tip to the surface is constant, and the tip can be moved with an accuracy of atomic dimensions. Vibration is suppressed due to the rigid construction and small size of the microscope (no more than a fist), as well as the use of multilayer rubber shock absorbers. High accuracy is ensured by piezoelectric materials that elongate and contract under the influence of an external electric field... Applying a voltage of the order of 10-5 V, it is possible to change the size of such materials by 0.1 nm or less. This makes it possible, by fixing the tip on an element made 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) is not applied; this is due to the success of the sample preparation technique. All techniques used in electron microscopy are aimed at obtaining an extremely thin sample and ensuring maximum contrast between it and the substrate, which it needs as a support. The basic technique is designed for samples 2-200 nm thick, supported by thin plastic or carbon films, which are placed on a grid with a mesh size of approx. 0.05 mm. (A suitable sample, no matter how it was obtained, is processed in such a way as to increase the intensity of electron scattering on the test object.) If the contrast is high enough, then the observer's eye can distinguish details that are at a distance of 0.1-0.2 mm without strain. apart. Consequently, in order for the details, separated on the sample by a distance of 1 nm, to be distinguishable in the image created by the electron microscope, a total magnification of about 100-200 thousand is necessary. The best microscopes can create an image of the sample on a photographic plate with such an increase, but at the same time too small area is displayed. 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 corresponds on the sample 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 with the help of SEM and RPEM, in which the image is recorded by an electronic system and is 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. Methods for fixation, embedding and obtaining of thin tissue sections for research 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, endoplasmic reticulum, ribosomes and many other organelles that make up the cell. The sample is first fixed with glutaraldehyde or other fixing agents, and then dehydrated and covered with plastic. Cryofixation methods (fixation at very low - cryogenic - temperatures) allow the structure and composition to be preserved without the use of chemical fixing agents. In addition, cryogenic methods allow images of frozen biological samples to be obtained without dehydration. Using ultramicrotomes with blades of polished diamond or chipped glass, tissue sections with a thickness of 30-40 nm can be cut. The mounted histological preparations can be stained with compounds of heavy metals (lead, osmium, gold, tungsten, uranium) to enhance the contrast of individual components or structures.
Biological research has 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 envelopes of viruses. In addition, the methods of positive and negative staining were able to reveal the structure with subunits in a number of other important biological microstructures. Methods for enhancing the contrast of nucleic acids 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. Then the sample is vacuum sprayed with very thin layer heavy metal. This layer of heavy metal "sets off" the sample, due to which the latter, when observed in OPEM or RPEM, looks as if illuminated from the side from which the metal was deposited. If you rotate the sample during spraying, then the metal accumulates around the particles from all sides evenly (like a snowball).
Non-biological materials. TEM is used 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 border, and then thinned so that the border is visible on the sharpened 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 picture; contrast strongly depends on the orientation, thickness and perfection of the crystal lattice. Contrast changes in the image allow you to study the crystal lattice and its imperfections on a scale of atomic dimensions. The information obtained in this case complements that which is 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 recorded 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 beams pass through it, then it is possible to obtain an image of a certain system of crystal planes, which gives this diffracted beam. Modern devices allow resolution of grating periods of 0.1 nm. Crystals can also be studied by the dark-field imaging method, in which the central beam is overlapped, so that the image is formed by one or more diffracted beams. All these methods provided important information about the structure of many materials and 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. At present, the industry produces high-voltage versions of OPEM and RPEM with accelerating voltages from 300 to 400 kV. Such microscopes have a higher penetrating power than low-voltage devices, and are almost on a par with 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 turns out to be a very valuable property when studying defects in thicker crystals, especially those from which it is impossible to make thin samples. In biology, their high penetrating ability makes it possible to examine whole cells without cutting them. In addition, these microscopes can be used to obtain volumetric images of thick objects.
Low voltage microscopy. SEMs are also produced 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 here is also limited by the aberrations of the magnetic lenses. However, since electrons of such low energy penetrate shallowly under the surface of the sample, almost all of the electrons involved in imaging come from an area very close to the surface, which improves the resolution of the surface relief. Using low-voltage SEMs, images were obtained on solid surfaces of objects less than 1 nm in size.
Radiation damage. Since electrons are ionizing radiation, the sample in the EM is constantly exposed to it. (As a result of this exposure, secondary electrons are generated, which are used in SEM.) Therefore, samples are always subject to radiation damage. A typical dose of radiation absorbed by a thin sample during the recording of a micrograph in an OPEM approximately corresponds to the energy that would be sufficient for the complete evaporation of 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 different methods its preparation: staining, pouring, freezing. In addition, it is possible to register an image at an electron dose that is 100-1000 times lower than using a standard technique, and then improve it using computer image processing methods.
HISTORICAL REFERENCE
The history of the creation of the electron microscope is a wonderful example of how independently developing fields of science and technology can, by exchanging information received and combining efforts, create a powerful new tool for scientific research. The pinnacle of classical physics was the theory of the electromagnetic field, which explained the propagation of light, the appearance 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 imaging, and the play of factors that determine resolution in a light microscope. We owe our successes in the field of theoretical and experimental physics to the discovery of the electron with its specific properties. These separate and seemingly independent paths of development led to the creation of the foundations of electronic optics, one of the most important applications of which was the invention of EM in the 1930s. A direct allusion to such a 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. Jermer in the USA and J. Thomson in England. Thus, an analogy was suggested that made it possible to construct an EM according to the laws of wave optics. H. Bush discovered that electric and magnetic fields can be used to form electronic images. In the first two decades of the 20th century. the necessary technical prerequisites were also created. Industrial laboratories working on a cathode-ray oscilloscope gave vacuum technology, stable sources of high voltage and current, 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 device was the forerunner of the modern OPEM. (Ruska was rewarded for his labors by becoming a Nobel Prize laureate in physics for 1986.) In 1938 Ruska and B. von Borris built a prototype of an industrial OPEM for Siemens-Halske in Germany; this device eventually allowed a resolution of 100 nm to be achieved. A few years later, A. Prebus and J. Hiller built the first high-resolution OPEM at the University of Toronto (Canada). The broad possibilities of OPEM became apparent almost immediately. Its industrial production was started simultaneously by Siemens-Halske in Germany and RCA in the USA. In the late 1940s, other companies began to produce such devices. 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 Zworykin and employees at the RCA corporation in the 1940s, but only Otley's device was able to serve as the basis for a number of technical improvements, culminating 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 rapidity of an explosion. Currently, there are a dozen industrial manufacturers of SEM "s on three continents and tens of thousands of such devices used in laboratories around the world. In the 1960s, ultra-high-voltage microscopes were developed for the study of thicker samples. The leader in this direction was G. Dupuy in France , 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 1979 in Zurich.This instrument, very simple in design, 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
Technological archeology)
Some electron microscopes restore, others are firmware of spacecraft, and others are engaged in reverse engineering of circuitry of microcircuits under a microscope. I suspect the activity is terribly exciting.
And, by the way, I remembered a wonderful post about industrial archeology.
Spoiler
There are two kinds of corporate memory: people and documentation. People remember how things work and they know why. Sometimes they write this information somewhere and keep their records somewhere. This is called "documentation". Corporate amnesia works the same way: people leave, and records disappear, rot, or are simply forgotten.
I spent several decades working for a large petrochemical company. In the early 1980s, we designed and built a plant that converts some hydrocarbons into other hydrocarbons. Over the next 30 years, the corporate memory of this plant waned. Yes, the plant is still running and making money for the firm; maintenance is done, and highly intelligent specialists know what to pull and where to kick to keep the plant running.
But the company has completely forgotten how this plant works.
This was due to several factors:
Recession in petrochemical industry in the 1980s and 1990s made us stop hiring new people. In the late 1990s, there were guys under 35 or over 55 working in our group - with very few exceptions.
We slowly switched to computer-assisted design.
Due to corporate reorganizations, we had to physically move the entire office from place to place.
A corporate merger a few years later completely dissolved our firm into a larger one, causing a global restructuring of departments and a reshuffle of personnel.
Industrial archeology
In the early 2000s, several of my colleagues and I retired.
In the late 2000s, the company remembered the factory and thought it would be nice to do something with it. Let's say increase production. For example, you can find a bottleneck in the production process and improve it - the technology has not stood still for these 30 years - and, perhaps, add another workshop.
And then the company from all over the place is imprinted on the brick wall. How was this plant built? Why was it built this way and not otherwise? How exactly does it work? What is vat A needed for, why are workshops B and C connected by a pipeline, why does the pipeline have a diameter of exactly D and not D?
Corporate amnesia in action. Giant machines, built by aliens with the help of their alien technology, chomp as if they were running, giving out piles of polymers to the mountain. The company has a rough idea of how to maintain these machines, but has no idea what amazing magic is going on inside, and no one has the slightest idea of how they were created. In general, the people are not even sure what exactly to look for, and do not know from which side this tangle should be unraveled.
We are looking for guys who, during the construction of this plant, already worked in the company. They now occupy high positions and sit in separate, air-conditioned offices. They are given the task of finding documentation for the aforementioned plant. This is no longer corporate memory, it is more like industrial archeology. Nobody knows what kind of documentation for this plant exists, whether it exists at all, and if so, in what form it is stored, in what formats, what it includes and where it physically lies. The plant was designed project team that no longer exists, in a company that has since been taken over, in an office that has been closed, using methods from the pre-computer age that no longer apply.
The guys remember their childhood with the obligatory swarming in the mud, roll up the sleeves of expensive jackets and get to work.