Technological archeology)
Some electron microscopes are restoring, others are restoring firmware of spacecraft, and others are engaged in reverse engineering of circuitry of microcircuits under a microscope. I suspect that the occupation is terribly exciting.
And, by the way, I remembered a wonderful post about industrial archeology.
Spoiler
There are two types of corporate memory: people and documentation. People remember how things work and know why. Sometimes they record this information somewhere and keep their records somewhere. It's called "documentation". Corporate amnesia works the same way: people leave, and documentation disappears, rots, or is simply forgotten.
I spent several decades working for a large petrochemical company. In the early 1980s, we designed and built a plant that converts hydrocarbons into other hydrocarbons. Over the next 30 years, the corporate memory of this plant has waned. Yes, the plant is still running and making money for the firm; maintenance is being done, and wise people know what they need to twitch and kick to keep the plant running.
But the company has completely forgotten how this plant works.
This happened due to several factors:
The downturn in the petrochemical industry in the 1980s and 1990s caused us to stop hiring new people. In the late 1990s, our group consisted of guys under the age of 35 or over 55 - with very rare exceptions.
We slowly switched to designing with the help of computer systems.
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 massive reshuffling of departments and personnel.
Industrial archeology
In the early 2000s, I and several of my colleagues retired.
In the late 2000s, the company remembered the plant and thought it would be nice to do something with it. 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 here the company is imprinted in a brick wall from all over. How was this plant built? Why was it built this way and not otherwise? How exactly does it work? Why is vat A needed, why are workshops B and C connected by a pipeline, why does the pipeline have a diameter of G, and not D?
Corporate amnesia in action. Giant machines built by aliens with their alien technology champ like clockwork, spitting out heaps of polymers. The company has a vague 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 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 were already working in the company during the construction of this plant. Now they occupy high positions and sit in separate, air-conditioned offices. They are given the task of finding documentation on the said plant. It's no longer corporate memory, it's more like industrial archaeology. No one knows what kind of documentation on 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 is located physically. The plant was designed by a design team that no longer exists, in a company that has since been taken over, in an office that has been closed, using pre-computer age methods that are no longer in use.
The guys remember their childhood with obligatory swarming in the mud, roll up the sleeves of expensive jackets and get to work.
How does an electron microscope work? What is its difference from an optical microscope, is there any analogy between them?
The operation of an electron microscope is based on the property of inhomogeneous electric and magnetic fields, which have rotational symmetry, to exert a focusing effect on electron beams. Thus, the role of lenses in an electron microscope is played by a set of suitably calculated electric and magnetic fields; the corresponding devices that create these fields are called "electronic lenses".
Depending on the type of electronic lenses electron microscopes are divided into magnetic, electrostatic and combined.
What type of objects can be examined with an electron microscope?
Just as in the case of an optical microscope, objects, firstly, can be "self-luminous", i.e., serve as a source of electrons. This is, for example, an incandescent cathode or an illuminated photoelectron cathode. Secondly, objects that are "transparent" for electrons with a certain speed can be used. In other words, when operating in transmission, the objects must be thin enough and the electrons fast enough to pass through the objects and enter the electronic lens system. In addition, by using reflected electron beams, the surfaces of massive objects (mainly metals and metallized samples) can be studied. This method of observation is similar to the methods of reflective optical microscopy.
By the nature of the study of objects, electron microscopes are divided into transmission, reflection, emission, raster, shadow and mirror.
The most common at present are electromagnetic microscopes of the transmission type, in which the image is created by electrons passing through the object of observation. It consists of the following main components: an illumination system, an object camera, a focusing system, and a final image registration unit consisting of a camera and a fluorescent screen. All these nodes are connected to each other, forming the so-called microscope column, inside which pressure is maintained. The lighting system usually consists of a three-electrode electron gun (cathode, focusing electrode, anode) and a condenser lens (we are talking about electronic lenses). It forms a beam of fast electrons of the desired cross section and intensity and directs it to the object under study located in the object chamber. The electron beam passing through the object enters the focusing (projection) system, which consists of an objective lens and one or more projection lenses.
Electron microscopy is a method for studying structures that are beyond the visibility of a light microscope and have dimensions of less than one micron (from 1 micron to 1-5 Å).
The action of an electron microscope (Fig.) is based on the use of a directed flow, which acts as a light beam in a light microscope, and magnets (magnetic lenses) play the role of lenses.
Due to the fact that different parts of the object under study retain electrons in different ways, a black-and-white image of the object under study is obtained on the screen of the electron microscope, magnified by tens and hundreds of thousands of times. In biology and medicine, transmission-type electron microscopes are mainly used.
Electron microscopy originated in the 1930s when the first images of some viruses (tobacco mosaic virus and bacteriophages) were obtained. Currently, electron microscopy has found the widest application in, and virology, causing the creation of new branches of science. In electron microscopy of biological objects, special preparation methods are used. This is necessary to identify individual components of the objects under study (cells, bacteria, viruses, etc.), as well as to preserve their structure under high vacuum conditions under an electron beam. With the help of electron microscopy, the external shape of the object, the molecular organization of its surface are studied, with the help of the method of ultrathin sections, the internal structure of the object is studied.
Electron microscopy in combination with biochemical, cytochemical research methods, immunofluorescence, as well as X-ray diffraction analysis make it possible to judge the composition and function of the structural elements of cells and viruses.
Electron microscope of the 70s of the last century
Electron microscopy - the study of microscopic objects using an electron microscope.
The electron microscope is an electron-optical instrument with a resolution of several angstroms and allows you to visually study the fine structure of microscopic structures and even some molecules.
A three-electrode gun consisting of a cathode, a control electrode, and an anode serves as an electron source for creating an electron beam that replaces the light beam (Fig. 1).
Rice. 1. Three-electrode gun: 1 - cathode; 2 - control electrode; 3 - electron beam; 4 - anode.
Electromagnetic lenses used in an electron microscope instead of optical lenses are multilayer solenoids enclosed in shells of soft magnetic material with a non-magnetic gap on the inside (Fig. 2).
Rice. 2. Electromagnetic lens: 1 - pole tip; 2 - brass ring; 3 - winding; 4 - shell.
The electric and magnetic fields generated in the electron microscope are axially symmetrical. Due to the action of these fields, charged particles (electrons) emerging from one point of the object within a small angle are again collected in the image plane. The entire electron-optical system is enclosed in the column of the electron microscope (Fig. 3).
Rice. 3. Electron-optical system: 1 - control electrode; 2 - diaphragm of the first capacitor; 3 - diaphragm of the second capacitor; 4 - stigmatator of the second capacitor; 5 - object; 6 - objective lens; 7 - stigmatator of the objective lens; 8 - stigmatator of the intermediate lens; 9 - aperture of the projection lens; 10 - cathode; 11 - anode; 12 - the first capacitor; 13 - second capacitor; 14 - focus corrector; 15 - object holder table; 16 - lens aperture; 17 - selector diaphragm; 18 - intermediate lens; 19 - projection lens; 20 - screen.
The electron beam created by the electron gun is directed into the field of action of condenser lenses, which allow changing the density, diameter and aperture of the beam incident on the object under study in a wide range. A table is installed in the chamber of the object, the design of which ensures the movement of the object in mutually perpendicular directions. In this case, you can consistently examine an area equal to 4 mm 2 and select the most interesting areas.
Behind the camera of the object is an objective lens, which allows you to achieve a sharp image of the object. It also gives the first enlarged image of the object, and with the help of subsequent, intermediate and projection lenses, the total increase can be increased to the maximum. An image of an object appears on a screen that luminesces under the action of electrons. Behind the screen are photographic plates. The stability of the operation of the electron gun, as well as the clarity of the image, along with other factors (the constancy of high voltage, etc.), largely depend on the depth of rarefaction in the column of the electron microscope, so the quality of the device is largely determined by the vacuum system (pumps, pumping channels, taps, valves, seals) (Fig. 4). The required negative pressure inside the column is achieved due to the high efficiency of the vacuum pumps.
Preliminary vacuum in the entire vacuum system creates a mechanical foreline pump, then the oil diffusion pump comes into action; both pumps are connected in series and provide a high vacuum in the microscope column. The introduction of an oil booster pump into the electron microscope system made it possible to turn off the fore pump for a long time.
Rice. Fig. 4. Vacuum scheme of the electron microscope: 1 - trap cooled with liquid nitrogen (cold pipe); 2 - high vacuum valve; 3 - diffusion pump; 4 - bypass valve; 5 - small buffer cylinder; 6 - booster pump; 7 - mechanical fore-vacuum pump of preliminary rarefaction; 8 - four-way valve valve; 9 - large buffer cylinder; 10 - column of an electron microscope; 11 - air inlet valve into the microscope column.
The electrical circuit of the microscope consists of high voltage sources, cathode incandescence, power supply of electromagnetic lenses, as well as a system that provides alternating mains voltage to the electric motor of the fore-vacuum pump, the oven of the diffusion pump, and lighting of the control panel. Very high requirements are imposed on the power supply: for example, for a high-resolution electron microscope, the degree of high voltage instability should not exceed 5·10 -6 per 30 sec.
An intense electron beam is formed as a result of thermal emission. The cathode, which is a V-shaped tungsten filament, is heated by a high-frequency generator. The generated voltage with an oscillation frequency of 100-200 kHz provides a monochromatic electron beam. The power supply of the electron microscope lenses is provided by a highly stabilized direct current.
Rice. 5. Electron microscope UEMV-100B for the study of living microorganisms.
Devices are produced (Fig. 5) with a guaranteed resolution of 4.5 Å; Separate unique images show a resolution of 1.27 Å, approaching the size of an atom. The useful increase in this case is 200,000.
An electron microscope is a precision instrument that requires special preparation methods. Biological objects have low contrast, so it is necessary to artificially enhance the contrast of the drug. There are several ways to increase the contrast of preparations. When the preparation is shaded at an angle with platinum, tungsten, carbon, etc., it becomes possible to determine the dimensions on all three axes of the spatial coordinate system on electron microscope images. With positive contrasting, the drug combines with water-soluble salts of heavy metals (uranyl acetate, lead monoxide, potassium permanganate, etc.). With negative contrasting, the preparation is surrounded by a thin layer of a high-density amorphous substance impervious to electrons (ammonium molybdate, uranyl acetate, phosphotungstic acid, etc.).
Electron microscopy of viruses (viroscopy) has led to significant progress in the study of the ultrathin, submolecular structure of viruses (see). Along with physical, biochemical and genetic research methods, the use of electron microscopy also contributed to the emergence and development of molecular biology. The subject of this new branch of biology is the submicroscopic organization and functioning of human, animal, plant, bacteria, and mycoplasma cells, as well as the organization of rickettsiae and viruses (Fig. 6). Viruses, large molecules of protein and nucleic acids (RNA, DNA), individual fragments of cells (for example, the molecular structure of the shell of bacterial cells) can be examined using an electron microscope after special processing: shading with a metal, positive or negative staining with uranyl acetate or phosphotungstic acid, as well as other compounds (Fig. 7).
Rice. Fig. 6. Cell tissue culture of the heart tissue of the cynomolgus monkey infected with variola virus (X 12,000): 1 - nucleus; 2 - mitochondria; 3 - cytoplasm; 4 - virus.
Rice. 7. Influenza virus (negative staining (X450,000): 1 - shell; 2 - ribonucleoprotein.
Using the method of negative staining on the surface of many viruses, regularly arranged groups of protein molecules - capsomeres (Fig. 8) were found.
Rice. 8. A fragment of the surface of the herpes virus capsid. Individual capsomeres are visible (X500 000): 1 - side view; 2 - top view.
Rice. Fig. 9. Ultrathin section of the bacterium Salmonella typhimurium (X80 000): 1 - core; 2 - shell; 3 - cytoplasm.
The internal structure of bacteria and viruses, as well as other larger biological objects, can only be studied after dissecting them with an ultratome and preparing the thinnest sections 100-300 Å thick. (Fig. 9). Thanks to improved methods of fixation, embedding, and polymerization of biological objects, the use of diamond and glass knives for ultratomy, and the use of highly contrasting compounds for staining serial sections, it was possible to obtain ultrathin sections of not only large, but also the smallest viruses of humans, animals, plants, and bacteria.
The history of the electron microscope
In 1931, R. Rudenberg received a patent for a transmission electron microscope, and in 1932, M. Knoll and E. Ruska built the first prototype of a modern instrument. This work of E. Ruska in 1986 was awarded the Nobel Prize in Physics, which was awarded to him and the inventors of the scanning probe microscope, Gerd Karl Binnig and Heinrich Rohrer. The use of the transmission electron microscope for scientific research began in the late 1930s, and at the same time, the first commercial instrument built by Siemens appeared.
In the late 1930s - early 1940s, the first scanning electron microscopes appeared, which form an image of an object by sequentially moving an electron probe of a small cross section over the object. The mass use of these devices in scientific research began in the 1960s, when they reached significant technical perfection.
A significant leap (in the 70s) in development was the use of Schottky cathodes and cathodes with cold field emission instead of thermionic cathodes, but their use requires a much larger vacuum.
In the late 90s and early 2000s, computerization and the use of CCD detectors greatly increased stability and (relatively) ease of use.
In the last decade, modern advanced transmission electron microscopes use correctors for spherical and chromatic aberrations (which introduce the main distortion in the resulting image), but their use sometimes significantly complicates the use of the device.
Types of electron microscopes
Transmission electron microscopy
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The original view of the electron microscope. The transmission electron microscope uses a high-energy electron beam to form an image. The electron beam is created by means of a cathode (tungsten, LaB 6 , Schottky or cold field emission). The resulting electron beam is usually accelerated to +200 keV (various voltages from 20 keV to 1 meV are used), focused by a system of electrostatic lenses, passes through the sample so that part of it passes through scattering on the sample, and part does not. Thus, the electron beam passed through the sample carries information about the structure of the sample. Next, the beam passes through a system of magnifying lenses and forms an image on a luminescent screen (usually made of zinc sulfide), a photographic plate, or a CCD camera.
TEM resolution is limited mainly by spherical aberration. Some modern TEMs have spherical aberration correctors.
The main disadvantages of TEM are the need for a very thin sample (on the order of 100 nm) and the instability (decomposition) of the samples under the beam. aaaaa
Transmission scanning (scanning) electron microscopy (SEM)
Main article: Transmission scanning electron microscope
One of the types of transmission electron microscopy (TEM), however, there are instruments that operate exclusively in the TEM mode. An electron beam is passed through a relatively thin sample, but, unlike conventional transmission electron microscopy, the electron beam is focused to a point that moves across the sample along the raster.
Raster (scanning) electron microscopy
It is based on the television principle of sweeping a thin electron beam over the sample surface.
Low voltage electron microscopy
Fields of application of electron microscopes
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Semiconductors and storage
Biology and biological sciences
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Scientific research
Industry
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The main world manufacturers of electron microscopes
see also
Notes
Links
- Top 15 Electron Microscope Images of 2011 The images on the recommended site are randomly colored, and are of artistic rather than scientific value (electron microscopes produce black and white images rather than color).
Wikimedia Foundation. 2010 .
See what the "electron microscope" is in other dictionaries:
A device for observing and photographing a multiply (up to 106 times) enlarged image of an object, in which, instead of light rays, electron beams accelerated to high energies (30-1000 keV and more) in deep vacuum are used. Phys… Physical Encyclopedia
A device for observing and photographing a multiply (up to 106 times) enlarged image of objects, in which, instead of light rays, beams of electrons accelerated to high energies (30-100 keV and more) in deep vacuum are used. Physical… … Physical Encyclopedia
Electron microscope- (scheme). ELECTRONIC MICROSCOPE, a vacuum electron-optical device for observing and photographing a multiply (up to 106 times) enlarged image of objects obtained using electron beams accelerated to high energies. ... ... Illustrated Encyclopedic Dictionary
ELECTRONIC MICROSCOPE, MICROSCOPE, which "illuminates" the object under study with a stream of electrons. Instead of ordinary lenses, it has magnets that focus the electron beam. This device allows you to see objects of very small sizes, because ... ... Scientific and technical encyclopedic dictionary
We are starting to publish a blog by an entrepreneur, information technology specialist 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 complex scientific equipment - a scanning electron microscope - practically at home. Read about what engineering, technical and scientific challenges Alexey had to face and how he coped with them.
Once a friend called me and said: I found an interesting thing, I need to bring it to you, however, it weighs half a ton. So I got a column from a JEOL JSM-50A scanning electron microscope in my garage. She was decommissioned from some research institute a long time ago and taken to scrap metal. The electronics were lost, but the electron-optical column, together with the vacuum part, was saved.
Since the main part of the equipment was preserved, the question arose: is it possible to save the entire microscope, that is, to 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, I had never before dealt with such scientific equipment, not to mention being able to use it, and had no idea how it works. But it's interesting not just to put the old piece of iron into working condition - it's interesting to figure everything out on your own and check whether it is possible, using the 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 about what I have already managed to do 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, as well as talk about the many technical obstacles that had to be overcome in the course of work. So let's get started.
In order to restore the microscope I had 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 the principles of operation of electron microscopes. They are of two types:
Transmission electron microscope
TEM is very similar to a conventional optical microscope, only the sample under study is irradiated not with light (photons), but with electrons. The wavelength of an electron beam is much smaller than that of a photon beam, so much higher resolution can be obtained.
The electron beam is focused and controlled by 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. By the way, 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 disadvantages: the samples to be studied must be very thin, thinner than 1 micron, which is not always convenient, especially when working at home. For example, to see your hair through the light, it must be cut along at least 50 layers. This is due to the fact that the penetrating power of an electron beam is much worse than a photon one. In addition, TEM, with rare exceptions, is quite cumbersome. This apparatus, shown below, does not seem to be that big (although it is taller than a human being and has a solid cast-iron frame), but it also comes with a power supply unit the size of a large cabinet - in total, almost a whole room is needed.
But the resolution of TEM is the highest. 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 virus analytics of the 20th 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 ceased.
For example, here's what the H1N1 flu looks like "through the light":
University of Calgary
Scanning electron microscope
SEM is mainly used to study the surface of samples with very high resolution (million times magnification, versus 2 thousand for optical microscopes). And this is much more useful in the household :)
For example, this is how a single 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 screen phosphor, and the image is formed on the basis of information from sensors that record secondary electrons, elastically reflected electrons, and so on. It is this type of electron microscope that will be discussed in this blog.
Both the kinescope of the TV 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)
