Hydrogen atom capturing electron clouds. And although modern physicists can even determine the shape of a proton with the help of accelerators, the hydrogen atom, apparently, will remain the smallest object, the image of which makes sense to call a photograph. Lenta.ru presents an overview modern methods photographing the microcosm.
Strictly speaking, there is almost no ordinary photography left these days. Images that we habitually call photographs and can be found, for example, in any Lenta.ru photo essay, are actually computer models. A photosensitive matrix in a special device (traditionally it is still called a “camera”) determines the spatial distribution of light intensity in several different spectral ranges, the control electronics stores this data in digital form, and then another electronic circuit, based on this data, gives a command to the transistors in the liquid crystal display . Film, paper, special solutions for their processing - all this has become exotic. And if we remember the literal meaning of the word, then photography is “light painting”. So what to say that the scientists succeeded to photograph an atom, is possible only with a fair amount of conventionality.
More than half of all astronomical images have long been taken by infrared, ultraviolet and X-ray telescopes. Electron microscopes irradiate not with light, but with an electron beam, while atomic force microscopes scan the relief of the sample with a needle. There are X-ray microscopes and magnetic resonance imaging scanners. All these devices give us accurate images of various objects, and despite the fact that it is, of course, not necessary to speak of "light painting" here, we still allow ourselves to call such images photographs.
Experiments by physicists to determine the shape of a proton or the distribution of quarks inside particles will remain behind the scenes; our story will be limited to the scale of atoms.
Optics never get old
As it turned out in the second half of the 20th century, optical microscopes still have room to develop. A decisive moment in biological and medical research was the emergence of fluorescent dyes and methods that allow selective labeling of certain substances. It wasn't "just new paint", it was a real revolution.
Contrary to common misconception, fluorescence is not a glow in the dark at all (the latter is called luminescence). This is the phenomenon of absorption of quanta of a certain energy (say, blue light) followed by the emission of other quanta of lower energy and, accordingly, a different light (when blue is absorbed, green will be emitted). If you put in a filter that allows only the quanta emitted by the dye to pass through and blocks the light that causes fluorescence, you can see a dark background with bright spots of dyes, and dyes, in turn, can color the sample extremely selectively.
For example, you can color the cytoskeleton of a nerve cell red, highlight the synapses in green, and highlight the nucleus in blue. You can make a fluorescent label that will allow you to detect protein receptors on the membrane or molecules synthesized by the cell under certain conditions. The method of immunohistochemical staining has revolutionized biological science. And when genetic engineers learned how to make transgenic animals with fluorescent proteins, this method experienced a rebirth: mice with neurons painted in different colors became a reality, for example.
In addition, engineers came up with (and practiced) a method of so-called confocal microscopy. Its essence lies in the fact that the microscope focuses on a very thin layer, and a special diaphragm cuts off the light created by objects outside this layer. Such a microscope can sequentially scan a sample from top to bottom and obtain a stack of images, which is a ready-made basis for a three-dimensional model.
The use of lasers and sophisticated optical beam control systems has made it possible to solve the problem of dye fading and drying of delicate biological samples under bright light: the laser beam scans the sample only when it is necessary for imaging. And in order not to waste time and effort on examining a large preparation through an eyepiece with a narrow field of view, the engineers proposed an automatic scanning system: you can put a glass with a sample on the object stage of a modern microscope, and the device will independently capture a large-scale panorama of the entire sample. At the same time, in the right places, he will focus, and then glue many frames together.
Some microscopes can accommodate live mice, rats, or at least small invertebrates. Others give a slight increase, but are combined with an X-ray machine. To eliminate vibration interference, many are mounted on special tables weighing several tons indoors with a carefully controlled microclimate. The cost of such systems exceeds the cost of other electron microscopes, and competitions for the most beautiful frame have long become a tradition. In addition, the improvement of optics continues: from the search for the best types of glass and the selection of optimal lens combinations, engineers have moved on to ways to focus light.
We have specifically listed a number of technical details in order to show: progress in the field of biological research has long been associated with progress in other areas. If there were no computers capable of automatically counting the number of stained cells in several hundred photographs, supermicroscopes would be of little use. And without fluorescent dyes, all millions of cells would be indistinguishable from each other, so it would be almost impossible to follow the formation of new ones or the death of old ones.
In fact, the first microscope was a clamp with a spherical lens attached to it. An analogue of such a microscope can be a simple playing card with a hole made in it and a drop of water. According to some reports, such devices were used by gold miners in Kolyma already in the last century.
Beyond the diffraction limit
Optical microscopes have a fundamental drawback. The fact is that it is impossible to restore the shape of those objects that turned out to be much smaller than the wavelength from the shape of light waves: you can just as well try to examine the fine texture of the material with your hand in a thick welding glove.
The limitations created by diffraction have been partly overcome, and without violating the laws of physics. Two circumstances help optical microscopes dive under the diffraction barrier: the fact that during fluorescence quanta are emitted by individual dye molecules (which can be quite far apart from each other), and the fact that by superimposing light waves it is possible to obtain a bright spot with a diameter smaller than wavelength.
When superimposed on each other, light waves are able to cancel each other out, therefore, the illumination parameters of the sample are such that the smallest possible area falls into the bright region. In combination with mathematical algorithms that can, for example, remove ghosting, such directional lighting provides a dramatic improvement in image quality. It becomes possible, for example, to examine intracellular structures with an optical microscope and even (combining the described method with confocal microscopy) to obtain their three-dimensional images.
Electron microscope before electronic instruments
In order to discover atoms and molecules, scientists did not have to look at them - molecular theory did not need to see the object. But microbiology became possible only after the invention of the microscope. Therefore, at first, microscopes were associated precisely with medicine and biology: physicists and chemists who studied much smaller objects managed by other means. When they also wanted to look at the microcosm, diffraction limitations became a serious problem, especially since the methods of fluorescence microscopy described above were still unknown. And there is little sense in increasing the resolution from 500 to 100 nanometers if the object to be considered is even less!
Knowing that electrons can behave both as a wave and as a particle, physicists from Germany created an electron lens in 1926. The idea underlying it was very simple and understandable to any schoolchild: since the electromagnetic field deflects electrons, it can be used to change the shape of the beam of these particles by pulling them in different directions, or, on the contrary, to reduce the diameter of the beam. Five years later, in 1931, Ernst Ruska and Max Knoll built the world's first electron microscope. In the device, the sample was first illuminated by an electron beam, and then the electron lens expanded the beam that passed through before it fell on a special luminescent screen. The first microscope only gave a magnification of 400 times, but the replacement of light with electrons opened the way to photographing with magnification hundreds of thousands of times: the designers had only to overcome a few technical obstacles.
The electron microscope made it possible to examine the structure of cells in a quality that was previously unattainable. But from this picture it is impossible to understand the age of the cells and the presence of certain proteins in them, and this information is very necessary for scientists.
Now electron microscopes allow you to photograph viruses close-up. There are various modifications of devices that allow not only to shine through thin sections, but also to consider them in "reflected light" (in reflected electrons, of course). We will not talk in detail about all the options for microscopes, but we note that recently researchers have learned how to restore an image from a diffraction pattern.
Touch, not see
Another revolution came at the expense of a further departure from the principle of "illuminate and see." An atomic force microscope, as well as a scanning tunneling microscope, no longer shines on the surface of the samples. Instead, a particularly thin needle moves across the surface, which literally bounces even on bumps the size of a single atom.
Without going into the details of all such methods, we note the main thing: the needle of a tunneling microscope can not only be moved along the surface, but also used to rearrange atoms from place to place. This is how scientists create inscriptions, drawings and even cartoons in which a drawn boy plays with an atom. A real xenon atom dragged by the tip of a scanning tunneling microscope.
It is called a tunneling microscope because it uses the effect of tunneling current flowing through the needle: electrons pass through the gap between the needle and the surface due to the predicted quantum mechanics tunnel effect. This device requires a vacuum to operate.
The atomic force microscope (AFM) is much less demanding on environmental conditions - it can (with a number of limitations) work without air pumping. In a sense, the AFM is the nanotech successor to the gramophone. A needle mounted on a thin and flexible cantilever bracket ( cantilever and there is a “bracket”), moves along the surface without applying voltage to it and follows the relief of the sample in the same way as the gramophone needle follows along the grooves of a gramophone record. The bending of the cantilever causes the mirror fixed on it to deviate, the mirror deflects the laser beam, and this makes it possible to very accurately determine the shape of the sample under study. The main thing is to have a fairly accurate system for moving the needle, as well as a supply of needles that must be perfectly sharp. The radius of curvature at the tips of such needles may not exceed one nanometer.
AFM allows you to see individual atoms and molecules, but, like a tunneling microscope, it does not allow you to look under the surface of the sample. In other words, scientists have to choose between being able to see atoms and being able to study the entire object. However, even for optical microscopes, the insides of the studied samples are not always accessible, because minerals or metals usually transmit light poorly. In addition, there are still difficulties with photographing atoms - these objects appear as simple balls, the shape of electron clouds is not visible in such images.
Synchrotron radiation, which occurs during the deceleration of charged particles dispersed by accelerators, makes it possible to study the petrified remains of prehistoric animals. Rotating the sample under x-rays, we can get three-dimensional tomograms - this is how, for example, the brain was found inside the skull of fish that became extinct 300 million years ago. You can do without rotation if the registration of the transmitted radiation is by fixing the x-rays scattered due to diffraction.
And that's not all the possibilities that open up x-rays. When irradiated with it, many materials fluoresce, and the nature of the fluorescence can be used to determine chemical composition substances: in this way, scientists coloring ancient artifacts, the works of Archimedes erased in the Middle Ages, or coloring the feathers of long-extinct birds.
Posing atoms
Against the backdrop of all the possibilities provided by X-ray or optical fluorescence methods, a new way of photographing individual atoms no longer seems like such a big breakthrough in science. The essence of the method that made it possible to obtain the images presented this week is as follows: electrons are plucked from ionized atoms and sent to a special detector. Each act of ionization strips an electron from a certain position and gives one point on the "photo". Having accumulated several thousand such points, the scientists formed a picture showing the most likely places for finding an electron around the nucleus of an atom, and this, by definition, is an electron cloud.
In conclusion, let's say that the ability to see individual atoms with their electron clouds is more like a cherry on the cake of modern microscopy. It was important for scientists to study the structure of materials, to study cells and crystals, and the development of technologies resulting from this made it possible to reach the hydrogen atom. Anything less is already the sphere of interest of specialists in elementary particle physics. And biologists, materials scientists and geologists still have room to improve microscopes even with a rather modest magnification compared to atoms. Experts in neurophysiology, for example, have long wanted to have a device that can see individual cells inside a living brain, and the creators of rovers would sell their souls for an electron microscope that would fit on board spacecraft and could work on Mars.
In fact, the author of RFC in his “reflections” went so far that it is time to call up heavy counterarguments, namely, the data of the experiment of Japanese scientists on photographing the hydrogen atom, which became known on November 4, 2010. The picture clearly shows the atomic shape, confirming both discreteness and roundness of atoms: “A group of scientists and specialists from the University of Tokyo photographed a single hydrogen atom for the first time in the world - the lightest and smallest of all atoms, news agencies report.
The picture was taken using one of the latest technologies - a special scanning electron microscope. Using this device, along with a hydrogen atom, a separate vanadium atom was also photographed.
The diameter of a hydrogen atom is one ten-billionth of a meter. Previously, it was believed that it was almost impossible to photograph it with modern equipment. Hydrogen is the most common substance. Its share in the entire Universe is approximately 90%.
According to scientists, other images can be captured in the same way. elementary particles. “Now we can see all the atoms that make up our world,” said Professor Yuichi Ikuhara. “This is a breakthrough to new forms of production, when in the future it will be possible to make decisions at the level of individual atoms and molecules.”
Hydrogen atom, conditional colors
http://prl.aps.org/abstract/PRL/v110/i21/e213001
A group of scientists from Germany, Greece, the Netherlands, the USA and France took pictures of the hydrogen atom. These images, obtained with a photoionization microscope, show the electron density distribution, which completely coincides with the results of theoretical calculations. The work of the international group is presented in the pages of Physical Review Letters.
The essence of the photoionization method is the sequential ionization of hydrogen atoms, that is, the removal of an electron from them due to electromagnetic irradiation. The separated electrons are directed to the sensitive matrix through a positively charged ring, and the position of the electron at the moment of collision with the matrix reflects the position of the electron at the moment of ionization of the atom. The charged ring, which deflects the electrons to the side, plays the role of a lens and with its help the image is magnified millions of times.
This method, described in 2004, has already been used to take "pictures" of individual molecules, but physicists have gone further and used a photoionization microscope to study hydrogen atoms. Since hitting one electron gives only one point, the researchers accumulated about 20,000 individual electrons from different atoms and averaged the image of the electron shells.
According to the laws of quantum mechanics, an electron in an atom does not have any definite position by itself. Only when an atom interacts with the external environment, an electron with one or another probability appears in a certain neighborhood of the atomic nucleus: the region in which the probability of finding an electron is maximum is called the electron shell. The new images show differences between atoms of different energy states; scientists were able to visually demonstrate the shape of the electron shells predicted by quantum mechanics.
With the help of other instruments, scanning tunneling microscopes, individual atoms can not only be seen, but also moved to Right place. This technique, about a month ago, allowed IBM engineers to draw a cartoon, each frame of which is composed of atoms: such artistic experiments do not have any practical effect, but demonstrate the fundamental possibility of manipulations with atoms. For applied purposes, it is no longer a atomic assembly, but chemical processes with self-organization of nanostructures or self-limitation of the growth of monatomic layers on a substrate.
As you know, everything material in the Universe consists of atoms. An atom is the smallest unit of matter that carries its properties. In turn, the structure of an atom is made up of a magical trinity of microparticles: protons, neutrons and electrons.
Moreover, each of the microparticles is universal. That is, you cannot find two different protons, neutrons or electrons in the world. All of them are absolutely similar to each other. And the properties of the atom will depend only on the quantitative composition of these microparticles in the general structure of the atom.
For example, the structure of a hydrogen atom consists of one proton and one electron. Next in complexity, the helium atom is made up of two protons, two neutrons, and two electrons. A lithium atom is made up of three protons, four neutrons and three electrons, etc.
Structure of atoms (from left to right): hydrogen, helium, lithium
Atoms combine into molecules, and molecules combine into substances, minerals and organisms. The DNA molecule, which is the basis of all life, is a structure assembled from the same three magical building blocks of the universe as the stone lying on the road. Although this structure is much more complex.
Even more amazing facts open when we try to take a closer look at the proportions and structure of the atomic system. It is known that an atom consists of a nucleus and electrons moving around it along a trajectory that describes a sphere. That is, it cannot even be called a movement in the usual sense of the word. The electron is rather located everywhere and immediately within this sphere, creating an electron cloud around the nucleus and forming an electromagnetic field.
Schematic representations of the structure of the atom
The nucleus of an atom consists of protons and neutrons, and almost the entire mass of the system is concentrated in it. But at the same time, the nucleus itself is so small that if you increase its radius to a scale of 1 cm, then the radius of the entire structure of the atom will reach hundreds of meters. Thus, everything that we perceive as dense matter consists of more than 99% of the energy connections between physical particles alone and less than 1% of the physical forms themselves.
But what are these physical forms? What are they made of, and how material are they? To answer these questions, let's take a closer look at the structures of protons, neutrons, and electrons. So, we descend one more step into the depths of the microcosm - to the level of subatomic particles.
What is an electron made of?
The smallest particle of an atom is an electron. An electron has mass but no volume. In the scientific view, the electron does not consist of anything, but is a structureless point.
An electron cannot be seen under a microscope. It is observed only in the form of an electron cloud, which looks like a fuzzy sphere around atomic nucleus. At the same time, it is impossible to say with accuracy where the electron is located at a moment in time. Devices are capable of capturing not the particle itself, but only its energy trace. The essence of the electron is not embedded in the concept of matter. It is rather like an empty form that exists only in and through movement.
No structure has yet been found in the electron. It is the same point particle as the quantum of energy. In fact, an electron is energy, however, this is its more stable form than the one represented by photons of light.
IN currently The electron is considered indivisible. This is understandable, because it is impossible to divide something that has no volume. However, there are already developments in the theory, according to which the composition of an electron contains a trinity of such quasiparticles as:
- Orbiton - contains information about the orbital position of the electron;
- Spinon - responsible for the spin or torque;
- Holon - carries information about the charge of an electron.
However, as we see, quasi-particles have absolutely nothing in common with matter, and carry only information.
Photographs of atoms of different substances in an electron microscope
Interestingly, an electron can absorb energy quanta, such as light or heat. In this case, the atom moves to a new energy level, and the boundaries of the electron cloud expand. It also happens that the energy absorbed by an electron is so great that it can jump out of the atomic system and continue its movement as an independent particle. At the same time, it behaves like a photon of light, that is, it seems to cease to be a particle and begins to exhibit the properties of a wave. This has been proven in an experiment.
Young's experiment
In the course of the experiment, a stream of electrons was directed onto a screen with two slits cut into it. Passing through these slits, the electrons collided with the surface of another projection screen, leaving their mark on it. As a result of this “bombardment” by electrons, an interference pattern appeared on the projection screen, similar to that which would appear if waves, but not particles, passed through two slits.
Such a pattern occurs due to the fact that the wave, passing between the two slots, is divided into two waves. As a result of further movement, the waves overlap each other, and in some areas they cancel each other out. As a result, we get many stripes on the projection screen, instead of one, as it would be if the electron behaved like a particle.
The structure of the nucleus of an atom: protons and neutrons
Protons and neutrons make up the nucleus of an atom. And despite the fact that in the total volume the core occupies less than 1%, it is in this structure that almost the entire mass of the system is concentrated. But on the account of the structure of protons and neutrons, physicists are divided in opinion, and on this moment there are two theories.
- Theory #1 - Standard
The Standard Model says that protons and neutrons are made up of three quarks connected by a cloud of gluons. Quarks are point particles, just like quanta and electrons. And gluons are virtual particles that ensure the interaction of quarks. However, neither quarks nor gluons have been found in nature, so this model is subject to severe criticism.
- Theory #2 - Alternative
But according to the alternative unified field theory developed by Einstein, the proton, like the neutron, like any other particle of the physical world, is an electromagnetic field rotating at the speed of light.
Electromagnetic fields of man and the planet
What are the principles of the structure of the atom?
Everything in the world - subtle and dense, liquid, solid and gaseous - is just the energy states of countless fields that permeate the space of the Universe. The higher the energy level in the field, the thinner and less perceptible it is. The lower the energy level, the more stable and tangible it is. In the structure of the atom, as well as in the structure of any other unit of the Universe, lies the interaction of such fields - different in energy density. It turns out that matter is only an illusion of the mind.
Physicists from the United States managed to capture individual atoms in a photo with a record resolution, Day.Az reports with reference to Vesti.ru
Scientists from Cornell University in the United States managed to capture individual atoms in a photo with a record resolution of less than half an angstrom (0.39 Å). Previous photographs had half the resolution - 0.98 Å.
Powerful electron microscopes that can see atoms have been around for half a century, but their resolution is limited by the long wavelength of visible light, which is larger than the diameter of an average atom.
Therefore, scientists use a kind of analogue of lenses that focus and magnify the image in electron microscopes - they are a magnetic field. However, fluctuations magnetic field distort the result. To remove distortions, additional devices are used that correct the magnetic field, but at the same time increase the complexity of the electron microscope design.
Previously, physicists at Cornell University developed the Electron Microscope Pixel Array Detector (EMPAD), which replaces a complex system of generators that focus incoming electrons with a single small array of 128x128 pixels that is sensitive to individual electrons. Each pixel registers the angle of electron reflection; Knowing it, scientists using the technique of ptyicography reconstruct the characteristics of the electrons, including the coordinates of the point from which it was released.
Atoms in the highest resolution
David A. Muller et al. Nature, 2018.
In the summer of 2018, physicists decided to improve the quality of the resulting images to a record-breaking resolution to date. Scientists fixed a sheet of 2D material - molybdenum sulfide MoS2 - on a movable beam, and released electron beams by turning the beam at different angles to the electron source. Using EMPAD and ptyicography, scientists determined the distances between individual molybdenum atoms and obtained an image with a record resolution of 0.39 Å.
"In fact, we have created the smallest ruler in the world," explains Sol Gruner (Sol Gruner), one of the authors of the experiment. In the resulting image, it was possible to see sulfur atoms with a record resolution of 0.39 Å. Moreover, we even managed to see the place where one such atom is missing (indicated by an arrow).
Sulfur atoms at record resolution
Ever seen atoms? We are one of them, so in fact, yes. But have you ever seen one single atom? Recently, an amazing photo of just one atom, captured electric fields, won the prestigious competition of scientific photography, awarded the highest award. The photo entered the competition under the quite logical name “Single Atom in Ion Trap” (One atom in an ion trap), and its author is David Nadlinger from Oxford University.
The British Engineering and Physical Sciences Research Council (EPSRC) has announced the winners of its national science photography competition, with a photo of a single atom winning the grand prize.
In the photo, the atom is represented as a tiny speck of light between two metal electrodes spaced about 2 mm apart.
Photo caption:
"A small bright dot is visible in the center of the photograph - a single positively charged strontium atom. It is held almost motionless by electric fields emanating from the metal electrodes surrounding it. When illuminated by a blue-violet laser, the atom absorbs and re-emit light particles quickly enough, due to which a conventional camera could have photographed it with a long exposure."
"The photo was taken through the window of the ultrahigh vacuum chamber in which the trap is located. Laser-cooled atomic ions are an excellent base for studying and exploiting the unique properties quantum physics. They are being used to create extremely precise clocks or, in this case, as particles to build the quantum computers of the future that can solve problems that outshine today's even the most powerful supercomputers."
If you still failed to consider the atom, then here it is
"The idea that you can see one atom naked eye struck me to the core, being a kind of bridge between the tiny quantum world and our macroscopic reality," said David Nadlinger.
