The conquest of nature by man has not yet ended. In any case, we have not yet captured the nanoworld and established our own rules in it. Let's see what it is and what opportunities the world of objects measured in nanometers gives us.
What is "nano"?
Once upon a time the achievements of microelectronics were heard. We have now entered a new era of nanotechnology. So what is this "nano", which here and there began to add to the usual words, giving them a new modern sound: nanorobots, nanomachines, nanoradio and so on? The prefix "nano" is used in the International System of Units (SI). It is used to form the notation for decimal units. This is one billionth of the original unit. In this case, we are talking about objects whose dimensions are determined in nanometers. This means that one nanometer is one billionth of a meter. For comparison, a micron (aka the micrometer that gave the name to microelectronics, and besides, microbiology, microsurgery, etc.) is one millionth of a meter.
If we take millimeters as an example (the prefix "milli" is one thousandth), then in a millimeter there are 1,000,000 nanometers (nm) and, accordingly, 1,000 micrometers (μm). Human hair has an average thickness of 0.05–0.07 mm, that is, 50,000–70,000 nm. Although hair diameter can be written in nanometers, it is far from the nanoworld. Let's go deeper and see what is there already now.
The average size of bacteria is 0.5–5 µm (500–5000 nm). Viruses, one of the main enemies of bacteria, are even smaller. The average diameter of most of the viruses studied is 20–300 nm (0.02–0.3 µm). But the DNA helix has a diameter of 1.8-2.3 nm. It is believed that the smallest atom is a helium atom, its radius is 32 pm (0.032 nm), and the largest is cesium 225 pm (0.255 nm). In general, a nanoobject is considered to be an object whose size in at least one dimension is in the nanoscale (1–100 nm).
Can you see the nanoworld?
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Of course, I want to see everything that is said with my own eyes. Well, at least through the eyepiece of an optical microscope. Is it possible to look into the nanoworld? The usual way, as we observe, for example, microbes, is impossible. Why? Because light, with some degree of convention, can be called nanowaves. The wavelength of the violet color, from which the visible range begins, is 380–440 nm. The wavelength of the red color is 620-740 nm. Visible radiation has wavelengths of hundreds of nanometers. In this case, the resolution of conventional optical microscopes is limited by the Abbe diffraction limit at about half the wavelength. Most of the objects of interest to us are even smaller.
Therefore, the first step towards penetration into the nanoworld was the invention of the transmission electron microscope. Moreover, the first such microscope was created by Max Knoll and Ernst Ruska back in 1931. In 1986, the Nobel Prize in Physics was awarded for his invention. The principle of operation is the same as that of a conventional optical microscope. Only instead of light, a stream of electrons is directed to the object of interest, which is focused by magnetic lenses. If an optical microscope gave an increase of about a thousand times, then an electron microscope was already millions of times. But it also has its drawbacks. First, it is necessary to obtain sufficiently thin samples of materials for work. They must be transparent in an electron beam, so their thickness varies in the range of 20–200 nm. Secondly, it isthat the sample under the influence of electron beams can decompose and become unusable.
Another version of the electron flow microscope is the scanning electron microscope. It does not shine through the sample, like the previous one, but scans it with an electron beam. This allows thicker samples to be examined. The processing of the analyzed sample with an electron beam generates secondary and back-reflected electrons, visible (cathodoluminescence) and X-rays, which are captured by special detectors. Based on the data received, an idea of the object is formed. The first scanning electron microscopes appeared in the early 1960s.
Scanning probe microscopes are a relatively new class of microscopes that appeared already in the 80s. The already mentioned 1986 Nobel Prize in Physics was divided between the inventor of the transmission electron microscope, Ernst Ruska, and the creators of the scanning tunneling microscope, Gerd Binnig and Heinrich Rohrer. Scanning microscopes make it possible not to examine, but to "feel" the relief of the sample surface. The resulting data is then converted into an image. Unlike the scanning electron microscope, the probe uses a sharp scanning needle for operation. The needle, the tip of which is only a few atoms thick, acts as a probe, which is brought to a minimum distance of 0.1 nm to the sample. During scanning, the needle moves over the sample surface. A tunneling current arises between the tip and the sample surface,and its value depends on the distance between them. The changes are recorded, which allows building a height map on their basis - a graphic representation of the object's surface.
A similar principle of operation is used by another microscope from the class of scanning probe microscopes - atomic force. There is also a probe tip, and a similar result - a graphic representation of the surface relief. But it is not the magnitude of the current that is measured, but the force interaction between the surface and the probe. First of all, the van der Waals forces are meant, but also elastic forces, capillary forces, adhesion forces, and others. Unlike the scanning tunneling microscope, which can only be used to study metals and semiconductors, the atomic force microscope also allows the study of dielectrics. But this is not its only advantage. It allows not only to look into the nanoworld, but also to manipulate atoms.
Pentacene molecule. A is a model of a molecule. B - image obtained by a scanning tunneling microscope. C - image obtained by an atomic force microscope. D - several molecules (AFM). A, B and C on the same scale
Photo: Science
Nanomachines
In nature, at the nanoscale, that is, at the level of atoms and molecules, many processes take place. We can, of course, still influence how they proceed. But we do it almost blindly. Nanomachines are a targeted instrument for working in the nanoworld; they are devices that allow one to manipulate single atoms and molecules. Until recently, only nature could create and control them. We are one step away from the day when we can do this too.
Nanomachines
Photo: warosu.org
What can nanomachines do? Take chemistry, for example. The synthesis of chemical compounds is based on the fact that we create the necessary conditions for a chemical reaction to proceed. As a result, we have a certain substance at the output. In the future, chemical compounds can be created, relatively speaking, mechanically. Nanomachines will be able to connect and separate individual atoms and molecules. As a result, chemical bonds will be formed or, conversely, existing bonds will be broken. Building nanomachines will be able to create the molecular structures we need from atoms. Chemist nanorobots - synthesize chemical compounds. This is a breakthrough in the creation of materials with desired properties. At the same time, it is a breakthrough in environmental protection. It is easy to assume that nanomachines are an excellent tool for recycling waste,which under normal conditions are difficult to dispose of. Especially if we talk about nanomaterials. After all, the further technical progress goes, the more difficult it is for the environment to cope with its results. For too long, the decomposition of new materials invented by man takes place in the natural environment. Everyone knows how long it takes to decompose discarded plastic bags - a product of the previous scientific and technological revolution. What will happen to nanomaterials, which sooner or later turn out to be garbage? The same nanomachines will have to do their processing.how long discarded plastic bags take to decompose - a product of a previous scientific and technological revolution. What will happen to nanomaterials, which sooner or later turn out to be garbage? The same nanomachines will have to do their processing.how long discarded plastic bags take to decompose - a product of a previous scientific and technological revolution. What will happen to nanomaterials, which sooner or later turn out to be garbage? The same nanomachines will have to do their processing.
Fullerene wheel nanomachine
Photo: warosu.org
Scientists have been talking about mechanosynthesis for a long time. It is a chemical synthesis that takes place through mechanical systems. Its advantage is seen in the fact that it will allow the positioning of reactants with a high degree of accuracy. But so far there is no tool that would allow to effectively implement it. Of course, atomic force microscopes existing today can act as such instruments. Yes, they allow not only to look into the nanoworld, but also to operate with atoms. But they, as objects of the macrocosm, are not best suited for the mass application of technology, which cannot be said about nanomachines. In the future, they will be used to create entire molecular conveyors and nanofactories.
But there are already whole biological nanofactories. They exist in us and in all living organisms. That is why breakthroughs in medicine, biotechnology and genetics are expected from nanotechnology. By creating artificial nanomachines and introducing them into living cells, we can achieve impressive results. First, nanomachines can be used for targeted transport of drugs to the desired organ. We do not have to take medicine, realizing that only part of it will get to the diseased organ. Second, nanomachines are already taking over the genome editing functions. CRISPR / Cas9 technology, peeped from nature, allows you to make changes in the genome of both unicellular and higher organisms, including humans. Moreover, we are talking not only about editing the genome of embryos, but also the genome of living adult organisms. And the nanomachines will do all this.
Nanoradio
If nanomachines are our instrument in the nanoworld, then they somehow need to be controlled. However, there is no need to invent something fundamentally new here either. One of the most likely control methods is radio. The first steps in this direction have already been taken. Scientists at Lawrence Berkeley National Laboratory, led by Alex Zettle, have created a radio receiver from just one nanotube about 10 nm in diameter. Moreover, the nanotube acts simultaneously as an antenna, selector, amplifier and demodulator. The nanoradio receiver can receive both FM and AM waves with a frequency of 40 to 400 MHz. According to the developers, the device can be used not only for receiving a radio signal, but also for transmitting it.
Received radio waves make the nanoradio antenna vibrate
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Music by Eric Clapton and the Beach Boys served as a test signal. The scientists transmitted a signal from one part of the room to another, where the radio they created was located. As it turned out, the signal quality was good enough. But, naturally, the purpose of such a radio is not listening to music. The radio receiver can be applied in a variety of nanodevices. For example, in the same nanorobots delivering drugs that will make their way to the desired organ through the bloodstream.
Nanomaterials
The creation of materials with properties that were previously impossible to imagine is another opportunity that nanotechnology offers us. To be considered "nano", a material must have one or more dimensions in the nanoscale. Either be created using nanoparticles or through nanotechnology. The most convenient classification of nanomaterials today is according to the dimension of the structural elements of which they are composed.
Zero-dimensional (0D) - nanoclusters, nanocrystals, nanodispersions, quantum dots. None of the sides of the 0D nanomaterial goes beyond the nanoscale. These are materials in which nanoparticles are isolated from each other. The first complex zero-dimensional structures obtained and applied in practice are fullerenes. Fullerenes are the strongest antioxidants known today. In pharmacology, hopes for the creation of new drugs are pinned on them. Fullerene derivatives show themselves well in the treatment of HIV. And when creating nanomachines, fullerenes can be used as parts. The nanomachine with fullerene wheels is shown above.
Fullerene
Photo: wikipedia.org
One-dimensional (1D) - nanotubes, fibers and rods. Their length ranges from 100 nm to tens of micrometers, but their diameter falls within the nanoscale. The most famous one-dimensional materials today are nanotubes. They have unique electrical, optical, mechanical and magnetic properties. In the near future, nanotubes should find application in molecular electronics, biomedicine, and in the creation of new super-strong and ultra-light composite materials. Nanotubes are already used as needles in scanning tunneling and atomic force microscopes. Above, we spoke about the creation of nanoradio based on nanotubes. And, of course, hope is pinned on carbon nanotubes as a material for the space elevator cable.
Carbon nanotube
Photo: wikipedia.org
Two-dimensional (2D) - films (coatings) of nanometer thickness. This is the well-known graphene - a two-dimensional allotropic modification of carbon (the Nobel Prize in Physics for 2010 was awarded for graphene). Less well known to the public are silicene - a two-dimensional modification of silicon, phosphorus - phosphorus, germanene - germanium. Last year, scientists created borofen, which, unlike other two-dimensional materials, turned out to be not flat, but corrugated. The arrangement of boron atoms in the form of a corrugated structure provides the unique properties of the obtained nanomaterial. Borofen claims to be the leader in tensile strength among two-dimensional materials.
Borophene structure
Photo: MIPT
Two-dimensional materials should find application in electronics, in the design of filters for desalination of seawater (graphene membranes) and the creation of solar cells. In the near future, graphene may replace indium oxide - a rare and expensive metal - in the production of touch screens.
Three-dimensional (3D) nanomaterials are powders, fibrous, multilayer and polycrystalline materials, in which the above zero-dimensional, one-dimensional and two-dimensional nanomaterials are structural elements. Closely adhering to each other, they form interfaces between themselves - interfaces.
Types of nanomaterials
Photo: thesaurus.rusnano.com
A little more time will pass and nanotechnology - technologies for manipulating nanoscale objects will become commonplace. Just as microelectronic technologies have become familiar, giving us computers, mobile phones, satellites and many other attributes of the modern information age. But the impact of nanotechnology on life will be much broader. Changes await us in almost all spheres of human activity.
Sergey Sobol
