The carbon future of electronics. Carbon nanotubes and nanowolves

http://www.nsu.ru/materials/ssl/text/news/Physics/135.html
Many of the promising areas in materials science, nanotechnology, nanoelectronics, and applied chemistry have recently been associated with fullerenes, nanotubes and other similar structures, which can be called the general term carbon frame structures. What is it?
Carbon framework structures are large (and sometimes gigantic!) molecules made entirely of carbon atoms. One can even say that carbon frame structures are a new allotropic form of carbon (in addition to the long-known ones: diamond and graphite). The main feature of these molecules is their skeleton shape: they look like closed, empty “shells” inside.
Finally, the variety of applications that have already been invented for nanotubes is striking. The first thing that suggests itself is the use of nanotubes as very strong microscopic rods and threads. As the results of experiments and numerical modeling show, the Young's modulus of a single-walled nanotube reaches values ​​of the order of 1-5 TPa, which is an order of magnitude greater than that of steel! True, currently the maximum length of nanotubes is tens and hundreds of microns - which, of course, is very large on an atomic scale, but too short for everyday use. However, the length of nanotubes obtained in the laboratory is gradually increasing - now scientists have already come close to the millimeter mark: see the work, which describes the synthesis of a multi-walled nanotube 2 mm long. Therefore, there is every reason to hope that in the near future scientists will learn to grow nanotubes centimeters and even meters long! Of course, this will greatly influence future technologies: after all, a “cable” as thick as a human hair, capable of holding a load of hundreds of kilograms, will find countless applications.
The unusual electrical properties of nanotubes will make them one of the main materials for nanoelectronics. Prototypes of field-effect transistors based on a single nanotube have already been created: by applying a blocking voltage of several volts, scientists have learned to change the conductivity of single-walled nanotubes by 5 orders of magnitude!
Several applications of nanotubes in the computer industry have already been developed. For example, prototypes of thin flat displays operating on a matrix of nanotubes have been created and tested. Under the influence of a voltage applied to one end of the nanotube, electrons begin to be emitted from the other end, which fall on the phosphorescent screen and cause the pixel to glow. The resulting image grain will be fantastically small: on the order of a micron!

http://brd.dorms.spbu.ru/nanotech/print.php?sid=44
An attempt to photograph nanotubes using a conventional camera with a flash resulted in a block of nanotubes making a loud bang in the light of the flash and, flashing brightly, exploding.
Stunned scientists claim that the unexpectedly discovered phenomenon of the “explosiveness” of tubes can find new, completely unexpected applications for this material - even using it as detonators to detonate warheads. And also, obviously, will call into question or complicate their use in certain areas.

http://www.sciteclibrary.com/rus/catalog/pages/2654.html
The prospect opens up for a significant extension of the life of rechargeable batteries

http://vivovoco.nns.ru/VV/JOURNAL/VRAN/SESSION/NANO1.HTM
Carbon nanotube structures are a new material for emission electronics.

http://www.gazetangn.narod.ru/archive/ngn0221/space.html
Back in 1996, it was discovered that individual carbon nanotubes can spontaneously twist into ropes of 100-500 fiber tubes, and the strength of these ropes turned out to be greater than that of diamond. More precisely, they are 10-12 times stronger and 6 times lighter than steel. Just imagine: a thread with a diameter of 1 millimeter could withstand a 20-ton load, hundreds of billions of times greater than its own weight! It is from such threads that you can get super-strong cables of great length. From equally light and durable materials, you can build an elevator frame - a giant tower three times the diameter of the Earth. Passenger and cargo cabins will move along it at enormous speed - thanks to superconducting magnets, which, again, will be suspended on ropes made of carbon nanotubes. The colossal cargo flow into space will allow us to begin active exploration of other planets.
If anyone is interested in this project, details (in Russian) can be found, for example, on the website http://private.peterlink.ru/geogod/space/future.htm. Only there is not a word about carbon tubes.
And at http://www.eunet.lv/library/win/KLARK/fontany.txt you can read Arthur C. Clarke’s novel “The Fountains of Paradise,” which he himself considered his best work.

http://www.inauka.ru/science/28-08-01/article4805
According to experts, nanotechnology will make it possible by 2007 to create microprocessors that will contain about 1 billion transistors and will be able to operate at frequencies of up to 20 gigahertz with a supply voltage of less than 1 volt.

Nanotube transistor
The first transistor consisting entirely of carbon nanotubes has been created. This opens up the prospect of replacing conventional silicon chips with faster, cheaper and smaller components.
The world's first nanotube transistor is a Y-shaped nanotube that behaves like a conventional transistor - the potential applied to one of the “legs” allows you to control the passage of current between the other two. At the same time, the current-voltage characteristic of the “nanotube transistor” is almost ideal: current either flows or not.

http://www.pool.kiev.ua/clients/poolhome.nsf/0/a95ad844a57c1236c2256bc6003dfba8?OpenDocument
According to an article published May 20 in the scientific journal Applied Physics Letters, IBM specialists have improved transistors based on carbon nanotubes. As a result of experiments with various molecular structures, the researchers were able to achieve the highest conductivity for carbon nanotube transistors to date. The higher the conductivity, the faster the transistor operates and the more powerful integrated circuits can be built on its basis. In addition, the researchers found that the conductivity of carbon nanotube transistors was more than double that of the fastest silicon transistors of the same size.

http://kv.by/index2003323401.htm
The group of UC Berkeley professor Alex Zettl has made another breakthrough in the field of nanotechnology. Scientists have created the first smallest nanoscale motor based on multi-walled nanotubes, as reported in the journal Nature on July 24. The carbon nanotube acts as a kind of axis on which the rotor is mounted. The maximum dimensions of a nanomotor are about 500 nm, the rotor has a length from 100 to 300 nm, but the nanotube-axis has a diameter of only a few atoms, i.e. approximately 5-10 nm.

http://www.computerra.ru/hitech/tech/26393/
The other day, the Boston company Nantero made a statement about the development of memory boards of a fundamentally new type, created on the basis of nanotechnology. Nantero Inc. is actively engaged in the development of new technologies, in particular, pays considerable attention to finding ways to create non-volatile random access memory (RAM) based on carbon nanotubes. In his speech, a company representative announced that they are one step away from creating memory boards with a capacity of 10 GB. Due to the fact that the structure of the device is based on nanotubes, the new memory is proposed to be called NRAM (Nonvolatile (non-volatile) RAM).

http://www.ixs.nm.ru/nan0.htm
One of the results of the research was the practical use of the outstanding properties of nanotubes to measure the mass of extremely small particles. When the particle being weighed is placed at the end of the nanotube, the resonant frequency decreases. If the nanotube is calibrated (that is, its elasticity is known), the mass of the particle can be determined from the shift in the resonant frequency.

http://www.mediacenter.ru/a74.phtml
Among the first commercial applications will be the addition of nanotubes to paints or plastics to make these materials electrically conductive. This will make it possible to replace metal parts with polymer ones in some products.
Carbon nanotubes are an expensive material. CNI currently sells it for $500 per gram. In addition, the technology for purifying carbon nanotubes - separating the good tubes from the bad - and the way the nanotubes are introduced into other products require improvement. Solving some problems may require Nobel-level discoveries, says Joshua Wolf, managing partner at nanotechnology venture capital firm Lux Capital.

Researchers became interested in carbon nanotubes because of their electrical conductivity, which was higher than that of any known conductor. They also have excellent thermal conductivity, are chemically stable, have extreme mechanical strength (1000 times stronger than steel) and, most amazingly, acquire semiconducting properties when twisted or bent. To work, they are shaped into a ring. The electronic properties of carbon nanotubes can be like those of metals or like semiconductors (depending on the orientation of the carbon polygons relative to the axis of the tube), i.e. depend on their size and shape.

http://www.ci.ru/inform09_01/p04predel.htm
Metallic conductive nanotubes can withstand current densities 102-103 times higher than conventional metals, and semiconducting nanotubes can be electrically turned on and off via a field generated by an electrode, allowing the creation of field-effect transistors.
IBM scientists developed a method called "constructive destruction" that allowed them to destroy all metal nanotubes while leaving semiconductor ones intact.

http://www.pr.kg/articles/n0111/19-sci.htm
Carbon nanotubes have found another application in the fight for human health - this time, Chinese scientists used nanotubes to purify drinking water from lead.

http://www.scientific.ru/journal/news/n030102.html
We regularly write about carbon nanotubes, but there are actually other types of nanotubes made from a variety of semiconductor materials. Scientists are able to grow nanotubes with precisely specified wall thickness, diameter and length.
Nanotubes can be used as nanotubes for transporting liquids, and they can also act as tips for syringes with a precisely controlled number of nanodroplets. Nanotubes can be used as nanodrills, nanotweezers, and tips for scanning tunneling microscopes. Nanotubes with sufficiently thick walls and a small diameter can serve as supporting supports for nanoobjects, while nanotubes with a large diameter and thin walls can serve as nanocontainers and nanocapsules. Nanotubes made from silicon-based compounds, including silicon carbide, are especially good for making mechanical products because these materials are strong and elastic. Solid-state nanotubes can also find application in electronics.

http://www.compulenta.ru/2003/5/12/39363/
The research division of IBM Corporation announced an important achievement in the field of nanotechnology. IBM Research specialists managed to make carbon nanotubes glow, an extremely promising material that underlies many nanotechnological developments around the world.
The light-emitting nanotube has a diameter of only 1.4 nm, that is, 50 thousand times thinner than a human hair. This is the smallest solid-state light-emitting device in history. Its creation was the result of a program studying the electrical properties of carbon nanotubes conducted at IBM over the past several years.

http://bunburyodo.narod.ru/chem/solom.htm
In addition to the creation of metal nanowires already mentioned above, which is still very far from being realized, the development of so-called cold emitters on nanotubes is popular. Cold emitters are a key element of the flat-panel TV of the future; they replace the hot emitters of modern cathode ray tubes, and also make it possible to get rid of the gigantic and unsafe acceleration voltages of 20-30 kV. At room temperature, nanotubes are capable of emitting electrons, producing a current of the same density as a standard tungsten anode at almost a thousand degrees, and even at a voltage of only 500 V. (And to produce X-rays you need tens of kilovolts and a temperature of 1500 degrees (nan))

http://www.pereplet.ru/obrazovanie/stsoros/742.html
The high elastic modulus of carbon nanotubes makes it possible to create composite materials that provide high strength at ultra-high elastic deformations. From such material it will be possible to make ultra-light and ultra-strong fabrics for firefighters and astronauts.
The high specific surface area of ​​nanotube material is attractive for many technological applications. During the growth process, randomly oriented helical nanotubes are formed, which leads to the formation of a significant number of cavities and voids of nanometer size. As a result, the specific surface area of ​​the nanotube material reaches values ​​of about 600 m2/g. Such a high specific surface area opens up the possibility of their use in filters and other chemical technology devices.

http://www.1september.ru/ru/him/2001/09/no09_1.htm
A nanocable from the Earth to the Moon from a single tube could be wound on a reel the size of a poppy seed.
Nanotubes are 50-100 times stronger than steel (although nanotubes are six times less dense). Young's modulus - a characteristic of a material's resistance to axial tension and compression - is on average twice as high for nanotubes as for carbon fibers. The tubes are not only durable, but also flexible; their behavior resembles not brittle straws, but hard rubber tubes.
A thread with a diameter of 1 mm, consisting of nanotubes, could withstand a load of 20 tons, which is several hundred billion times its own mass.
An international group of scientists has shown that nanotubes can be used to create artificial muscles, which, with the same volume, can be three times stronger than biological ones, and are not afraid of high temperatures, vacuum and many chemical reagents.
Nanotubes are an ideal material for safely storing gases in internal cavities. First of all, this applies to hydrogen, which would have long been used as a fuel for cars, if bulky, thick-walled, heavy and unsafe hydrogen storage cylinders had not deprived hydrogen of its main advantage - a large amount of energy released per unit mass ( only about 3 kg of H2 is required for 500 km of vehicle mileage). The “gas tank” with nanotubes could be filled stationary under pressure, and the fuel could be removed by slightly heating the “gas tank”. To surpass conventional gas cylinders in terms of mass and volumetric density of stored energy and (the mass of hydrogen divided by its mass together with the shell or its volume together with the shell), nanotubes with cavities of a relatively large diameter are needed - more than 2-3 nm.
Biologists were able to introduce small proteins and DNA molecules into the cavity of nanotubes. This is both a method for producing a new type of catalysts and, in the future, a method for delivering biologically active molecules and drugs to certain organs.

Structure and classification of nanotubes

Carbon nanotubes

Carbon nanotubes(carbon nanotubes, CNTs) are molecular compounds belonging to the class of allotropic modifications of carbon. They are extended cylindrical structures with a diameter from one to several tens of nanometers and a length from one to several microns.

Figure 8. Carbon nanotube

Nanotubes consist of one or more layers rolled into a tube, each of which represents a hexagonal network of graphite (graphene), the basis of which is hexagons with carbon atoms located at the vertices of the corners. In all cases, the distance between layers is 0.34 nm, that is, the same as between layers in crystalline graphite.

The upper ends of the tubes are closed with hemispherical caps, each layer of which is composed of hexagons and pentagons, reminiscent of the structure of half a fullerene molecule.

It is believed that the discoverer of carbon nanotubes is an employee of the Japanese NEC corporation, Sumio Iijima, who in 1991 observed the structures of multi-walled nanotubes while studying under an electron microscope the sediments that formed during the synthesis of molecular forms of pure carbon with a cellular structure.

An ideal nanotube is a graphite plane rolled into a cylinder, i.e. a surface lined with regular hexagons, at the vertices of which carbon atoms are located.

The parameter indicating the coordinates of the hexagon, which, as a result of folding the plane, should coincide with the hexagon located at the origin of coordinates, is called the chirality of the nanotube. The chirality of a nanotube determines its electrical characteristics.

As observations made using electron microscopes have shown, most nanotubes consist of several graphite layers, either nested one inside the other or wound on a common axis.

Single-walled nanotubes(single-walled nanotubes, SWNTs) are the simplest type of nanotubes. Most of them have a diameter of about 1 nm with a length that can be many thousands of times greater.

Figure 9. Model of a single-walled nanotube.

Such a tube ends with hemispherical vertices containing, along with regular hexagons, also six regular pentagons.

The structure of single-walled nanotubes observed experimentally differs in many respects from the idealized picture presented above. First of all, this concerns the vertices of the nanotube, the shape of which, as follows from observations, is far from an ideal hemisphere.

Figure 10. Cross-sectional models of multiwalled nanotubes

Multiwalled nanotubes differ from single-walled nanotubes in a much wider variety of shapes and configurations, both in the longitudinal and transverse directions. Possible types of transverse structure of multiwalled nanotubes are presented in Figure 10.

The “Russian dolls” type structure is a collection of single-walled nanotubes coaxially nested within each other. ( Figure 10 a). The last of the structures shown (Figure 10 b) resembles a scroll. For the above structures, the distances between adjacent graphite layers are close to 0.34 nm, i.e. the distance between adjacent planes of crystalline graphite. The implementation of a particular structure in a specific experimental situation depends on the conditions for the synthesis of nanotubes. 2.2 Preparation of carbon nanotubes

The most common methods for synthesizing nanotubes are electric arc method, laser ablation and chemical vapor deposition (CVD).

Arc discharge - The essence of this method is to obtain carbon nanotubes in an arc discharge plasma burning in a helium atmosphere in technological installations for the production of fullerenes. However, other arc combustion modes are used here: low arc discharge current densities, higher helium pressure (~ 500 Torr), larger diameter cathodes. To obtain the maximum number of nanotubes, the arc current must be 65-75 A, voltage - 20-22 V, electron plasma temperature - about 4000 K. Under these conditions, the graphite anode intensively evaporates, delivering individual atoms or pairs of carbon atoms, of which the cathode or on the water-cooled walls of the chamber and carbon nanotubes are formed.

To increase the yield of nanotubes in sputtering products, a catalyst (a mixture of iron group metals) is introduced into the graphite rod, the pressure of the inert gas and the sputtering mode are changed.

The content of nanotubes in the cathode deposit reaches 60%. The resulting nanotubes, up to 40 microns in length, grow from the cathode perpendicular to its surface and are combined into cylindrical bundles with a diameter of about 50 nm.

A typical diagram of an electric arc installation for the production of material containing nanotubes and fullerenes, as well as other carbon formations, is shown in Figure 11.

Figure 11. Scheme of the installation for producing nanotubes using the electric arc method.

The laser ablation method was invented by Richard Smalley and employees at Rice University and is based on the evaporation of a graphite target in a high-temperature reactor. Nanotubes appear on the cooled surface of the reactor as graphite evaporation condensate. A water-cooled surface can be included in a nanotube collection system. The product yield in this method is about 70%. It is used to produce predominantly single-walled carbon nanotubes with a diameter controlled by the reaction temperature. However, the cost of this method is much more expensive than others.

Chemical vapor deposition (CVD) - a method of catalytic deposition of carbon vapor was discovered back in 1959, but until 1993 no one imagined that nanotubes could be obtained in this process.

Figure 12. Diagram of the installation for producing nanotubes by chemical deposition.

Fine metal powder (most often nickel, cobalt, iron or combinations thereof) is used as a catalyst, which is poured into a ceramic crucible located in a quartz tube. The latter, in turn, is placed in a heating device that allows maintaining a controlled temperature in the range from 700 to 1000°C. A mixture of hydrocarbon gas and buffer gas is purged through a quartz tube. Typical composition of a mixture of C 2 H 2: N 2 in a ratio of 1:10. The process can last from several minutes to several hours. Long carbon filaments and multiwalled nanotubes up to several tens of micrometers in length with an internal diameter of 10 nm and an external diameter of 100 nm grow on the surface of the catalyst. The diameter of nanotubes grown in this way depends on the size of the metal particles.

This mechanism is the most common commercial method for producing carbon nanotubes. Among other methods for producing nanotubes, CVD is the most promising on an industrial scale due to the best ratio in terms of unit price. In addition, it allows the preparation of vertically oriented nanotubes on the desired substrate without additional collection, as well as controlling their growth through a catalyst.

Broad prospects for the use of nanotubes in materials science open up when superconducting crystals (for example, TaC) are encapsulated inside carbon nanotubes. The possibility of obtaining superconducting crystals encapsulated in nanotubes makes it possible to isolate them from the harmful effects of the external environment, for example, from oxidation, thereby opening the way to more efficient development of corresponding nanotechnologies.

The large negative magnetic susceptibility of nanotubes indicates their diamagnetic properties. It is assumed that the diamagnetism of nanotubes is due to the flow of electron currents around their circumference. The magnitude of the magnetic susceptibility does not depend on the orientation of the sample, which is associated with its disordered structure.

Many technological applications of nanotubes are based on their property of high specific surface area (in the case of a single-walled nanotube, about 600 sq. m per 1/g), which opens up the possibility of their use as a porous material in filters, etc.

Nanotube material can be successfully used as a supporting substrate for heterogeneous catalysis, and the catalytic activity of open nanotubes significantly exceeds the corresponding parameter for closed nanotubes.

It is possible to use nanotubes with a high specific surface area as electrodes for electrolytic capacitors with high specific power. Carbon nanotubes have proven themselves well in experiments using them as a coating that promotes the formation of a diamond film.

Such properties of a nanotube as its small size, which varies significantly depending on the synthesis conditions, electrical conductivity, mechanical strength and chemical stability, allow us to consider the nanotube as the basis for future microelectronic elements.

Nanotubes can serve as the basis for extremely thin measuring instruments used to monitor surface irregularities in electronic circuits.

Interesting applications can be obtained by nanotubes when filled with various materials. In this case, the nanotube can be used both as a carrier of the material filling it, and as an insulating shell that protects this material from electrical contact or from chemical interaction with surrounding objects.

Stronger than a radial tire? All indications are that the emergence of TUBALL carbon nanotubes in the tire industry will create an even greater technical revolution than the emergence of silicon in the 90s, and will compare with the discovery of the radial tire after the war. Even a small number of these amazingly small tubes with a diameter of one nanometer (1 billionth of a meter), with walls just one (!) carbon atom thick, can improve the performance of any rubber on an incredible scale. The history of this invention, born in the very heart of Siberia, is as grandiose as it is original.

In 1945, a nuclear bomb was used for the first time in history. It was then that people learned that matter is a storehouse of enormous energy. At that stage, the main difficulty turned out to be - correct energy extraction. It is the need to work with carbon nanotubes at the atomic level that makes them both unusual in their characteristics and difficult to synthesize.

So as not to die an idiot...

Going into such advanced technology with minimal knowledge is a guarantee that you will not understand anything about this research, even if you think you know what carbon is. Probably more than 500,000 years ago, our ancestors began using it for heating or cooking with charcoal. Approximately 3 centuries ago, the beginning of the use of coal (stone) and the steam engine marked the advent of the industrial era. However, this prehistoric period in the history of carbon has nothing to do with modern nanochemistry...

Broadly speaking, everything that grows and lives on earth depends on carbon. And man, who is 65% water, 3% nitrogen, 18% carbon and 10% hydrogen, is a perfect example of this. In nature, there are more than a million compounds made from a combination of carbon and hydrogen; we should not forget that after coal, the main source of energy for us is hydrocarbons: in general, it is not so easy to do without irreplaceable carbon.

In its natural state, it has only two crystalline and very different forms: diamond and graphite. The first is a prestigious, extremely rare and hard material, the second is a greasy to the touch, a much less exclusive type of carbon, mined in a volume of approximately one and a half million tons per year. Few people know that a diamond over time (a very long period!) breaks down into graphite, which is ultimately the most stable form of carbon. We are very familiar with this black or gray mineral; it is worth remembering, for example, Chinese ink or pencil lead. Today, among other things, graphite helps ensure the safety of nuclear power plants and also gives us millions of electric batteries. It is he who is the indisputable ancestor of all forms of structures from carbon atoms that man will subsequently create.

From a micrometer...

Such beneficial lubricating properties of graphite, which is reminiscent in its structure of carbon “yarrow” or “thousand-layer,” are due to the ease with which the layers slide over each other. These flat and extremely thin layers are shaped like a “honeycomb”, which consists of tightly packed hexagonal rings, the top of each of which is a carbon atom bonded to three of its neighbors. There are even layers one atom thick! This special structure makes it easier (everything is relative!) to access the carbon atoms. The enormous potential of graphite has long been known, but the use of all the positive qualities of graphite is hampered by a number of problems that arise when working with graphite at the atomic level. The first pitfall is that it will be possible to clearly see such structures only after the advent of new powerful electron microscopes with high resolution.

Initially, chemists viewed carbon through the ease with which it was converted into fiber. By connecting long and flat microcrystals and aligning them along parallel lines, it is possible to synthesize fibers with a diameter of 5-10 microns. An assembly of 1, 3, 6, 12, 24, 48 thousand of these carbon fibers depending on the type of use for which they were intended,
helps synthesize surprisingly strong threads, despite their weightlessness. In an effort to rebuild the war-damaged textile industry, the Japanese began developing carbon fiber in 1959. The first research center would later become Toray, which is still one of the world's largest companies.

A quick overview of the exceptional properties of single-walled nanotubes: they conduct better than copper, are five times lighter and 100 times stronger than steel, are a million times longer than their diameter, and 1 gram of developed surface area covers the area of ​​2 basketball courts!

These new fibers were not entirely suitable for traditional textiles, but given their exceptional mechanical properties, they were quickly appreciated by the military and aviation industries. Today, the latest generation of civil aircraft consists of more than 50% carbon fiber, and the A380 would not be able to fly at all without its help... And wherever efficiency and low weight are required - sporting goods, sailboats and racing cars, prosthetics, etc. .d. – it is no longer possible to do without carbon fiber.

...to the nanometer

However, we had to wait until 1985, when man created the third crystalline form of carbon, this time completely artificial - fullerenes. The scale changes radically and a dive into the depths of infinitely small quantities begins; the micron of fiber is replaced by a nanometer. The prefix "nano" ("nein" in Greek) means 1 billionth of a meter. When you play with atoms on the nanometer scale, you have to divide the micron measurements by 1,000! The discovery of fullerenes occurred in the laboratory, when astrophysicists tried to find an answer to the question about the nature of the origin of long carbon-containing chains discovered in space.

Using their knowledge of molecules confined to two-dimensional flat layers of graphite, chemists were able to create new 3-D molecules that were still 100% carbon, but took on more varied and interesting shapes: spheres, ellipsoids, tubes, rings, etc. d. What method of creation was used? Evaporation of a graphite disk in a neutral environment by laser ablation under very specific conditions. The idea itself, as well as its implementation, is not within the capabilities of everyone... This was officially recognized in 1996, when the Nobel Prize in Chemistry was awarded to the Anglo-American team of inventors consisting of Kroto, Curl, Smalley. And it was fair.

The very first product obtained using this generation method initially had the shape of a soccer ball! Just like the ball, the structure was divided into 20 hexagons, and just like graphite, it was connected to 12 pentagons. This structure, called C60, is just 0.7 nanometers thick and has an internal space of just one nanometer, which is 200 million times smaller than a real soccer ball! However, it is precisely this feature, associated with the Anglo-Saxon culture of the research team, that will lead to the assignment of a very original name to the product. In honor of the architect Buckminster Fuller, the inventor of geodesic spheres, C60 was called “futballene” for some time, then became the first buckminsterfullerene, and was later shortened (fortunately!) to fullerene.

After the door to the creation of an innovative material was opened, the process began: numerous research groups rushed to obtain fullerenes, inventing various methods for its synthesis. A wide variety of fullerene forms began to appear, more effective than the previous ones, with qualities as varied as they were outstanding! It is now believed that there are more than 250,000 types of fullerons (and that's not the end!), which can be useful in any industry: pharmaceuticals, cosmetics, electronics, photovoltaics, lubricants, etc. After money, nanoparticles are the most used things in the world.

And then nanotubes and, finally, graphene appear.

Following C60, it was possible to obtain “footballs” of 70, 76, 84, 100, 200 atoms, and even 20, and this was just the beginning. Under the influence of temperature, carbon molecules divide (you just have to learn how to do this), and their constituent atoms are reunited in an infinite variety of forms, and it seems that any configuration is possible. Balls, megatubes, nanotubes, dimers, polymers, nanobulbs, etc., the huge family of fullerenes is constantly growing, but it is small nanotubes that remain the main hope for serious industrial development to this day.

If 1959 and 1985 are the generally accepted birth dates for carbon fiber and fullerenes, then nanotubes appeared somewhere between 1991 and 1993. In 1991, the discoverer, the Japanese Sumio Iijima (NEC), during his research on the synthesis of fullerenes, obtained the first multi-walled nanotubes, the number of graphene layers in which ranged from 2 to 50. He received them again in 1993, but now these are nanotubes with one wall, and at the same time Donald S. Bethune, IBM, achieves this, each in his own way.

At this stage of the modern history of carbon, a material appears that forms the walls of a single wall nanotube, that is, graphene. This is the famous two-dimensional crystal, with a flat honeycomb-shaped layer and only one atom thick, the layering of which forms graphite. In fact, what seemed simple, given its natural origin, was not so, so we had to wait until 2004, when the Dutchman André Geim was able to isolate this carpet (or rather mesh?) one atom thick in one original way. He used duct tape to peel off the matter layer by layer until he had a layer 1 atom thick. Of course, other methods for producing graphene were discovered, but for this, Game shared the Nobel in 2010 with Konstantin Novoselov, a Briton of Russian origin who, like him, worked in the UK.

From a generally accepted point of view, graphene will revolutionize our lives in the future. According to some, this is a technological shock comparable in scope to the transition from the Bronze Age to the Iron Age! Graphene, which is both flexible and elastic, conducts electricity better than copper. Colorless graphene is 6 times lighter than steel and 100 or even 300 times stronger. This unique guy can do anything: despite his size, he can enhance almost everything. It is 1 million times thinner than a hair - 3 million layers of graphene stacked together, no thicker than 1 mm. However, the entire planet, starting with Europe, is spending billions to learn how to synthesize such layers to the required size at reasonable prices. Unfortunately, not everyone has managed to achieve this yet!

Single wall nanotube

In the meantime, the launch of the serial synthesis of graphene has not been established, another form of fullerene with graphene walls has begun to gain momentum: a nanotube. Initially, Iijima obtained it using two graphite electrodes: when an electric current creates a plasma of 6000 ° C: the anode (+) evaporates, and a blackish deposit is formed on the cathode (-), that is, nanotubes. In addition to this method of “sputtering in arc discharge plasma,” there are others: at high and medium temperatures, in a gaseous state. The results are different, although, immediately after their release, the carbon atoms immediately begin to reunite, forming bizarre shapes. Thus, most of the synthesized nanotubes, as heirs of the fullerene family, are “closed” at the ends with one or two hemispherical caps. These “soccer ball halves” can be kept or removed to open up the tube at both ends and fill it with other products and make it even more interesting.

Multiwall nanotubes (MW, multiwall) resemble Russian nesting dolls in their structure: many tubes of decreasing diameter, twisted into each other, or a single layer twisted around itself, like a scroll. There are also gaps, holes in cellular or other structures with 5 or 7 sides, and sometimes impurities, deposits from metal catalysts, which cannot be avoided in this operation: then, before using such nanotubes, their purification or restoration is required. Single wall (SW, single wall) can also have very different structures (helical or not), which gives them a great advantage in terms of mechanical or electrical characteristics and gives them the properties of a conductor or semiconductor, etc.

Mastering the method of nanotube synthesis is not a journey along a long and calm river, but an extremely complex process that involves working with a very small volume of substance at a high level of cost. There are still a lot of difficulties, and getting around them is still very difficult. This became clear in 2013, when the chemical giant Bayer lost a lot of money by closing, just three years after opening, its plant in Leverkusen for the synthesis of 200 tons of nanotubes in year. It appears that this decision was driven by technical (carbon fiber and Kevlar are still in use) and commercial competition, as well as an overestimation of demand, both in terms of its volume and growth rate.

OCSiAl, child of the silicon taiga

Like many great modern inventions with multiple creators, the discovery of nanotubes is not solely due to Iijima and Bethune. Many teams worked on this issue, sometimes they did not even know each other and used different methods. A closer look at the history of the issue indicates that in 1952, Soviet scientists Radushkevich and Lukyanovich were already conducting research on 50 nanometer tubes, and in 1976 Oberlin, Endo and Koyama were investigating hollow fibers and single wall carbon nanotubes (single wall nano carbon tubes, abbreviated as SWCNT). In 1981, Soviet scientists imaged curling graphene, single-walled tubes in the 0.6 to 6 nm range.

The Cold War and the protection of industrial secrets slowed the spread of information about nanotubes, which explains the emergence of OCSiAl, a Russian firm based in Akademgorodok, a research town 20 km from Novosibirsk, in the heart of Siberia, on the world market. It was conceived and created in 1957 by Academician Lavrentyev, Doctor of Physical and Mathematical Sciences. Nikita Khrushchev patronized the creation of the best living and working conditions for the elite of Soviet science. Abandoned due to the collapse of the USSR, Academy Town was later reborn in a new, more modern and capitalist form. This city of 60,000 inhabitants is today home to world-class startups. In 2006, a new technology park was created there. The dynamics, creativity and high concentration of advanced enterprises allow us to call Academy Town the “Silicon Taiga” - by analogy with the Silicon Valley of California...

The name OCSiAl itself is a hint at the chemical symbols of the main elements with which the company works: O – oxygen, C6 – carbon with its atomic number 6, Si – silicon, Al – aluminum.

Three Musketeers OCSiAl

As tradition requires, there were four musketeers who founded OCSiAl! Even if officially Mikhail Predtechensky is only the Senior Vice President, the author of the synthesis technology, he is still a key figure of the company and a man of the future. It was this scientist and inventor who was able to develop a “plasmochemical” reactor capable of synthesizing single-walled carbon nanotubes of the highest quality in large volumes, and, therefore, at market prices, which no one has ever managed before. This scientist, the bearer of the most advanced technology, was joined by three other co-founders, financiers and managers of the same high level: Yuri Igorevich Koropachinsky, Oleg Igorevich Kirilov and now living in Israel Yuri Zelvensky. They were able to identify the global market potential (estimated at $3 billion!) and raise the $350 million required to found OCSiAl in 2009, and then in 2013 they registered patents and built a “Graphetron 1.0” reactor capable of synthesizing 10 tons of single-walled carbon nanotubes per year.

« Graphetron 1.0 "was put into circulation in 2014. And in 2016, the company already had 260 people on its staff, of which 100 people are scientists of the highest level working in the laboratories of Akademgorodok. The rest of the company's staff are engineers and businessmen who sell branded nanotubes under the TUBALL brand around the world. Initially, to enter all major markets, offices were opened in Columbus, Incheon, Mumbai, Shenzhen, Hong Kong, and Moscow. The company's headquarters are located in Luxembourg. The team consists of specialists of various profiles, since there are a large number of industries (and very diverse ones) whose products can be “stimulated” by TUBALL. Technical and commercial specialists are confident in the quality and wide range of possibilities for using TUBALL. OCSiAl's marketing sets a fairly high target bar for them. In 2017, it is planned to launch a second reactor capable of synthesizing 50 tons per year. Short-term forecasts are exponential, based on 800 tons in 2020 and 3,000 tons in 2022.

And if the first two graphetrons will begin to synthesize 60 tons each in Academgorodok in 2018, then the third should, in theory, appear closer to Europe and its main markets. And since the basic specifications require “a lot of energy and gas,” bets are already being made on the future location: why not Luxembourg, since the company’s headquarters are located here?

Obvious superiority

One might consider such forecasts too optimistic and be afraid of going down the drain, as happened with the Bayer company, but in Luxembourg no one is afraid of this - TUBALL single-walled carbon nanotubes are so superior in their characteristics to multi-walled nanotubes. This is the belief of Cristoph Siara, Director of Marketing and Sales at Ocsial Europe, and Jean-Nicolas Helt, Lead Development and Customer Support, Elastomers, OCSiAl Europe. By the name of Christophe Siara, you wouldn’t even be able to tell that he’s German. Christophe was educated as a lawyer. Living in France since 1983, his career moves from one cutting-edge industry to another have given him the expertise to understand the most complex technologies. When Christophe Ciara talks about nanotubes, he can be mistaken for a real chemist. Engineer Jean-Nicolas Helt is from France. He received his degree in Physics of Environments from the University of Nancy and then from the ESEM of Orléans. Thanks to his excellent education, he was able to join the Goodyear company in Luxembourg. In its 17 years of operation, it can boast of having several major achievements in the tire industry for heavy duty trucks and passenger cars. In 2015, he joined OCSiAl as a project manager and was the one who said that TUBALL nanotubes could bring something valuable to the tire industry.

Christophe Siara explains that the emergence of TUBALL single-walled carbon nanotubes is a significant breakthrough for the industry when compared with their predecessors, multi-walled nanotubes. With a diameter ranging from 25 to 40 nm, consisting of several twisted layers, these multiwalled nanotubes are quite rigid in nature, which has had a negative impact on their mechanical properties. Unlike multi-walled nanotubes, TUBALL single-walled carbon nanotubes are thin, on the order of 1.5 nm, and very long > 5 microns: “They are 3,000 times longer than they are wide, which becomes clearer with this example: this is your garden watering hose 100 meters long!

This means that there is also a linguistic side to the issue, because the names “serpentine”, “noodles”, “hollow and long carbon fiber” look much more suitable than a tube. But still, a nanotube is much simpler!

Other aspects in which TUBALL has no rivals: its 1 nm thick layer is absolutely smooth, amorphous carbon< 10 %, остаточные неорганические примеси (Fer) < 15 % заключены в капсулах, то есть не действуют. В отличие от своих конкурентов TUBALL не требует никакой очистки. Кроме того к отличительным чертам нанотрубок TUBALL можно отнести: содержание углерода >85%, G/D band ratio (Raman spectrometry) > 70, confirming excellent conductivity. All results are confirmed by independent laboratories, one of which is Intertek (May 2014).

Incredible growth and significant improvement in all parameters with a hermetic seal made of synthetic nitrile rubber.

It's all in the process

"Graphetron 1.0" Mikhail Predtechensky is probably one of those machines that will revolutionize the 21st century. We are talking about a reactor capable of processing large volumes using precursors and inexpensive catalysts. How it works? This is an absolute secret that is very well guarded. Christophe Siara and Jean-Nicolas Helt assured with a laugh that they knew nothing about this and would never know. And the very first of all the employment papers that they signed, like all the staff, was a non-disclosure agreement! " Graphetron 1.0 "are going to be shown during a scientific conference in November, but we bet it won't give us anything. But most importantly, it allows for a continuous flow of synthesis of high-quality single-walled carbon nanotubes at reasonable prices. It is estimated that these annual 10 tons represent 90% of the global synthesis of single-walled nanotubes today. Starting in 2017, the company plans to begin synthesizing 50 tons more nanotubes!

Prices for TUBALL products? – It’s forbidden to talk about this. Trade secret. Only the company's brochures reveal it: there is a feeling that this is very far from the correct estimates, but at least it gives an idea of ​​​​the approximate cost of nanotubes: shipping from Novosibirsk costs 8 US dollars per gram for a small order volume, 2 US dollars for large order. OCSiAl modestly assures that it has reduced the price by at least 25 times.

This frantic race to increase production volumes is explained by the versatility of TUBALL. OCSiAl sells not just carbon nanotubes, but an almost universal additive capable of providing explosive growth in the characteristics of approximately 70% of useful materials on our planet.

Versatile additive, incredible performance

Mentioning the properties of TUBALL is practically the same as doing the splits: the further you dive into depths that are visible only under a microscope, the higher you get to the heights of efficiency! Let's go over it briefly: its thermal stability remains up to 1,000°C, it is 100 times stronger than steel, and its area exceeds any reasonable understanding: 1 gram of the developed surface of a TUBALL nanotube covers 2 basketball courts, that is, 3,000 m 2 .

All this would be of little use without one additional fundamental property - its amazing dispersibility. Thanks to very thin and long tubes, TUBALL creates numerous networks that invisibly mix with other elements and make them stronger. Thus, some ridiculous volume of TUBALL, from 1/1,000 to 1/10,000 of the total weight, is enough to give the material characteristics an explosive increase. Single Wall Nanotube (SW) is the true SOLUTION to many of the technological breakthroughs of the 21st century.

A small bottle with 1 gram of TUBALL, which the OCSiAl company places in the visitor’s hand so that he can better “evaluate” the product, is a guarantee of 100% success when they begin to talk in detail about its contents: 1015 pieces, that is, 1,000,000,000,000,000 ( one million billion) tubes! If they were placed end to end, the resulting length would be approximately 50 million kilometers!

OCSiAl briefly represents everything that TUBALL is capable of in one diagram in the form of a beautiful flower with numerous petals. By selecting its properties, conductivity, strength, chemical neutrality, transparency, etc., or adding them together, you open up a large number of possible applications. TUBALL is truly the “universal amplifier” that it claims to be.

And to facilitate the use of a conductive additive, TUBALL nanotubes are rarely supplied only in powder form. They are offered in much more convenient options for use: in the form of liquid, polymer, oil, rubber, etc. even in the form of a suspension in solvents. This ensures ease of mixing and dispersing. For example, 50 grams of TUBALL nanotubes dissolved in 50 kg of epoxy resin or polyester immediately provide the materials with conductivity, which is very practical for floors that can even be colored!

Flexibility – safety

Ready-to-use concentrates have another advantage: they ensure safety when working with nanotubes. Their primary form and very small size allow them to reach the very heart of the cells of the human body, so precautions must be taken even if carbon is not toxic to humans. Nanotubes introduced into the matrix cannot evaporate in the atmosphere, which makes their use safe and reassures those who are afraid of carcinogenic effects like asbestos. The World Health Organization (WHO) suggests that nanotubes are similar to fibers. However, the characteristics of TUBALL single-walled carbon nanotubes are very different from the characteristics of multi-walled carbon nanotubes that we mentioned at the very beginning. “To be clear,” summarizes Christophe Ciara, “if multi-walled carbon nanotubes are a golf club, then TUBALL single-walled carbon nanotubes are a sprinkler hose. The solid shape and presence of roughness allow multi-walled carbon nanotubes to enter the cell and attach to it. But at the same time, the hard and inflexible form of multi-walled nanotubes creates a number of problems that can be avoided by using flexible and long single-walled TUBALL nanotubes, which, due to their characteristics, do not penetrate into the cell itself.

OCSiAl is very attentive to the study of this problem, therefore it monitors all research carried out in the world. In particular, since 2008, the company has been overseeing the work of BAuA, a German government institute responsible for developing industrial standards, and, in particular, determining the characteristics of products to ensure the safety of workers. TUBALL was taken in its simplest form - powder, which is purchased by 10% of customers. Nanotubes have received positive results regarding the safety of their use for the environment. There was only one problem: there was no way to clear the air of nanotubes through filtration, because, due to their too small size, they eluded all known materials! In the meantime, the search for a solution is ongoing (they are working on it), OCSiAl does not forget about the precautionary principle, proposing to use the most effective types of protection for the powder form of TUBALL, which in themselves are already mandatory when working with the most dangerous chemical reagents: a mask that covers the entire face, overalls, gloves, boots. For the liquid composition of the substance, glasses, gloves and overalls are enough.

OCSiAl also cares about the integrity of the life cycle of its products. The news is encouraging because, once introduced into a matrix and then into new materials, the nanotubes remain there. Having received every degree of protection from the dangers they may pose, TUBALL nanotubes become a “normal” chemical reagent that is subject to the most stringent regulations recently introduced. Thus, with pleasure, but without much surprise, OCSiAl received REACH certification in October, allowing it to henceforth supply up to 10 tons of nanotubes per year to the European market.

The Great Tire Revolution

Since the very moment tires appeared, all manufacturers have been looking for technologies that could enhance the characteristics of the material. From additives such as clay and talc to carbon, we are still striving to improve tire strength. The emergence of silicon in 1991 completely changed the existing situation on the market. Silicon allows rubber to be given universal proportions that adapt to specific loads. Silicon has become an essential condition for tire performance, but all this is nothing compared to the sharp leap that will occur after TUBALL enters the tire industry.

With more than 17 years of experience at Goodyear, Jean-Nicolas Helt is right on target. The diagram on page 53 shows the dispersion of TUBALL in tire compounds. On the left are two black carbon particles that appear quite isolated in the polymer cube. The central picture shows the results of strengthening a product using multi-walled carbon nanotubes - fairly short, hard and stacked. Looking at the picture you can see that the gain turned out to be quite weak and ineffective. On the right - TUBALL, at a ratio of only 1/1,000 to the total weight, fills the cube 100% with a very dense network of single-walled carbon nanotubes that are tightly intertwined with each other. Thus, this mini-filler has a great reinforcing effect due to the fact that it is highly structured and allows for increased cohesion of the components. In any case, such reinforced connections have a better effect, reducing the mobility of components and, therefore, their wear. It is quite logical that this A 3D network of single-walled carbon nanotubes forms a second skeleton in the tire rubber, allowing it to slow down the wear process. In addition, TUBALL is chemically neutral, so it is more resistant to heat, ultraviolet radiation and hydrocarbon pollution than other starting components.

“Be careful,” says Jean-Nicolas Helt, “TUBALL deals with soot just like silicon. The tire retains its basic characteristics, moreover, when adding even very small quantities of single-walled carbon nanotubes, the characteristics begin to improve significantly. Another advantage of TUBALL is thatthat it is an extremely strong conductor, so it is possible to make a bus cover that is 100% silicon but also 100% conductive of static electricity, rather than having to insulate it. This eliminates the need for a strip of NdC rubber along the equator of premium tires, which releases static electricity into the ground.” This is another significant gain received.

Diagram A. The blue spiders represent the performance of the classic mixture, the pink areas show the gain that can be obtained by adding silicon. Circuits to compare with the following Circuit B, which addresses this problem by adding TUBALL.

Scheme B. The principle is the same as in the previous diagram A, the scale of values ​​is the same. It can be concluded that the pink surfaces showing improved performance with the addition of TUBALL.

Polymers with the addition of TUBALL

TUBALL has the same effect on polymers as on reinforcing fillers. Thus, engineers can easily develop tires “a la carte” by adding one or another polymer, maintaining one or another characteristic, which will not be impaired in any way by the powerful development of other indicators. For example, the shortcomings of some tires on dry or wet surfaces can be compensated for using TUBALL. It will also be a good option for motorcycle tires, as it will simultaneously improve grip and wear. “It can improve anything,” sums up Jean-Nicolas Helt succinctly. But what is the price? Given the negligible volume to add to the mixture (a few thousandths of the total weight) and the reasonable cost of TUBALL, Jean-Nicolas Helt estimates that manufacturing costs will increase from US$2 to US$3 per tire, which is comparatively expensive but manageable for a premium tire , which should be the first to adopt TUBALL, since increasing efficiency comes first for them. And this is absolutely true, because a large number of manufacturers are already looking towards TUBALL, especially after receiving positive results from tests carried out in independent laboratories, for example, in the No. 1 laboratory in the world Smithers. That's when all of OCSiAl's claims were tested and confirmed, including the fact that exceeding the small volumes prescribed by TUBALL does not bring any improvement. “You don’t need to add more than you need,” is the conclusion!

The conclusion also states that dosing TUBALL for mixtures is very simple, since the process itself does not change (mixing, extrusion, cooking, etc.) and you only need to open the TUBALL tank to pour its contents into the Banbury mixer. OCSiAl supplies its TUBALL MATRIX 603 to the market in the form of a ready-to-use concentrate - nanotubes mixed with synthesized rubbers (natural, styrene butadiene, nitrile butadiene, etc.) plus tridecyl alcohol ethoxylate (TDAE) process oil, which most often used for tires. TUBALL also exists in the form of a suspension in a wide range of solvents (MEK, isopropanol, ethylene glycol, ethyl acetate, N-methylpyrrolidone, glycerin or even water). Ideal in terms of safety, these formulations are extremely easy to use.

Simple and ideal to use, this solution can be made even easier by adding TUBALL to the polymer at the moment of its polymerization: no more additional operations are required during mixing! This method of introducing a polymer at the “moment of birth” shifts the problem from the manufacturer to the supplier of the synthesized rubber, but OCSiAl has already thought about this, having begun cooperation with LANXESS. In other words, TUBALL is preparing to enter the tire industry through two doors at once, that is, its progress will go even faster.

Even if the addition of natural rubbers can only occur at the time of mixing, the use of TUBALL will provide excellent prospects even when added directly during the manufacturing process to other synthesized rubbers, isoprene or nitrile butadiene. The latter has made a real leap in the industry, moving to a new level of gasket strength in all areas... Simply put, the market for tires, industrial rubber (latex surgeon gloves switched to using TUBALL), polymers, elastomers, composites, batteries, photovoltaics, flexible screens, magnetic ink, anti-static concrete, paints, ceramics, copper, semiconductors, stained glass, adhesive tapes, etc. – these are all target areas where TUBALL can be applied. And now we better understand all the prospects for the project." Graphetron 50", aimed at providing explosive growth in the characteristics of 70% of existing products in the industry...

Diagram C. The straight line below is the classic mixtures, the green dotted line is the mixtures with the addition of silicon, and the blue transverse line shows the improvement in tire performance when adding TUBALL.

Already competition...

For those who still doubt the benefits available to tire manufacturers when using TUBALL, Jean-Nicolas Helt presents three schemes. The first two are classic “spiders” that compare the performance indicators of three different types of tires - conventional ones, improved thanks to silicon and tires with the addition of TUBALL. The first table (A) visualizes in the form of light pink zones, the breakthrough achieved through the use of silicon is of course important, but is still far from influencing the entire range of tire characteristics.

The second (B) is based on the same principle, but this time, the light pink TUBALL zones take up most of the area, showing a significant increase in performance in almost all parameters. Moreover, the low volumes of material used are surprising: 0.2% in the natural rubber concentrate, 0.1% for the other two, in the form of oil concentrate.

The third scheme (C) has long been known in the specialized press. Two straight lines determine the characteristics of “soot” mixtures (below, dark blue) and the more effective “silicon” indicators, which are highlighted in green dotted lines. The third straight line, which runs clearly from above, visualizes mixtures with the addition of TUBALL - highlighted in blue at the top. The graph clearly shows the benefits provided by single-walled carbon nanotubes.

Some manufacturers are already ready to be proactive by announcing the use of nanocarbon. This does not mean that other manufacturers are not already using nanocarbon, although they are not talking about it... Since the beginning of the year, bicycle tire manufacturer Vittoria has been selling tires with the addition of graphene, the base material for TUBALL nanotubes (return to the beginning of the article if you have already forgotten! ). Vittoria uses it in the form of layers embedded in the tire and claims to have found a hitherto unattainable compromise: simultaneously improving rolling resistance while also achieving puncture resistance, an important characteristic for cyclists. “Improve everything at once,” - now the competition confirms the words of Jean-Nicolas Elt...

The second news came from China, where in August an agreement was concluded between Sentury Tire and Huago on the terms of production of tires with the addition of graphene. We don't know how yet, but in any case, the technology will definitely be different from Vittoria tires. Such news indicates overall progress: rolling resistance and mileage multiplied by 1.5. And then two representatives of the company showed their graphene “firstborn” at a major meeting of carbon specialists “GrapChina” on September 22. At the same time and at the same meeting, the manufacturer Shangdong officially announced that it will now produce tires with the addition of graphene. And all those who use it cite the fact that it was invented by Nobel laureates. This is an argument in the debate that TUBALL cannot claim, even if nanotubes were invented before graphene!

We bet that the number of news of this kind will grow very quickly. 2016 marks the starting point for carbon in the tire industry. And this shift has just begun, and OCSiAl with its nanotubes is at the forefront of this transformation. And this is a process worthy of our attention... For many years to come...

Jean-Pierre Gosselin

Carbon nanotubes CNTs are peculiar cylindrical molecules with a diameter of approximately half a nanometer and a length of up to several micrometers. Carbon nanotubes are hollow, elongated cylindrical structures with a diameter on the order of a few to tens of nanometers; the length of traditional nanotubes is calculated in microns, although in laboratories structures with a length of the order of millimeters and even centimeters are already being obtained. The mutual orientation of the hexagonal graphite network and the longitudinal axis of the nanotube determines a very important...

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INTRODUCTION

Nowadays, technology has reached such a level of perfection that microcomponents are becoming less and less used in modern technology, and are gradually being replaced by nanocomponents. This confirms the trend towards greater miniaturization of electronic devices. There is a need to master a new level of integration - the nanolevel. As a result, there was a need to produce transistors and wires with sizes in the range from 1 to 20 nanometers. The solution to this problem was in 1985. the discovery of nanotubes, but they began to be studied only since 1990, when they learned to produce them in sufficient quantities.

Carbon nanotubes (CNTs) are peculiar cylindrical molecules

with a diameter of approximately half a nanometer and a length of up to several micrometers. These polymer systems were first discovered as by-products of the synthesis of fullerene C 60 . However, electronic devices of nanometer (molecular) size are already being created based on carbon nanotubes. It is expected that in the foreseeable future they will replace elements of a similar purpose in the electronic circuits of various devices, including modern computers.

1. The concept of carbon nanotubes

In 1991, Japanese researcher Izhima was studying the deposit formed on the cathode when graphite is sputtered in an electric arc. His attention was attracted by the unusual structure of the sediment, consisting of microscopic threads and fibers. Measurements made using an electron microscope showed that the diameter of such threads does not exceed several nanometers, and the length is from one to several microns. Having managed to cut a thin tube along the longitudinal axis, the scientists discovered that it consists of one or several layers, each of which is a hexagonal graphite network, the basis of which is made up of hexagons with carbon atoms located at the vertices of the corners. In all cases, the distance between layers is 0.34 nm, that is, the same as between layers in crystalline graphite. As a rule, the upper ends of the tubes are closed with multilayer hemispherical caps, each layer of which is composed of hexagons and pentagons, reminiscent of the structure of half a fullerene molecule.

Extended structures consisting of folded hexagonal networks with carbon atoms at the nodes are called nanotubes. The discovery of nanotubes has aroused great interest among researchers involved in the creation of materials and structures with unusual physicochemical properties.

Carbon nanotubes are hollow, elongated cylindrical structures with a diameter on the order of a few to tens of nanometers (the length of traditional nanotubes is measured in microns, although structures on the order of millimeters and even centimeters in length are already being produced in laboratories).

An ideal nanotube is a cylinder obtained by rolling up a flat hexagonal mesh of graphite without seams.The mutual orientation of the hexagonal graphite network and the longitudinal axis of the nanotube determines a very important structural characteristic of the nanotube, which is called chirality. Chirality is characterized by two integers ( m, n ), which indicate the location of the grid hexagon that, as a result of folding, should coincide with the hexagon located at the origin.

This is illustrated in Fig. 1.1, which shows part of a hexagonal graphite network, the rolling of which into a cylinder leads to the formation of single-walled nanotubes with different chirality. The chirality of a nanotube can also be uniquely determined by the angle a formed by the direction of folding of the nanotube and the direction in which neighboring hexagons share a common side. These directions are also shown in Fig. 1.1. There are many options for folding nanotubes, but among them, those that do not result in distortion of the structure of the hexagonal network stand out. These directions correspond to the angles a = 0 and a = 30°, which corresponds to chirality(m, 0) and (2 n, n).

The chirality indices of a single-layer tube determine its diameter D:

where d 0 = 0.142 nm distance between carbon atoms in the hexagonal network of graphite. The above expression allows us to determine its chirality based on the diameter of the nanotube.

Fig.1.1. A model of the formation of nanotubes with different chiralities when a hexagonal graphite network is rolled into a cylinder.

Carbon nanotubes are characterized by a wide variety of shapes. For example, they can be single-walled or multi-walled (single-layer or multi-layer), straight or spiral, long and short, etc.

In Fig. 1.2. and Fig. 1.3 show the model of single-walled carbon nanotubes and the model of multi-walled carbon nanotubes, respectively.

Fig. 1.2. Model of a single-walled carbon nanotube

Fig. 1.3. Model of a carbon multiwall nanotube

Multiwalled carbon nanotubes differ from single-walled carbon nanotubes in a wider variety of shapes and configurations. Possible types of transverse structure of multiwalled nanotubes are shown in Fig. 1.4.a and b. The structure shown in Fig. 1.4.a, received the name of the Russian nesting doll. It consists of single-walled cylindrical nanotubes coaxially nested within each other. The structure shown in Fig. 1.4.b, resembles a rolled up roll or scroll. For all structures considered, the average distance between adjacent layers, as in graphite, is 0.34 nm.

Fig.1.4. Models of the cross section of multiwalled nanotubes: a - Russian nesting doll, b scroll.

As the number of layers increases, deviations from the ideal cylindrical shape become more and more apparent. In some cases, the outer shell takes the shape of a polyhedron. Sometimes the surface layer is a structure with a disordered arrangement of carbon atoms. In other cases, defects in the form of pentagons and heptagons are formed on the ideal hexagonal network of the outer layer of the nanotube, leading to disruption of the cylindrical shape. The presence of a pentagon causes a convex, and a heptagon, a concave bend of the cylindrical surface of the nanotube. Such defects lead to the appearance of curved and spiral-shaped nanotubes, which during the growth process wriggle and twist among themselves, forming loops and other extended structures of complex shape.

Importantly, the nanotubes turned out to be unusually strong in tension and bending. Under the influence of high mechanical stresses, nanotubes do not tear or break, but their structure is simply rearranged. By the way, since we are talking about the strength of nanotubes, it is interesting to note one of the latest studies of the nature of this property.

Researchers at Rice University, led by Boris Jacobson, have found that carbon nanotubes behave as “smart, self-healing structures” (the study was published February 16, 2007 in the journal Physical Review Letters). Thus, under critical mechanical stress and deformation caused by temperature changes or radioactive radiation, nanotubes are able to “repair” themselves. It turns out that in addition to 6-carbon cells, nanotubes also contain five- and seven-atom clusters. These 5/7-atom cells exhibit unusual behavior, moving cyclically along the surface of the carbon nanotube like steamships on the sea. When damage occurs at the site of the defect, these cells take part in “wound healing” by redistributing energy.

In addition, nanotubes demonstrate many unexpected electrical, magnetic, and optical properties, which have already become the objects of a number of studies. A special feature of carbon nanotubes is their electrical conductivity, which turned out to be higher than that of all known conductors. They also have excellent thermal conductivity, are chemically stable and, most interestingly, can acquire semiconductor properties. In terms of electronic properties, carbon nanotubes can behave like metals or semiconductors, which is determined by the orientation of the carbon polygons relative to the tube axis.

Nanotubes tend to stick tightly together, forming arrays consisting of metal and semiconductor nanotubes. Until now, a difficult task is the synthesis of an array of only semiconductor nanotubes or the separation of semiconductor nanotubes from metal ones.

2. Properties of carbon nanotubes

Capillary effects

To observe capillary effects, it is necessary to open the nanotubes, that is, remove the upper part of the cap. Fortunately, this operation is quite simple. One way to remove the caps is to anneal the nanotubes at a temperature of 850° C for several hours in a stream of carbon dioxide. As a result of oxidation, about 10% of all nanotubes become open. Another way to destroy the closed ends of nanotubes is to soak them in concentrated nitric acid for 4.5 hours at a temperature of 240° C. As a result of this treatment, 80% of the nanotubes become open.

The first studies of capillary phenomena showed that there is a connection between the value of the surface tension of the liquid and the possibility of its being drawn into the nanotube channel. It turned out that the liquid penetrates into the nanotube channel if its surface tension is not higher than 200 mN/m. Therefore, to introduce any substances into nanotubes, solvents with low surface tension are used. For example, to introduce nanotubes of some metals into the channel, concentrated nitric acid is used, the surface tension of which is low (43 mN/m). Then annealing is carried out at 400° C for 4 hours in a hydrogen atmosphere, which leads to the reduction of the metal. In this way, nanotubes containing nickel, cobalt and iron were obtained.

Along with metals, carbon nanotubes can be filled with gaseous substances, such as molecular hydrogen. This ability is of great practical importance, because it opens up the possibility of safe storage of hydrogen, which can be used as an environmentally friendly fuel in internal combustion engines.

Electrical resistivity of carbon nanotubes

Due to the small size of carbon nanotubes, it was only in 1996 that it was possible to directly measure their electrical resistivity p using the four-contact method. To appreciate the experimental skill required for this, we will give a brief description of this method. Gold stripes were applied to the polished surface of silicon oxide in a vacuum. Nanotubes 2 x 3 µm long were deposited into the gap between them. Then, four tungsten conductors 80 nm thick were applied to one of the nanotubes selected for measurement, the location of which is shown in Fig. 2. Each of the tungsten conductors had contact with one of the gold strips. The distance between the contacts on the nanotube ranged from 0.3 to 1 μm. The results of direct measurements showed that the resistivity of nanotubes can vary within significant limits from 5.1 10-6 up to 0.8 Ohm/cm. The minimum p value is an order of magnitude lower than that of graphite. Most of the nanotubes have metallic conductivity, and a smaller part exhibits the properties of a semiconductor with a band gap from 0.1 to 0.3 eV.

Fig.2. Scheme for measuring the electrical resistance of an individual nanotube using the four-probe method: 1 - silicon oxide substrate, 2 - gold contact pads, 3 - tungsten conductive tracks, 4 - carbon nanotube.

3.Methods for the synthesis of carbon nanotubes

3.1. Electric arc method

The most widely used method for producing nanotubes is

using thermal spraying of a graphite electrode in plasma

arc discharge burning in a helium atmosphere.

In an arc discharge between the anode and cathode at a voltage of 20-25V, a stabilized direct arc current of 50-100A, an interelectrode distance of 0.5-2 mm and a pressure of He 100-500 Torr, intense sputtering of the anode material occurs. Part of the sputtering products containing graphite, soot, and fullerenes is deposited on the cooled walls of the chamber, while the part containing graphite and multiwalled carbon nanotubes (MWNTs) is deposited on the surface of the cathode. The yield of nanotubes is influenced by many factors.

The most important is the He pressure in the reaction chamber, which in optimal conditions from the point of view of NT production is 500 Torr, and not 100-150 Torr, as in the case of fullerenes. Another equally important factor is the arc current: the maximum LT output is observed at the minimum possible arc current necessary for its stable combustion. Effective cooling of the chamber walls and electrodes is also important to avoid cracking of the anode and its uniform evaporation, which affects the content

NT in the cathode deposit.

The use of an automatic device for maintaining the interelectrode distance at a fixed level helps to increase the stability of arc discharge parameters and enrich the cathode material with nanotubes.

deposit.

3.2.Laser spraying

In 1995, a report appeared on the synthesis of carbon NTs by sputtering a graphite target under the influence of pulsed laser radiation in an atmosphere of inert (He or Ar) gas. The graphite target is placed in a quartz tube at a temperature of 1200 O C, along which the buffer gas flows.

A laser beam focused by a lens system scans the surface

graphite target to ensure uniform evaporation of the target material.

The resulting vapor as a result of laser evaporation enters the stream

inert gas and is carried from the high-temperature region to the low-temperature region, where it is deposited on a water-cooled copper substrate.

Soot containing NT is collected from the copper substrate, the walls of the quartz tube and the back side of the target. Just like in the arc method it turns out

several types of final material:

1) in experiments where pure graphite was used as a target, MWNTs were obtained that had a length of up to 300 nm and consisted of 4-24 graphene cylinders. The structure and concentration of such NTs in the starting material were mainly determined by temperature. At 1200 O All observed NTs did not contain defects and had caps at the ends. When the synthesis temperature is lowered to 900 O C, defects appeared in the NT, the number of which increased with a further decrease in temperature, and at 200 O No NT formation was observed.

2) when a small amount of transition metals was added to the target, SWNTs were observed in the condensation products. However, during the evaporation process, the target was enriched in metal, and the yield of SWNTs decreased.

To solve this problem, they began to use two simultaneously irradiated targets, one of which is pure graphite, and the other consists of metal alloys.

The percentage yield of NT varies dramatically depending on the catalyst. For example, a high yield of NT is obtained on Ni, Co catalysts, a mixture of Ni and Co with other elements. The resulting SWNTs had the same diameter and were combined into bundles with a diameter of 5-20 nm. Ni/Pt and Co/Pt mixtures give high NT yield, while the use of pure platinum results in low SWNT yield. The Co/Cu mixture gives a low yield of SWNTs, and the use of pure copper does not lead to the formation of SWNTs at all. Spherical caps were observed at the ends of SWNTs free of catalyst particles.

As a variation, a method became widespread where focused solar radiation was used instead of pulsed laser radiation. This method was used to obtain fullerenes, and then

modifications to obtain NT. Sunlight, falling on a flat mirror and being reflected, forms a plane-parallel beam incident on a parabolic mirror. At the focal point of the mirror is a graphite boat filled with a mixture of graphite and metal powders. The boat is located inside a graphite tube, which acts as a heat shield. The entire system is placed in a chamber filled with inert gas.

Various metals and their mixtures were taken as catalysts. Depending on the chosen catalyst and inert gas pressure, different structures were obtained. Using a nickel-cobalt catalyst under low buffer gas pressure, the synthesized sample consisted mainly of bamboo-shaped MWNTs. With increasing pressure, SWNTs with a diameter of 1-2 nm appeared and began to dominate; SWNTs were combined into bundles with a diameter of up to 20 nm with a surface free of amorphous carbon.

3.3.Catalytic decomposition of hydrocarbons

A widely used method for producing NT is based on the use of the process of decomposition of acetylene in the presence of catalysts. Particles of metals Ni, Co, Cu and Fe with a size of several nanometers were used as catalysts. A ceramic boat with 20-50 mg of catalyst is placed in a quartz tube 60 cm long, with an internal diameter of 4 mm. A mixture of acetylene C2H2 (2.5-10%) and nitrogen is pumped through the tube for several hours at a temperature of 500-1100 O C. After which the system is cooled to room temperature. In an experiment with a cobalt catalyst, four types of structures were observed:

1) amorphous layers of carbon on catalyst particles;

2) metal catalyst particles encapsulated in graphene layers;

3) threads formed by amorphous carbon;

4) MWNT.

The smallest inner diameter of these MWNTs was 10 nm. The outer diameter of NTs free from amorphous carbon was in the range of 25-30 nm, and for NTs coated with amorphous carbon - up to 130 nm. The length of the NT was determined by the reaction time and varied from 100 nm to 10 μm.

The yield and structure of NT depends on the type of catalyst - replacing Co with Fe gives a lower concentration of NT and the number of defect-free NT is reduced. When using a nickel catalyst, most of the filaments had an amorphous structure; sometimes NTs with a graphitized, defect-free structure were encountered. On a copper catalyst, filaments with an irregular shape and an amorphous structure are formed. The sample contains metal particles encapsulated in graphene layers. The resulting NT and threads take various forms - straight; curved, consisting of straight sections; zigzag; spiral. In some cases, the spiral pitch has a pseudo-constant value.

Currently, there is a need to obtain an array of oriented NTs, which is dictated by the use of such structures as emitters. There are two ways to obtain arrays of oriented NTs: orientation of already grown NTs and growth of oriented NTs using catalytic methods.

It was proposed to use porous silicon, the pores of which are filled with iron nanoparticles, as a substrate for NT growth. The substrate was placed in a buffer gas and acetylene environment at a temperature of 700 O C, where iron catalyzed the process of thermal decomposition of acetylene. As a result, over areas of several mm 2 , perpendicular to the substrate, oriented multilayer NTs were formed.

A similar method is to use anodized aluminum as a substrate. The pores of anodized aluminum are filled with cobalt. The substrate is placed in a flowing mixture of acetylene and nitrogen at a temperature of 800 O C. The resulting oriented NTs have an average diameter of 50.0 ± 0.7 nm with a distance between tubes of 104.2 ± 2.3 nm. The average density was determined to be 1.1x1010 NT/cm 2 . TEM of the nanotubes revealed a well-graphitized structure with a distance between graphene layers of 0.34 nm. It is reported that by changing the parameters and processing time of the aluminum substrate, it is possible to change both the diameter of the NT and the distance between them.

A method that occurs at lower temperatures (below 666 O C) is also described in the articles. Low temperatures during the synthesis process make it possible to use glass with a deposited nickel film as a substrate. The nickel film served as a catalyst for the growth of NTs by vapor deposition in activated plasma with a hot filament. Acetylene was used as a carbon source. By changing the experimental conditions, you can change the diameter of the tubes from 20 to 400 nm and their length in the range of 0.1-50 μm. The resulting MWNTs of large diameter (>100 nm) are straight and their axes are directed strictly perpendicular to the substrate. The observed NT density according to scanning electron microscopy is 107 NT/mm 2 . When the NT diameter becomes less than 100 nm, the predominant orientation perpendicular to the substrate plane disappears. Aligned MWNT arrays can be created over areas of several cm 2 .

3.4.Electrolytic synthesis

The basic idea of ​​this method is to produce carbon NTs by passing an electric current between graphite electrodes located in a molten ionic salt. The graphite cathode is consumed during the reaction and serves as a source of carbon atoms. As a result, a wide range of nanomaterials are formed. The anode is a boat made of highly pure graphite and filled with lithium chloride. The boat is heated to the melting point of lithium chloride (604 O C) in air or in an atmosphere of inert gas (argon). The cathode is immersed in molten lithium chloride and a current of 1-30 A is passed between the electrodes for one minute. During the passage of the current, the part of the cathode immersed in the melt erodes. Next, the electrolyte melt containing particlescarbon, cooled to room temperature.

In order to isolate the carbon particles resulting from cathode erosion, the salt was dissolved in water. The precipitate was isolated, dissolved in toluene and dispersed in an ultrasonic bath. The electrolytic synthesis products were studied using TEM. It was revealed that they

consist of encapsulated metal particles, bulbs and carbon NTs of various morphologies, including spiral and highly curved. Depending

Depending on the experimental conditions, the diameter of nanotubes formed by cylindrical graphene layers ranged from 2 to 20 nm. The length of MWNTs reached 5 μm.

Optimal current conditions were found - 3-5 A. At a high current value (10-30 A), only encapsulated particles and amorphous carbon are formed. At

low current values ​​(<1А) образуется только аморфный углерод.

3.5.Condensation method

In the quasi-free vapor condensation method, carbon vapor is generated by resistive heating of a graphite strip and condenses onto a highly ordered pyrolytic graphite substrate cooled to a temperature of 30 O C in vacuum 10-8 Torr. TEM studies of the resulting films with a thickness of 2–6 nm show that they contain carbon NTs with a diameter of 1–7 nm and a length of up to 200 nm, most of which end in spherical ends. The NT content in the sediment exceeds 50%. For multilayer NTs, the distance between the graphene layers that form them is 0.34 nm. The tubes are located almost horizontally on the substrate.

3.6.Method of structural destruction

This method was developed by researchers at the IBM laboratory. As it was

stated earlier, nanotubes have both metallic and

semiconductor properties. However, for the production of a number of devices based on them, in particular transistors and, further, processors using them, only semiconductor nanotubes are needed. IBM scientists developed a method called “constructive destruction” that allowed them to destroy all metal nanotubes while leaving semiconductor ones intact. That is, they either sequentially destroy one shell at a time in a multi-walled nanotube, or selectively destroy metal single-walled nanotubes.

Here's a brief description of the process:

1. Glued “ropes” of metal and semiconductor tubes are placed on a silicon oxide substrate.

2. A lithography mask is then projected onto the substrate to form

electrodes (metal spacers) on top of the nanotubes. These electrodes

act as on/off switches

semiconductor nanotubes.

3. Using the silicon substrate itself as an electrode, scientists “turn off”

semiconductor nanotubes that simply block the passage of any current through them.

4.Metal nanotubes remained unprotected. A suitable voltage is then applied to the substrate, destroying the metal nanotubes while the semiconductor nanotubes remain isolated. The result is a dense array of intact, functional semiconductor nanotubes - transistors - that can be used to create logic circuits - i.e. processors. Now let's look at these processes in more detail. Different MWNT shells can have different electrical properties. As a result, the electronic structure and electron transfer mechanisms in MWNTs are different. This structural complexity allows the selection and use of only one MWNT shell: the one with the desired properties. The destruction of multi-walled nanotubes occurs in air at a certain power level, through rapid

oxidation of outer carbon shells. During destruction, the current flowing through the MWNT changes in steps, and these steps coincide with the destruction of an individual shell with amazing consistency. By controlling the process of removing the shells one by one, it is possible to create tubes with the desired characteristics of the outer shell, metal or semiconductor. By choosing the diameter of the outer shell, the desired band gap can be obtained.

If “ropes” with single-walled nanotubes are used to create a field-effect transistor, then metal tubes cannot be left in them, since they will dominate and determine the transport properties of the device, i.e. will not allow the field effect to be realized. This problem is also solved by selective destruction. Unlike MWNTs, in a thin “rope” each SWNT can be connected individually to external electrodes. Thus, a “rope” with MWNTs can be represented as independent parallel conductors with a total total conductivity calculated by the formula:

G(Vg) = Gm + Gs(Vg),

where Gm is produced by the metal nanotubes, and Gs is the gate-dependent conductivity of the semiconductor nanotubes.

In addition, multiple SWNTs in a rope are exposed to air, a potentially oxidizing environment, so multiple tubes can be destroyed simultaneously, unlike the case with MWNTs. Finally, single-walled nanotubes in a small “rope” do not protect each other electrostatically as effectively as concentric shells of MWNTs. As a result, the control electrode can be used to effectively reduce electrical current carriers (electrons or

holes) in semiconductor SWNTs in the “rope”. This turns the semiconductor tubes into insulators. In this case, the current-induced oxidation can be directed only to the metallic SWNTs in the “rope.”

The production of semiconductor nanotube arrays is carried out

simple: by placing SWNT “ropes” on an oxidized silicon substrate,

And then a set of current source, ground and insulated electrodes is lithographically placed on top of the “ropes”. The concentration of tubes is pre-selected such that on average only one "rope" short-circuits the source and ground. In this case, no special orientation of nanotubes is required. The bottom gate (the silicon substrate itself) is used to seal the semiconductor tubes, and then excess voltage is applied to break the metal tubes in the "cable" that creates the FET. Using this selective destruction technology, the size of a carbon nanotube can be controlled, allowing nanotubes to be built with predetermined electrical properties that meet the desired performance of electronic devices. Nanotubes can be used as nano-sized wires or active components in electronic devices, such as field-effect transistors. It is clear that, unlike silicon-based semiconductors, which require the creation of aluminum or copper-based conductors to connect the semiconductor elements within the chip, this technology can only use carbon.

Today, processor manufacturers are trying to reduce the length of channels in transistors to increase frequencies. The technology proposed by IBM can successfully solve this problem by using carbon nanotubes as channels in transistors.

4.Practical use of carbon nanotubes

4.1.Field emission and shielding

When a small electric field is applied along the axis of the nanotube, very intense electron emission occurs from its ends. Such phenomena are called field emission. This effect can be easily observed by applying a small voltage between two parallel metal electrodes, one of which is coated with a nanotube composite paste. A sufficient number of tubes will be perpendicular to the electrode, allowing field emission to be observed. One application of this effect is to improve flat panel displays. TV and computer monitors use a controlled electron gun to irradiate a fluorescent screen, which emits light in the desired colors. The Korean corporation Samsung is developing a flat-panel display using electron emission from carbon nanotubes. A thin film of nanotubes is placed on a layer with control electronics and covered on top with a glass plate coated with a layer of phosphor. One Japanese company is using electron emission in lighting vacuum tubes that are as bright as incandescent bulbs but more efficient and longer lasting. Other researchers are using the effect to develop new ways to generate microwave radiation.

The high electrical conductivity of carbon nanotubes means that they will not transmit electromagnetic waves well. Composite plastic with nanotubes may turn out to be a lightweight material that shields electromagnetic radiation. This is a very important issue for the military, developing ideas for digital representation of the battlefield in command, control and communications systems. Computers and electronic devices that are part of such a system must be protected from weapons that generate electromagnetic pulses.

4.2.Fuel cells

Carbon nanotubes can be used to make batteries.

Lithium, which is the charge carrier in some batteries, can be placed

inside the nanotubes. It is estimated that the tube can accommodate one lithium atom for every six carbon atoms. Another possible use of nanotubes is to store hydrogen, which could be used in the design of fuel cells as sources of electrical energy in future cars. A fuel cell consists of two electrodes and a special electrolyte that allows hydrogen ions to pass between them, but does not allow electrons to pass through. Hydrogen is directed to the anode, where it is ionized. Free electrons move to the cathode along the external circuit, and hydrogen ions diffuse to the cathode through the electrolyte, where water molecules are formed from these ions, electrons and oxygen. Such a system requires a source of hydrogen. One possibility is to store hydrogen inside carbon nanotubes. According to current estimates, to be used effectively in this capacity, the tube must absorb 6.5% hydrogen by weight. Currently, only 4% hydrogen by weight has been able to fit into the tube.
An elegant method for filling carbon nanotubes with hydrogen is to use an electrochemical cell. Single-walled nanotubes, shaped like a sheet of paper, make up the negative electrode in the KOH electrolyte solution. The other electrode consists of Ni(OH) 2 . Electrolyte water decomposes to form positive hydrogen ions (H+ ), moving towards the negative electrode made of nanotubes. The presence of hydrogen bound in the tubes is determined by the decrease in the intensity of Raman scattering.

4.3. Catalysts

A catalyst is a substance, usually a metal or alloy, that increases the rate of a chemical reaction. For some chemical reactions, carbon nanotubes are catalysts. For example, multiwalled nanotubes with externally bound ruthenium atoms have a strong catalytic effect on the hydrogenation reaction of cinnamaldehyde (C 6 N 5 CH=CHCHO) in the liquid phase compared to the effect of the same ruthenium located on other carbon substrates. Chemical reactions were also carried out inside carbon nanotubes, for example, the reduction of nickel oxide NiO to metallic nickel and A l C1 3 to aluminum. Hydrogen gas flow H 2 at 475°C partially reduces Mo O 3 to Mo O 2 with the accompanying formation of water vapor inside multiwalled nanotubes. Cadmium sulfide crystals CdS are formed inside nanotubes by the reaction of crystalline cadmium oxide CdO with hydrogen sulfide (H 2 S) at 400°C.

4.4.Chemical sensors

It has been established that a field-effect transistor made on a semiconducting chiral nanotube is a sensitive detector of various gases. The field-effect transistor was placed in a 500 ml vessel with power supply terminals and two valves for the input and output of gas flowing around the transistor. Flow of gas containing 2 to 200 ppm N O2 , at a rate of 700 ml/min for 10 minutes led to a threefold increase in the conductivity of the nanotube. This effect is due to the fact that upon binding N O2 with a nanotube, charge is transferred from the nanotube to the N group O2 , increasing the concentration of holes in the nanotube and its conductivity.

4.5.Quantum wires

Theoretical and experimental studies of the electrical and magnetic properties of nanotubes have revealed a number of effects that indicate the quantum nature of charge transfer in these molecular wires and can be used in electronic devices.

The conductivity of an ordinary wire is inversely proportional to its length and directly proportional to the cross section, but in the case of a nanotube it does not depend on its length or its thickness and is equal to the conductivity quantum (12.9 kOhm 1 ) - the limiting value of conductivity, which corresponds to the free transfer of delocalized electrons along the entire length of the conductor.

At ordinary temperatures, the observed value of the current density (107 A(cm2)) is two orders of magnitude higher than the currently achieved current density in

superconductors.

A nanotube that is in contact with two superconducting electrodes at temperatures around 1 K becomes a superconductor itself. This effect is due to the fact that Cooper electron pairs formed

in superconducting electrodes, do not disintegrate when passing through

nanotube.

At low temperatures, a stepwise increase in current (conductivity quantization) was observed on metal nanotubes with increasing bias voltage V applied to the nanotube: each step corresponds to the appearance of the next delocalized level of the nanotube in the gap between the Fermi levels of the cathode and anode.

Nanotubes have pronounced magnetoresistance: electrical conductivity strongly depends on the magnetic field induction. If an external field is applied in the direction of the nanotube axis, noticeable oscillations of electrical conductivity are observed; if the field is applied perpendicular to the LT axis, then its increase is observed.

4.6.LEDs

Another application of MWNTs is the production of LEDs based on organic materials. In this case, the following method was used for their manufacture: NT powder was mixed with organic elements in toluene and irradiated with ultrasound, then the solution was allowed to settle for 48 hours. Depending on the initial amount of components, different mass fractions of NT were obtained. To produce LEDs, the upper part of the solution was removed and applied to a glass substrate by centrifugation, after which aluminum electrodes were sprayed onto polymer layers. The resulting devices were studied by electroluminescence, which revealed a peak of their emission in the infrared region of the spectrum (600-700 nm).

CONCLUSION

Currently, carbon nanotubes are attracting a lot of attention due to the possibility of manufacturing nanometer-sized devices based on them. Despite numerous studies in this area, the question of mass production of such devices remains open, which is associated with the impossibility of precise control over the production of NTs with specified parameters and properties.

However, rapid development in this area should be expected in the near future due to the possibility of producing microprocessors and chips based on nanotransistors and, as a result, investment in this area by corporations specializing in computer technology.

BIBLIOGRAPHY

1. Carbon nanotubes. Materials for computers of the XXI century, P.N. Dyachkov. Nature No. 11, 2000
2. Rakov E.G. Methods for producing carbon nanotubes // Advances in Chemistry. -2000. - T. 69. - No. 1. - P. 41-59.
3. Rakov E.G. Chemistry and application of carbon nanotubes // Advances in Chemistry. -2001. - T. 70. - No. 11. - P. 934-973.
4. Eletsky A.V. // Success physics. Sci. 1997. T. 167, No. 9. P. 945972.
5. Zolotukhin I.V. Carbon nanotubes. Voronezh State Technical Institute.
6. http://skybox.org.ua/

PAGE 15

Another class of clusters were elongated cylindrical carbon formations, which later, after their structure was elucidated, were called " carbon nanotubes" (CNTs). CNTs are large, sometimes even ultra-large (over 10 6 atoms) molecules built from carbon atoms.

Typical structural scheme single-walled CNT and the result of computer calculation of its molecular orbitals are shown in Fig. 3.1. At the vertices of all hexagons and pentagons, shown as white lines, there are carbon atoms in a state of sp 2 hybridization. To ensure that the structure of the CNT framework is clearly visible, the carbon atoms are not shown here. But they are not difficult to imagine. The gray tone shows the appearance of the molecular orbitals of the lateral surface of the CNT.

Fig 3.1

The theory shows that the structure of the side surface of a single-walled CNT can be imagined as one layer of graphite rolled into a tube. It is clear that this layer can be rolled up only in those directions in which the alignment of the hexagonal lattice with itself is achieved when closing the cylindrical surface. Therefore, CNTs have only a certain set of diameters and are classified By vectors indicating the direction of folding of the hexagonal lattice. Both the appearance and variations in the properties of CNTs depend on this. Three typical options are shown in Fig. 3.2.

The set of possible CNT diameters overlaps range from slightly less than 1 nm to many tens of nanometers. A length CNTs can reach tens of micrometers. Record By The length of CNTs has already exceeded the limit of 1 mm.

Sufficiently long CNTs (when length much larger in diameter) can be considered as a one-dimensional crystal. On them one can distinguish a “unit cell”, which is repeated many times along the axis of the tube. And this is reflected in some of the properties of long carbon nanotubes.

Depending on the rollup vector of the graphite layer (experts say: “from chirality") nanotubes can be both conductors and semiconductors. CNTs of the so-called “saddle” structure always have a fairly high, “metallic” electrical conductivity.

Rice. 3.2

The “lids” that close the CNTs at the ends may also be different. They have the shape of “halves” of different fullerenes. Their main options are shown in Fig. 3.3.

Rice. 3.3 The main options for “covers” of single-walled CNTs

There are also multiwalled CNTs. Some of them look like a layer of graphite rolled into a scroll. But most consist of single-layer tubes inserted into one another, interconnected by van der Waals forces. If single-walled CNTs are almost always covered with lids, then multiwalled CNTs They are also partially open. They usually exhibit many more small structural defects than single-walled CNTs. Therefore, for applications in electronics, preference is still given to the latter.

CNTs grow not only straight, but also curvilinear, bent to form a “knee,” and even completely rolled up in the form of a torus. Often, several CNTs are tightly connected to each other and form “bundles”.

Materials used for nanotubes

The development of methods for the synthesis of carbon nanotubes (CNTs) has followed the path of lowering synthesis temperatures. After the creation of the technology for producing fullerenes, it was discovered that during electric arc evaporation of graphite electrodes, along with the formation of fullerenes, extended cylindrical structures are formed. Microscopist Sumio Iijima, using a transmission electron microscope (TEM), was the first to identify these structures as nanotubes. High-temperature methods for producing CNTs include the electric arc method. If you evaporate a graphite rod (anode) in an electric arc, then a hard carbon build-up (deposit) is formed on the opposite electrode (cathode), the soft core of which contains multi-walled CNTs with a diameter of 15-20 nm and a length of more than 1 μm.

The formation of CNTs from fullerene soot under high-temperature thermal influence on soot was first observed by Oxford and Swiss groups. The installation for electric arc synthesis is metal-intensive and energy-consuming, but is universal for producing various types of carbon nanomaterials. A significant problem is the non-equilibrium of the process during arc combustion. The electric arc method at one time replaced the method of laser evaporation (ablation) with a laser beam. The ablation unit is a conventional resistive heating oven producing a temperature of 1200°C. To obtain higher temperatures in it, it is enough to place a carbon target in the furnace and direct a laser beam at it, alternately scanning the entire surface of the target. Thus, Smalley’s group, using expensive installations with a short-pulse laser, obtained nanotubes in 1995, “significantly simplifying” the technology of their synthesis.

However, the yield of CNTs remained low. The introduction of small additions of nickel and cobalt (0.5 at.%) into graphite made it possible to increase the CNT yield to 70-90%. From this moment on, a new stage began in understanding the mechanism of nanotube formation. It became obvious that the metal was a catalyst for growth. This is how the first works appeared on the production of nanotubes by a low-temperature method - the method of catalytic pyrolysis of hydrocarbons (CVD), where iron group metal particles were used as a catalyst. One of the installation options for producing nanotubes and nanofibers by the CVD method is a reactor into which an inert carrier gas is supplied, carrying the catalyst and hydrocarbon to a high-temperature zone.

In a simplified way, the growth mechanism of CNTs is as follows. The carbon formed during the thermal decomposition of hydrocarbons dissolves in the metal nanoparticle. When a high concentration of carbon in a particle is reached, an energetically favorable “release” of excess carbon occurs on one of the faces of the catalyst particle in the form of a distorted semifulerene cap. This is how a nanotube is born. The decomposed carbon continues to enter the catalyst particle, and in order to discharge its excess concentration in the melt, it is necessary to constantly get rid of it. The rising hemisphere (semi-fullerene) from the melt surface carries with it dissolved excess carbon, the atoms of which outside the melt form a C-C bond, which is a cylindrical nanotube frame.

The melting temperature of a particle in a nanosized state depends on its radius. The smaller the radius, the lower the melting temperature, due to the Gibbs-Thompson effect. Therefore, iron nanoparticles with a size of about 10 nm are in a molten state below 600°C. At the moment, low-temperature synthesis of CNTs has been carried out using the catalytic pyrolysis of acetylene in the presence of Fe particles at 550°C. Reducing the synthesis temperature also has negative consequences. At lower temperatures, CNTs with a large diameter (about 100 nm) and a highly defective structure such as “bamboo” or “nested nanocones” are obtained. The resulting materials consist only of carbon, but they do not even come close to the extraordinary characteristics (for example, Young's modulus) observed in single-walled carbon nanotubes obtained by laser ablation or electric arc synthesis.