Properties and applications of carbon nanotubes. Carbon nanotubes: types and applications

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 that can be called 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). main feature of these molecules is their skeleton form: 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 have already been developed in computer industry. 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 - 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 travel 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 on May 20 in scientific journal Applied Physics Letters, IBM specialists have improved carbon nanotube transistors. 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. Maximum dimensions The nanomotor is 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 energy-independent 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 study was practical use outstanding properties of nanotubes for measuring 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, replacing the hot emitters of modern cathode ray tubes, in addition, they allow you to get rid of gigantic and unsafe accelerating 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 - perfect material for safe storage of 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 - large quantity energy and released per unit mass (for 500 km of vehicle mileage only about 3 kg of H2 is required). 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 the ordinary gas cylinders according to the mass and volume 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 are needed relatively large diameter- 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.

Energy is an important industry that plays a huge role in human life. The energy situation in the country depends on the work of many scientists in this industry. Today they are searching for these purposes, they are ready to use anything, from sunlight and water to air energy. Equipment that can generate energy from the environment is highly valued.

General information

Carbon nanotubes are long, rolled graphite planes that have a cylindrical shape. As a rule, their thickness reaches several tens of nanometers, with a length of several centimeters. At the end of the nanotubes a spherical head is formed, which is one of the parts of the fullerene.

There are two types of carbon nanotubes: metallic and semiconductor. Their main difference is current conductivity. The first type can conduct current at a temperature equal to 0ºС, and the second - only at elevated temperatures.

Carbon nanotubes: properties

Most modern fields, such as applied chemistry or nanotechnology, are associated with nanotubes, which have a carbon frame structure. What it is? This structure refers to large molecules connected to each other only by carbon atoms. Carbon nanotubes, whose properties are based on a closed shell, are highly prized. In addition, these formations have a cylindrical shape. Such tubes can be obtained by rolling up a graphite sheet, or grown from a specific catalyst. Carbon nanotubes, photos of which are presented below, have an unusual structure.

They come in different shapes and sizes: single-layer and multi-layer, straight and curved. Despite the fact that nanotubes look quite fragile, they are a strong material. As a result of many studies, it was found that they have properties such as stretching and bending. Under the influence of serious mechanical loads, the elements do not tear or break, that is, they can adapt to different voltages.

Toxicity

As a result of multiple studies, it was found that carbon nanotubes can cause the same problems as asbestos fibers, that is, various malignant tumors occur, as well as lung cancer. Degree negative influence asbestos depends on the type and thickness of its fibers. Since carbon nanotubes are small in weight and size, they easily enter the human body along with air. Next, they enter the pleura and enter the chest, and over time cause various complications. Scientists conducted an experiment and added nanotube particles to the food of mice. Products of small diameter practically did not linger in the body, but larger ones dug into the walls of the stomach and caused various diseases.

Receipt methods

Today, there are the following methods for producing carbon nanotubes: arc charge, ablation, vapor deposition.

Electric arc discharge. Preparation (carbon nanotubes are described in this article) in plasma electric charge, which burns using helium. This process can be carried out using special technical equipment for producing fullerenes. But this method uses other arc burning modes. For example, it is reduced, and cathodes of enormous thickness are also used. To create an atmosphere from helium, it is necessary to increase the pressure of this chemical element. Carbon nanotubes are produced by sputtering. To increase their number, you must enter graphite rod catalyst. Most often it is a mixture of different metal groups. Next, the pressure and spray method change. Thus, a cathode deposit is obtained, where carbon nanotubes are formed. The finished products grow perpendicular to the cathode and are collected into bundles. They are 40 microns long.

Ablation. This method was invented by Richard Smalley. Its essence is to evaporate different graphite surfaces in a reactor operating at high temperatures. Carbon nanotubes are formed by the evaporation of graphite at the bottom of the reactor.

They are cooled and collected using a cooling surface. If in the first case, the number of elements was equal to 60%, then with this method the figure increased by 10%. The cost of the laser absolation method is more expensive than all others. As a rule, single-walled nanotubes are obtained by changing the reaction temperature.

Vapor deposition. The carbon vapor deposition method was invented in the late 50s. But no one even imagined that it could be used to produce carbon nanotubes. So, first you need to prepare the surface with the catalyst. It can be small particles of various metals, for example, cobalt, nickel and many others. Nanotubes begin to emerge from the catalyst layer. Their thickness directly depends on the size of the catalytic metal. The surface is heated to high temperatures, and then a gas containing carbon is supplied. Among them are methane, acetylene, ethanol, etc. Ammonia serves as an additional technical gas. This method obtaining nanotubes is the most common. The process itself takes place at various industrial enterprises, due to which less financial resources are spent on producing a large number of tubes. Another advantage of this method is that vertical elements can be obtained from any metal particles that serve as a catalyst. The production (carbon nanotubes are described from all sides) was made possible thanks to the research of Suomi Iijima, who observed their appearance under a microscope as a result of carbon synthesis.

Main types

Carbon elements are classified by the number of layers. The simplest type is single-walled carbon nanotubes. Each of them is approximately 1 nm thick, and their length can be much greater. If we consider the structure, the product looks like wrapping graphite using a hexagonal mesh. At its vertices are carbon atoms. Thus, the tube has the shape of a cylinder, which has no seams. The upper part of the devices is closed with lids consisting of fullerene molecules.

The next type is multi-walled carbon nanotubes. They consist of several layers of graphite, which are folded into a cylinder shape. A distance of 0.34 nm is maintained between them. Structure of this type described in two ways. According to the first, multilayer tubes are several single-layer tubes nested inside each other, which looks like a nesting doll. According to the second, multiwalled nanotubes are a sheet of graphite that wraps around itself several times, similar to a folded newspaper.

Carbon nanotubes: application

The elements are an absolutely new representative of the class of nanomaterials.

As mentioned earlier, they have a frame structure, which differs in properties from graphite or diamond. That is why they are used much more often than other materials.

Due to characteristics such as strength, bending, conductivity, they are used in many fields:

• as additives to polymers;
• catalyst for lighting devices, as well as flat panel displays and tubes in telecommunication networks;
• as an absorber of electromagnetic waves;
• for energy conversion;
• production of anodes in various types of batteries;
• hydrogen storage;
• manufacturing of sensors and capacitors;
• production of composites and strengthening their structure and properties.

For many years, carbon nanotubes, whose applications are not limited to one specific industry, have been used in scientific research. This material has weak positions on the market, as there are problems with large-scale production. Another important point is the high cost of carbon nanotubes, which is approximately $120 per gram of such a substance.

They are used as a basic element in the production of many composites, which are used to make many sporting goods. Another industry is the automotive industry. The functionalization of carbon nanotubes in this area comes down to imparting conductive properties to polymers.

The thermal conductivity coefficient of nanotubes is quite high, so they can be used as a cooling device for various massive equipment. They are also used to make tips that are attached to probe tubes.

The most important application area is computer technology. Thanks to nanotubes, particularly flat displays are created. Using them you can significantly reduce dimensions the computer itself, as well as increase its technical performance. The finished equipment will be several times superior to current technologies. Based on these studies, high-voltage picture tubes can be created.

Over time, the tubes will be used not only in electronics, but also in the medical and energy fields.

Production

Carbon tubes, the production of which is divided between two types, are unevenly distributed.

That is, MWNTs are produced much more than SWNTs. The second type is done in case of urgent need. Various companies are constantly producing carbon nanotubes. But they are practically not in demand, since their cost is too high.

Production leaders

Today, the leading place in the production of carbon nanotubes is occupied by Asian countries, which are 3 times higher than in other countries of Europe and America. In particular, Japan is engaged in the production of MWNTs. But other countries, such as Korea and China, are in no way inferior in this indicator.

Production in Russia

Domestic production of carbon nanotubes lags significantly behind other countries. In fact, it all depends on the quality of the research being conducted in this area. There are not enough financial resources allocated here for the creation of scientific and technological centers in the country. Many people are not accepting of developments in nanotechnology because they do not know how it can be used in industry. Therefore, the transition of the economy to a new path is quite difficult.

Therefore, the President of Russia issued a decree indicating the development paths for various areas of nanotechnology, including carbon elements. For these purposes, a special development and technology program was created.

To ensure that all points of the order were carried out, the Rusnanotech company was created. A significant amount of money was allocated for its operation. state budget. It is she who should control the process of development, production and industrial implementation of carbon nanotubes. The allocated amount will be spent on the creation of various research institutes and laboratories, and will also strengthen the existing work of domestic scientists. These funds will also be used to purchase high-quality equipment for the production of carbon nanotubes. It is also worth taking care of those devices that will protect human health, since this material causes many diseases.

As mentioned earlier, the whole problem is raising funds. Most investors do not want to invest in scientific developments, especially on long time. All businessmen want to see profits, but nanodevelopment can take years. This is what repels representatives of small and medium-sized businesses. In addition, without government investment it will not be possible to fully launch the production of nanomaterials.

Another problem is the lack of a legal framework, since there is no intermediate link between different levels of business. Therefore, carbon nanotubes, the production of which is not in demand in Russia, require not only financial, but also mental investments. So far, the Russian Federation is far from the Asian countries that are leading in the development of nanotechnologies.

Today, developments in this industry are carried out at the chemical faculties of various universities in Moscow, Tambov, St. Petersburg, Novosibirsk and Kazan. The leading producers of carbon nanotubes are the Granat company and the Tambov plant Komsomolets.

Positive and negative sides

Among the advantages are the special properties of carbon nanotubes. They are a durable material that does not collapse under mechanical stress. In addition, they work well in bending and stretching. This was made possible thanks to the closed frame structure. Their use is not limited to one industry. The tubes have found application in the automotive industry, electronics, medicine and energy.

A huge disadvantage is the negative impact on human health.

Particles of nanotubes entering the human body lead to the occurrence of malignant tumors and cancer.

An essential aspect is the financing of this industry. Many people do not want to invest in science because it takes a lot of time to make a profit. And without the functioning of research laboratories, the development of nanotechnology is impossible.

Conclusion

Carbon nanotubes play an important role in innovative technologies. Many experts predict the growth of this industry in the coming years. There will be a significant increase in production capabilities, which will lead to a decrease in the cost of goods. With decreasing prices, tubes will be in great demand and will become an indispensable material for many devices and equipment.

So, we found out what these products are.

Carbon nanotubes are a material that many scientists dream of. High strength coefficient, excellent thermal and electrical conductivity, fire resistance and weight coefficient are an order of magnitude higher than most known materials. Carbon nanotubes are a sheet of graphene rolled into a tube. Russian scientists Konstantin Novoselov and Andrei Geim received the Nobel Prize in 2010 for its discovery.

For the first time, Soviet scientists were able to observe carbon tubes on the surface of an iron catalyst back in 1952. However, it took fifty years for scientists to see nanotubes as promising and useful material. One of the striking properties of these nanotubes is that their properties are determined by geometry. Thus, their electrical properties depend on the angle of twisting - nanotubes can demonstrate semiconductor and metallic conductivity.

What is this

Many promising directions in nanotechnology today they are associated specifically with carbon nanotubes. Simply put, carbon nanotubes are giant molecules or framework structures that consist only of carbon atoms. It is easy to imagine such a nanotube if you imagine that graphene is folded into a tube - this is one of the molecular layers of graphite. The method of folding nanotubes largely determines the final properties of this material.

Naturally, no one creates nanotubes by specially rolling them from a sheet of graphite. Nanotubes form themselves, for example, on the surface of carbon electrodes or between them during an arc discharge. During discharge, carbon atoms evaporate from the surface and connect with each other. As a result, nanotubes of various types are formed - multi-walled, single-walled and with different twist angles.

The main classification of nanotubes is based on the number of layers that make them up:

• Single-walled nanotubes are the simplest type of nanotubes. Most of them have a diameter of the order of 1 nm with a length that can be thousands of times greater;
• Multilayer nanotubes, consisting of several layers of graphene, they fold into the shape of a tube. A distance of 0.34 nm is formed between the layers, that is, identical to the distance between the layers in a graphite crystal.

Device

Nanotubes are extended cylindrical carbon structures that can have a length of up to several centimeters and a diameter of one to several tens of nanometers. At the same time, today there are technologies that make it possible to weave them into threads of unlimited length. They can consist of one or more graphene planes rolled into a tube, which usually end in a hemispherical head.

The diameter of nanotubes is several nanometers, that is, several billionths of a meter. The walls of carbon nanotubes are made of hexagons, at the vertices of which there are carbon atoms. The tubes may have different type structure, it is he who influences their mechanical, electronic and Chemical properties. Single-layer tubes have fewer defects; at the same time, after annealing at high temperatures in an inert atmosphere, it is possible to obtain defect-free tubes. Multiwalled nanotubes differ from standard single-walled nanotubes in a significantly wider variety of configurations and shapes.

Carbon nanotubes can be synthesized in different ways, but the most common are:

• Arc discharge. The method ensures the production of nanotubes at technological installations for the production of fullerenes in the plasma of an arc discharge that burns in a helium atmosphere. But different arc combustion modes are used here: higher helium pressure and low current densities, as well as larger diameter cathodes. The cathode deposit contains nanotubes up to 40 microns in length; they grow perpendicularly from the cathode and are combined into cylindrical bundles.
• Laser ablation method . The method is based on the evaporation of a graphite target in a special high-temperature reactor. Nanotubes are formed on the cooled surface of the reactor in the form of graphite evaporation condensate. This method allows one to predominantly obtain single-walled nanotubes with control of the required diameter by temperature. But this method is significantly more expensive than others.
• Chemical vapor deposition . This method involves preparing a substrate with a layer of catalyst - these can be particles of iron, cobalt, nickel or combinations thereof. The diameter of nanotubes grown using this method will depend on the size of the particles used. The substrate is heated to 700 degrees. To initiate the growth of nanotubes, carbon-containing gas and process gas (hydrogen, nitrogen or ammonia) are introduced into the reactor. Nanotubes grow on areas of metal catalysts.

Applications and Features

• Applications in photonics and optics . By selecting the diameter of nanotubes, it is possible to ensure optical absorption in a wide spectral range. Single-walled carbon nanotubes exhibit strong saturable absorption nonlinearity, meaning they become transparent under sufficiently intense light. Therefore, they can be used for various applications in the field of photonics, for example, in routers and switches, for creating ultrashort laser pulses and regenerating optical signals.
• Application in electronics . At the moment, many methods have been announced for using nanotubes in electronics, but only a small part of them can be realized. The greatest interest is in the use of nanotubes in transparent conductors as a heat-resistant interfacial material.

The relevance of attempts to introduce nanotubes in electronics is caused by the need to replace indium in heat sinks, which are used in high-power transistors, graphics processors and central processing units, because the reserves of this material are decreasing and its price is rising.

• Creation of sensors . Carbon nanotubes for sensors are one of the most interesting solutions. Ultrathin films of single-walled nanotubes may currently become the best basis for electronic sensors. They can be produced using different methods.
• Creation of biochips, biosensors , control of targeted delivery and action of drugs in the biotechnology industry. Work in this direction is currently underway. High-throughput analysis performed using nanotechnology will significantly reduce the time it takes to bring a technology to market.
• Today it is growing sharply production of nanocomposites , mostly polymer. When even a small amount of carbon nanotubes is introduced into them, a significant change in the properties of polymers is ensured. This increases their thermal and chemical stability, thermal conductivity, electrical conductivity, and improves mechanical characteristics. Dozens of materials have been improved by adding carbon nanotubes;

Composite fibers based on polymers with nanotubes;
ceramic composites with additives. The crack resistance of ceramics increases, protection of electromagnetic radiation appears, electrical and thermal conductivity increases;
concrete with nanotubes – increases grade, strength, crack resistance, reduces shrinkage;
metal composites. Especially copper composites, which have mechanical properties several times higher than that of ordinary copper;
hybrid composites, which contain three components at once: inorganic or polymer fibers (fabrics), binder and nanotubes.

Advantages and disadvantages

Among the advantages of carbon nanotubes are:

• Lots of unique and truly beneficial properties, which can be used in the implementation of energy-efficient solutions, photonics, electronics, and other applications.
• This is a nanomaterial that has high coefficient strength, excellent thermal and electrical conductivity, fire resistance.
• Improving the properties of other materials by introducing a small amount of carbon nanotubes into them.
• Open-ended carbon nanotubes exhibit a capillary effect, meaning they can draw in molten metals and other liquid substances;
• Nanotubes combine the properties of solids and molecules, which opens up significant prospects.

Among the disadvantages of carbon nanotubes are:

• Carbon nanotubes are not currently produced on an industrial scale, so their serial use is limited.
• The cost of producing carbon nanotubes is high, which also limits their application. However, scientists are working hard to reduce the cost of their production.
• The need to improve production technologies to create carbon nanotubes with precisely defined properties.

Prospects

In the near future, carbon nanotubes will be used everywhere; they will be used to create:

• Nanoscales, composite materials, super strong threads.
• Fuel cells, transparent conducting surfaces, nanowires, transistors.
• The latest neurocomputer developments.
• Displays, LEDs.
• Devices for storing metals and gases, capsules for active molecules, nanopipettes.
• Medical nanorobots for drug delivery and operations.
• Miniature sensors with ultra-high sensitivity. Such nanosensors could find use in biotechnological, medical and military applications.
• Space elevator cable.
• Flat transparent loudspeakers.
• Artificial muscles. In the future, there will be cyborgs, robots, and people with disabilities will return to a full life.
• Engines and power generators.
• Smart, light and comfortable clothing that will protect you from any adversity.
• Safe supercapacitors with fast charging.

All this is in the future, because industrial technologies for the creation and use of carbon nanotubes are at the initial stage of development, and their price is extremely expensive. But Russian scientists have already announced that they have found a way to reduce the cost of creating this material by two hundred times. This unique technology for producing carbon nanotubes is currently kept secret, but it is set to revolutionize industry and many other areas.

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. It depends on how appearance, and variations in the properties of CNTs. 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 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, energy-consuming, but universal for obtaining various types carbon nanomaterials. A significant problem is the non-equilibrium 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 it began new stage 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. With more low 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.

And other similar structures that can be called by 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. The most famous of the carbon framework structures is the C 60 fullerene, the completely unexpected discovery of which in 1985 caused a boom in research in this area (the Nobel Prize in Chemistry for 1996 was awarded to the discoverers of fullerenes Robert Curle, Harold Kroteau and Richard Smalley). In the late 80s and early 90s, after a technique for producing fullerenes in macroscopic quantities was developed, many other, both lighter and heavier fullerenes were discovered: starting from C 20 (the minimum possible fullerene) and up to C 70, C 82, C 96, and higher.

However, the diversity of carbon frame structures does not end there. In 1991, again completely unexpectedly, long, cylindrical carbon formations called nanotubes were discovered. Visually, the structure of such nanotubes can be imagined as follows: we take a graphite plane, cut a strip out of it and “glue” it into a cylinder (caution: such folding of a graphite plane is only a way to imagine the structure of a nanotube; in reality, nanotubes grow in a completely different way). It would seem that it is simpler - you take a graphite plane and roll it into a cylinder! - however, before the experimental discovery of nanotubes, none of the theorists predicted them! So scientists could only study them - and be surprised!

And there were many surprising things. Firstly, the variety of shapes: nanotubes could be large and small, single-walled and multi-layered, straight and spiral. Secondly, despite their apparent fragility and even delicacy, nanotubes turned out to be an extremely strong material, both in tension and bending. Moreover, under the influence of mechanical stresses exceeding critical ones, nanotubes also behave extravagantly: they do not “tear” or “break”, but simply rearrange themselves! Further, nanotubes demonstrate a whole range of the most unexpected electrical, magnetic, and optical properties. For example, depending on the specific folding pattern of the graphite plane, nanotubes can be both conductors and semiconductors! Can any other material with such simple chemical composition boast of at least some of the properties that nanotubes have?!

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 produced in the laboratory is gradually increasing - now scientists have already come close to the millimeter mark: see the work [Z. Pan et al, 1998], which describes the synthesis of a 2 mm long multiwalled nanotube. 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.

Another example where a nanotube is part of a physical device is when it is “mounted” on the tip of a scanning tunneling or atomic force microscope. Usually such an edge is a sharpened tungsten needle, but by atomic standards such sharpening is still quite rough. A nanotube is an ideal needle with a diameter of the order of several atoms. By applying a certain voltage, it is possible to pick up atoms and entire molecules located on the substrate directly under the needle and transfer them from place to place.

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!

Another application in nanoelectronics is the creation of semiconductor heterostructures, i.e. metal/semiconductor structures or the junction of two different semiconductors. Now, to produce such a heterostructure, it will not be necessary to grow two materials separately and then “weld” them together. All that is required is to create a structural defect in it during the growth of the nanotube (namely, to replace one of the carbon hexagons with a pentagon). Then one part of the nanotube will be metal, and the other will be a semiconductor!

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!

Using the same atomic microscope, it is possible to record and read information from a matrix consisting of titanium atoms lying on an -Al 2 O 3 substrate. This idea has also already been implemented experimentally: the achieved information recording density was 250 Gbit/cm 2 . However, in both of these examples, mass application is still far away - such high-tech innovations are too expensive. Therefore, one of the most important tasks here is to develop a cheap method for implementing these ideas.

The voids inside nanotubes (and carbon framework structures in general) have also attracted the attention of scientists. In fact, what will happen if an atom of some substance is placed inside a fullerene? Experiments have shown that intercalation (i.e. introduction) of atoms various metals changes the electrical properties of fullerenes and can even turn an insulator into a superconductor! Is it possible to change the properties of nanotubes in the same way? It turns out yes. In [K.Hirahara et al, 2000], scientists were able to place inside a nanotube a whole chain of fullerenes with gadolinium atoms already embedded in them! The electrical properties of such an unusual structure were very different from both the properties of a simple, hollow nanotube and the properties of a nanotube with empty fullerenes inside. How, it turns out, the valence electron, given by the metal atom at everyone’s disposal, means a lot! By the way, it is interesting to note that special chemical designations have been developed for such compounds. The structure described above is written as Gd@C 60 @SWNT, which means "Gd inside a C 60 inside a Single Wall NanoTube."

It is possible not only to “drive” atoms and molecules individually into nanotubes, but also to literally “pour” matter. As experiments have shown, an open nanotube has capillary properties, that is, it seems to draw a substance into itself. Thus, nanotubes can be used as microscopic containers for transporting chemically or biologically active substances: proteins, poisonous gases, fuel components and even molten metals. Once inside the nanotube, atoms or molecules can no longer get out: the ends of the nanotubes are securely “sealed”, and the aromatic carbon ring is too narrow for most atoms. In this form, active atoms or molecules can be safely transported. Once at their destination, the nanotubes open at one end (and the operations of “soldering” and “unsoldering” the ends of the nanotubes are quite possible with modern technology) and release their contents in strictly defined doses. This is not science fiction; experiments of this kind are already being carried out in many laboratories around the world. And it is possible that in 10-20 years, diseases will be treated on the basis of this technology: say, pre-prepared nanotubes with very active enzymes are injected into the patient’s blood, these nanotubes are collected in a certain place in the body by some microscopic mechanisms and are “opened” at a certain moment time. Modern technology almost ready for implementation...

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