2024: Russia has significantly improved the technology of producing nanotubes for touch screens and solar panels
Scientists from the Skolkovo Institute of Science and Technology (Skoltech) have developed an innovative method for the chemical processing of films from carbon nanotubes, which will significantly improve their manufacturing technology for use in touch screens, solar panels and other devices. This was reported in the press service of the institute on May 31, 2024.
Experimental studies have demonstrated that treating nanotubes with a small amount of nitrogen dioxide gas, known as "fox tail," at high temperatures results in their modification, improving transparency and electrical conductivity. Scientists stressed that the resulting effect is long-term.
As Professor Albert Nasibulin, who headed the research group, noted, doping nanotubes with impurities plays a key role in achieving the required characteristics. The developed method made it possible to obtain a material that combines high conductivity, transparency and stability of the effect.
 | We discovered the optimal option - gaseous nitrogen dioxide, which for its bright orange color was called the "fox tail," - said senior lecturer Dmitry Krasnikov, one of the authors of the study. |  |
He added that the process of doping with nitrogen dioxide is characterized by speed, scalability and lack of waste. The scientist stressed that it is easy to integrate it into existing technological processes of synthesis.
Nasibulin noted that transparent electrodes made from films of carbon nanotubes doped with nitrogen dioxide have a wide range of potential applications. They can be used in photovoltaic, touch displays, interactive surfaces in the interiors of residential premises, cars and public spaces. In addition, due to biocompatibility, such electrodes can be used in implantable devices.
According to the press service of the institute, the study was supported by a grant from the Russian Science Foundation and published in the authoritative scientific journal Carbon.[1]
2022: Scientists find a way to change the electronic properties of carbon nanotubes and adjust them for use in electronic devices
On February 10, 2022, representatives of MIPT reported that, together with Skoltech scientists, they found a way to change the electronic properties of carbon nanotubes and adjust them for use in electronic devices. The work is published in the magazine Carbon.
As reported, carbon nanomaterials represent a wide class of compounds: graphene, fullerenes, nanotubes, nanofibers and others. The physical properties of many of them have already entered textbooks, but scientists continue to create structures and find practical application for them. One such macrostructure is films composed of carbon nanotubes that are randomly oriented. Externally, the films are somewhat similar to the thinnest webs: their length and width can reach several tens of centimeters, and the thickness is millions of times smaller, several nanometers.
Carbon nanotube films have a combination of physical and chemical properties. They are mechanically stable, flexible and extensible, characterized by proper adhesion to various substrates, chemical inertness and exceptional electrical and optical properties.
With proper conductivity, films have advantages over metal films: ease and flexibility. They can be used in various electrical devices: screens, modulators, antennas, bolometers, etc.
In order to use the electrical and electrodynamic properties of films most effectively in practice, it is necessary to study which physical principles such properties determine. Of greatest interest are the terahertz and far infrared ranges (radiation wavelength - from 2 mm to 500 nm), in which films exhibit properties characteristic of metal conductors.
Scientists from MIPT and Skoltech investigated the conductivity of films in the terahertz and infrared frequency bands. For work, the authors took films synthesized by the method of deposition from the gas phase. A portion of the films were prepared from nanotubes of varying lengths, which ranged from 0.3 to 13 μm. Another group of films was exposed to oxygen plasma for 100-400 seconds. This effect changed the electrodynamic properties of the films.
Previously, the authors in their work proved that the conductivity of films is well described by a model of conductivity that is fair to metals. In such films, the free electron energy is sufficient to overcome potential barriers between individual contacting nanotubes. Such electrons move almost "freely" throughout the film, which leads to proper conductivity.
But with a decrease in the length of the tubes (up to 0.3 μm) or prolonged exposure to them with plasma (> 100 s), the conductivity at terahertz frequencies (<0,3 ТГц) значительно уменьшается. Оказалось, что изменения проводимости пленок при воздействии на них плазмой или при уменьшении длины нанотрубок аналогичны. Это связано с тем, что облучение плазмой приводит к увеличению числа дефектов в нанотрубках, а следовательно, росту числа потенциальных барьеров на пути электронов. С уменьшением длины нанотрубок число потенциальных барьеров на единицу площади также увеличивается. Эти барьеры существенно влияют на проводимость нанотрубок (а, следовательно, и пленок) на постоянном токе и на достаточно низких частотах. Эффект объясняется тем, что при низких температурах кинетическая энергия электронов слишком мала, чтобы электроны могли преодолеть потенциальный барьер. На достаточно высоких частотах, как показано авторами, электроны перестают чувствовать присутствие барьеров и ведут себя как свободные. Так что в пленках, составленных из коротких трубок или из трубок, обработанных плазмой, на достаточно низких частотах и на постоянном токе будет наблюдаться возрастание температурного коэффициента сопротивления, который показывает, как меняется сопротивление с изменением температуры.
If the exposure duration is more than 100 seconds or if the length of the nanotubes is less than 0.3 μm, the temperature coefficient of resistance becomes saturated: at these parameters, the original structure of the film is disturbed, and at the same time the original properties disappear.
MIPT and Skoltech scientists plan to continue studying modified films, for example, stretched in one or more directions.
| | If nanotubes have been studied in detail and long ago, then macro objects from these tubes - films - began to be studied relatively recently. Compared to metal films, they are much lighter, chemically and mechanically stable, making them attractive for electronics applications. Knowing the fundamental physics that determines the electrical properties of films, we can purposefully adjust these properties for specific practical applications. Particularly relevant are studies on the frequencies of the terahertz band, which will be working in the means of telecommunications of the near future. told Boris Gorshunov, head of the laboratory of terahertz spectroscopy of MIPT | |
| | It turned out that the controlled destruction of this material by treating films with microwave plasma leads to unexpected properties. In particular, we observe an increase in the temperature coefficient of resistance in films made of single-layer carbon nanotubes. This is due to the fact that competing contributions to conductivity from metal and semiconductor tubes cease to play an important role, and the conductivity of the film is mainly determined by the formed defects. This is of great interest for the creation of next-generation devices, for example high-speed bolometers operating at room temperature. told Albert Nasibulin, head of the laboratory of nanomaterials at the Skolkovo Institute of Science and Technology | |
2019: Physicists at RAS and MIPT identify type of quasiparticles in semiconductor carbon nanotubes
On December 5, 2019, the MIPT reported that scientists from the Institute of General Physics. A. M. Prokhorov RAS and MIPT together with colleagues investigated the influence of "traps" on the optical properties of carbon nanotubes. When treated with hydrochloric acid, individual hydrogen atoms remain on the surface of the tubes. They do not form chemical bonds with the surface, and, therefore, do not introduce defects into the structure of the nanotube. These atoms serve as "traps" - a quasi-particle that falls into their zone of influence cannot "escape" (becomes localized). Based on the data obtained by spectroscopy methods, physicists came to the conclusion that an exciton (consisting of an electron and a "hole") and a trion (exciton, which was joined by another hole or electron) fell into the "trap." The findings are published in the journal Scientific reports.
As noted in MIPT, carbon nanotubes are a light and durable material, promising from many points of view. Films made of carbon nanotubes with semiconductor conductivity in the future can replace indium-tin oxide, a solid transparent material that has been used to create transparent electrodes for 60 years. Without rare earth India, displays and touch screens will become cheaper, and in addition, they can be bent and rolled up without harm.
Thin-film transistors are responsible for switching pixels on a flexible screen. The faster the charge is able to move in the material, the faster the transistors react and the faster the screen response. To describe the processes of charge transfer in semiconductors, physicists introduced the concept of "quasi-particle." An example is the "hole" - the free space left after the separation of the electron on the orbital of the atom. The exciton quasiparticle (from the Latin "excite") is an electron-hole pair that moves as if the particles are "tied" to each other. If another particle attaches to the exciton, a trion is obtained.
To examine the quasiparticles, the scientists added hydrochloric acid to an aqueous suspension of carbon nanotubes with semiconductor conductivity. We further examined the absorption spectra of suspensions with different amounts of hydrochloric acid. The higher the concentration of acid, the more "traps" were formed - hydrogen atoms settled on the surface of the tubes - and the more excitons and trions came across them.
Nanotube energy can only take certain values. Energy levels are similar to cabinet shelves - the book can be placed on the second or tenth, but cannot be 9¾. Physicists obtain an absorption spectrum by exposing a substance to radiation: if the energy that a photon can transfer to a particle in a collision coincides with the "distance between the shelves," the particle absorbs it and goes to a higher level. By changing the wavelength of the incident radiation, it is possible to determine when it is absorbed by matter more strongly, and to determine the location of the "shelves."
In addition, scientists investigated photoluminescence spectra. In this method, the particles go into an excited state under the influence of radiation, and then return to the original one, emitting a photon (following the analogy, we push the books onto the upper shelves, and then record the noise from their fall on the lower ones). Scientists noted that with an increase in the number of hydrogen atoms settled on the tube, the number of excitons decreases. But a new energy transition appears, designated as the X-band. This transition is also noticeable on the absorption spectra. The researchers suggested that it corresponds to particles caught in the "traps."
The above methods do not allow separately to consider energy transitions separated by very small intervals of time (about 10-12 seconds) - they merge, and as a result it is not clear which particles are in the "trap." Therefore, the spectra were further investigated using the pump-probe spectroscopy method.
The processing of the information obtained by this method made it possible to distinguish energy levels that form at different times after the pulse. The first two corresponded to the formation of an exciton, free and caught in a proton trap. The third was formed after a noticeable time (about one picosecond) after exciton levels, based on which the authors associated it with the formation of a quasiparticle, a trion, in the "trap."
| | "Doped single-wall carbon nanotubes have demonstrated previously their unique properties as conductive transparent electrodes. In this work, we identified multi-particle optical excitations in such nanotubes and found out the mechanisms of energy migration. The development of this direction opens up wide prospects for nonlinear optics, " noted Timofey Eremin, junior researcher at the MIPT nanocarbon materials laboratory, one of the authors of the work | |
The findings contribute to a deeper understanding of the energy structure of carbon nanotubes with introduced impurities, which is important not only from a fundamental, but also from a practical point of view. In the future, scientists plan to investigate the energy levels of carbon nanotubes with various types of "traps."
The work was carried out by a team of scientists from MIPT, the Institute of General Physics. A.M. Prokhorov RAS, Moscow State University, MEPhI, FTI named after Ioffe, as well as the University of Eastern Finland. The work was supported by the Russian Science Foundation.
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