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Russian physicists gained insights in films from carbon nanotubes

Russian physicists from the Moscow Institute of Physics and Technology together with colleagues from Finland have created highly purified nanotubes from carbon monoxide (whitedamp) and ferrocene. Then, they have transformed obtained nanotubes into a film with exceptionally high indices of transparency and conductivity in a wide temperature range.
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Monolayer carbon nanotubes are one of the most perspective materials for electronics and optoelectronics. As these nanotubes have a width a single carbon atom, the resulting materials are almost transparent and at the same time have high durability and low unit weight. However, when trying to synthesize such nanotubes, one faces with a practical challenge as the properties of yielded nanotubes in various studies differ notably due to admixtures introduced by catalyst agents or by raw materials used in the synthesis.

In the new study, the Russian scientists have applied an alternative way of synthesis of nanotubes starting from carbon monoxide. To do so, they have created an unusual aerosol inside a chemical reactor. Ferrocene comprised of carbon, iron, and hydrogen has been sputtered to the carbon monoxide medium. During the heating, carbon monoxide decomposes, while the ferrocene compounds accelerate this process and simultaneously act as an inoculating for sedimentation of carbon part appearing in the course of decomposition of whitedamp. The precipitation results in assembling of highly purified carbon nanotubes without admixtures of carbon or iron. Herewith, the whole synthesis process is high-speed and requires about 10−12 seconds.

After the synthesis stage, the nanotubes have been deposited to a filter where a transparent film has been formed. The authors have shown that such tubes can be conveniently doped with iodine or copper chloride by placing them to a reacting camera with vapors of an admixture substance.

Using infrared and terahertz (the wavelengths of terahertz irradiation are longer than those of IR but shorter that radiowaves) spectroscopy, the researchers have measured the transparency of obtained film in a wide temperature range. It has been turned out that the transparency index of the newly synthesized film is relatively high for various temperature values. If compared to the data measured earlier for the same material, the new data are notably different. Importantly, in the previous studies, the authors had no access to the highly purified nanotubes, and consequently, the old spectroscopic data were measured not for the pure material.

Additionally, the authors have shown that the electrons can move through such film relatively free according to the Paul Drude conductivity model. According to this model, the transfer of charges in conductors is realized by free carriers similarly to the ideal gas atoms. They move between the ions of the cell and undergo dissipation while colliding with cells defects often introduced by admixtures. It has been ascertained that such «barriers» in the new thin film are very weak and charge carriers can move through it relatively free.

The film composed of nanotubes has a very high surface area/mass ratio which allows for using it for fabrication of light coatings for supercondensers — energy accumulators capable of releasing accumulated charge to the network in a very fast way.

The respective article has been published in the journal Carbon.

Previously, the research team from the USA and South Korea has shown that the carbon nanotubes can transform mechanical energy of stretching or twisting to electrical energy.

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