M. A. Kanygin

Anisotropic electromagnetic properties of polymer composites containing oriented multiwall carbon nanotubes in respect to terahertz polarizer applications

Polystyrene composites with 0.5 wt. % loading of oriented multiwall carbon nanotubes (MWCNTs) have been produced by forge rolling method. The composites showed anisotropy of transmission and reflection of terahertz radiation depending on sample orientation relative to the polarization of electromagnetic wave. The structural characteristics of composites (nanotube ordering, length, defectiveness) were estimated by fitting the theoretical dependencies calculated within the Clausius-Mossotti formalism for cylindrical particles to the experimental data. The presented model was used for prediction of electromagnetic response of composites containing oriented MWCNTs with various structural parameters in THz region.

Effect of nitrogen doping on the electromagnetic properties of carbon nanotube-based composites

Nitrogen-doped and pure carbon nanotube (CNT) based composites were fabricated for investigating their dielectric properties in static regime as well as electromagnetic response properties in microwave frequency range (Ka-band). Two classes of host matrix—polystyrene and phosphate unfired ceramics—have been used for composites fabrication. The study reveals miscellaneous effect of nitrogen doping on the dielectric permittivity, dc conductivity and electromagnetic interference shielding efficiency of CNT-based composites, produced with both polymer and ceramic matrices. The high-frequency polarizability, estimated for different-length CNTs, and static polarizability, calculated for nitrogen-containing CNT models using a quantum-chemical approach, show that this effect results from a decrease of the nanotube defect-free-length and deterioration of the polarizability with incorporation of nitrogen in pyridinic form.

Anisotropy of the Electromagnetic Properties of Polymer Composites Based on Multiwall Carbon Nanotubes in the Gigahertz Frequency Range

Polymer composite materials have been prepared of multiwall carbon nanotubes synthesized by aerosol assisted chemical vapor deposition. To give them anisotropic properties, the obtained films have been subjected to tension. As a result of this deformation, the carbon nanotubes have been preferably oriented in the direction of the tension. The anisotropy of the relative permittivity of the extended films has been measured in the frequency range of 26–37 GHz (Ka band). A model of the correlation between the extent of the response anisotropy and the strain of the composite film has been elaborated. A way to control the electromagnetic response of the material on the basis of the elaborated model has been proposed.

Memristive model of hysteretic field emission from carbon nanotube arrays

Abstract. Some instances of electron field emitters are characterized by frequency-dependent hysteresis in their current–voltage characteristics. We argue that such emitters can be classified as memristive systems and introduce a general framework to describe their response. As a specific example of our approach, we consider field emission from a carbon nanotube array. Our experimental results demonstrate a low-field hysteresis, which is likely caused by an electrostatic alignment of some of the nanotubes in the applied field. We formulate a memristive model of such phenomena, whose results are in agreement with the experimental results.

Interaction of ultrasoft X-rays with arrays of aligned carbon nanotubes

Angular dependence of X-ray emission and absorption spectra was measured for both graphite and films of carbon nanotubes (CNTs) oriented perpendicular to the substrate surface. The ratio of intensities of Π and σ peaks in the X-ray spectra of CNT films was found to depend not only on the orientation of nanotubes but also on the orientation of graphite-like layers inside multi-walled nanotubes. Fluorescence measurement for the samples also showed the dependence on the degree of CNT alignment as well as on the texture of CNT layers. A possibility of X-ray photon propagation in CNTs in the conditions of anomalous dispersion near the C K-edge is discussed.

Single-Walled Carbon Nanotube Reactor for Redox Transformation of Mercury Dichloride

Single-walled carbon nanotubes (SWCNTs) possessing a confined inner space protected by chemically resistant shells are promising for delivery, storage, and desorption of various compounds, as well as carrying out specific reactions. Here, we show that SWCNTs interact with molten mercury dichloride (HgCl2) and guide its transformation into dimercury dichloride (Hg2Cl2) in the cavity. The chemical state of host SWCNTs remains almost unchanged except for a small p-doping from the guest Hg2Cl2 nanocrystals. The density functional theory calculations reveal that the encapsulated HgCl2 molecules become negatively charged and start interacting via chlorine bridges when local concentration increases. This reduces the bonding strength in HgCl2, which facilitates removal of chlorine, finally leading to formation of Hg2Cl2 species. The present work demonstrates that SWCNTs not only serve as a template for growing nanocrystals but also behave as an electron-transfer catalyst in the spatially confined redox reaction by donation of electron density for temporary use by the guests.