A. S. Kolesnikova

Empirical modeling of longitudinal tension and compression of graphene nanoparticles and nanoribbons

Longitudinal tension and compression of graphene nanoparticles and nanoribbons have been studied using an empirical model. The pseudo-Young’s modulus of graphene nanoparticles and nanoribbons has been calculated. The size effect, i.e., the dependence of the elastic modulus on linear parameters of graphene objects, has been studied. An increase in pseudo-Young’s modulus discontinues as the length increases during the nanoparticle-to-nanoribbon transition. For the same perimeter, the graphene ribbon edges are characterized by smaller pseudo-Young’s moduli in comparison with uniaxial carbon nanotubes. Elastic deformation of graphene nanoparticles and nanoribbons has been observed in the relative length variation range of 0.93–1.12.

Elastic and electrostatic properties of bamboo-shaped carbon nanotubes

A technology has been developed to synthesize films of bamboo-shaped carbon nanotubes from simple nanotubes by high-frequency oxygen plasma etching for 30 and 60 s. The electronic structure and mechanical properties of bamboo-shaped single-walled carbon nanotubes have been studied theoretically. Compartments in these structures are located at an optimum distance that corresponds to a decrease in the ionization potential and an improvement of the emission properties. It has been revealed that the Young’s and torsion moduli of the bamboo-shaped carbon nanotubes depend on the number of compartments. These tubes have their own dipole moments in contrast to the hollow defect-free tubes. It has been shown that bamboo-shaped nanotubes 1.37 nm in diameter are the most stable nanoclusters.

Mechanical and emission properties of thinnest stable bamboolike nanotubes

We investigate the stability of carbon bamboo-like nanotubes (BCNTs) with different diameters. It is shown that BCNTs with a diameter of 2.024 nm are the most stable bamboo-like nanotubes with the smallest diameter. It is shown that bamboo-like nanotubes with a certain distance between the bridges have superior emission properties than that the hollow nanotubes. Emission properties of the infinite bamboo-like nanotubes can be improved by adding the potassium atoms into the nanotube atomic structure. In this case the potassium atoms concentration should exceed 0.59%.

Emissivity of a multibeam electron gun with a glassy carbon field-emission cathode

A multibeam triode electron gun with a glassy carbon field-emission cathode that is intended for an O-type microwave amplifier is studied. The electric field strength and the current density at the microtips versus the distance to the center of a cell of the cathode–grid unit are calculated. Calculation data are compared with experimental results. It is shown that about 70% of the cathode current in each cell is accounted for by microtips arranged in a circumferential ring no wider than 20 μm. The field-emission current density inside the ring exceeds 40 A/cm2, and the current per microtip equals 43.1 μA.

Atomic structure of energetically stable carbon nanotubes/graphene composites

The atomic structure of energetically stable composites based on carbon nanotubes and graphene has been studied. The energy stability has been determined from the change in the total energy of the studied system. It has been found that the geometric parameters of the nanotube affect the stability of the minimum structural link of the composite. The structural configuration of the composite with armchair nanotubes 12.12 Å in diameter and 18.44 Å in length exhibits the highest stability. It has been shown that the energy stability of the composite increases with an increase in the number of links in it.

Giga- and terahertz-range nanoemitter based on peapod structure

We propose a theoretical model of a nanoemitter for giga- and terahertz-range waves. The model is based on a peapod structure comprising a carbon nanotube with chiral indices (10, 10). Three encapsulated and partially polymerized fullerene C60 molecules and a positively charged C60 fullerene are trapped inside the nanotube. The motion of the charged fullerene and the radiation frequency were controlled using an external electric field. Stable terahertz radiation at a frequency of 0.36 THz was produced at 300 K with an external electrical field of 10 V/μm. Stable radiation in the gigahertz range was observed at 50 K with an electric field below 10 V/μm. A theoretical simulation was performed using the tight-binding molecular dynamics method with a description of the van der Waals interaction by the Morse potential. The system described by the theoretical model was experimentally observed.

Moving of fullerene between potential wells in the external icosahedral shell.

The results of the theoretical investigation of the behavior of fullerenes C20 and C60 inside the icosahedral external shell on example of carbon nanoclusters, C20@С240 and C60@С540, are presented in this article. The multiwell potential of interaction between fullerenes in investigated nanoclusters is calculated to reveal the regularities of moving for internal fullerene in the field of holding potential of the external shell. The possible variants of fullerenes C20 and C60 moving between the potential wells are predicted on base of topology data of the fullerenes relative positioning in nanoparticle and analysis of relief of the energy surface of interaction between fullerenes. The formulated prediction is confirmed by the data of the numerical experiment. The investigation of two‐shell fullerenes allows to conclude that the light fullerene С20 will probably jump between the potential wells already at small temperatures (139–400 K) if the external shell is slightly bigger.

Strain-hardening effect of graphene on a chain of the chitosan for the tissue engineering

We report the results of the chitosan dimer study, the mechanism of its interaction with the carbon nanostructures and also the mechanical properties of the chitosan/graphene, chitosan/nanotube complexes using the density function and the molecular dynamic methods. It was established that the physical adsorption of the chitosan with graphene is carried out by the Van der Waals interaction between the hexagonal links of the chitosan with the hexagonal cell of the atomic grid of graphene and nanotube.

Elastic properties of graphene-graphane nanoribbons

The results of theoretical investigation of the atomic structure, deformations, and elastic properties of graphene-graphane nanoribbons (GGN) are represented here. To study the properties of GGN we applied the empirical method based on the bond-order potential developed by Brenner and the tight-binding method. We calculated the Youngs pseudo-modulus of GGN and the strain energy of GGN subject to axial tension and compression. The curve of the strain energy collapse occurs at the axial compression of 0.03?0.04. Plane atomic network subject to axial compression becomes wave-like. This is a so-called phase transition. Elasticity of armchair-graphene nanoribbons is greater than elasticity of armchair nanotubes and graphane nanoribbons with the same width and length.

Prediction of stability for carbon nanotori

At the present time carbon nanostructures are the main functional material for the development of electronic devices of broad applications. One of the most perspective for practical application forms of carbon nanostructures are nanotori. This paper presents results of prediction the stability of toroidal structures using computer modeling methods. The stability of carbon nanotori are determined by scanning of the local stresses map. Obtained results showed that the highest stability is characterized for carbon nanotori (13, 0) formed by the folding of a zigzag carbon nanotube. These nanotori are characterized by the lowest enthalpy of structure formation (101 eV).