E. F. Kislyakov

Uniaxially deformed (5,5) carbon nanotube: Structural transitions

The Kekule structure of the ground state of (5,5) armchair carbon nanotube is revealed by semiempirical molecular orbital calculations. This structure has bonds with two different bond lengths, differing by 0.003 nm. The ground state has tripled (compared to undistorted case) translational period due to Peierls distortions. Two first order structural phase transitions controlled by the tension are predicted at zero temperature. These transitions correspond to 5% and 13% elongations of a uniaxially deformed (5,5) nanotube. The narrow gap semiconductor to metal transition is predicted at 5% elongation of the nanotube.

Nanotube-based nanoelectromechanical systems: Control versus thermodynamic fluctuations

Multi-scale simulations of nanotube-based nanoelectromechanical systems (NEMS) controlled by a nonuniform electric field are performed by an example of a gigahertz oscillator. Using molecular dynamics simulations, we obtain the friction coefficients and characteristics of the thermal noise associated with the relative motion of the nanotube walls. These results are used in a phenomenological one-dimensional oscillator model. The analysis based both on this model and the Fokker-Planck equation for the oscillation energy distribution function shows how thermodynamic fluctuations restrict the possibility of controlling NEMS operation for systems of small sizes. The parameters of the force for which control of the oscillator operation is possible are determined.

Magnetically operated nanorelay based on two single-walled carbon nanotubes filled with endofullerenes Fe@C20

Structural and energy characteristics of the smallest magnetic endofullerene Fe@C20 were calculated using the density functional theory. The ground state of Fe@C20 was found to be a septet state, and the magnetic moment of Fe@C20 was estimated to be 8 Bohr magnetons. The characteristics of an (8,8) carbon nanotube with a single Fe@C20 inside were studied with a semiempirical approach. The scheme of a magnetic nanorelay based on cantilevered nanotubes filled with magnetic endofullerenes was examined. This nanorelay is turned on as a result of bending of nanotubes by a magnetic force. The operational characteristics of such a nanorelay based on (8,8) and (21,21) nanotubes fully filled with Fe@C20 were estimated and compared to the ones of a nanorelay made of a (21,21) nanotube fully filled with experimentally observed (Ho3N)@C80 with the magnetic moment of 21 Bohr magnetons. The room-temperature opera- tion of (21,21) nanotube-based nanorelays was demonstrated.

Control of the motion of nanoelectromechanical systems based on carbon nanotubes by electric fields

A new method is proposed for controlling the motion of nanoelectromechanical systems based on carbon nanotubes. In this method, a single-walled nanotube acquires an electric dipole moment owing to the chemical adsorption of atoms or molecules at open ends of the nanotube. The electric dipole moments of carbon nanotubes with chemically modified ends are calculated by the molecular orbital method. These nanotubes can be set in motion under the effect of a nonuniform electric field. The possibility of controlling the motion of nanoelectromechanical systems with the proposed method is demonstrated using a nanotube-based gigahertz oscillator as an example. The operating characteristics of the gigahertz oscillator are analyzed, and its operation is simulated by the molecular dynamics method. The controlling parameters and characteristics corresponding to the controlled operating conditions at a constant frequency for the system under investigation are determined.

Electronic energy band structure of uniaxially deformed (5,5) armchair carbon nanotube

Semiempirical molecular orbital calculations of the (5,5) armchair carbon nanotube give the Kekule structure in its ground state with two essentially different bonds (the bond lengths difference is 0.003 nm). This is a result of the Peierls distortions leading to tripled (compared with undistorted case) translational period. When the armchair nanotube is elongated, two first order deformational structural phase transitions are predicted. The first one at the elongation of 5% leads to doubling of a translational period (instead of tripling at smaller elongations). The second one at the elongation of 13% leads to the quinoid type structure. The dependence of the electronic energy-band structure of the (5,5) carbon nanotube on elongation is investigated using the tight binding approximation. The transition from narrow-gap semiconductor to metal is predicted at the elongation of 5%, indicating that the uniaxially deformed armchair carbon nanotube at greater elongation (more than 5%) remains metallic at all temperatures.

Electronic band structure and magnetic states of zigzag graphene nanoribbons: quantum chemical calculations

Abstract. Quantum-chemical semi-empirical molecular-orbital calculations of zigzag graphene nanoribbons (nzGNRs) were done for the number of zigzag carbon chains n=4 and 10. The antiferromagnetic (AFM) nature of zGNRs’ ground state was confirmed. The energy difference between AFM and ferromagnetic (FM) states was calculated, and dimerization patterns of their chemical bond lengths were elucidated. The electron energy band structure calculations show that narrow nanoribbon (4 zGNR) is semiconducting in both AFM and FM states. For wider nanoribbon (10 zGNR), the AFM state is semiconducting (≈0.1  eV band gap), whereas the FM state is half-metallic (electrical conduction with only one spin orientation).

Effect of Peierls transition in armchair carbon nanotube on dynamical behaviour of encapsulated fullerene

The changes of dynamical behaviour of a single fullerene molecule inside an armchair carbon nanotube caused by the structural Peierls transition in the nanotube are considered. The structures of the smallest C20 and Fe@C20 fullerenes are computed using the spin-polarized density functional theory. Significant changes of the barriers for motion along the nanotube axis and rotation of these fullerenes inside the (8,8) nanotube are found at the Peierls transition. It is shown that the coefficients of translational and rotational diffusions of these fullerenes inside the nanotube change by several orders of magnitude. The possibility of inverse orientational melting, i.e. with a decrease of temperature, for the systems under consideration is predicted.

Interwall conductance in double-walled armchair carbon nanotubes

Abstract The dependence of the interwall conductance on distance between walls and relative positions of walls are calculated at the low voltage by Bardeen method for ( n , n ) @ ( 2 n , 2 n ) double-walled carbon nanotubes (DWCNTs) with n = 5 , 6 , … , 10 . The calculations show that interwall conductance does not depend on temperature (for T ⩽ 500 K ) and current-voltage characteristic is linear. The conductance decreases by 6 orders of magnitude when the interwall distance is doubled. Thus, depending on the interwall distance, DWCNTs can be used as temperature stable nanoresistors or nanocapacitors.

Control of the motion of nanoelectromechanical systems based on carbon nanotubes

A new method is proposed for controlling the motion of nanoelectromechanical systems based on carbon nanotubes. In this method, a single-walled nanotube acquires an electric dipole moment owing to the chemical adsorption of atoms or molecules at open ends of the nanotube and, then, the electric dipole moment thus induced can be set in motion under the effect of a nonuniform electric field. The electric dipole moments of chemically modified nanotubes are calculated for the first time. The possibility of controlling the motion of nanotube-based nanoelectromechanical systems with the proposed method is demonstrated using a gigahertz oscillator as an example. The operating characteristics of the gigahertz oscillator and the controlling electric field are calculated.

One-dimensional quantum transport in lead phthalocyanine nanostructures

A model of the electron structure of a nanoobject comprising a stack of lead phthalocyanine (PbPc) molecules with stacking faults is proposed. The results of the molecular orbital (MO) calculation indicate that a 0.6e charge is transferred from Pb atom to the Pc macrocycle ring and show that the nanostructure can be considered as a metal-filled nanotube. The proposed model provides for the first time a quantitative interpretation of the electric switching effect previously observed in PbPc films.