P. N. D’yachkov

Electronic structure of boron nitride nanotubes intercalated with transition metals

The electronic structure of semiconductor (5,5) boron nitride nanotubes intercalated with 3d metals has been studied by quantum-chemical methods. The linear augmented-cylindrical-wave method has been used for calculating the total and partial densities of electronic states as a function of metal concentration and nature and the structure of the carbon shell. Metallized nanowires based on (5,5) BN nanotubes with one, two, three, and four metal atoms in the cross section have been calculated. The introduction of metals is accompanied by the insulator-to-metal transition of the nanotubes. For forty inorganic materials, we have determined the total densities of states of the valence band and the conduction band and the density of states at the Fermi level, which determines the concentration of free electrons that can be involved in ballistic charge transport in the nanotube. The introduction of metals not only has an effect on the conductive state of the boron nitride nanotube but also change the whole pattern of the valence band of the nanotube, in particular, increases the valence band width by 2–10 eV owing to the low-energy shift of the boron and nitrogen states.

The effect of 3d-metal intercalation on the electronic structure of metallic and semiconducting nanotubes

The electronic structure of 3d-metal-intercalated metallic (5,5) and semiconducting (10,0) nanotubes has been studied by quantum-chemical methods. The total and partial densities of states of nanotubes as a function of metal concentration and nature and the carbon-shell structure have been calculated by the linear augmented-cylindrical-wave method. Metalized nanowires based on armchair (5,5) and zigzag (10,0) nanotubes with one, two, three, and four metal atoms in the cross-section have been calculated. The introduction of the metal is accompanied by a sharp increase in the density of states at the Fermi level of the nanowire, which determines the concentration of free electrons involved in charge transfer in the nanotube. The 3d electrons of the metal and the carbon shell are nearly equally involved in electron transport in intercalated wires. Both the 3d electrons of a metal and the carbon shell should be nearly equally involved in electron transport in intercalated wires. The introduction of metals not only affects the conductive state of the carbon nanotube but also changes the entire pattern of its valence band, in particular, increases the valence band width of the nanotube by 5–10 eV owing to the low-energy shift of the 2s(C) states.

Electronic structure of a gold nanotube

The electronic structure of a gold nanotube has been studied by quantum-chemical methods. The energy dependences of total and partial densities of states of a nanotube with 16 atoms in a translational unit cell have been calculated by the linearized augmented-cylindrical-wave method. It has been demonstrated that the nanotube has a metal-like band structure. The s(Au) states are located completely in the valence band and are not involved in electron transport. The Fermi level is located at the peak of the total and partial d(Au) densities of states, which should contribute to the high electron tunneling conductance of the system. The valence band width is 11 eV.

Linear augmented cylindrical wave Green’s function method for perfect nanotubes and nanotubes with regular and point impurities

Nanotubes are giant cage molecules looking like closed hollow cylindrical shells. This review deals with basic principles of the linear augmented cylindrical Green’s function method and its applications to calculation of the electronic structure of perfect nanotubes and those containing substitutional impurities. A major argument for using cylindrical waves to describe nanotubes is that such a choice of the basis set makes it possible to explicitly consider the actual cylindrical geometry of nanotubes, which, in particular, ensures rapid convergence of iterative procedures. A computation technique has been described and the results of calculations of the band structure and densities of states of carbon and boron nitride nanotubes have been reported. Special attention has been paid to the changes in the electronic properties of nanotubes induced by the substitution of nitrogen, boron, or oxygen for C atoms in the carbon nanotubes, as well as to the isoelectronic substitution of P, Sb, or As for the nitrogen and of Al, In, or Ga for the boron in boron nitride nanotubes.

Electronic structure of carbon nanotubes with copper core

The electronic structure of copper-intercalated carbon nanotubes has been studied by quantum-chemical methods. The total and partial densities of states of nanotubes have been calculated by the linear augmented-cylindrical-wave method. The armchair (5,5) nanotubes with one, two, three, and four copper atoms per unit cell have been calculated The introduction of the metal is accompanied by a sharp increase in the density of states at the Fermi level of the nanowire, which determines the concentration of free electrons involved in charge transfer in the nanotube. The 3d electrons of the metal and the carbon shell are nearly equally involved in electron transport in intercalated wires.

The effect of 3d-metal dopants on the electronic structure of carbon nanotubes

In the course of synthesis of nanotubes, atoms of transition metals used as a catalyst can be substituted for carbon atoms. The electronic properties of semiconducting (13,0) and metallic (5,5) nanotubes doped with Co and Ni atoms have been calculated by ab initio quantum-chemical methods. The total and partial densities of states have been determined. The conclusion has been made that Co and Ni substituted for carbon disturb the electronic structure of metallic and semiconducting nanotubes. Such dopants can be detected by spectral and electrical measurements.

Spin-dependent band structures of nanotubes

A quantum-mechanical ab initio method, with inclusion of spin–orbit coupling, has been suggested for the calculation of the electronic structure of carbon chains (carbynes) and nanotubes. Consideration of spin–orbit coupling leads to the formation of spin–orbit gaps with a width of 2–3 meV in carbynes and up to 1 meV in nanotubes, as well as to spin polarization in chiral nanotubes.

Band structures of atomic chains of group IV, III–V, and II–VI elements

The relativistic band structures of AN and ANB8–N chains have been calculated by the linear augmented-cylindrical-wave method, which is an extension of the augmented-plane-wave method for cylindrical polyatomic systems. The band structures of covalent monatomic chains of Group IV elements are characterized by σ(s), π+, and π–, and σ(pz)* bands. The C, Si, Ge, and Sn chains are metallic. There is a considerable difference between the relativistic and nonrelativistic band structures. Because of the cylindrical symmetry of chains in the nonrelativistic model, the π bands crossing the Fermi level are orbitally doubly degenerate (i.e., the π+ and π– band energies are exactly the same). The spin and orbital motion of electrons are coupled in the chains to split π bands, but each π+ and π- band is doubly spin-degenerate. The spin–orbit splitting energy for C and Sn chains varies from 1.7 meV to 0.67 eV. The mass–velocity correction reduces all valence band levels: the level shifts are 2–5 meV for C and up to 2.2 eV for Sn. The Darwin corrections are several-fold lower than the mass–velocity contributions. A sharp change in the band structure is observed in going from covalent to partially ionic chains. The carbon chain has a metallic band structure with a zero gap in the center of the Brillouin zone, and a boron nitride chain is an insulator with an optical gap of 8 eV and optical transitions between the occupied π and vacant π* states at the edge of the Brillouin zone (this is explained by the existence of the antisymmetric component of the electron potential in the BN wire, which mixes even bonding and odd antibonding π states). Going from the BN chain to the AlP, GaAs, and InSb chains is accompanied by a decrease in the chemical bond ionicity, which leads to a gradual decrease in the π–π* gaps.

Nonlinear current in modified nanotubes with exposure to alternating and constant electric fields

Nonlinear current density was studied as a function of the value of alternating and constant electric fields in modified carbon nanotubes (CNTs). The nonlinear current value in modified CNTs is one to two orders of magnitude higher than in unmodified CNTs. This trend makes it possible to decrease the surface density in an ensemble of weakly interacting nanotubes in considering the problem of electromagnetic radiation generation.

Electronic structure of carbon nanotubes with an impurity point defect

A method for calculating the electronic structure of point defects in nanotubes is developed on the basis of the linear augmented cylindrical wave (LACW) method. The Green function of a defect nanotube is calculated using the Dyson matrix equation. The consideration is carried out in terms of the local density functional theory and the muffin-tin approximation for the electronic potential. Local densities of state are calculated for boron and nitrogen dopants in metal, semimetal, and semiconductor and chiral and nonchiral nanotubes. An increased density of states at the Fermi level is the most significant effect of boron and nitrogen dopants in metal nanotubes. In all semiconductor nanotubes, localized boron states close the optical band-gap. The effect of nitrogen atoms is restricted to a small rise in local densities of state at the Fermi level.