Denis A. Areshkin

Semiconducting graphene nanostrips with edge disorder

Results of calculations are presented which show that edge disorder can easily transform semiconducting graphene nanostrips into Anderson insulators. However, it is also shown that this problem could be overcome by adjusting the nanostrip aspect ratio to decrease the effects of the edge disorder without making the nanostrip so wide as to close the semiconducting band gap or so short as to allow tunneling through the band gap.

Predicted structure and electronic properties of individual carbon nanocones and nanostructures assembled from nanocones

Calculations using an analytic potential show that carbon nanocones can exhibit conventional cone shapes or can form concentric wave-like metastable structures, depending on the nanocone radius. Single nanocones can be assembled into extended two-dimensional structures arranged in a self-similar fashion with fivefold symmetry as system size is increased. Calculations of the electronic properties of nanocones indicate that a pentagon in the centre of a cone is the most probable spot for emitting tunnelling electrons in the presence of an external field. This implies that nanocone assemblies, if practically accessible, could be used as highly localized electron sources for templating at scales below more traditional lithographies.

Bonding and Stability of Hybrid Diamond/Nanotube Structures

Geometrical considerations combined with detailed atomic modeling are used to define general classes of diamond/carbon nanotube interface structures with low residual stresses and no unsatisfied bonding. Chemically and mechanically robust interfaces are predicted, supporting recent experimental studies in which structures of this type were proposed.

Electron emission properties of detonation nanodiamonds

This paper summarizes the results of systematic studies of field electron emission from detonation nanodiamond coatings corresponding to nanodiamond powders of different modifications. The role of the chemical composition of the surface of detonation nanodiamond particles in field emission mechanisms is discussed. Field emission-related electronic properties of single diamond nanodots are studied using tight-binding calculations and continuum electrostatic simulations.

Carbon based nanostructures: diamond clusters structured with nanotubes

Feasibility of designing composites from carbon nanotubes and nanodiamond clusters is discussed based on atomistic simulations. Depending on nanotube size and morphology, some types of open nanotubes can be chemically connected with different facets of diamond clusters. The geometrical relation between different types of nanotubes and different diamond facets for construction of mechanically stable composites with all bonds saturated is summarized. Potential applications of the suggested nanostructures are briefly discussed based on the calculations of their electronic properties using environment dependent self-consistent tight-binding approach.

Convergence Acceleration Scheme for Self-consistent Orthogonal-basis-set Electronic Structure Methods

A new self-consistent convergence acceleration scheme that is a variant of the Newton-Raphson algorithm for non-linear systems of equations is presented. With this scheme, which is designed for use with minimal orthogonal basis set electronic structure methods, the conventional Newton-Raphson scaling with respect to the number of atoms is enhanced from quartic to cubic. The scheme is demonstrated using a self-consistent environment-dependent tight binding model for hydrocarbons that allows an efficient and reasonably precise simulation of charge density distortions due to external electric fields, finite system sizes, and surface effects. In the case of a metallic system, self-consistency convergence starts at a high fictitious temperature, typically 1500 K. As the electron density approaches the self-consistent configuration the temperature is decreased. Typically, seven to nine iterations are required to achieve self-consistency in metallic systems to a final temperature of 300 K. For systems with a finite band gap the convergence may start at the target temperature so that temperature reduction is unnecessary, and typically two iterations are needed to achieve self-consistency. The convergence algorithm can handle extremely high applied fields and is very robust with respect to initial electron densities.

A self-consistent tight binding model for hydrocarbon systems: application to quantum transport simulation

As elf-consistent environment-dependent (SC-ED) tight binding (TB) method for hydrocarbons that was developed for quantum transport simulations is presented. The method builds on a non-self-consistent environment-dependent TB model for carbon (Tang et al 1996 Phys. Rev. B 53 979) with parameters added to describe hydrocarbon bonds and to account for self-consistent charge transfer. The SC-EDTB model assumes an orthogonal basis set. Orthogonality is a key element for adapting the SC-EDTB scheme to transport problems because it substantially increases the efficiency of the Newton– Raphson algorithm used to accelerate self-consistency convergence under nonequilibrium conditions. Compared to most existing TB schemes the SC-EDTB scheme is distinctive in two respects. First, self-consistency is added through the exact evaluation of Hartree and linear expansio no f exchange integrals. Al lH amiltonian elements belonging to the same atom are affected by charge transfer, not just the diagonal elements. The second distinction is the choice of SC-EDTB parameters; they were fitted t oM ulliken populations and eigenvalue spectra rather than energies or elastic properties. The former are directly related to the conductivity and potential profile, which are essential for transport simulation. No two-centre repulsive term parametrization was performed. The functionality of the method is exemplified by computing I –V curves, nonequilibrium potential profiles and current density for a resonant tunnelling device. (Some figures in this article are in colour only in the electronic version)

Self-consistent tight binding model adapted for hydrocarbon systems

A self-consistent environment-dependent tight binding method is presented that was developed to simulate eigenvalue spectra, electron densities and Coulomb potential distributions for hydrocarbon systems. The method builds on a non-self-consistent environment-dependent tight binding model for carbon [Tang et al., Phys. Rev. B 53, 979 (1996)] with parameters added to describe hydrocarbon bonds and to account for self-consistent charge transfer. A detailed description of the parameterization procedure is given. Case studies that examine electron emission-related properties of carbon nanotubes demonstrate the utility of the method. The results of these calculations indicate that field enhancement in the vicinity of a nanotube tip is higher for open-ended than for capped nanotubes. At the same time open-ended nanotubes exhibit a higher potential barrier in the tip region. This barrier deteriorates the coupling between conducting states in the nanotube and free electron states in vacuum, and may increase the field emission threshold.

Radial-breathing Mode Frequencies for Single-Walled Carbon Nanotubes of Arbitrary Chirality: First-Principles Calculations

First-principles calculations are performed for the radial-breathing mode of all 105 single-walled carbon nanotubes within the rolling-geometry diameter range of 0.4 to 1.4 nm. The diameter dependence of the frequencies is analyzed in some detail, and compared with measurable parameters of bulk graphite. The frequencies are compared with those available from other first-principles work, and experimental studies.