Armchair Boron Nitride Nanotubes Research Articles

SiC-doped boron nitride nanotubes: computations of 11B and 14N quadrupole coupling constants

Density-functional theory calculations have been performed to investigate the properties of the electronic structures of silicon–carbon-doped boron nitride nanotubes (BNNTs). The geometries of zigzag and armchair BNNTs were initially optimized and the quadrupole coupling constants subsequently calculated. The results indicate that doping of B and N atoms by C and Si atoms has more influence on the electronic structure of the BNNTs than does doping of B and N atoms by Si and C atoms. The changes of the electronic sites of the N atoms are also more significant than those of the B atoms.

Density Functional Study of Defects in Boron Nitride Nanotubes

Abstract The electronic structure properties of two pristine and defected models of zigzag and armchair boron nitride nanotubes (BNNTs) are computationally studied. Chemical shielding (CS) tensors at the sites of various boron-11 (B-11) and nitrogen-15 (N-15) nuclei in each of the optimized structures are calculated and converted to isotropic and anisotropic chemical shieldings (ICS and ACS, respectively). The ACS values revel that boron atoms at the end of nanotube play the major role in determining the characteristic properties of the BNNTs. Defects are considered by removing a B-N bond from the pristine models yielding B-B and N-N bonds in the zigzag but not in the armchair BNNT. The changes of the CS tensors at the sites of those B-11 and N-15 nuclei in the B-B and N-N bonds are the most significant among other nuclei. The calculations are performed employing BLYP method and 6–31G* standard basis set using GAUSSIAN 98.

Effect of nanotube length on the aromaticity and CSI parameters of finite length single-wall zigzag and armchair boron nitride nanotubes

Density functional theory (DFT) is used to determine chemical-shielding isotropic (CSI) and nucleus-independent chemical shift (NICS), an index of local aromaticity, for the composing of finite length (6, 0) and (4, 4) single-wall boron nitride nanotubes (BNNTs) as a function of their length for the first time. One of the highlights of the study is different CSI values of middle layers for both zigzag and armchair BNNTs, whereas the values do not change much for the middle layers with increase of the nanotube lengths. So the computed CSI values may spread and apply to the longer nanotubes. The NICS variations beside zigzag BN nanotubes are more significant within armchair BNNTs with increase of nanotube length.

First-principles calculations: half-metallic Au–V(Cr) quantum wires as spin filters

The half-metallic behavior of Au–V(Cr) quantum wires adsorbed on an armchair (5, 5)boron nitride nanotube is obtained by performing spin-polarized density functionalcalculations. The density of states shows a metallic property at the Fermi level for themajority spin channel and a semiconductor gap in the minority spin channel. Thehalf-metallic behavior of the quantum wire/nanotube complex originates from thehalf-metallic behavior of the free-standing Au–V(Cr) quantum wires. The calculations ofspin-polarized transport indicate that such a one-dimensional half-metallic magnet can beused as a spin filter.

Structural Study of Boron - Nitride Nanotube with Magnetic Resonance (NMR) Parameters Calculation via Density Functional Theory Method (DFT)

Abstract — A model of (4, 4) single-walled boron-nitride nanotube as a representative of armchair boron-nitride nanotubes studied. At first the structure optimization performed and then Nuclear Magnetic Resonance parameters (NMR) by Density Functional Theory (DFT) method at 11 B and 15 N nuclei calculated. Resulted parameters evaluation presents electrostatic environment heterogeneity along the nanotube and especially at the ends but the nuclei in a layer feel the same electrostatic environment. All of calculations carried out using Gaussian 98 Software package. Keywords — Boron-nitride nanotube, Density Functional Theory, Nuclear Magnetic Resonance (NMR). I. I NTRODUCTION INCE the discovery of carbon nanotubes (CNTs)[1], considerable attention has been attracted for synthesizing them due to their unique properties[2] and potential applications[3]-[5]. People have so far synthesized various structural and morphological CNTs such as multi-, single-, and double- walled[6],[7], as well as Y-, bamboo-, and cone-shaped CNTs[8],[9]. Recently boron nitride nanotubes (BNNT) in which BN unit is isoelectronic to C-C unit in CNT, have attracted increasing attention. The stability of BNNT was predicted firstly on the basis of semi-experiential tight binding (TB)[10] and local density approximated (LDA) density functional theory[11] calculations in 1994, and their synthesis was realized in 1995 with arc-charging method using the BN electrode packed into a metal casing[12] . Other preparation methods have been developed subsequently, such as arc-melting[13], high temperature chemical reaction[14], carbon nanotube templates[15], and laser ablating[16]. At same time, further theoretical investigations for the structures and electronic properties of BNNT have been reported [17]–[27]. Nuclear Magnetic Resonance (NMR) is a powerful tool for

THEORETICAL STUDIES ON THE LASER-DRIVEN MANY-ELECTRON DYNAMICS OF FINITE-SIZE BORON-NITRIDE NANOTUBES

We present a theoretical study on the electronic dynamics of finite-size Boron-Nitride Nanotubes (BNNTs) driven by the linearly polarized (LP) and circularly polarized (CP) intense laser fields. The many-electron dynamics is described by propagating the reduced one-electron density matrix in real-time domain. The high harmonic generation (HHG) spectra and the time evolution of charge density during harmonic generation are demonstrated. Comparison is made with Carbon Nanotubes (CNTs). The selection rules (SRs) for HHG of finite-size nanotubes are established. One of the important consequences of our results is that HHG of finite-size nanotubes are dependent not only on the molecular point-groups but also on the strength of inter chain interactions. The characteristic difference in nonlinear optical properties between finite and infinitely extended zigzag and armchair BNNTs is significant. Another important consequence is that the laser pulse can drive the electrons to move along or normal to tube axis and produce a charge current on the tube wall.

Electronic Structure of Carbon Doped Boron Nitride Nanotubes: A First-Principles Study

We determine atomic and electronic structures of arm-chair and zigzag boron nitride nanotubes (BN-NTs) of different diameters using first-principles pseudopotential-based density functional theory calculations. We find that the structure of BN-NTs in bundled form is slightly different from that of the isolated BN-NTs, reflecting on the inter-tube interactions. Effects of carbon doping on the electronic structure of (5,5) and (5,0) BN-NTs are determined: carbon substitution either at B-site, being energetically very stable, or at N-site can yield magnetically polarized semiconducting state, whereas carbon substitution at neighbouring B and N sites yields a non-magnetic insulating structure.

Chemisorption-Induced Polarization of Boron Nitride Nanotube

We performed density functional theory (DFT) calculations to investigate the adsorption of atomic hydrogen (H) on the wrapping axis of nonpolar arm-chair (5,5) and chiral (8,4) boron nitride nanotubes (BNNTs) with a view toward understanding the chemisorption-induced polarization field in BNNTs. The adsorption of H along the zigzag B−N bonds that lie on the wrapping axis of the BNNT enhances the macroscopic polarization field. Depending on whether the B or N site near the edge of the nanotube is adsorbed with H, the direction of the polarization field, as well as the work function of the tube ends, can be changed significantly. The relationship between the chemical effect as well as the geometric distortion of the tube caused by chemisorption and the induced polarization were investigated, respectively. The results have implications for the application of BNNTs as electron emitters.

CARBON-SUBSTITUTING IN (4,4) BORON NITRIDE NANOTUBE: DENSITY FUNCTIONAL STUDY OF BORON-11 AND NITROGEN-14 ELECTRIC FIELD GRADIENT TENSORS

Density functional theory (DFT) study is performed to investigate the influence of carbon substituting in a representative model of armchair boron nitride nanotubes (BNNTs). To this aim, the electric field gradient (EFG) tensors at the sites of11B and11N nuclei are calculated in two models of (4,4) single-walled BNNT. Model one (raw) consists of 36 B and 36 N atoms with 12 saturating H atoms of two mouths while 7 B and 7 N atoms are substituted by 14 C atoms like a wire in model two ( C -substituted). The converted EFG tensors to measurable nuclear quadrupole resonance (NQR) parameters, quadrupole coupling constant (CQ) and asymmetry parameter (ηQ), reveal that the CQvalues in the length of raw BNNT are divided into some layers with equal magnitude and among them the mouth layers have the largest CQmagnitudes. In the C -substituted model, in addition to the mouth layers, the CQof those B and N nuclei directly bonded to C atoms are increased to the magnitudes as large as those mouth nuclei meaning that the active sites are increased in the C -substituted BNNT model. It is worth noting that the NQR parameters of other nuclei rather than those directly bonded to C and also those in the first neighborhood of C atoms are almost in equal values in the two models. Comparing the results with a recent study on zigzag BNNT (Mirzaei M et al., Z. Naturforsch A62:56, 2007) reveals that armchair and zigzag BNNTs show almost similar electronic properties. However, there is a significant difference in the electronic properties of those B and N atoms located at the mouth of the two BNNTs whose mouths are similar in armchair, whereas there are two different mouths ( B -mouth and N -mouth) in zigzag BNNT.

Theoretical explorations on the armchair BN nanotube with defects

A systematic study of armchair boron nitride nanotubes (BNNTs) with defects has been carried out within density functional theory. The effect brought by the defects is localized. The defect sites have major contribution to the frontier molecular orbital and change the conductivity of the BNNTs. The defect sites are reactive centers. The substitution of boron with carbon enhances the field emission of the tubes. Doping or vacancy defect creates active center on nanotubes, thus broadening the applications of nanotubes in chemistry and material sciences through functionalization.

Junctions between a boron nitride nanotube and a boron nitride sheet

For future nanoelectromechanical signalling devices, it is vital to understand how toconnect various nanostructures. Since boron nitride nanostructures are believed to begood electronic materials, in this paper we elucidate the classification of defectgeometries for combining boron nitride structures. Specifically, we determinepossible joining structures between a boron nitride nanotube and a flat sheet ofhexagonal boron nitride. Firstly, we determine the appropriate defect configurations onwhich the tube can be connected, given that the energetically favourable rings forboron nitride structures are rings with an even number of sides. A new formulaE = 6+2J relating the number ofedges E and the numberof joining positions J is established for each defect, and the number of possible distinct defects is related to theso-called necklace and bracelet problems of combinatorial theory. Two least squaresapproaches, which involve variation in bond length and variation in bond angle, areemployed to determine the perpendicular connection of both zigzag and armchair boronnitride nanotubes with a boron nitride sheet. Here, three boron nitride tubes, which are (3,3), (6, 0) and (9, 0) tubes, are joined with the sheet, and Euler’s theorem is used to verifygeometrically that the connected structures are sound, and their relationship withthe bonded potential energy function approach is discussed. For zigzag tubes(n,0), it is proved that such connections investigated here are possible only forn divisible by 3.

Density functional calculations of 14N and 11B NQR parameters in the H-capped (6,0) and (4,4) single-walled BN nanotubes

Density functional theory (DFT) calculations were performed to calculate nitrogen-14 and boron-11 nuclear quadrupole resonance (NQR) spectroscopy parameters in the representative considered models of zigzag and armchair boron nitride nanotubes (BNNTs) for the first time. The considered models consisting of 1 nm length of H-capped (6,0) and (4,4) single-walled BNNT were first allowed to fully relax and then the NQR calculations were performed on the geometrically optimized models. The evaluated nuclear quadrupole coupling constants and asymmetry parameters for the mentioned nuclei reveal that the considered models can be divided into four layers of nuclei with an equivalent electrostatic environment where those nuclei at the ends of tubes have a very strong electrostatic environment compared to the other nuclei along the length of tubes. Those nuclei at the center of the tube length also have an equivalent electrostatic environment. The calculations were performed based on the B3LYP DFT method and 6-311G** and 6-311++G** standard basis sets using the Gaussian 98 package of program.

Adsorption and Surface Reactivity on Single-Walled Boron Nitride Nanotubes Containing Stone−Wales Defects

Adsorption of chemical species H, O, CO, H2, O2, H2O, and NH3 on the sidewall of zigzag (8,0) and armchair (5, 5) boron nitride nanotubes (BNNTs) is studied using density-functional theory. Particular attention is paid to searching for the most-stable configuration of the adsorbates at a perfect site (PS) and near a Stone−Wales (SW) defect, and the surface reactivity at the PS and near the SW defect. Reactivity near the SW defect is generally higher than that at the PS because of the formation of frustrated B−B and N−N bonds and the local strain caused by pentagonal and heptagonal pairs. O2 is prone to dissociative chemisorption near SW defects, but is more likely physisorbed at the PS. The adsorption of H2O and NH3 on the sidewall of BNNT can be described as molecular chemisorption due to modest interaction between HOMO of H2O or NH3 with LUMO of BNNT. Adsorption of NH3 can affect electronic properties of BNNT through lifting the Fermi level. As such, NH3 can be viewed as an n-type impurity. CO and H2 ca...

Structure and electronic properties of armchair boron nitride nanotubes

The structure and electronic properties of armchair boron nitride nanotubes have been investigated as a function of tube diameter using density functional theory. The length of each nanotube is kept constant. The structural parameters of the open end nanotube are studied. The variation in structural parameters is analyzed based on atomic charges of Mulliken and natural population analyses schemes. A topological analysis for charge density ( ρ), and its second derivative (∇ 2 ρ) for bonds have been performed using atoms in molecules (AIM) theory. Finally, the analysis of the charge distribution and charge transfer processes have been studied using the NBO partitioning scheme, which helps us to understand the interactions inside the boron nitride nanotubes which are responsible for the stabilization of the armchair boron nitride nanotubes.

Spin-polarized electron current from carbon-doped open armchair boron nitride nanotubes: Implication for nano-spintronic devices

Spin-polarized density functional calculations show that the substitutional doping of carbon (C) atom at the mouth changes the atomic and spin configurations of open armchair boron nitride nanotubes (BNNTs). The occupied/unoccupied deep gap states are observed with the significant spin-splitting. The structures and spin-polarized properties are basically stable under the considerable electric field, which is important for practical applications. The magnetization mechanism is attributed to the interactions of s, p states between the C and its neighboring B or N atoms. Ultimately, advantageous geometrical and electronic effects mean that C-doped open armchair BNNTs would have promising applications in nano-spintronic devices.

The structure and electronic property of BN nanotube

The structure, stability of the zigzag ( n,0; n=3–17) and armchair ( m, m; m=2–10) boron nitride nanotubes have been investigated within the framework of generalized gradient approximated (GGA) density functional theory. Significant differences in structure and stability are found between both forms with small tube size with the fact that the armchair form has larger binding energy and band gap than the zigzag form, while both forms have equal properties in infinite size. These differences provide the basis for the fine-tuning of the chemical and physical properties of these nanotubes.

Ab initio calculations on the open end of single-walled BN nanotubes

Geometrical and electronic structures of open-ended armchair and zigzag single-walled boron nitride (BN) nanotubes are calculated using density functional theory with the generalized gradient approximation. The BN dimers at the open end of armchair BN nanotubes are buckled greatly, i.e., B atoms move inward and N atoms move outward, on which the size of BN nanotubes has a very small influence. The ionization potential of the B-terminated zigzag BN nanotube is smaller than that of the N-terminated BN nanotube due to the opposite direction of the surface dipole moment, which makes a B-terminated zigzag BN nanotube more efficient for field electron emission than the corresponding N-terminated BN nanotubes.

Phonon structure and dynamics of boron nitride single wall nanotube

We report a detailed study of the phonon properties of hexagonal boron nitride (BN) monolayers as well as nanotubes by using De Launay type of angular force model. The force constants used for calculation of phonon dispersion relations of the nanotube are derived from those for the monolayers of hexagonal by employing force constant method. These force constants have been modified to include the effect of curvature of the tubule. The results are then used to derive the phonon dispersion relations for (10,10) BN nanotubes using ‘zone-folding’ method. Calculated phonon modes are in good agreement with the experimental values obtained so far, for (10,10) armchair BN nanotubes.

Symmetry properties of single-walled boron nitride nanotubes

The symmetry operations for armchair, zigzag, and chiral boron nitride nanotubes (BN-NT's) are identified. It is found that each type belongs to a different family of nonsymmorphic rod groups. Armchair BN-NT's with even index n are found to be centrosymmetric. We determine the numbers of Raman- and infrared-active vibrations in single-walled BN-NT's. We find that, in contrast to achiral carbon nanotubes, zigzag BN-NT's possess almost twice the Raman- and infrared-active vibrations as armchair BN-NT's.