Single-walled Boron Nitride Nanotubes Research Articles

Theoretical study of physisorption of nucleobases on boron nitride nanotubes: a new classof hybrid nano-biomaterials

We investigate the adsorption of the nucleic acid bases—adenine (A), guanine (G),cytosine (C), thymine (T) and uracil (U)—on the outer wall of a high curvaturesemiconducting single-walled boron nitride nanotube (BNNT) by first-principles densityfunctional theory calculations. The calculated binding energy shows the order:G > A≈C≈T≈U, implying that the interaction strength of the high curvature BNNT with thenucleobases, G being an exception, is nearly the same. A higher binding energy for theG–BNNT conjugate appears to result from hybridization of the molecular orbitals ofG and the BNNT. A smaller energy gap predicted for the G–BNNT conjugaterelative to that of the pristine BNNT may be useful in the application of thisclass of biofunctional materials to the design of next-generation sensing devices.

Theoretical Study of Li, Si, and Sn Adsorption on Single-Walled Boron Nitride Nanotubes

The adsorption of Si, Sn, and Li on single-walled boron nitride nanotubes has been studied by density functional theory calculation. Both single Si or Sn atoms and their dimers are able to adsorb on the outer surface of (8,0) BNNT exothermically. The adsorption of dimers is weaker than that of a single atom. With increasing the tube diameter from (8,0) to (16,0), the adsorption energy of a single atom decreases slightly. The adsorption of single Si and Sn atoms induces magnetism whereas dimers do not. None of the single adatoms or dimers is stable inside the (8,0) BNNT. Except for a single Li atom, all other single adatoms and dimers are stable inside (12,0) BNNT with an adsorption energy of less than −0.4 eV. The alloying of a Li atom with Si or Sn further stabilizes the system, showing that BNNTs encapsulated Si or Sn might be a potential Li storage material.

Theoretical studies on the adsorption of small molecules on Pt-doped BN nanotubes

The adsorption of a series of small gaseous molecules (O 2, CO 2, C 2H 4, C 2H 2, H 2O, NH 3) on the metal center in Pt-doped (5, 5) armchair single-wall BN nanotubes (BNNTs) has been explored within density functional theory. For all these gases studied, the overall process of adsorption was found to be exothermic, where the affinity correlates with the nature of the molecule adsorbed. Charge transfer is an important factor in changing the conductivity of analyte–substrate system. The two kinds of Pt-doped BNNTs exhibit different sensitivity and selectivity to gas molecules. The electronic structure of these materials is strongly influenced by the presence of gases, hence, application of Pt-doped single-wall BNNTs as gas sensors was proposed to motivate experimental trial.

Theoretical investigation of methane adsorption onto boron nitride and carbon nanotubes

Methane adsorption onto single-wall boron nitride nanotubes (BNNTs) and carbon nanotubes (CNTs) was studied using the density functional theory within the generalized gradient approximation. The structural optimization of several bonding configurations for a CH4 molecule approaching the outer surface of the (8,0) BNNT and (8,0) CNT shows that the CH4 molecule is preferentially adsorbed onto the CNT with a binding energy of −2.84 kcal mol−1. A comparative study of nanotubes with different diameters (curvatures) reveals that the methane adsorptive capability for the exterior surface increases for wider CNTs and decreases for wider BNNTs. The introduction of defects in the BNNT significantly enhances methane adsorption. We also examined the possibility of binding a bilayer or a single layer of methane molecules and found that methane molecules preferentially adsorb as a single layer onto either BNNTs or CNTs. However, bilayer adsorption is feasible for CNTs and defective BNNTs and requires binding energies of −3.00 and −1.44 kcal mol−1 per adsorbed CH4 molecule, respectively. Our first-principles findings indicate that BNNTs might be an unsuitable material for natural gas storage.

Excitons in optical spectra of boron–nitride (BN) nanotubes

Exciton effects are studied in single-wall boron–nitride nanotubes. The Coulomb interaction dependence of the band gap, the optical gap, and the binding energy of excitons are discussed. The optical gap of the (5,0) nanotube is about 6 eV at the on-site interaction U=2 t with the hopping integral t=1.1 eV. The binding energy of the exciton is 0.50 eV for these parameters. This energy agrees well with that of other theoretical investigations. We find that the energy gap and the binding energy are almost independent of the geometries of nanotubes. This novel property is in contrast with that of the carbon nanotubes, which show metallic and semiconducting properties depending on the chiralities.

Deformation-Induced Electronic Structure Changes in Boron Nitride Nanotubes

Electronic structures of (6,0), (8,0), and (10,0) single-walled boron nitride nanotubes (SWBNNTs) under tension, torsion and flattening are investigated using first-principles calculations. Energy bands and charge distributions of the SWBNNTs are calculated within the density-functional theory, and forces required to deform the SWBNNTs are estimated from the energy variation with deformation. Our calculations show that the tension, torsion and flattening decrease energy gaps of the SWBNNTs because of a decrease in the energy of the conduction band minimum (CBM). The decrease in the CBM energy is caused by an overlap of CBM charge densities between boron atoms. It is found that the flattening deformation leads to the larger decrease in energy gaps of the SWBNNTs with the smaller force than the tension and torsion.

The Fluorinated (10, 0) Boron Nitride Nanotube: A Computational Nuclear Magnetic Resonance and Nuclear Quadrupole Resonance Study

Quantum chemical calculations at the level of density functional theory (DFT) were carried out to investigate the influence of fluorination boron and nitrogen nuclear magnetic resonance (NMR) and also nuclear quadrupole resonance (NQR) parameters in the (10, 0) single-wall boron nitride nanotube (SWBNNT). To achieve this aim three models of (10, 0) boron nitride nanotubes (BNNTs), raw and two F-attached (exohedral and endohedral) derivatives were studied. The results of calculations showed that while the boron atom chemically bonded to F atom has the largest chemical shielding isotropy (CSI); it has the smallest quadrupole coupling constant (CQ) value among the other boron nuclei.

Molar Binding Energy of Zigzag and Armchair Single-Walled Boron Nitride Nanotubes

Molar binding energy of the boron nitride single-walled zigzag and armchair nanotubes is calculated within the qua-si-classical approach. We find that, in the range of ultra small radii, the binding energy of nanotubes exhibit an oscil-latory dependence on tube radius. Nanotubes (1,1), (3,0), and (4,0) are predicted to be more stable species among sin-gle-walled boron nitride nanotubes. The obtained binding energies of BN single-walled nanotubes corrected with zero-point vibration energies lies within the interval (12.01-29.39) eV. In particular, molar binding energy of the ul-tra-large-radius tube is determined as 22.95 eV. The spread of the molar zero-point vibration energy of BN nanotubes itself is (0.25-0.33) eV and its limit for ultra-large-radius tubes is estimated as 0.31 eV. The binding energy peak lo-cated at 2.691 Å corresponds to the equilibrium structural parameter of all realized stable BN nanotubular structures.

A theoretical study of silicon-doped boron nitride nanotubes serving as a potentialchemical sensor for hydrogen cyanide

In order to search for a novel sensor to detect and control exposure to hydrogen cyanide(HCN) pollutant molecule in environments, the reactivities of pristine and silicon-doped(Si-doped) (8, 0) single-walled boron nitride nanotubes (BNNTs) towards the HCNmolecule are investigated by performing density functional theory (DFT) calculations. TheHCN molecule presents strong chemisorption on both the silicon-substituted boron defectsite and the silicon-substituted nitrogen defect site of the BNNT, which is insharp contrast to its weak physisorption on pristine BNNT. A remarkable chargetransfer occurs between the HCN molecule and the Si-doped BNNT as proved bythe electronic charge densities. The calculated data for the electronic densityof states (DOSs) further indicate that the doping of the Si atom improves theelectronic transport property of the BNNT, and increases its adsorption sensitivitytowards the HCN molecule. Based on calculated results, the Si-doped BNNTis expected to be a potential resource for detecting the presence of toxic HCN.

First principle study of unzipped boron nitride nanotubes

Systematic first principle calculations have been used to explain the dangling bonds behaviour in the rolling up of a boron nitride nanoribbon (BNNR) to construct a single-walled boron nitride nanotube (BNNT). We found in armchair BNNR two degenerate dangling bonds split and move up to higher energies due to symmetry breaking of system. While in zigzag BNNR changing the topology of system does not affect on metallic features of the band structure, but in unzipped BNNT case a metallic–semimetallic phase transition occurs. Considering the width dependent electronic properties of hydrogen passivated armchair BNNRs, exhibit zigzag behaviour of energy gap in agreement with previous results.

Adsorption of Nucleic Acid Bases and Amino Acids on Single-Walled Carbon and Boron Nitride Nanotubes: A First-Principles Study

We study the adsorptions of nucleic acid bases adenine (A), cytosine (C), guanine (G), thymine (T), and uracil (U) and four amino acids phenylalanine, tyrosine, tryptophan, alanine on the single-walled carbon nanotubes (SWCNTs) and boron nitride nanotubes (SWBNNTs) by using density functional theory. We find that the aromatic content plays a critical role in the adsorption. The adsorptions of nucleic acid bases and amino acids on the (7, 7) SWBNNT are stronger than those on the (7, 7) SWCNT. Oxidative treatment of SWCNTs favors the adsorption of biomolecules on nanotubes.

Exciton Effects in Optical Absorption Spectra of Boron-Nitride Nanotubes

AbstractExciton effects are studied in single-wall boron-nitride (BN) nanotubes. Linear absorption spectra are calculated with changingthe chiral index of the zigzag nanotubes. We consider the extended Hubbard model with atomic energies at the boron and nitrogen sites.Exciton effects are calculated using the configuration interaction technique. The Coulomb interaction dependence of the band gap,the lowest exciton energy, and the binding energy of the exciton are discussed. The optical gap of the (5,0) nanotube is about 6 eVat the onsite interaction U=2t with the hopping integral t=1.1 eV. The binding energy of the exciton is 0.50 eV for these parameters.This energy agrees well with that of other theoretical investigations. We find that the energy gap and the binding energy are almostindependent of the geometries of the nanotubes. This novel property is in contrast with that of the carbon nanotubes which show metallicand semiconducting properties depending on the chiral index. Comparison with recent experiments will be discussed.

Gate field induced electronic current modulation in a single wall boron nitride nanotube: Molecular scale field effect transistor

We report a first-principles quantum transport study in a single wall boron nitride nanotube sandwiched between a pair of gold electrodes. The non-equilibrium Green’s function approach, in which the electric field effect is explicitly included within a many body framework, is used to calculate the channel current, I sd , in the presence of a transverse gate field, E g . The E g is found to have a profound effect on the electronic current between the source and drain – revealing transistor behavior. The significant modulation in electronic current (ON–OFF current ratio of ∼ 18 at V sd of 3 V) is attributed to the giant Stark shift caused by the gate field.

BN Domains Included into Carbon Nanotubes: Role of Interface

We present a density functional theory study on the shape and arrangement of small BN domains embedded into single-walled carbon nanotubes. We show a strong tendency for BN hexagon formation at the simultaneous inclusion of B and N atoms within the walls of carbon nanotubes. The work emphasizes the importance of a correct description of the BN−C frontier. We suggest that a BN−C interface will be formed preferentially with the participation of N−C bonds. Thus, we propose a new way of stabilizing the small BN inclusions through the formation of nitrogen-terminated borders. The comparison between the obtained results and the available experimental data on the formation of BN plackets within the single-walled carbon nanotubes is presented. The mirror situation of inclusion of carbon plackets within single-walled BN nanotubes is considered within the proposed formalism. Finally, we show that the inclusion of small BN plackets inside the CNTs strongly affects the electronic character of the initial systems, opening a band gap. The nitrogen excess in the BN plackets introduces donor states in the band gap, and it might, thus, result in a promising way for n-doping single-walled carbon nanotubes.

Thermal-conductivity and tensile-properties of BN, SiC and Ge nanotubes

Thermal-conductivity and axial tension of single-wall BN (Boron Nitride), SiC (Silicon Carbide) and Ge (Germanium) nanotubes are simulated through the MD (Molecular Dynamics) method, and the conductivity-temperature and loading-strain curves of the nanotubes are given. According to the obtained results, the differences of the nanotubes in thermal-conductivity and tensile-properties are investigated. The results show that the thermal-conductivity of all the tubes decreases with the increase of temperature and diameter; at the same temperature the BN tube has the best thermal-conductivity, whereas the SiC and Ge tubes have the comparable one; the Ge tube has both the worst anti-deformation and anti-loading capability, the BN tube the best anti-deformation one, and the BN and SiC tubes the comparable anti-loading one.

Raman spectrum of single-walled boron nitride nanotube

Using the spectral moments method, the calculations of the Raman spectra of single-walled boron nitride nanotubes (SW-BNNTs) were performed in the framework of the force constants model. Spectra were computed for chiral and achiral nanotubes for different diameters and lengths. The Raman scattering intensities were determined using the bond-polarizability model and a good agreement with group theory analysis was found. We show that the modes in the low frequency region are very sensitive to the nanotube diameter variation, whereas the ones associated to the tangential region are chirality dependent. The number of Raman active modes, their frequencies, and intensities depend on the length of the nanotube.

A boroxol ring doped zigzag boron nitride nanotube: a computational DFT study of the quadrupole coupling constant

Based upon density functional theory, we investigate the influence of oxygen dopant atoms that make a boroxol ring on the electrostatic properties of a zigzag (10, 0) boron nitride nanotube in which three of the nitrogen atoms are replaced by oxygen dopant atoms. The electric field gradient (EFG) tensors at the sites of 11B and 14N nuclei were calculated and converted to quadrupole coupling constants (CQ) in the two models of a perfect and a boroxol ring O-doped (10, 0) single-walled boron nitride nanotube (BNNT). Our calculations showed that the CQ values of the boron and nitrogen nuclei along the length of a perfect BNNT are divided into layers. Among the layers the mouth layers have the largest CQ magnitudes. In the doped model, in addition to the mouth layers, the CQ values of those nitrogen nuclei which directly bond to the boroxol ring are increased. However, the CQ values of the boron nuclei that make the boroxol ring and directly bond to the boroxol ring are decreased.

Boron nitride nanosystems of regular geometry

The explicit expressions in term of B-N bond length are obtained for atomic site coordinates and intersite distances in regular boron nitride nanotubes and fullerenes. The radii of single-walled BN nanotubes and single-shelled BN fullerenes are estimated, and their most stable associations in form of double-walled nanotubes and double-shelled fullerenes are predicted. The differences between radii of regular boron nitride fullerenes with indexes of (n + 3) and (n) are almost equal to the interlayer distance in layered boron nitride structures. Description made for the boron nitride nanosystems of regular geometries may serve as basis for further ground state and electron structure calculations.

First principle electric field response of single-walled boron nitride nanotube: a case study of zigzag (4,0) model

Structural and electrical responses of the (4,0) zigzag model of single-walled boron nitride (BN) nanotube (NT) (with edges terminated by H atoms) have been investigated under the external electric fields (parallel and transverse) with strengths 0−2.0 × 10−2 a.u. using DFT-B3LYP/6-31G* method. Calculated electric dipole moment shows a significant change in the presence of the parallel and perpendicular external electric fields which result in much stronger interactions at higher electric field strengths. Natural bond orbital (NBO) atomic charges analysis shows that the separation of the center of the positive and the center of the negative electric charges of (4,0) zigzag BNNT increase with increase the applied parallel and transverse electric field strengths. The applied fields change the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies and decrease the HOMO–LUMO gap (HLG) values. The calculated electronic spatial extent (ESE) showed small changes of <0.63% and <1.53% over the entire range of the applied parallel and perpendicular electric field strengths, respectively. Results of this study indicate that the properties of BNNTs can be controlled by applying the proper external electric field.

Ab initio simulations on the atomic and electronic structure of single-walled BN nanotubes and nanoarches

To simulate the perfect single-walled boron nitride nanotubes and nanoarches with armchair- and zigzag-type chiralities and uniform diameter of ∼5 nm, we have constructed their one-dimensional (1D) periodic models. In this study, we have compared the calculated properties of nanotubes with those for both hexagonal and cubic phases of bulk: bond lengths, binding energies per B–N bond, effective atomic charges as well as parameters of total and projected one-electron densities of states. For both phases of BN bulk, we have additionally verified their lattice constants. In the density functional theory (DFT), calculations performed using formalism of the localized Gaussian-type atomic functions as implemented in the CRYSTAL-06 code we have applied Hamiltonians containing either PWGGA or hybrid (DFT+HF) B3PW exchange-correlation functionals. After calculation of Hessian matrix for the optimized structures of BN bulk (both phases) and nanotubes (both chiralities) using the CRYSTAL code we have estimated their normal phonon modes within the harmonic approximation. Applying both atomistic and continuum models we have calculated the elastic energies and moduli for SW BN nanoarches. Our calculations clearly show a reproducibility of the atomic structure, effective charges and total energy, as well as phonon and elastic properties when using either PWGGA or hybrid B3PW Hamiltonians. On other hand, there is a high sensitivity of the discrete energy spectra parameters (including band gap) to the choice of the first principles approach (the hybrid method reproduce them noticeably better).