Homogeneous nanocables from double-walled boron-nitride nanotubes using first-principles calculations

Zhuhua Zhang, Xiao Cheng Zeng, and Wanlin Guo

Phys. Rev. B 82, 035412 – Published 12 July 2010

Abstract

Since electrons injected to a homogenous wire always tend to concentrate on its surface, heterogeneous coaxial structures are generally necessary to make nanocables with an insulating sheath. Here we reveal from first-principles calculations that double-walled boron-nitride nanotubes could be natural homogeneous nanocables as injected electrons prefer abnormally to concentrate on the inner semiconducting tube while the outer tube remains insulating. The ratio of extra electrons on the inner tube to total carriers in the double-walled nanotubes can be tuned widely by changing either the tube diameter or the local tube curvature through radial deformation, both attributed to the predominant band filling and weak enhancement in Coulomb interaction within the inner wall where the sublattice asymmetry is strongly attenuated by curvature effect. This exotic charge screening is universal for any form of electron-doping sources.

Received 23 April 2010

DOI:https://doi.org/10.1103/PhysRevB.82.035412

Authors & Affiliations

Zhuhua Zhang^1,2, Xiao Cheng Zeng², and Wanlin Guo^1,*

¹Institute of Nano Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
²Department of Chemistry and Nebraska Center for Materials and Nanoscience, University of Nebraska–Lincoln, Lincoln, Nebraska 68588, USA

^*wlguo@nuaa.edu.cn

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Issue

Vol. 82, Iss. 3 — 15 July 2010

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Images

Figure 1
(Color online) Distribution of injected electrons in DBNNTs with different diameters. (a) Ratio $n_{i n n e r} / n_{t o t a l}$ for the $(n, 0) @ (n + 8, 0)$ DBNNTs $(n = 3 - 7)$ as a function of charge-injection level. Black dash line is for an idea case of a (5,0) CNT sheathed in a (14,0) BNNT. (b) Charge redistribution of the injected electrons in the (5,0)@(13,0) DBNNT at the charge-injection level of 0.007 electrons/atom. The solid lines represent the isosurface of charge accumulation while the dash lines represent the isosurface of charge depletion. The isosurface spacing is set to $1.0 \times 10^{- 3} e / Å^{3}$ . (c) Band structures for the (5,0)@(13,0) DBNNT at charge-injection levels of 0.0, 0.007, and 0.014 electrons/atom (left to right). The highest valence band and the lowest conduction band due to the inner tube are marked by red solid lines. The nearly free electron states are denoted by blue line of triangles.Reuse & Permissions
Figure 2
(Color online) Mechanism for the preference of injected electrons on the inner tube of DBNNTs. (a) EIE of $(n, 0) @ (n + 8, 0)$ DBNNTs as a function of the charge-injection level. (b) Difference between average core potentials at B and N atoms as a function of BNNT size. The three insets display slices of charge densities of the unoccupied states within an energy interval of 2 eV above the conduction band minimum, for the (5,0), (8,0), and (16,0) BNNTs, respectively. Red (gray), yellow (white), green (light gray), and blue (dark) colors represent the magnitude of the charge density in descending order.Reuse & Permissions
Figure 3
(Color online) (a) Ratio $n_{i n n e r} / n_{t o t a l}$ for the (8,0)@(16,0) DBNNT under various radial strains in the y direction: $ε_{y} = 0$ (squares), 0.32 (circles), and 0.38 (triangles) as a function of the charge-injection level. Inset: the charge redistribution induced by introducing 0.007 electrons/atom in the squashed (8,0)@(16,0) DBNNT with $ε_{y} = 0.32$ ; the solid lines represent the isosurface of charge accumulation while the dash lines represent the isosurface of charge depletion. (b) Ratio $n_{i n n e r} / n_{t o t a l}$ for the (12,0)@(20,0) DBNNT as a function of radial strain $ε_{y}$ at charge-injection levels of 0.008 (blue squares) and 0.012 electrons/atom (red circles). The inset shows the axial view of the DBNNT deformation. (c) EIE of the (8,0)@(16,0) DBNNTs under different radial strain $ε_{y}$ as a function of the charge-injection level. (d) Band structure of the squashed (8,0)@(16,0) DBNNT with $ε_{y} = 0.38$ and at an charge-injection level of 0.0073 electrons/atom. The highest valence band and the lowest conduction band due to the inner tube are marked by red solid lines.Reuse & Permissions
Figure 4
(Color online) (a) Ratio $n_{i n n e r} / n_{K}$ in the (5,0)@(13,0) DBNNT as a function of charge-injection level from potassium (K) atoms. Insets show the charge redistribution induced by doping two and four K atoms per supercell. The number at each point denotes the amount of K atoms per tube cell. (b) The charge redistribution induced by doping a Li atom per tube cell at different locations with respect to the (5,0)@(13,0) DBNNTs, where the values at the top right corner denote the ratio $n_{i n n e r} / n_{Li}$ . The solid lines represent the isosurface of charge accumulation while the dash lines represent the isosurface of charge depletion The isosurface spacing is set to $0.8 \times 10^{- 3} e / Å^{3}$ . The pink balls denote K (Li) atoms.Reuse & Permissions
Figure 5
(Color online) Schematic illustration of mechanism for the preference of injected electrons to reside on the inner wall of the (5,0)@(13,0) DBNNT. The fresh green regions (around the inner wall) illustrate the empty states to be occupied by the injected electrons. The regions around the outer wall are forbidden for electron occupation. The head balls illustrate only the relative amount of charge. The dash line illustrates the potential profile across the DBNNT for injected electrons.Reuse & Permissions

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