Abstract
We have used density functional theory (DFT) and time dependent (TD)-DFT to systematically investigate the dependency of the geometric and vibro-electronic properties of zigzag and armchair-type doublewalled boron nitride nanotubes ((0,m)@(0,n) and (m,m) @(n,n)-DWBNNTs) on the interwall distance (ΔR) and the number of unit cells. The results of the calculations showed that their structural stability strongly depends on the interwall distance, but not on the number of unit cells, and the (0,m) @(0,m+9/10) and (m,m) @(n,n) with n=m+5/6 are the most energetically stable structures. The predicted electronic structures for DWBNNTs with cell lengths of one unit exhibit a strong red-shift for the ΔR below ~0.4 nm and remain almost constant for the ΔR > 0.45 nm. The calculated nonresonance Raman spectra of (0,6) @(0,n)-DWBNNTs (with cell lengths of one unit and n=12–18) indicated that the radial breathing modes (RBMs) of inner (0,6) and outer (0,n) tubes are not only diameter dependent, but also exhibit a strong blue-shift for the ΔR below ~0.35 nm and rapidly approach zero with increasing ΔR reference to the position of the RBM in the spectrum of the corresponding single wall boron nitride nanotubes, (0,n)-SWBNNTs. The calculated IR spectra of the (0,6) @(0,n)-DWBNNTs did not indicate any significant dependence on the ΔR for n > 13.
Highlights
SWBNNTs, respectively, and N indicates the total number of atoms in the DWBNNT
The results of the calculations indicate that the energetic stability of the DWBNNT strongly depend on the interwall spacing between the inner and outer tubes, but the dependence on the length of the nanotube is insignificant
We theoretically investigate the dependence of the geometric and spectroscopic properties for the zigzag and armchair DWBNNTs on the interwall distance (ΔR) and unit cell length using the density functional theory (DFT)
Summary
Since the discovery of carbon nanotubes in 1991 by Iijima [1], they have received much interest in several fields due to their near-perfect geometric structure with almost endless applications in new technologies such as one dimensional quantum wires [2], transistors and sensors [3], in heat conduction systems [4], in specialty electronics [5], molecular memories [6], optics [7], photonic devicesMetin AydNina:nDoempaetnedreNnacneootfecGhenooml,e2t0ri1c 4a,n4d:2S8pe|cdtoroi:sc1o0p.5ic7P7r2o/p5e9r4ti0e2s 1 of Double-walled Boron Nitride Nanotubes on Interwall Distance [8, 9], optical switches [10] and passively mode-locked lasers [11], electrically excited single-molecule light sources [12, 13], high-performance adsorbent electrode material for energy-storage devices [14], and protein functionalization [15]. Boron nitride nanotubes (BNNTs) are resistant to oxidation up to 1100 C [27, 28], have excellent piezoelectricity [29], are good electrical insulators at room temperature [30] and have a potential hydrogen storage capability [31]. Because of their ionic bonding properties, BNNTs are wide band gap materials like other nitride materials and possess electronic properties that are not sensitive to a change in their diameter, chirality and number of tubular walls [19, 23, 32]. This is to be expected since the number of layers becomes larger, leading to an increase in the total interaction energy between them relative to a couple of sheets
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