Theoretical Studies of the Interaction of an Open-Ended Boron Nitride Nanotube (BNNT) with Gas Molecules
We have systematically studied the effects of several gaseous adsorbates (H2, N2, O2, and H2O) on the electronic properties of open edges of boron nitride nanotubes (BNNTs) by using density functional theory calculations. The results indicate that all of the molecules, except N2, dissociate and chemisorb on open BNNT edges with large adsorption energies because the tube edge has either an open or capped structure and thus has dangling bonds or pentagonal defects. The high reactivity of an open-ended BNNT even can be comparable with that of its carbon counterpart, although the wall of the BNNT is chemically more stable than a single-walled carbon nanotube’s wall. Moreover, we note that adsorption of gases at the tips of open BNNTs can modify their electronic properties in various ways. A considerable amount of charge transferred for the adsorption of gases on the open BNNTs may account for the changes of the electronic properties. Interestingly, the open (5,5) BNNT exhibits the properties of wide-band-gap materials when gases are adsorbed at top sites, while a smaller band gap is observed when these gases are adsorbed on seat sites. Additionally, the magnetic moments of gas-adsorbed N atoms in the open N-rich-ended (8,0) are significantly decreased because the dangling bonds are “saturated”. The present results might be helpful in the design of BNNT-based nanomaterials such as field emitters or nanojunctions.
Available from: Farzaneh Shayeganfar
- "(A colour version of this figure can be viewed online.) F. Shayeganfar, R. Shahsavari / Carbon 99 (2016) 523e532 529 graphene/BNNT junction, the energy gap (Fig. 5iek) and band dispersion seem to be constant, owing to the intrinsic widebandgap  of BNNT, which exhibit insulating properties. Our results for CNT corroborates the recent finding of electronic transport between connected nanotubes and defected graphene . "
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ABSTRACT: Low dimensional materials such as Boron Nitride nanotube (BNNT) and graphene are attractive for demonstrating several fundamental physical properties and development of novel technologies in nano/micro-scale devices. Although various 3D carbon-based architectures are reported via covalent connection of carbon allotropes, the introduction of analogous 3D hybrid carbon/BN allotropes and determining their exquisite junction-induced properties remain elusive. Here, we focus on mono- and double-layer hybrid graphene/BNNT and graphene/carbon nanotubes (CNT) architectures and explore their diverse junction configuration-induced electronic and pseudomagnetic properties via ab-initio calculations and elasticity theory. By introducing heptagonal and octagonal rings in the junctions, we find that the mismatch between the defected graphene and the BNNT/CNT diameters creates a bond strain at the junction, thus inducing a gauge field and pseudomagnetic field, which decay exponentially along the radial distance of the junction. Furthermore, our analysis of the band structures and density of states in hybrid double-layer architectures demonstrate that there exists a flat band and band dispersion near the Fermi level of graphene/CNT junctions, a feature not present in the graphene/BNNT junction due to the intrinsic wide band gap of BNNT. Finally, our size-effect study shows that while the band gap energy of heptagonal graphene/CNT junction and octagonal graphene/BNNT junctions is sensitive to the nanotube length, this is not the case for octagonal graphene/CNT junctions due to the less perturbation of the electronic states of the valence bond (VB) in the octagonal graphene/CNT junctions. Together, these findings have important implications on science-based engineering of numerous hybrid carbon and boron nitride allotropes while significantly broadening the spectrum of strategies for fabricating new hybrid nanomaterials through covalent connection of dissimilar low-dimensional materials.
Available from: Abdolvahab Seif
- "For example, BNNTs are highly appropriate to construct insulating nanocables    , they can be used as an ideal nanosized luminescent material   and may be used in nanodevices working at elevated temperature and in hazardous environment. Despite numerous superiorities of BNNTs to CNTs     , fewer studies have been reported about adsorption of gases on BNNTs, compared to the CNTs. Apparently, an important reason could be the electronic properties of BNNTs partially influenced by the presence of external fields or adsorption of foreign gases . "
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ABSTRACT: Adsorption of methane (CH4) on inside and outside of aluminum-doped (Al-doped) zigzag single-walled boron nitride nanotubes, BNNTs/Al, has been studied using density-functional theory (DFT) method. The effect of diameter and type of atom of BNNT replaced by the Al atom on the adsorption properties of CH4 were investigated. Our results indicate that, compared to pristine BNNTs, replacing both B atom by Al, BNNT/Al(B) and N atom by Al, BNNT/Al(N), can notably enhance the binding energy of CH4 on BNNTs and the latter case has been more superior. The average binding energy for the most stable configuration of CH4 on BNNTs/Al(N) and BNNTs/Al(B) are about −26.12 and −16.53 kJ mol−1, respectively, which are typical for the physisorption and suitable for technical applications. The results show that while the geometry of BNNT/Al(N or B)–CH4 complexes is determined by weak electrostatic forces, the binding energy mainly determines by dispersion forces. For all complexes, the energy gaps, natural bond orbital (NBO) analysis, dipole moments, natural charge and density of state (DOS) diagrams were extracted. Finally, the applicability of BNNTs/Al(N) both as a medium for storage and gas sensor for methane detection were confirmed.
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ABSTRACT: Whether adsorbates might effectively lower the ionization potential (IP) of open-ended boron nitride nanotubes (BNNTs) in order to design BNNTs based on flat-panel display devices is an unanswered question. In the present work, through density functional theory (DFT) calculations we present the first attempt on the effects of O(2) and H(2)O adsorption on the field-emission properties of an open-ended (8, 0) BNNT. The two adsorbates can chemisorb at the tips of the open-ended BNNT with large adsorption energies and significant charge transfer. An applied electric field of 1 eV A(-1) at the tube tip (a) significantly increases the adsorption energy to stabilize the adsorbates, and (b) alters the emission properties such as ionization potential (IP) or bandgap. The IP of the open N-rich-ended BNNT is lowered, thereby making it easier to lose electrons. However, there is a slight increase of the IP for the open B-rich-end BNNT. Our results would be useful not only to better understand the property of open-ended BNNTs, but also to design more efficient field emitters of molecular electronic devices in experiments.
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