Carbon-chain inserting effect on electronic behavior of single-walled carbon nanotubes: a density functional theory stud
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Carbon-chain inserting effect on electronic behavior of single-walled carbon nanotubes: a density functional theory study Hao Cui, State Key Laboratory of Power Transmission Equipment & System Security and New Technology, Chongqing University, Chongqing 400044, China Qingjuan Li, Guibao Qiu, and Jian Wang, College of Materials Science and Engineering, Chongqing University, Chongqing 400040, China Address all correspondence to Guibao Qiu at [email protected] (Received 5 December 2017; accepted 12 February 2018)
Abstract By inserting a carbon chain, the geometric structure and electronic properties of carbon nanotube (CNT) would undergo a significant change. Numerous studies have conducted to experimentally find the insertion effect of carbon chains on CNTs. This paper in a theoretical way studied the geometry of carbon chains inserted CNTs and analyzed the mechanism for conductivity change after insertion of carbon chains. Results indicate that carbon chains in the innermost channel of the tube are effective methods for transforming the electrical properties of the CNT, leading to the redistribution of electron and thereby causing the conductivity change in obtained configurations.
Introduction A linear carbon chain composed of both sp2 and sp bonding is expected to be a potential candidate for further enriching the characteristics and functions of carbon nanotube (CNT) that contributed to various applications such as gas storage, sensors, and catalysis[1] by inserting it inner the tube hollow. Considering the degeneracy of π orbitals of each carbon atom, two forms of carbon chains have been hypothesized.[2] One of the forms, cumulene (= C = C = C = C =), is connected with the equidistant carbon atoms, while the other form, polyyne (−C ≡ C ≡ C≡ C−), with the alternating single and triple bonds.[3] Such carbon chains possess average conjugation length of about 8–12 carbon atoms, which could stably exist inner the CNT, showing that these long C chains were entirely protected by outside CNT,[4] and once the carbon chain includes more than 20 atoms, they become energetically unstable.[5] On the other hand, high-resolution transmission electron microscopy observations and Raman scattering studies indicate that the most stable structure of CNT with carbon chain inserted into its innermost tube is the one with 0.7 nm in diameter.[3] This very small tube diameter provides the limited space for remaining carbon atoms to arrange themselves to form a chain, resulting in the expected van der Waals spacing between C chains and the innermost tube, 0.34 nm.[6] To systemically illustrate the inserting effect of carbon chain for CNTs, this paper gives a theoretical investigation on the structures and electronic behavior of two kinds of chains inserted CNTs. We chose (9, 0) and (5, 5) CNTs as our representative samples because the stable geometry for carbon chain requires a diameter of the tube to be 0.7 nm that similar to what we selected ones according to the previous report.[2,7] The
results infer that the inserti
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