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采用密度泛函理论计算系统研究了单壁碳纳米管(Single-walled carbon nanotube,SWCNT)改变手性外延生长(手性指数从(n,m)变化到(n±Δ,m±Δ),其中Δ=1和2)的热力学过程。结果表明,碳管手性变化后外延生长在热力学上都需要吸收能量,其所需吸收的能量随着管径的减小线性减小。在Δ=1的情况下,由于近扶手椅型碳管改变手性时,所引入的5~7元环对与管轴的夹角比近锯齿型碳管更大,导致5~7元环对的形成能增加,使得管径相同的近扶手椅型碳管比近锯齿型碳管在改变手性生长时需要吸收更多的能量。在Δ=2的情况下,发现只有当两个必须引入的5~7元环对相互毗邻,手性改变的外延生长所需能量最小,预测其为实验上最易于实现的碳管手性指数由(n,m)变化到(n±Δ,m±Δ)的外延生长模式。这些理论研究结果有助于深入理解SWCNTs手性变化后外延生长的热力学行为,可为基于外延生长可控制备单一手性SWCNTs提供理论依据。
The effects of single-walled carbon nanotubes (SWCNT) on chiral epitaxial growth (chiral index changes from (n, m) to (n ± Δ, m ± Δ) were studied by using density functional theory Where Δ = 1 and 2) thermodynamic processes. The results show that the epitaxial growth of carbon nanotubes requires thermodynamics to absorb the energy, and the energy required for absorption decreases linearly with the decrease of the tube diameter. In the case of Δ = 1, since the near-armchair carbon tube changes its chirality, the angle between the 5-7-membered ring introduced and the tube axis is larger than that of the near serrated carbon tube, resulting in a 5-7-membered ring Pairs of formations can be increased so that near-armchair carbon tubes of the same caliber need to absorb more energy than near-serrated carbon tubes in changing chiral growth. In the case of Δ = 2, we found that only the two 5-7-membered ring pairs that must be introduced are adjacent to each other and the chirally-modified epitaxial growth requires the least amount of energy and is predicted to be the most experimentally achievable carbon nanotube chiral index The epitaxial growth mode changes from (n, m) to (n ± Δ, m ± Δ). The results of these theoretical studies help to understand the thermodynamic behavior of SWCNTs after the chiral variation and provide a theoretical basis for the controllable preparation of SWCNTs based on epitaxial growth.