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1.
Effects of doping, Stone Wales and vacancy defects on thermal conductivity of single-wall carbon nanotubes
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The thermal conductivity of carbon nanotubes with certain defects (doping, Stone-Wales, and vacancy) is investigated by using the non-equilibrium molecular dynamics method. The defective carbon nanotubes (CNTs) are compared with perfect tubes. The influences of type and concentration of the defect, length, diameter, and chirality of the tube, and the ambient temperature are taken into consideration. It is demonstrated that defects result in a dramatic reduction of thermal conductivity. Doping and Stone-Wales (SW) defects have greater effect on armchair tubes, while vacancy affects the zigzag ones more. Thermal conductivity of the nanotubes increases, reaches a peak, and then decreases with increasing temperature. The temperature at which the thermal conductivity peak occurs is dependent on the defect type. Different from SW or vacancy tubes, doped tubes are similar to the perfect ones with a sharp peak at the same temperature. Thermal conductivity goes up when the tube length grows or diameter declines. It seems that the length of thermal conductivity convergence for SW tubes is much shorter than perfect or vacancy ones. The SW or vacancy tubes are less sensitive to the diameter change, compared with perfect ones. 相似文献
2.
It has been shown that the two different orientations of Stone-Wales (SW) defects, i.e. longitudinal and circumferential SW defects, on carbon nanotubes (CNTs) result in two different electronic structures. Based on density functional theory we have shown that the longitudinal SW defects do not open a bandgap near the Fermi energy, while a relatively small bandgap emerges in tubes with circumferential defects. We argue that the bandgap opening in the presence of circumferential SW defects is a consequence of long-range symmetry breaking which can spread all the way along the tube. Specifically, the distribution of contracted and stretched bond lengths due to the presence of defects, and hopping energies for low-energy electrons, i.e. the 2p(z) electrons, show two different patterns for the two types of defects. Interplay between the geometric features and the electronic properties of the tubes have also been studied for different defect concentrations. Considering π-orbital charge density, it has also been shown that the deviations of bond lengths from their relaxed length result in different doping for two defect orientations around the defects-electron-rich for a circumferential defect and hole-rich for a longitudinal one. We have also shown that, in the tubes having both types of defects, circumferential defects would dominate and impose their electronic properties. 相似文献
3.
基于Stone-Wales缺陷演变理论与分子动力学、Monte Carlo计算方法, 进行了碳纳米管(CNTs)对接成异质结器件的计算模拟.首先, 提出了一种模拟CNTs端帽位置变化的新算法, 并计算模拟了单根CNT的端帽从开口到闭合的过程. Stone-Wales缺陷演变被设计模拟这些端帽变化的跃变过程, 以模拟C–C键的生成与断裂, 而分子动力学则作为跃变后构型弛豫的渐变模拟. 同时, 研究了不同管型CNTs的端帽打开并对接形成异质结的过程.研究结果显示, 对接初期在对接处先产生大量的缺陷, 以促进反应的发生. 这些缺陷趋向于演变成稳定的六元环结构, 或者五元环/七元环的结构, 使异质结趋于稳定.
关键词:
碳纳米管
Monte Carlo
Stone-Wales缺陷
分子动力学 相似文献
4.
ABSTRACTSingle-wall carbon nanotubes (CNTs) have been suggested as potential materials for use in next-generation gas sensors. The sidewall functionalisation of CNTs facilitates gas molecule adsorption. In this study, density functional theory (DFT)-based ab initio molecular dynamics simulations are performed for a periodic zigzag single-wall (4,0) CNT surrounded by a monolayer of hydrogen peroxide molecules in an attempt to find conditions that favour sidewall functionalisation. The dependency of dynamics on charge states of the system is examined. It is found negative charges favour reactions that result in the functionalisation of the CNT. First principles molecular dynamics of defect formation yields chemically reasonable structure of stable defects, which can be reproduced in CNTs of any diameter and chirality. The explored hydroxyl and hydroperoxyl defects increase conductivity in a large diameter (10,0) CNT, while decrease conductivities in a small diameter (4,0) CNT. 相似文献
5.
The interaction and coupling between the electrical, mechanical properties and formation energy for SW defective (10,0) carbon nanotube is studied in density functional theory. The investigated configurations include the axial and circumferential orientations for single defect as well as four distribution types for double ones. The more stable defective configurations, namely, SW-I configurations for single SW defective carbon nanotube and II–II-(2) and I–I ones for double SW defective tubes are related to high symmetry distribution of the defects. Moreover, we found that the σ?–π* hybridization induced by curvature effect causes the semiconductor to metal transition for double axial SW defects case. Young's modulus reduction of SW defective carbon nanotube with respect to defect-free one is less than 8%. The energy bands and Young's moduli of double SW defective tubes are mostly affected by the defect distribution and concentration but insensitive to the circumferential distance between the double defects. 相似文献
6.
Bingcheng Fang Jiajun Li Chunsheng Shi Liying Ma Chunnian He 《Composite Interfaces》2018,25(12):1101-1114
Carbon nanotube (CNT)/metal interface interaction is critical to the mechanical properties of CNT-reinforced metal matrix composites (MMCs). In this paper, in order to realize the chemical modification of the interface interaction between CNTs and Mg matrix, different types of defects (monovacancy, carbon and oxygen adatoms, as well as p-type boron and n-type nitrogen substitution) are introduced in CNTs to investigate the effect of the defects on the interface interaction (Eib) between CNT and Mg (0 0 0 1) surface. Moreover, two models (adsorption model and interface model) are compared and validated to investigate the interface interaction. It is revealed that the CNT with the carbon adatom has the highest Eib with the Mg (0 0 0 1), and the effect of boron doping on Eib is superior to the intermediate oxygen which has already been proved experimentally in the enhancement of the interface interaction in MMCs. In terms of the electronic structure analysis, we reveal the micro-mechanism of the increase of Eib under the action of different types of defects, and propose that the presence of holes (boron dopant) and the unsaturated electrons in CNTs can generate the chemical interaction between CNT and Mg matrix effectively. Our results are of great scientific importance to the realization of robust interfacial bonding between CNTs and Mg matrix via the reinforcement modification, so as to enhance the mechanical properties of CNTs reinforced Mg matrix composites. 相似文献
7.
We report the influence of catalyst formulation and reaction temperature on the formation of carbon nanotube (CNT) thin films
by the chemical vapour deposition (CVD) method. Thin films of CNTs were grown on Fe-Mo/Al2O3-coated silicon wafer by thermal decomposition of methane at different temperatures ranging from 800 to 1000°C. The electron
microscopic investigations, SEM as well as HRTEM, of the as-grown CNT thin films revealed the growth of uniform multi-walled
CNTs in abundance. The intensity ratio of D-band to G-band and FWHM of G-band through Raman measurements clearly indicated
the dependency of structural defects and crystallinity of CNTs in thin films on the catalyst formulation and CVD growth temperature.
The results suggest that thin films of multi-walled CNTs with negligible amount of defects in the nanotube structure and very
high crystallinity can be obtained by thermal CVD process at 925°C. 相似文献
8.
The initial stage of the formation of defects in the fullerene C46 has been investigated using the atomistic computer simulation. It has been found that the relatively low symmetry of this fullerene leads to the emergence of channels of defect formation, which have not been revealed in the fullerenes C20, C36, and C60. These channels consist in breaking a single C-C bond (in contrast to the simultaneous breaking of two bonds in the course of the Stone-Wales transformation, which is characteristic of high-symmetry fullerenes). For some typical channels, the paths of transformation of the C46 fullerene into the corresponding defect isomers have been determined and the heights of the potential barriers encountered in these paths have been calculated. 相似文献
9.
Diffusion, coalescence, and reconstruction of vacancy defects in graphene layers are investigated by tight-binding molecular dynamics (TBMD) simulations and by first principles total energy calculations. It is observed in the TBMD simulations that two single vacancies coalesce into a 5-8-5 double vacancy at the temperature of 3000 K, and it is further reconstructed into a new defect structure, the 555-777 defect, by the Stone-Wales type transformation at higher temperatures. First principles calculations confirm that the 555-777 defect is energetically much more stable than two separated single vacancies, and the energy of the 555-777 defect is also slightly lower than that of the 5-8-5 double vacancy. In TBMD simulation, it is also found that the four single vacancies reconstruct into two collective 555-777 defects which is the unit for the hexagonal haeckelite structure proposed by Terrones et al. [Phys. Rev. Lett. 84, 1716 (2000)]. 相似文献
10.
C. Wang C. Y. Wang 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(2):243-247
An ideal single vacancy can be formed by removing one carbon atom
from a hexagonal network. The vacancy is one of the most important
defect structures in carbon nanotubes (CNTs). Vacancies can
affect the mechanical, chemical, and electronic properties of CNTs.
We have systematically investigated single vacancies and their
related point defects for achiral, single-walled carbon nanotubes
(SWNTs) using first-principles calculations. The structures around
single vacancies undergo reconstruction without constraint, forming ground-stateor metastable-state structures. The 5-1DB
and 3DB point defects can be
formed in armchair CNTS, while the 5-1DB-P and 5-1DB-T point defects can be
formed in zigzag CNTs. The related point defects can transform into
each other under certain conditions. The formation energies of
armchair CNTs change smoothly with the tube radius, while in the
case of the 3DB defect, as the radius get larger, the formation energies
tend towards a constant value. 相似文献
11.
使用Matlab自编简单Hückel分子轨道法(SHMO)计算程序,分析空位、Stone-Wales缺陷位、N和B原子掺杂的CNT(5,5)碳纳米管,计算π电子密度和前线分子轨道(HOMO和LUMO)为研究掺杂相对碳纳米管的化学反应性提供依据.具有不同电特性的掺杂相打破了碳纳米管的π电子、HOMO和LUMO的均衡分布.掺杂相和/或邻近的碳原子为HOMO或LUMO贡献了较其它原子更大的轨道系数,在不同的化学反应中表现出良好的亲核性或亲电性.此外,HOMO-LUMO能量差很好地反映了掺杂纳米碳管的导电性.计算结果与已报道的实验和理论结果吻合良好. 相似文献
12.
Yuri F. Zhukovskii Sergei Piskunov Eugene A. Kotomin Stefano Bellucci 《Central European Journal of Physics》2011,9(2):530-541
In the current study, we have performed ab initio DFT calculations on the gradually growing 2D periodic models of capped single-wall carbon nanotubes (SW CNTs) upon their
perpendicular junctions with the Ni(111) substrate, in order to understand the peculiarities of the initial stage of their
growth on either smooth or nanostructured catalytic particles. Appearance of the adsorbed carbon atoms upon the substrate
follows from the dissociation of CVD hydrocarbon molecules, e.g., CH4: (CH4)ads → (CH)ads+3Hads and (CH)ads → Cads+Hads. (Since the effective growth of CNTs upon Ni nanoparticles occur inside the nanopores of amorphous alumina, we have also
simulated analogous surface reactions upon the θ-Al2O3(010) slabs). Association of the adsorbed carbon atoms upon the catalyst surface precedes further swelling of the (Cn)ads islands after appearance of pentagonal defects within a honeycomb sheet which are more probable upon the catalyst surface
containing either defects or nanoclusters (as in the case of the nanostructured substrate). The gradual growth of the capped
CNTs is considerably more effective upon the nanostructured Ni(111) substrate compared to a smooth nickel substrate (cf. values of CNT adhesion energy per boundary C atom for chiralities of either armchair-type, 4.04 vs. 2.51 eV, or zigzag-type, 4.61 vs. 2.14 eV, respectively). The electronic charge transfer from the Ni catalyst towards the CNTs has been calculated for both
chiralities (> 1 e per C atom), i.e., quite strong chemical bonds are formed within the CNT/Ni(111) interconnects. 相似文献
13.
The structural and electronic properties of semiconductors (Si and Ge) and metal (Au and Tl) atoms doped armchair (n, n) and zigzag (n, 0); n=4–6, single wall carbon nanotubes (SWCNTs) have been studied using an ab-initio method. We have considered a linear chain of dopant atoms inside CNTs of different diameters but of same length. We have studied variation of B.E./atom, ionization potential, electron affinity and HOMO–LUMO gap of doped armchair and zigzag CNTs with diameter and dopant type. For armchair undoped CNTs, the B.E./atom increases with the increase in diameter of the tubes. For Si, Ge and Tl doped CNTs, B.E./atom is maximum for (6, 6) CNT whereas for Au doped CNTs, it is maximum for (5, 5) CNTs. For pure CNTs, IP decreases slightly with increasing diameter whereas EA increases with diameter. The study of HOMO–LUMO gap shows that on doping metallic character of the armchair CNTs increases whereas for zigzag CNTs semiconducting character increases. In case of zigzag tubes only Si doped (5, 0), (6, 0) and Ge doped (6, 0) CNTs are stable. The IP and EA for doped zigzag CNTs remain almost independent of tube diameter and dopant type whereas for doped armchair CNTs, maximum IP and EA are observed for (5, 5) tube for all dopants. 相似文献
14.
In this work, we investigate the effect of temperature, defect, and strain rate on the mechanical properties of multi-layer graphene using coarse-grained molecular dynamics (CGMD) simulations. The simulation results reveal that the mechanical properties of multi-layer graphene tend to be less sensitive to temperature as the layer increases, but they are sensitive to the distribution and coverage of Stone-Wales (SW) defects. For the same number of defect, there is less decline in the fracture stress and Young's modulus of graphene when the defects have a regular distribution, in contrast to random distribution. In addition, Young's modulus is less influenced by temperature and defect, compared to fracture stress. Both the fracture stress and Young's modulus have little dependence on strain rate. 相似文献
15.
Maciej Bazarnik Maciej Cegiel Piotr Biskupski Monika Jazdzewska S??awomir Mielcarek Ma??gorzata Sliwinska-Bartkowiak Ryszard Czajka 《Central European Journal of Physics》2009,7(2):295-298
This paper reports our scanning tunneling microscopy and spectroscopy (STM/STS) study of double-walled and multi-walled carbon
nanotubes (CNTs) of different diameter deposited on Bi2Te3 (narrow gap semiconductor). The approximate diameter of the studied double-walled and multi-walled CNTs was 2 nm and 8 nm,
respectively. Crystalline Bi2Te3 was used as a substrate to enhance the contrast between the CNTs and the substrate in the
STS measurements performed to examine peculiarities of CNT morphology, such as junctions, ends or structural defects, in terms
of their electronic structure.
相似文献
16.
本文采用基于密度泛函理论的第一性原理对zigzag型石墨烯纳米带中含有不同Stone-Wales缺陷的电子结构特性和光学性能进行研究. 考虑了两种模型:不计电子自旋和考虑电子自旋的情况.研究发现:不计电子自旋情况下,含对称Stone-Wales缺陷的石墨烯纳米带在缺陷区域出现了凹凸不平的折皱构型,两种不同的Stone-Wales缺陷都引起了电荷的重新分布.考虑电子自旋时,Stone-Wales缺陷的引入对石墨烯纳米带自旋密度有显著影响,也引起了不同自旋的电子态密度的变化.进一步研究了纳米带的光学性能,发现
关键词:
石墨烯纳米带
Stone-Wales缺陷
电子结构
光学性能 相似文献
17.
Bessem Ben Doudou Jun Chen Alexandre Vivet Christophe Poîlane M’hamed Ayachi 《Physica E: Low-dimensional Systems and Nanostructures》2011,44(1):120-123
Using first-principle calculations, we have investigated the chemical functionalization of (8,0) zigzag single wall carbon nanotubes (SWNTs) by the amine group on Stone–Wales (SW) defects. The binding of NH2 with the defective (8,0) nanotube was explored and the preferential grafting sites have been identified. On the other hand, the modifications induced by SW defect and functional groups in the structural and electronic properties of (8,0) SWNT have also been investigated. The role of SW defects in the chemical reactivity of carbon nanotubes was well identified. 相似文献
18.
B. Zhu Y. X. Wang Z. Y. Pan D. Cheng M. Hou 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2010,57(2):219-226
The coalescence of Au13, Au55 and Au147 icosahedral clusters
encapsulated inside single walled carbon nanotubes (CNTs) of different
diameters are investigated using molecular dynamics simulation with
semi-empirical potentials. Three steps needed for the formation of
encapsulated nanowires are followed in detail, namely, the penetration of
clusters in CNTs, the coalescence between two clusters inside CNTs and their
accumulation to form wires. It is suggested that no significant energy
barrier is encountered during the penetration of free clusters into CNTs
provided the CNT radius is large enough, that is, about 0.3 nm larger than
the cluster radius. The relative orientation of clusters imposed by the CNT
favors their spontaneous coalescence. After coalescence of two clusters, the
Au atoms are rearranged to form new structures of cylindrical symmetry that
may be seven fold, six fold, five fold, helical or fcc depending on the CNT
diameter. The thermal stability of these structures is discussed and the
structural properties of nanowires formed by accumulation of many clusters
in CNTs are analyzed in detail. A geometrical method is presented which
allows the prediction of the structure of multi-shell helical wires, when
knowing only the CNT radius.
These modeling results suggest the possibility of synthesizing metallic
nanowires with controlled diameter and structure by embedding clusters into
nanotubes with suitable diameters. 相似文献
19.
Qing-Xiao Zhou Chao-Yang Wang Zhi-Bing Fu Yong-Jian Tang Hong Zhang 《Frontiers of Physics》2014,9(2):200-209
The geometries,formationenergies and electronic band structures of (8, 0) and (14, 0) singlewailed carbon nanotubes (SWCNTs) with various defects, inehlding vaeaney, Stone-Wales defect, and octagon pentagon pair defect, have been investigated within the framework of the density- huictional theory (DFT), and the influence of the concentration within the same style of deflect on the physical and chenfical properties of SWCNTs is also studied. The results suggest that the existeilcc of vacancy and octagon-pentagon pair deflect both reduce the band gap, whereas the SW- defect induces a band gap opening in CNTs. More int, erestingly, the band gaps of (8, 0) and (14, 0) SWCNTs eonfigurations with two octagon pentagon pair defect presents 0.517 eV and 0.163/eV, which arc a little smaller than the perfectt CNTs. Furthermore, with the concentration of defects increasing, there is a decreasing of band ga.p making the two types of SWCNTs change from a semiconductor to a metallic conductor. 相似文献
20.
Anisotropic mechanical properties and Stone-Wales defects in graphene monolayer: A theoretical study
We investigate the mechanical properties of graphene monolayer via the density functional theoretical (DFT) method. We find that the strain energies are anisotropic for the graphene under large strain. We attribute the anisotropic feature to the anisotropic sp2 hybridization in the hexagonal lattice. We further identify that the formation energies of Stone-Wales (SW) defects in the graphene monolayer are determined by the defect concentration and also the direction of applied tensile strain, correlating with the anisotropic feature. 相似文献