共查询到20条相似文献,搜索用时 125 毫秒
1.
在紧束缚理论的基础上,推导出轴向拉伸和扭转形变时碳纳米管(CNT)的能带公式.结果显示拉伸和扭转形变都可以改变CNT的导电性质,在金属型和半导体型之间转变,特别是对于锯齿型CNT,根据n 与3的余数关系,在拉伸和扭转中分别显示出三种不同的变化规律.进一步应用场效应晶体管Natori理论模拟计算形变对CNT场效应晶体管的电流-电压特性的影响,锯齿型CNT根据n 与3的余数关系表现出不同的电流变化趋势,而对于扶手椅型CNT轴向拉伸不改变电流;在扭转形变时,CNT电流急剧升高,特别是扶手椅型CNT.锯齿型CNT和扶手椅型CNT的电流随扭转角度和外电压行为明显不同.在某些特定的扭转角度,电流随扭转角度变化非常显著,显示出锯齿型CNT和扶手椅型CNT发生半导体型与金属型之间的转变.
关键词:
碳纳米管
紧束缚理论
费米能级
能带结构 相似文献
2.
The stability and electronic structure of hypothetical InN nanotubes were
studied by first-principles density functional theory. It was found that the
strain energies of InN nanotubes are smaller than those of carbon nanotubes
of the same radius. Single-wall zigzag InN nanotubes were found to be
semiconductors with a direct band gap while the armchair counterparts
have an indirect band gap. The band gaps of nanotubes decrease with
increasing diameter,
similar to the case of carbon nanotubes. 相似文献
3.
Within tight-binding model, the band gaps of armchair and zigzag carbon nanotubes (CNTs) under both uniaxial tensile and torsional strains have been studied. It is found that the changes in band gaps of CNTs depend strongly on the strain type. The torsional strain can induce a band gap for armchair CNTs, but it has little effect on band gap of the zigzag CNTs. While the tensile strain has great effect on band gap of zigzag CNTs, but it has no effect on that of the armchair CNTs. More importantly, when both the tensile and torsional strains are simultaneously applied to the CNTs, the band gap changes of armchair CNTs are not equal to a simple sum over those induced separately by uniaxial tensile and torsional strains. There exists a cooperative effect between two kinds of strains on band gap changes of armchair CNTs. But for zigzag CNTs, the cooperative effect was not found. Analytical expressions for the band gaps of armchair and zigzag CNTs under combined uniaxial–torsional strains have been derived, which agree well with the numerical results. 相似文献
4.
O. S. Lebedeva N. G. Lebedev 《Russian Journal of Physical Chemistry B, Focus on Physics》2014,8(5):745-751
The results of a theoretical research into the band gap of strained doped carbon nanotubes of two structural modifications of the “armchair” and “zigzag” types are described. The electronic states in the doped nanotubes are considered in terms of the periodic Anderson model. Nitrogen and boron atoms are selected as donor and acceptor substitutional defects, respectively. The dependences of the band gap of the carbon nanotubes on impurity concentration and compressive and tensile strain are studied. 相似文献
5.
碳纳米管作为最先进的纳米材料之一, 在电子和光学器件领域有潜在的应用前景, 因此引起了广泛关注. 掺杂、变形及形成超晶格为调制纳米管电子、光学性质提供了有效途径. 为了理解相关机理, 利用第一性原理方法研究了不同剪切形变下扶手椅型硼氮交替环状掺杂碳纳米管超晶格的空间结构、电子结构和光学性质. 研究发现, 剪切形变会改变碳纳米管的几何结构, 当剪切形变大于12%后, 其几何结构有较大畸变. 结合能计算表明, 剪切形变改变了掺杂碳纳米管超晶格的稳定性, 剪切形变越大, 稳定性越低. 电荷布居分析表明, 硼氮掺杂碳纳米管超晶格中离子键和共价键共存. 能带和态密度分析发现硼氮交替环状掺杂使碳纳米管超晶格从金属转变为半导体. 随着剪切形变加剧, 纳米管超晶格能隙逐渐减小, 当剪切形变大于12%后, 碳纳米管又从半导体变为金属. 在光学性能中, 剪切形变的硼氮掺杂碳纳米管超晶格的光吸收系数及反射率峰值较未受剪切形变的均减小, 且均出现了红移. 相似文献
6.
First-principles calculations have been employed to investigate the structural transformation and direct to indirect band gap transition of ZnO nanotubes under uniaxial strain. The results show that armchair and zigzag nanotubes can be transformed to each other via unusual fourfold-coordinated structures under the applied strain. Both the armchair and zigzag nanotubes exhibit direct band gap while the unusual fourfold-coordinated ones display indirect band gap. The origin of such a direct-to-indirect band gap transition is explained based on the analyses of atomic orbital contributions. 相似文献
7.
Dikandé A. M. 《The European Physical Journal B - Condensed Matter and Complex Systems》2004,42(2):247-253
Small and large-amplitude elastic deformations of the armchair structure of single-walled carbon nanotubes are investigated with emphasis on the cylindrical geometry. As starting model, we consider a discrete one-dimensional lattice of atoms interacting via a Lennard-Jones type two-body potential. In an expansion scheme using cylindrical coordinates where radial displacements are assumed negligible compared to the angular motions, a sine-lattice Hamiltonian is derived. In the limit of small-amplitude angular displacements, the dispersion spectrum of acoustic phonons is derived and the associate characteristic frequency is given as a function of parameters of the model. In the large-amplitude regime, lattice vibrations give rise to kink-type deformations which move undergoing lattice dispersion and lattice discreteness effects. The dispersion law of the kink motion is obtained and shown to lower the effect of lattice discreteness, giving rise to a vanishing Peierls stress for kink sizes of the order of a few lattice spacings. Implications of the coupling of two armchair structures on the stability of vibrational modes of an individual armchair nanotube are also discussed. A gap of forbidden modes is predicted in the phonon spectrum while the energy needed to create a kink deformation in individual nanotubes is shifted in the presence of a wall-to-wall interaction.Received: 2 August 2004, Published online: 14 December 2004PACS:
81.07.De Nanotubes - 62.30. + d Mechanical and elastic waves-vibrations - 63.22. + m Phonons in low-dimensional nanoscale materials - 63.20.Ry Anharmonic lattices modes 相似文献
8.
Encapsulation of fullerene into nanotubes based on a C2N sheet, known as nitrogenated holey graphene, was investigated using density functional theory. The structural and electronic properties of these carbon hybrid materials, consisting of nitrogenated holey nanotubes and a small C20 fullerene, were studied. The formation energies showed that encapsulation of the fullerene into the nitrogenated holey nanotube is an exothermic process. To characterise the electronic properties, the electronic band structure and density of states of armchair and zigzag nitrogenated holey nanotubes were calculated. Filling these nanotubes with the C20 fullerene resulted in a p-type semiconducting character. The energy band gap of the nitrogenated holey nanotubes decreased with fullerene encapsulation. The results are indicative of the possibility of band gap engineering by encapsulation of small fullerenes into nitrogenated holey nanotubes. 相似文献
9.
We investigate electronic transport properties of the squashed armchair carbon nanotubes, using tight-binding molecular dynamics and the Green's function method. We demonstrate a metal-to-semiconductor transition while squashing the nanotubes and a general mechanism for such a transition. It is the distinction of the two sublattices in the nanotube that opens an energy gap near the Fermi energy. We show that the transition has to be achieved by a combined effect of breaking of mirror symmetry and bond formation between the flattened faces in the squashed nanotubes. 相似文献
10.
N. Zibouche A. Kuc T. Heine 《The European Physical Journal B - Condensed Matter and Complex Systems》2012,85(1):49
MoS2 and WS2 layered transition-metal dichalcogenides are indirect
band gap semiconductors in their bulk forms. Thinned to a monolayer, they undergo a
transition and become direct band gap materials. Layered structures of that kind can be
folded to form nanotubes. We present here the electronic structure comparison between
bulk, monolayered and tubular forms of transition metal disulfides using first-principle
calculations. Our results show that armchair nanotubes remain indirect gap semiconductors,
similar to the bulk system, while the zigzag nanotubes, like monolayers, are direct gap
materials, what suggests interesting potential applications in optoelectronics. 相似文献
11.
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
12.
The total carbo-mer of single-walled carbon nanotubes (C-SWCNTs) are constructed by inserting two sp carbon atoms into each C-C bond in pristine single-walled carbon nanotubes (SWCNTs). The geometric, mechanical and electronic properties for these novel structures are investigated by self-consistent-field crystal calculations. The calculated zigzag and chiral C-SWCNTs are all small gap semiconductors, whereas the metallic property is still kept in the armchair C-SWCNT. The calculated Young's moduli of C-SWCNTs are smaller than those of SWCNTs. Our calculations show that the zigzag C-SWCNTs have higher mobility than the corresponding SWCNTs. Moreover, the calculated mobility of the C-SWCNTs has a periodic change with the change of the tube diameters. 相似文献
13.
We investigate the nitrogen substitutional impurity in semiconducting zigzag and metallic armchair single-wall carbon nanotubes using ab initio density functional theory. At low concentrations (less than 1 at. %), the defect state in a semiconducting tube becomes spatially localized and develops a flat energy level in the band gap. Such a localized state makes the impurity site chemically and electronically active. We find that if two neighboring tubes have their impurities facing one another, an intertube covalent bond forms. This finding opens an intriguing possibility for tunnel junctions, as well as the functionalization of suitably doped carbon nanotubes by selectively forming chemical bonds with ligands at the impurity site. If the intertube bond density is high enough, a highly packed bundle of interlinked single-wall nanotubes can form. 相似文献
14.
采用分子动力学方法模拟了氮化硼纳米管在轴压和扭转复合荷载作用下的屈曲和后屈曲行为.在各加载比例下,给出了初始线性变形阶段和后屈曲阶段原子间相互作用力的变化,确定了屈曲临界荷载关系.通过对屈曲模态的细致研究,从微观变形机理上分析了纳米管对不同外荷载力学响应的差异.研究结果表明,扶手型和锯齿型纳米管均呈现出非线性的屈曲临界荷载关系,复合加载下的屈曲行为具有强烈的尺寸依赖性.温度升高将导致屈曲临界荷载的下降,且温度的影响随加载比例的变化而变化.无论在简单加载或复合加载中,同尺寸的碳纳米管均比氮化硼纳米管具有更强地抵抗屈曲荷载的能力. 相似文献
15.
16.
17.
Using the -band tight-binding (TB) model and the quantum box boundary
condition, we have discussed how both of the applied strain and
finite-length affect the energy bands of metallic carbon nanotubes (CNTs).
It is found that, for finite-length CNTs, energy gap for the armchair tube
under uniaxial strain and metallic zigzag tube under torsional strain will
oscillate with increasing strain, which do not exist in the case of
infinite-length CNTs, and will be able to be observed by experiments in
future. 相似文献
18.
Hamze Mousavi 《Solid State Communications》2010,150(15-16):755-758
We study the gas molecule adsorption effects on the electrical conductivity of both zigzag (9, 0) and armchair (5, 5) carbon nanotubes. Using the tight-binding model, Green’s function technique and coherent potential approximation, it is found that the adsorption of some gas molecules can cause a change in the electrical conductivity of metallic single-walled carbon nanotubes. 相似文献
19.
In this article, density functional theory calculations were employed to investigate the electronic properties of (4,4) armchair
zinc oxide single-walled nanotubes (ZNONTs) under uniaxial mechanical deformations. It was found that the highest-occupied
molecular orbital and the lowest-unoccupied molecular orbital gap and the value of radial buckling will both decrease linearly
with the increase of axial strain. The elongation of the ZNONT mainly originates from the decrease and increase of two characteristic
bond angles rather than Zn–O ionic bond elongation. This mechanical behavior is very different from the uniaxial tensional
processes of carbon nanotubes and silicon carbide nanotubes formed by covalent bonds. The partial densities of states of the
Zn atom and O atom show that the unoccupied states are gradually left-shifted as ZNONT elongates from 0 to 15%. Neither Mulliken
charge nor deformation density clearly changes with the different tension strains. Bond order analysis also indicates the
bonding strength will decrease as the strain increases from 0 to 15%. 相似文献
20.
Y. Zhang M. Han 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,76(2):277-282
Using the π orbital tight-binding model and the
multi-channel Laudauer-Büttiker formula, the combined effect of
Aharonov-Bohm effect (induced by an axial magnetic field) and uniaxial
strain on quantum conductance oscillations of the electronic Fabry-Perot
resonators composed of armchair and metallic zigzag single-walled carbon
nanotubes (SWNTs) has been studied. It is found that, for the case of the
armchair SWNT, conductance oscillations near the band gap are dominated by
Aharonov-Bohm effect, while the conductance oscillations in other regions
are dominated by the uniaxial strains. The combined effect of Aharonov-Bohm
effect and uniaxial strains on quantum conductance oscillations is not
obvious. But, for the case of the metallic zigzag SWNTs, obvious
single-channel transport and one or two conductance oscillations existing in
two different gate voltage ranges were found by the combined effect of
uniaxial strain and axial magnetic field. 相似文献