扶手椅型硅纳米管电子结构的研究

在本文中,我们使用密度泛函理论的第一性原理方法来研究手性指数m=n=K(K为3～15的整数)的扶手型硅纳米管的能带结构和态密度.计算结果表明,扶手型(3,3)硅纳米管为间接带隙结构,其余均为直接带隙结构;随着手性指数增加,硅纳米管的直径增大,硅纳米管的禁带宽度逐渐减小,导带逐渐向下移动,并且总态密度图峰值强度增加;扶手型(3,3)硅纳米管的禁带宽度最大化;扶手型(13,13)硅纳米管的禁带宽度最小,说明其导电性优于其他手性指数的扶手椅型硅纳米管;同时,扶手型(4,4)硅纳米管的导带和价带重叠,表明扶手型(4,4)硅纳米管是金属纳米管;态密度图显示扶手型(9,9)硅纳米管的价带顶部主要由Si-3p电子态组成,导带的底部由Si-3s态电子和Si-3p态电子组成.     

扶手椅型硅纳米管电子结构的研究

在本文中，我们使用密度泛函理论的第一性原理方法来研究手性指数m=n=K(K为3～15的整数)的扶手型硅纳米管的能带结构和态密度.计算结果表明，扶手型(3,3)硅纳米管为间接带隙结构，其余均为直接带隙结构;随着手性指数增加，硅纳米管的直径增大，硅纳米管的禁带宽度逐渐减小，导带逐渐向下移动，并且总态密度图峰值强度增加;扶手型(3,3)硅纳米管的禁带宽度最大化;扶手型(13,13)硅纳米管的禁带宽度最小，说明其导电性优于其他手性指数的扶手椅型硅纳米管;同时，扶手型(4,4)硅纳米管的导带和价带重叠，表明扶手型(4,4)硅纳米管是金属纳米管;态密度图显示扶手型(9,9)硅纳米管的价带顶部主要由Si-3p电子态组成，导带的底部由Si-3s态电子和Si-3p态电子组成.     

六角氮化硼纳米带的几何和电子结构理论研究

本文采用密度泛函B3LYP方法在6-31G*水平上,对一系列不同宽度的锯齿型和扶手椅型六角氮化硼纳米带进行了理论研究。结果表明纳米带宽度对体系的性质有规律性的影响。随着宽度的增加,纳米带不同位置的硼氮键键长差异逐步减小从而提高了整个体系的共轭性;锯齿型纳米带的能隙单调减小而扶手椅型纳米带的能隙在减小的同时出现振荡,且振幅随宽度逐渐减小。锯齿型氮化硼纳米带的化学势在特定宽度出现了极值点。前线分子轨道的分布随着宽度的增加出现了非均匀分布,呈现出向边界偏移的现象。     

扶手椅型氮化镓纳米管电子结构与传输特性的研究（英文）

本文采用密度泛函理论和非平衡格林函数对扶手椅型氮化镓纳米管(n,n)(2≤n≤10)的电子结构和输运性质进行了研究.结果表明,所有的扶手椅型氮化镓纳米管都是间接带隙半导体,带隙随着纳米管直径的增加而增加,并且得到了两极体系下氮化镓纳米管的电流-电压曲线.氮化镓纳米管的半导体特性随着纳米管直径的增加越来越明显,电子态密度和电子透射光谱都具有脉冲型尖峰并且最大峰值随着n的增加而增加.这说明电子态密度和电子透射光谱峰在能量范围内,有较好的对应关系.     

六角氮化硼纳米带的几何和电子结构理论研究

本文采用密度泛函B3LYP方法在6-31G*水平上，对一系列不同宽度的锯齿型和扶手椅型六角氮化硼纳米带进行了理论研究。结果表明纳米带宽度对体系的性质有规律性的影响。随着宽度的增加，纳米带不同位置的硼氮键键长差异逐步减小从而提高了整个体系的共轭性；锯齿型纳米带的能隙单调减小而扶手椅型纳米带的能隙在减小的同时出现振荡，且振幅随宽度逐渐减小。锯齿型氮化硼纳米带的化学势在特定宽度出现了极值点。前线分子轨道的分布随着宽度的增加出现了非均匀分布，呈现出向边界偏移的现象。     

扶手椅型碳化硅纳米管电子结构和光学性质的研究

本文基于密度泛函理论研究了扶手椅型碳化硅纳米管(SiCNT)的电子结构、成键机制以及其光学性质。研究结果表明:当碳和硅的原子比为1∶1时,SiCNT的结构最为稳定,并且表现出诸多的优良性质。通过分析计算结果我们发现,SiCNT是间接带隙材料,并且管子的带隙随着直径的增加而增加。从SiCNT的轨道图谱中我们看到碳和硅原子之间属于sp2杂化,同时硅原子周围的电子密度明显要低于碳原子周围的电子密度。对能态密度的计算我们得知碳原子和硅原子分别主导价带和导带。与其它纳米管(BN)有所不同,SiCNT的光学性质更接近于各向同性材料。     

扶手椅型氮化镓纳米管电子结构与传输特性的研究

本文采用密度泛函理论和非平衡格林函数对扶手椅型氮化镓纳米管（n,n）（2≤ n ≤10）的电子结构和输运性质进行了研究。结果表明,所有的扶手椅型氮化镓纳米管都是间接带隙半导体,带隙随着纳米管直径的增加而增加,并且得到了两极体系下氮化镓纳米管的电流-电压曲线。氮化镓纳米管的半导体特性随着纳米管直径的增加越来越明显,电子态密度和电子透射光谱都具有脉冲型尖峰并且最大峰值随着n的增加而增加。这说明电子态密度和电子透射光谱峰在能量范围内,有较好的对应关系。     

扶手椅型硅纳米管的电学性质研究

本文采用密度泛函理论的第一性原理方法,对手性指数m=n=K（K为3～15的整数）的扶手型硅纳米管的能带结构和态密度进行了研究。计算结果表明,扶手型（3,3）硅纳米管为间接带隙结构,其余均为直接带隙结构;随着手性指数的增加,硅纳米管的直径增大,硅纳米管的禁带宽度逐渐减小,且导带逐渐下移,总态密度图峰值强度增大;扶手型（3,3）硅纳米管的禁带宽度最大;扶手型（13,13）硅纳米管的禁带宽度最小,说明其导电性优于其他手性指数的扶手椅型硅纳米管;同时,扶手型（4,4）硅纳米管的导带和价带出现重叠,说明扶手型（4,4）硅纳米管为金属性纳米管;态密度图表明扶手型（9,9）硅纳米管的价带顶主要由Si-3p电子态构成,导带底由Si-3p态电子和Si-3s态电子共同构成。     

C/SiC纳米管异质结电子结构的第一性原理研究

采用基于密度泛函理论的第一性原理计算,对扶手椅型(4,4)和(6,6)及锯齿型(8,0)和(10,0)C/SiC纳米管异质结的电子结构进行了研究.结果表明两类异质结结构都表现为半导体特性.扶手椅型纳米管异质结形成了Ⅰ型异质结,电子和空穴都限制在碳纳米管部分.锯齿型纳米管异质结中价带顶主要分布在碳纳米管部分及C/SiC界面处,而导带底均匀分布在整个纳米管异质结上.这两种异质结结构在未来纳米器件中具有潜在的应用价值. 关键词： C/SiC纳米管异质结 第一性原理 电子结构     

曲率效应对超小碳纳米管电子性质的影响

在考虑曲率效应的情况下,在螺旋坐标系下解析地推导了非手性的碳纳米管(SWNTs)(包括扶手椅型和锯齿型)的能量色散关系,并分析了曲率效应对超小扶手椅型SWNTs的能带、能隙和导电能力及其对超小锯齿型SWNTs(包括扶手椅型和锯齿型)的能隙的影响.     

Band-gap modulation of graphane-like SiC nanoribbons under uniaxial elastic strain

The band-gap modulation of zigzag and armchair graphane-like SiC nanoribbons (GSiCNs) under uniaxial elastic strain is investigated using the density functional theory. The results show that band gap of both structures all decreases when being compressed or tensed. In compression, both zigzag and armchair GSiCNs are semiconductors with a direct band gap. However, in tension, the armchair GSiCNs undergo a direct-to-indirect band-gap transition but the zigzag GSiCNs still have a direct band gap. These results are also proved by HSE06 method. This implies a potential application of the graphane-like SiC nanoribbons in the future pressure sensor and optical electronics nanodevices.     

单壁碳纳米管能带及其电子特性研究

从能带理论出发,采用电子紧束缚能量色散关系,推导锯齿,扶手椅和手性单壁碳纳米管(SWCNT)的电子能带结构表达式,指出单壁碳纳米管或为金属或为半导体的判据。结果表示:单壁碳纳米管的电子结构与其几何结构密切相关,如扶手椅型单壁碳纳米管是金属性的,而对其它类型的单壁碳纳米管是与碳纳米管的手性指数有关,只有手性指数n和m的差别等于3的倍数时,单壁碳纳米管是金属性的,否则会显出有带隙的半导体特性。这意味着单壁碳纳米管是由特殊的电子传输和光学性质,在纳米电子学领域具有巨大的潜在应用价值。     

Structure and electronic properties of MoS2 nanotubes

Structural and electronic properties as well as the stability of MoS2 nanotubes are studied using the density-functional-based tight-binding method. It is found that MoS2 zigzag ( n,0) nanotubes exhibit a narrow direct band gap and MoS2 armchair ( n,n) possess a nonzero moderate direct gap. Interestingly, the ( n,n) tubes show a small indirect gap similar to the direct gap of ( n,0) nanotubes. Simulated electron diffraction patterns confirm the existence of armchair and zigzag disulphide nanotubes. The structure of the MoS2 nanotube tips is explained by introducing topological defects which produce positive and negative curvature.     

Structure,Electronic, and Mechanical Properties of Three Fully Hydrogenation h-BN:Theoretical Investigations

The structural, electronic, elastic, mechanical properties and stress-strain relationship of chair, boat, and stirrup conformers of fully hydrogenated h-BN(fh-BN) are investigated in this work using the Perdew-Burke-Ernzerhof(PBE) function in the frame of density functional theory. The achieved results for the lattice parameters and band gaps of three conformers in this research are in good accordance with other theoretical results. The band structures of three conformers show that the chair, boat, and stirrup are direct band gap with a band gaps of(3.12, 4.95, and4.95 e V), respectively. To regulate the band structures of fh-BN, we employ a hybrid functional of Heyd-ScuseriaErnzerhof(HSE06) calculations and the band gaps are 3.84(chair), 6.12(boat), and 6.18 e V(stirrup), respectively.The boat and stirrup fh-BN exhibits varying degrees of mechanical anisotropic properties with respect to the Young's modulus and Poisson's ratio, while the chair fh-BN exhibits the mechanical isotropic properties. Furthermore, tensile strains are applied in the armchair and zigzag directions related to tensile deformation of zigzag and armchair nanotubes,respectively. We find that the ultimate strains in zigzag and armchair deformations in stirrup conformer are 0.34 and0.25, respectively, larger than the strains of zigzag(0.29) and armchair(0.18) deformations in h-BN although h-BN can surstain a surface tension up to the maximum stresses higher than those of three conformers of fh-BN. Furthermore, the band gap energies in three conformers can be modulated effectively with the biaxial tensile strain.     

First-principles study of narrow single-walled GaN nanotubes

Structural and electronic properties of narrow single-walled GaN nanotubes with diameter from 0.30 to 0.55 nm are investigated using the density functional method with generalized-gradient approximation. The calculations of total energies predict that the most likely GaN nanotubes in our calculation are (2,2), (3,2) and (3,3) nanotubes. From a detailed analysis we find that these narrow single-walled GaN nanotubes are all semiconductors, of which the armchair and chiral tubes are indirect-band-gap semiconductors whereas the zigzag ones have a direct gap except for (4,0) tube. The indirect band gap of (4,0) tube can stem from band sequence change induced by curvature effect. Our results show that the π-π hybridization effect and the formation of benign buckling separations play a key role in the band sequence changes of (4,0) tube.     

Strain-induced structural and direct-to-indirect band gap transition in ZnO nanotubes

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.     

Gallium doped in armchair and zigzag models of boron phosphide nanotubes (BPNTs): A NMR study

The electrical properties and NMR parameters of the pristine and Ga-doped structures of two representative (8, 0) zigzag and (4, 4) armchair of boron phosphide nanotubes (BPNTs) have been investigated. The structural geometries of above nanotubes have been allowed to relax by optimization and then the isotropic and anisotropic chemical shielding parameters (CSI and CSA) of ¹¹B and ³¹P have been calculated based on DFT theory. The results reveal that the influence of Ga-doping was more significant on the geometries of the zigzag model than the armchair one. The difference of band gap energies between the pristine and Ga-doped armchair BPNTs was larger than the zigzag model. Significant differences of NMR parameters of those nuclei directly contributed to the Ga-doping atoms have been observed.     

Band gap of carbon nanotubes under combined uniaxial–torsional strain

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.     

P掺杂硅纳米管电子结构与光学性质的研究

采用基于密度泛函理论的第一性原理计算,研究了P掺杂对单壁扶手型硅纳米管电子结构和光学性质的影响.结果表明:经过P掺杂,单壁扶手型硅纳米管的能带结构从间接带隙变为直接带隙,其价带顶主要由Si-3p态电子构成,导带底主要由Si-3p态电子和Si-3s态电子共同决定;同时通过P掺杂,使单壁扶手型硅纳米管的禁带宽度变窄,导电性增强,吸收光谱产生红移.研究结果为硅纳米管在光电器件方面的应用提供了理论基础.